REPLICACcedilAtildeO DE DNA
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual o padratildeo de
replicaccedilatildeo do DNA
O experimento de Meselson-Stahl elucidou o padratildeo de
replicaccedilatildeo como sendo semi-conservativo
RESULTADO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual o padratildeo de
replicaccedilatildeo do DNA
O experimento de Meselson-Stahl elucidou o padratildeo de
replicaccedilatildeo como sendo semi-conservativo
RESULTADO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Qual o padratildeo de
replicaccedilatildeo do DNA
O experimento de Meselson-Stahl elucidou o padratildeo de
replicaccedilatildeo como sendo semi-conservativo
RESULTADO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
O experimento de Meselson-Stahl elucidou o padratildeo de
replicaccedilatildeo como sendo semi-conservativo
RESULTADO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
RESULTADO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
RESULTADO NAtildeO ENCONTRADO
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
RESULTADO NAtildeO ENCONTRADO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Adiccedilatildeo de novas bases a fita crescente de DNALigaccedilatildeo fosfodieacutester
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Adiccedilatildeo de novas bases a fita crescente de DNAReaccedilatildeo enzimaacutetica
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
DNA polimerase
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Qual a direccedilatildeo da polimerizaccedilatildeo
5rsquo rarr 3rsquo
3rsquo rarr 5rsquo
Se este raciociacutenio estiver correto precisamos de duas polimerases
para realizar a replicaccedilatildeo
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Figure 5-11
An explanation for the 5prime-to-3prime direction of DNA chain
growth Growth in the 5prime-to-3prime direction shown on the
right allows the chain to continue to be elongated when a
mistake in polymerization has been removed by
exonucleolytic proofreading (see Figure 5-9) In contrast
exonucleolytic proofreading in the hypothetical 3prime-to-5prime
polymerization scheme shown on the left would block
further chain elongation For convenience only the primer
strand of the DNA double helix is shown
A direccedilatildeo de polimerizaccedilatildeo eacute exclusivamente 5rsquo rarr 3rsquo
bull Econocircmica metabolicamente
(somente 1 polimerase)
bullViaacutevel energeticamente
bullPassiacutevel de correccedilatildeo na
ocorrecircncia de erros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Figure 5-9
Exonucleolytic proofreading by DNA polymerase during DNA replication
In this example the mismatch is due to the incorporation of a rare transient
tautomeric form of C indicated by an asterisk But the same proofreading
mechanism applies to any misincorporation at the growing 3prime-OH end
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Correccedilatildeo de erros de polimerizaccedilatildeo devido tautomerizaccedilatildeo
Se natildeo ocorrer teremos mutaccedilotildees
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
As trecircs etapas que garantem a fidelidade
de incorporaccedilatildeo dos nucleotiacutedeos
Passo da replicaccedilatildeo Taxa de eficiecircncia acumulada
(erro acertos)
5primerarr 3prime polimerizaccedilatildeo 1105
Correccedilatildeo exonucleotiacutedica (3rsquo rarr 5rsquo) 1107
Reparo de mau pareamento
diretamente na fita (sistema de
reparo)
1109
CO-REPLICACcedilAtildeO
POacuteS-REPLICACcedilAtildeO
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Origens de replicaccedilatildeo
bullA replicaccedilatildeo do material geneacutetico se inicia em pontos especiacuteficos
denominados origens de replicaccedilatildeo
bullA duplicaccedilatildeo do cromossomo circular de E coli eacute bidirecional
bullA siacutentese de DNA eacute unidirecional (5rsquo - 3rsquo)
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Origens de replicaccedilatildeo
bullProcariotos = 1 origem Eucariotos = muacuteltiplas origens
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Quem organiza a replicaccedilatildeo no DNA molde
Um complexo multiproteacuteico iraacute cumprir vaacuterias tarefas
REPLISSOMO
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
Soluccedilatildeo para necessidade de
uma ponta 3rsquoOH
Soluccedilatildeo para abertura das fitas
Soluccedilatildeo para a processividade
Enzimas envolvidas na replicaccedilatildeo
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
RNA primer synthesis A schematic view of the reaction catalyzed
by DNA primase the enzyme that synthesizes the short RNA primers
made on the lagging strand using DNA as a template Unlike DNA
polymerase this enzyme can start a new polynucleotide chain by
joining two nucleoside triphosphates together The primase
synthesizes a short polynucleotide in the 5prime-to-3prime direction and then
stops making the 3prime end of this primer available for the DNA
polymerase
ENZIMAS DO REPLISSOMO RNA Primase
Soluccedilatildeo para necessidade de uma ponta 3rsquoOH
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Figure 5-16 The structure of a DNA helicase (A) A schematic diagram of the protein as a hexameric ring (B) Schematic
