This Slide Is explanation of Mechanism of DNA Replication In Eukaryotes. As we know we all have DNA as the genetic material and So we should know how this DNA getting Duplicated so that it'll pass to daughter cells.

1. DNA REPLICATION
IN EUKARYOTES

2. ❖WHAT IS DNA REPLICATION.
❖MECHANISM OF DNA REPLICATION IN EUKARYOTES.
❖DNA REPLICATION IN EUKARYOTES.

3. DNA REPLICATION :
▪ The process by which DNA molecule synthesizes it's own
identical copy (DNA TO DNA) is known as replication. The DNA
so formed is exactly similar to the parent DNA.
▪ Replication occurred inside the chromosome .the parent
DNA strand function as a template for the synthesis of new
DNA strand.the new DNA is formed in the semi-
conservative process .
• It has 2 strand ,one is lagging strand and another one
is leading strand .
• Lagging strand discontinuously synthesis and it is also know as
okazaki fragments.And leading strand continues synthesis of
deoxyribonucleotide.

4. ( FIG : Replication fork showing major event in DNA replication.)

5. REPLICATION:-
• Replication in eukaryots is more complex,than in prokaryotic.
• Replication In eukaryots like SACCAROMYCES cerevisiae.
• The origin of replication is known
as autonomous replication sequence (ARS), Which is found in
more than one number.
• Each being 200 base pair in length .
• Eukaryotes replication also comprises three phases, they are:-
➢Initiation.
➢Elongation.
➢Termination.

6. ◦ Contains multiple Origin of Replication called
Autonomously replicating Sequences or ARS.
◦ In Yeast ARS is 200 bp in length containing several sub
domains.
◦ ACS (A-T rich consensus sequence) domain of 11 bp long
is the core component in ARS.
◦ Second domain to 3’ end called Domain B is the site for
binding of initiator protein called ORC (Origin Recognition
Complex)
◦ Sequences 5’ to T rich strand of ARS is called Domain C.
Replication in Eukaryotes (ex. Yeast)
INITIATION:-

7. •The melting at ARS is introduced by DNA binding
Protein called ARS Binding Factor-I or ABF-1, which attaches to
Sub domain B3.
•The opening of DNA also requires replication factor-A or
eukaryotes SSB ,T-antigen protein and topoisomerase -I and II.
•The T-antigen by using it's DNA binding domain and in
presence of ATP,it cause local unwinding .
•Two DNA polymerases are required for replication i.e.
DNA pol α & DNA pol δ.
Replication in Eukaryotes

8. •Both polymerases are required for leading & lagging
strand synthesis.
•The primer synthesized by primase which is directly associated
with DNA polymerases α.
•DNA pol δ has 2 subunits & it depends on PCNA (proliferating
Cell Nuclear Anigen).
Replication in Eukaryotes

9. Replication in Eukaryotes
ELONGATION :-
• DNA pol α sythesizes only a short segment of DNA called i-
DNA & the RNA primer is extended by
DNA pol α upto short length & then DNA pol δtakes over DNA
synthesis on both strands due to high processivity.
• Polymerase α cooperates with Primase enzyme for attachment
of RNA primer of both the strands
• 8 components are involved in replication such as, T-
antigen, Replication Protein-A (Eukaryotic
SSB), Topoisomerase-I, Topoisomerase-II, DNA pol α ,
DNA pol δ ,PCNA or Cyclin, Replication Factor C.

10. •Primase associated with DNA pol α to synthesize
RNA primer. Once synthesiszed primer is extended by DNA
pol α upto 20 NTs & then get replaced by DNA
pol δ (called Switching)
•Loading of DNA pol δ is accompanied by RF-C at 3’
end along with PCNA
Replication in Eukaryotes

12.  Removal of primers are done by FEN-1 (Flap
Endonuclease-1) which is associated with DNA pol
δ at 3’ end & degrade the primer from 5’ end of
adjacent fragment .
 Rnase H degrade RNA part of a base paired RNA-Dna
hybrid, but it can’t cleave the phosphodiester bond
between the last rNT & 1st dNT. So this monophosphate
is cleaved by FEN-1.
 DNA pol α has no 3’-5’ proof reading activity &
therefore DNA synthesis occurs with high error.
 Removal of Primer by FEN-1 is followed by resynthesis
of DNA by DNA pol δ with proof reading activity.
Removal of Primers

13. The 'flap endonuclease' FEN1 cannot initiate primer
degradation
because its activity is blocked by the triphosphate group
present at the 5 end of
the primer.

16. • DNA pol δ causes accurate copy synthesis of template strands.
• And after the DNA polymerase delta add the final deoxyribonucleotide ,in
the gap left by the excised primer was filled by DNA ligase.
• Termination: -
• No sequence equivalent to Ter site is known in eukaryotes. In eukaryotes
DNA polymerase cannot replicate the terminal DNA segment of lagging
strand of linear chromosomes.
• The terminal region of DNA is know as telomer .Telomers have unique
features and and enzymes that facilitates rereplication.
• But in case of linear ds DNA telomerase homologous ter-protein helps to
restore the original site of eukaryotes bt not in case of circular DNA.

17. THANK YOU