DNA replication - Minia...Basic requirement for DNA replication 1- Substrate 4 nucleotide of DNA...
Transcript of DNA replication - Minia...Basic requirement for DNA replication 1- Substrate 4 nucleotide of DNA...
DNA replication
By
Dr. Ahmed Okasha
Semiconservative
replication1-Separation of DNA strand occur
2-The new strand synthesized that
are complementary to parent
strand
3-The new DNA contain 2 strands
one from parents and the other is
new strand
Basic requirement for DNA
replication
1- Substrate
4 nucleotide of DNA (ATP, GTP,
CTP, TTP) must present
2- Template (parent strand)
Parent strand are required to
add complementary nucleotide
on the new strand
3- RNA primer
Present in the first new strand
and its function is to receive
the first new nucleotide that
added on the new strand
4- Enzyme :
DNA polymerase , Pol I, II , III
Step of replication in
prokaryotic (E. coli)
Origin of replication1-Replication start at
particular DNA sequence
called origin (ori)
2- Dna A &B& C protein bind
to strand produce
separation of 2 strand
2- Formation of replication fork
Replication fork represent the
unwinding the DNA strand by the
effect of helicase (Dna B) made
broken in hydrogen bond lead to
separation in helix
This need 2 ATP for each base pair
broken
Helicaes helped by 2 enzyme
TopoisomerasePrevent super coil (super twist)
that if occur lead to prevent
replication
Topoisomerase II
(Gyrase)
Topoisomerase I
1- Cut in 2 strand
2- Need ATP
3- Make negative
supercoil by making
break in phosphodiester
bond
1- Cut in one strand
2- Don’t need ATP
3- Prevent positive
supercoil
Single stranded binding
protein (SSBP)
Bind to single stranded DNA
prevent it from reunion
Formation of new complementary
strand
Always new DNA strand grow from
5 to 3
direction
strand Leading A-
This strand grow from 5 to 3
indirection of origin of replication
This grow continuously and made by
Pol III
B) Okazaki fragment (lagging strand)
This strand grow from 5 to 3 direction in
opposite of origin of replication
This grow discontinuously and made by
Pol III
The gap (space) filled by DNA Pol I and
the space is ligated By DNA ligase
enzyme
Leading strand
Lagging strand
Synthesis of DNA include
following main steps
RNA primer
1- RNA primer are required to
receive new nucleotide that
added on new strand
2- Primase enzyme synthesize
RNA primer
Pol I remove primer after termination of
replication
There are 1 primer on leading
strand and many primer in lagging
strand
Prof reading effect of DNA Pol III
Prof reading means ability to
remove any wrong nucleotide
added during synthesis as pairing
A=G must be A=T
DNA Pol IIHas role in repair of DNA
NB. Replication of DNA has high
fidelity means any error during
synthesis is corrected
Role in replication Comment
Broke hydrogen bond separation of helixDNA helicase (dan
B)
Bind to single stranded DNA prevent it
from reunionSSBP
synthesize RNA primerPrimase
Synthesis of leading strand
Okazaki fragmentDNA Pol III
Remove primer
Fill the gap in lagging strandDNA Pol I
Prevent super coil (super twist)Gyrase
(topoisomerase II)
Join the 2 end of DNA need ATPDNA ligase
Eukaryotic DNA replication
What are telomeres and telomerase?
A telomere is a repeating DNA
sequence (TTAGGG) at the end of the
body's chromosomes. . Telomeres
function by preventing chromosomes
from fusion of their ends.
Telomerase, is an enzyme
made of protein and RNAsubunits that elongates
chromosomes by adding
TTAGGG sequences to
the end chromosomes.
Because these somatic cells has
little telomerase, they age.
The result of aging cells an
aging body.
If telomerase is activated in a
cell, the cell will continue to grow
and divide. lead to cancer.
Telomerase has reverse
transcriptase activity
DNA transcription RNA
RNA reverse transcriptase (RT) DNA
telomerase Telomer
Eukaryotic DNA polymerase
Pol α synthesis of RNA primer and
lagging strand
Pol β DNA repair
Pol γ synthesis of mitochondrial DNA
Pol δ synthesis of leading strand
Pol ε removal of RNA primer
Difference between Eukaryotic
and prokaryotic DNA
replication
Prokaryotic DNA
replication
Eukaryotic DNA
replication
One
One
Primase
DNA Pol III
DNA Pol II
Pol III
Absent
Multiple
Multiple
DNA Pol α
DNA Pol α
DNA Pol β
Pol δ
Present
1.Origin of
replication
2.Replication fork
3.Primer synthesis
4.Lagging strand
synthesis
5.DNA repair
6.Leading strand
7.Telomerase