diagram showing a DNA replication fork and helicase to scale (C) Detailed structure of the bacteriophage T7 replicative
helicase as determined by x-ray diffraction Six identical subunits bind and hydrolyze ATP in an ordered fashion to propel
this molecule along a DNA single strand that passes through the central hole Red indicates bound ATP molecules in the
structure (B courtesy of Edward H Egelman C from MR Singleton et al Cell 101589ndash600 2000 copy Elsevier)
ENZIMAS DO REPLISSOMO DNA Helicase
Procariotos (primase + helicase = primossomo)
Soluccedilatildeo para abertura das fitas Com quebra de ATP
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Figure 5-17 The effect of single-strand DNA-binding
proteins (SSB proteins) on the structure of single-stranded
DNA Because each protein molecule prefers to bind next to a
previously bound molecule long rows of this protein form on a
DNA single strand This cooperative binding straightens out the
DNA template and facilitates the DNA polymerization process
The ldquohairpin helicesrdquo shown in the bare single-stranded DNA
result from a chance matching of short regions of
complementary nucleotide sequence they are similar to the
short helices that typically form in RNA molecules (see Figure
1-6)
Figure 5-18 The structure of the single-strand binding protein
from humans bound to DNA (A) A front view of the two DNA
binding domains of RPA protein which cover a total of eight
nucleotides Note that the DNA bases remain exposed in this proteinndash
DNA complex (B) A diagram showing the three-dimensional structure
with the DNA strand (red) viewed end-on (B from A Bochkarev et
al Nature 385176ndash181 1997 copy Macmillan Magazines Ltd)
ENZIMAS DO REPLISSOMO Proteiacutenas ligadoras de fita simples (SSB)
Soluccedilatildeo para impedir a renaturaccedilatildeo da fita molde
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
ENZIMA DISTRIBUTIVA OU ENZIMA PROCESSIVA
DISSOCIACcedilAtildeO E REASSOCIACcedilAtildeO A CADA INCORPORACcedilAtildeO
LIMITARIA A POLIMERIZACcedilAtildeO PELA DNA POL
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
The regulated sliding clamp that holds DNA polymerase on the DNA (A) The structure of the clamp protein from E coli as
determined by x-ray crystallography with a DNA helix added to indicate how the protein fits around DNA (B) A similar protein is
present in eucaryotes as illustrated by this comparison of the E coli sliding clamp (left) with the PCNA protein from humans (right)
(C) Schematic illustration showing how the clamp is assembled to hold a moving DNA polymerase molecule on the DNA In the
simplified reaction shown here the clamp loader dissociates into solution once the clamp has been assembled At a true replication
fork the clamp loader remains close to the lagging-strand polymerase ready to assemble a new clamp at the start of each new
Okazaki fragment (see Figure 5-22) (A and B from X-P Kong et al Cell 69425ndash437 1992 copy Elsevier)
ENZIMAS DO REPLISSOMO Cinta deslizante dimeacuterica e montador da cinta
Soluccedilatildeo para processividade da polimerizaccedilatildeo
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
The structure of a DNA replication fork Because both daughter DNA
strands are polymerized in the 5prime-to-3prime direction the DNA synthesized on
the lagging strand must be made initially as a series of short DNA
molecules called Okazaki fragments
A polimerizaccedilatildeo exclusiva no sentido 5rsquo rarr 3rsquo cria um problema espacial para
siacutentese de uma das fitas
1 Segmentos transitoacuterios chamados de fragmentos de Okasaki foram descobertos em bacteacuterias
apoacutes incubaccedilatildeo por alguns segundos com timidina triciada [3H]
2 Esse arranjo de replicaccedilatildeo cria uma fita contiacutenua (liacuteder) e uma fita descontiacutenua (retardada)
Coacutepia da fita Retardada
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
In eucaryotes RNA
primers are made at
intervals spaced by
about 200
nucleotides on the
lagging strand and
each RNA primer is
approximately 10
nucleotides long
Coacutepia da fita retardada ndash Siacutentese de primers de RNA
bullPrimase
(procariotos)
bullDNA polimerase
(eucariotos)
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Coacutepia da fita retardada ndash Siacutentese dos fragmentos de okasaki
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
This primer is erased
by a special DNA
repair enzyme (an
RNAse H) that
recognizes an RNA
strand in an
RNADNA helix and
fragments it this
leaves gaps that are
filled in by DNA
polymerase and DNA
ligase
Coacutepia da fita retardada ndash Remoccedilatildeo do primer de RNA
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Coacutepia da fita retardada ndash Fechamento de nicks
nick
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
The proteins at a bacterial DNA replication fork The major types of proteins that act at a DNA replication fork
are illustrated showing their approximate positions on the DNA
E em movimento Como ocorre
Modelo para o replissomo procarioacutetico
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Modelo para o replissomo procarioacutetico
