k6- replikasi dna
TRANSCRIPT
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as c
Science
Departemen
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The nucleus contains a blueprint for all cells structures & activities
encoded in DNA
The information that makes each individual life unique must be
preserved & then passed on to progeny
Cells divisions does not stop with the formation of mature organism
but continous in certain tissues throughout life
New cells originate from other living cellscells division
More than 1013cells form a human bodythe whole organism has
been generated by cell divisions from a single cell
One of the hallmarks of life is its ability to reproduce
Introduction
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Tissues of the body divided into three
groups base on proliferative activity
of their cells:
Continuously
dividing tissues
(labile tissues)
Quiescent
tissues (stable
tissues)
Nondividing
tissues
(permanent
tissues)
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Example:
Surface epithelia
i.e. stratifiedsquamous
epithelia of skin,
oral cavity, vagina& cervix
The lining mucosa
of all excretoryducts of glands
(e.g., salivary
glands, pancreas,biliary tract)
The columnar
epithelium of the
GI tract & uterus
The transitionalepithelium of urinary
tract, and cells of
bone marrow &
hematopoietic
tissues
Cells proliferate throughout life Replacing that destroyed
Continuously dividing tissues (labile tissues):
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Example :
Parenchymal cells of
liver, kidneys, &
pancreas
Mesenchymal cells
such as fibroblasts &
smooth muscle
Vascular endothelial
cells; & lymphocytes
& other leukocytes
Normally have a low level of replication but cells can undergo rapid
division in response to stimuli & capable of reconstituting the tissue
of origin
Quiescent tissues (stable tissues)
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Example : neurons & skeletal & cardiac muscle cells
Contain cells that have left the cell cycle & cannot undergomitotic division in postnatal life
Nondividing tissues(permanent tissues)
t
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ynt es s occurs ns e
the nuclues
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Cell nucleus contain 3 major components:
Nuclearenvelopecomposed of two
parallel unit membranes that fuse witheach other at certain regions to form
perforations known as nuclear pores
Chromatin: a complex of DNA and
proteins and represents the relaxed,
uncoiled chromosomes of the interphase
nucleus
Nuclelolus: the deeply staining-non
membrane bounded structure within
nucleus that is involeved in rRNA synthesisand in the assembly of small and large
ribosomal units
CELL NUCLEUS
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Chromatin: a complex of DNA and
proteins and represents the relaxed,
uncoiled chromosomes of the interphasenucleus
DNA: the cells genetic material
Like a computer tape that stores many
programs
DNA present in each cell in the form of anumber of chromosomes
Chromosomesare chromatin fibers that
becomes so condensed and thightlycoiled during mitosis and meiosis that
they become visible with the light
microscope
Chromatin
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Chromatin Depending on
transcriptional activity:
Heterochromatin:
Condensed inactive form of chromatin
Located mostly at periphery of nucleus
Euchromatin:
Active form of chromatin where the
genetic material being trancribed intoRNA
Composed of thread like material 30
nm thick: Nucleosomes: unwound material
resembling beads on stringconsist
of histone
DNAmoleculesthin filament
resembling string
Chromatin contd
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The Nucleus
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Chromatin-Histone
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Genome: is total number of genes within one mature cell (60 -
100.000).
Genes:
Basic unit of genetic information.
They determine the inherited characters
Each gene is a part of DNA sequences that contains genetic information
coding for synthesis of a certain protein
Chromosomesstorage units of genes.
Most human cells contain 46 chromosomes:
22 pairs of chromosomes , named autosomes.
1 pair of sex chromosomes (X and Y):
XYin males, XXin females
Genom & Gene
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Interphase (G1-S-G2)
may extend for days,
weeks or longer
depending on the celltype
M phaseusually lasts
only an hour or so
S PHASE
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DNA contains all informations for human.
Before any cell division, a cell must duplicate all its DNA.Replication occurs during S phase of cell cycle (synthesis
phase of interphase)
Cells also synthesize the additional histones (needed asthe cells double the nucleosomes in its chromosomes)
S-PHASE
DNA R li i
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DNA Replication
Replication means making a
replica(an exact or identicalcopy)
DNA replication is the process of
making an exact copy of DNA byusing one of the parent DNA
strands as templateThe
original DNA strands are used as
templates for the synthesis of
new strands
DNA functions to :
Store genetic information &
transferring it to daughter cells during
mitosis by replication &
Transferof genetic information from
DNA to RNA to be expressed as
proteins
It occurs very quickly, very
accurately and at the appropriate
time in the life of the cell
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Models of DNA Replication
In the late 1950s, three different
mechanisms were proposed for the
replication of DNA
Conservative
model
Both parental
strands stay together
after DNA replication
Semiconservative
model
The double-stranded
DNA contains one
parental & one
daughter strand
following replication
Dispersive model
Parental & daughterDNA are
interspersed in both
strands following
replication
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Models of DNA Replication
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replication
1. Semi-conservative mode2. Ordered and sequential
3. Semi-discontinuous
One strand synthesized continuously(Leading strand)
Other strand synthesized
discontinuously ( Lagging strand)
Fragments called Okazaki fragments
4. Accurate
5. Bi-directional
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Three Steps for Replication
1. Initiation
2. Elongation
3. Termination
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DNA template
Nucleotides : A ,T & G, and C
RNA primers
Enzymes
DNA Helicase
RNA polymerase ( Primase)
DNA polymerases
Topoisomerase I , II
Ligase
Some Additional factors
SSB proteins (Single-strand binding proteins (SSBs)
Requirements
DNA l T
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DNA Ploymerase
Synthesis of lagging strand & gap filling
DNA polymerase
DNA repair
DNA polymerase
Mitochondrial DNA synthesis
DNA polymerase Synthesis of leading strand
DNA polymerase
DNA repair
DNA polymerase Types
rep ca on s n a e a or g ns
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rep ca on s n a e a or g nsof replication
Hetereochromatin replicateslater in S Phase than
euchromatin Replication initiated at
multiple points known asReplications origins
DNA double helix is split open
by DNA helicase to expose thebase sequences
The resulting separation ofDNA strand are calledReplication bubbles
Two replication complexesform at each origin. One ateach end of the bubble and isa Y-shaped structure calledReplication fork
DNA R li ti I iti ti
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The two DNA strands are separated
SSB proteins stabilize the single stranded DNA
Two replication forks are created
Each strand acts as a template
Replication proceeds from 5 to 3 end
DNA Replication Initiation
DNA El ti
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1. DNA polymerase clamps to the leading strand & adds DNA
nucleotides to the RNA primer2. DNA polymerase proofreading activity checks and replaces
in correct bases
3. Continous (Leading) strand synthesis produces new
fragments on the 3to 5 template but in a 5 to 3
direction
4. Discontinous (lagging) strand synthesis produces okazaki
fragments but in 5 to 3 direction5. Replication proceeds along the single strands about 40-50
nucleotides persecond simultaneously in both directions
6. DNA Ligasejoined Okazaki fragment together
DNA Elongation
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Replication orientation: 5 3
Movement of Replication fork
3
553
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3
5
Okazaki fragment
Leading strand
(continous)
Lagging strand
(discontinous)Replication fork
1. Continous (Leading) strand synthesis produces new fragments on
the 3to 5 template but in a 5 to 3 direction
2. Discontinous (lagging) strand synthesis produces okazaki fragments
but in 5 to 3 direction
3. Replication proceeds along the single strands about 40-50
nucleotides persecond simultaneously in both directions
4. DNA Ligasejoined Okazaki fragment together
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