03. dna replication and repair

7/25/2019 03. DNA Replication and Repair

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Basic

MolecularGenetic

Mechanisms

Molecular Cell Biology

7thed

Chapter 4

(Part 3 )

DNA Replication

and Repair

DNA polymerase

(pol )


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Major Points of DNA Replication

New strand is built 5 3 usin an

e!istin strand as a te"plate (3 5)

DNA pol#"erase adds new dN$Ps% different DNA pol#"erases are in&ol&ed

(pol and pol )

'nl# e!tends 3 end of a duple! (primer)

Nu"erous oter en#"es assist


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Pri"ers

*ort strand of co"ple"entar#nucleotides (DNA or RNA)

s#ntesied b# pri"ase

co"posed of RNA (+ ,- dN$Ps lon)e!tended 5 3 b# pol

"ust be

e!cised RNA


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.eadin &ersus .ain *trands

.eadin strand(continuous s#ntesis)'nl# one pri"er re/uired

Replication proceeds toward replicationfor01 (DNA Pol 2)

.ain strand (discontinuous s#ntesis)

Re/uires "ultiple pri"ersReplication proceeds awa# fro"

replication for0 (DNA Pol Pol 4)


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*ce"atic Diara" of a

Replication or0
http://home/pkores/Desktop/Biol%202C%20Spring%202013/Lectures/Lecture%20Annimations/DNA_Replication_leading_lagging.swf


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*67- DNA

Replication or0


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Replication Proteins (,)

helicase(separates parental strands of DNA)

8o"posed of 9 o"oloous M8M: proteins

(.are $;antien in *67-)

Primase(s#ntesies sort RNA pri"er)

DNA Polymerases

pol !e!tends RNA pri"er on bot strands

pol "!replaces pol 1 lain strand s#nslidin cla"p? P8NA)

DNA ligase(re;for"s pospodiester bond

between nucleotides1 joins >nic0s?) *opoisomerases (relie&e torsional stress in

dsDNA caused b# elicase)

topo @ sinle strand cutter1 creates nic0s topo @@ double strand cutter


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u0ar#otic 8la"p .oader

(Replication factor 8)

DNA *lidin 8la"p(Proliferatin cell

nuclear antien)

PCNA

RC


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*67-.are $;antien


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Bidirectional

DNA

Replication in

*67-

circular DNA

"olecule

, cut b# coR,

8enter of repli;

cation bubble

stationar#


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RPA $inds ssDNA

Primase synthesis RNA primer

Topo I relie+es tensional strain


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Pol e,tends primers

PCNA!RC!Pol

comple, replaces pol - e,tends strand


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Primase synthesi.es ne/ primers or lagging strands


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PCNA!RC!Pol com!

ple, replaces pol -

e,tends strand

Pol e,tends primers

Ri$onuclease % and &'N 0 e,cise primers

PCNA!RC!Pol

comple, ills in dN*Ps

DNA ligase 1oins ragments


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DNA Replication 8ontrol

8ontrol of initiation is reulated

Acti&ation of M8M elicase is re/uired

to initiate cellular DNA replicationM8M is reulated b# *;pase cyclin!

dependent 2inase

u0ar#otes a&e "ultiple oriins ofreplication alon eac cro"oso"e


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DNA Pol#"erase 8oordination

replication for0 "ust coordinate

s#ntesis of bot strands

leadin strand s#ntesis is faster tanlain strand s#ntesis

two elicase co"ple!es are connected

discontinuous s#ntesis of lainstrand follows >$ro"bone Model?
http://home/pkores/Desktop/Biol%202C%20Spring%202013/Lectures/Lecture%20Annimations/DNA_Replication_Fork.mp4


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*ources of rrors in DNA

DNA Replication errors

< coli nati&e error rate , ! ,-;71 obser&ed

error rate in cells , ! ,-;C

DNA pol#"erase proof readin corrects

"an# "ista0es

8e"ical and Radiation da"aedea"ination can con&ert 5;

"et#lc#tosine to t#"ine


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DNA Pol#"erase Proofreadin5'-3' polymerase site

3'-5' exonuclease site

E. coli

DNA

pol#"erase

nati&e error rate , ! ,-;7

Measured "utation rate , ! ,-;C

Ani"al cells Poland Polbot a&e proofreadin


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Dea"ination;Based Point Mutations

Why is cytosine

methylated?


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Major 8lasses of DNA Repair

n#"es *inle *trand Repair (deals wit sinlebase;pairs)

DNA "is"atc repairNucleotide e!cision repair

Double *trand Repair (deals wit

larer areas)=o"oloous reco"bination (error free)nd;Eoinin (error prone)


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Base !cisionRepair of F;$ Mis"atces

,< DNA l#cos#lase identifies F;$

"is"atc1 e!cises N;base (*)

03. dna replication and repair

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