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
A mammalian replication fork The fork is drawn to emphasize its similarity to the bacterial replication fork depicted in Figure 5-21
Although both forks use the same basic components the mammalian fork differs in at least two important respects First it uses two
different DNA polymerases on the lagging strand Second the mammalian DNA primase is a subunit of one of the lagging-strand DNA
polymerases DNA polymerase α while that of bacteria is associated with a DNA helicase in the primosome The polymerase α (with its
associated primase) begins chains with RNA extends them with DNA and then hands the chains over to the second polymerase (δ)
which elongates them It is not known why eucaryotic DNA replication requires two different polymerases on the lagging strand The
major mammalian DNA helicase seems to be based on a ring formed from six different Mcm proteins this ring may move along the
leading strand rather than along the lagging-strand template shown here
Modelo para o replissomo eucarioacutetico
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bullTelocircmeros e replicaccedilatildeo
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
A replicaccedilatildeo gera um problema de supertorccedilatildeo positiva que se acumula na frente da
forquilha de replicaccedilatildeo na medida que os filamentos parentais se separam para replicaccedilatildeo
Natildeo importa se o replissomo eacute procarioacutetico ou eucarioacutetico o problema vai existir
Super-torccedilatildeo do DNA X Replicaccedilatildeo
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Super-torccedilatildeo do DNA X Replicaccedilatildeo
A separaccedilatildeo das duas fitas do DNA provoca a
formaccedilatildeo de super-heacutelices
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
The ldquowinding problemrdquo that arises during DNA replication For a bacterial replication fork moving at 500 nucleotides per second the
parental DNA helix ahead of the fork must rotate at 50 revolutions per second
O problema gerado pela replicaccedilatildeo torccedilatildeo
positiva na moleacutecula
As topoisomerases
resolvem
Topoisomerase tipo I
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
A model for topoisomerase II action As indicated ATP binding to the two
ATPase domains causes them to dimerize and drives the reactions shown
Because a single cycle of this reaction can occur in the presence of a non-
hydrolyzable ATP analog ATP hydrolysis is thought to be needed only to reset
the enzyme for each new reaction cycle This model is based on structural and
mechanistic studies of the enzyme (Modified from JM Berger Curr Opin
Struct Biol 826ndash32 1998)
The DNA-helix-passing reaction catalyzed by DNA topoisomerase II Identical
reactions are used to untangle DNA inside the cell Unlike type I topoisomerases type
II enzymes use ATP hydrolysis and some of the bacterial versions can introduce
superhelical tension into DNA Type II topoisomerases are largely confined to
proliferating cells in eucaryotes partly for that reason they have been popular targets
for anticancer drugs
Topoisomerase tipo II
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
REPLICACcedilAtildeO DE DNA
bull Replicaccedilatildeo eacute Semiconservativa
bull Polimerase liga e copia uma fita simples
bull Coacutepia da fita de DNA eacute Unidirecional (5rsquo ndash 3rsquo)
bull Coacutepia possui sistema de correccedilatildeo de erros
bull Origens de replicaccedilatildeo
bull Enzimas envolvidas na replicaccedilatildeo
bull Coacutepia da fita liacuteder e retardada
bull Super-torccedilatildeo de DNA e replicaccedilatildeo
bull Telocircmeros e replicaccedilatildeo
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
Telocircmeros e replicaccedilatildeo
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros
The structure of telomerase The telomerase is a proteinndash
RNA complex that carries an RNA template for synthesizing a
repeating G-rich telomere DNA sequence Only the part of the
telomerase protein homologous to reverse transcriptase is
shown here (green) A reverse transcriptase is a special form
of polymerase enzyme that uses an RNA template to make a
DNA strand telomerase is unique in carrying its own RNA
template with it at all times (Modified from J Lingner and TR
Cech Curr Opin Genet Dev 8226ndash232 1998)
Figure 5-43 Telomere replication Shown here are the reactions
involved in synthesizing the repeating G-rich sequences that form the
ends of the chromosomes (telomeres) of diverse eucaryotic organisms
The 3prime end of the parental DNA strand is extended by RNA-templated
DNA synthesis this allows the incomplete daughter DNA strand that is
paired with it to be extended in its 5prime direction This incomplete lagging
strand is presumed to be completed by DNA polymerase α which
carries a DNA primase as one of its subunits (see Figure 5-28) The
telomere sequence illustrated is that of the ciliate Tetrahymena in which
these reactions were first discovered The telomere repeats are
GGGTTG in the ciliate Tetrahymena GGGTTA in humans and G1ndash3A
in the yeast S cerevisiae
Extensatildeo de telocircmeros