DNA IN EUKARYOTES

1. DNA Replication In
Eukaryotes
Amol pawar

2. Content
• Introduction
• DNA replication
• Initiation
• Elongation
• Termination

3. Introduction
• DNA replication is the most fundamental action .
• It is a biological process & occurs in all living beings .
• It is basis of biological heritance

4. DNA replication
• DNA replication like all other biological process proceed in co -
ordinated process
• Initiation
• Elongation
• Termination

5. Initiation
• DNA replication initiate from specific sequences origin of replication
(ORI) called Replisoms
• It lead to formation of Pre – replication complex ( Pre – RC )
• 1st steps :- association of origin recognizing complex (ORI) with
replication origin
• 2nd steps :- binding of cdc6 protein to ORC
• 3rd steps :- binding of cdt1 & mini chromosome maintenance protein .
• This replication complex assembly occurs during G1 phase prior to S
phase

6. • During the transition between G1 & phase to S phase , CDK proteins
& DDK proteins get attached to the Pre – replication complex
• It transforms the Pre-replication complex into active replication fork .

7. Elongation
• Once the complex forms & cell pass into S phase , then unwinding of
DNA strand takes place
• Unwinding takes places by Helicases & it leads of exposure of 2 DNA
templates
• After unwinding , polymerization of daughter strands takes place
• It occurs with help of DNA polymerase enzymes , there are total 15
DNA polymerase enzymes identified till now but only 3 are involved in
replication process , they are
• DNA polymerase Alpha α , Epsilon ɛ , Delta δ

8. • DNA polymerase alpha (α) :- Associated with enzyme primase , forms
RNA primer which are 8-10 nucleotide long & elongates this RNA
primer by more than 20 nucleotide & then leaves the place
• DNA polymerase epsilon (ɛ) :- It will continuously add nucleotides
leading to continuous process of replication , thus it will require only
one RNA primer at the beginning .
• DNA polymerase delta (δ) :- On lagging strand , DNA polymerase δ
synthesize small fragments of DNA called Okazaki fragments . At the
end of each okazaki fragment DNA polymerase δ runs to previous
okazaki fragment & replace the RNA primer nucleotides with DNA
nucleotides

10. Termination
• The end regions where primers are left are known as Telomere
• Telomers extend the 3’ end of parental strand beyond the 5’ end of
daughter strand , it then behaves as ORI region & recruit telomerase
• Telomerase forms RNA complementary base pair & the process
continues
• Then primers & DNA polymerase helps in further replication

11. Reference
• I – genetics by Peter Russell