DNA replication in eukaryotes occurs in the nucleus and proceeds in the 5' to 3' direction. It involves several enzymes including helicase, which opens the DNA helix, and DNA polymerase epsilon and delta, which synthesize the leading and lagging strands respectively. Replication occurs through initiation, elongation, and termination steps. At the origin of replication, a pre-replication complex forms and the replication fork bubbles outwards. RNA primers are laid down and DNA synthesis occurs continuously on the leading strand but discontinuously on the lagging strand. The primers are later removed and the gaps filled in.

1. DNA replication in
eukaryotes
Presented by;
Name; Sadia Abid
Roll Number; 855

3. . It occurs in nucleus.
. Synthesis occurs in 5__3 direction.
Enzymes of DNA Replication;
Helicase;
Opens up the DNA helix.
RF_A or replication factor A;
Held two strands separately.
Topoisomerase 1 and 2;
Relax supercoiling in the DNA a
head of replication fork.
PCNA;
Isa DNA clamp that act as a procesdivety
factor for DNA polymerase.

4. Replication factor C or RF_C;
Load PCNA on DNA.
Primase;
Form RNA primer.
DNA pol epsilon;
Synthesis of leading strand.
DNA pol delta;
Synthesis of lagging strand.
RNAse H;
Remove primers.
Lygase;
Nick is sealed and formation of phosphodiester
bond.

5. Steps of eukaryotic replication;
It has 3 steps.
1. Initiation.
2. Elongation.
3. Termination.
Initiation;
It inovlves the identification of origin sites which
are usually rich in adenine and thymine.
. Eukayotic cells have mutiple origin sites which are present
on special sequence of DNA known as autonomously
replicating sequence.
. At the origin site of replication, a pre replication complex
is made by the combination of many initiation proteins .This
pre replicating complex is then converted into initiation
complex.

7. Replication fork;
At origin replication bubble forms.
A helicase using the energy from ATP hydrolysis opens up
the dna helix and establish replication fork that will
progressively move away from the origin.

8. Rf A bind to unwound singal stranded DNA.
The opening of double helix causes supercoiling in
the DNA ahead of replication fork . These are
resolved with the action of topoisomerases.

9. Elongation;
After unwinding RNA primer
synthesis is performed by primase which is tightly
associated with DNA pol alpha.
. After the formation of primer synthesis of leading
and lagging strand take place in continous and
discontinous manner.

11. Leading strand synthesis;
DNA pol epsilon synthesize nucleotides on leading
strand.
. It will continously add nucleotides leading to
continous process of replication in 5_3 direction. Thus
it will require only a single RNA primer.
. Finally the primers are removed by RNAse H and the
gap is filled by DNA pol.
. Nick is sealed by DNA ligase.

12. Significance of eukaryotic replication;
Replication is a fundamental process which is essential
for cell growth and division.
.DNA replication involves the generation of new
molecule of DNA which is crucial for life.
. It conserves the all genome for next generation.