DNA REPLICATION,SEMI CONSERVATIVE DNA POLYMERASE ENZYME AND ITS ROLE STEPS OF DNA REPLICATION

1. DNA REPLICATION
By – Dr R. K. Upadhyay
PGT, Biology

2. • DNA replication is the process of producing two
identical replicas of DNA from one o DNA
molecule
DNA REPLICATION
• DNA replication occur during the S Phase of
Interphase of cell cycle.

3. DNA Replication is Semiconservative
• Proved by Messelson & Stahl
• Newly synthesised DNA contains one old
strand and one new strand of DNA

4. ENZYMES
ENZYMES ROLES
DNA POLYMERASE POLYMERIZATION
HELICASE UNWINDING OF DNA HELIX ( DENATURATION)
SSB (SNGLE STRAND BINDING PROTEIN) STABILIZES SINGLE STRANDED DNA
TOPOISOMERASE/ GYRASE REDUCE SUPERCOILING IN DNA
PRIMASE SYNTHESIS OF PRIMEERS
DNA LIGASE BINDING OF DNA STRANDS NICK

5. HELICASE ENZYME

6. SSB and TOPOISOMERASE

7. PRIMASE

9. POLYMERIZATION

10. STEPS
• INITIATION
• ELONGALTION
• TERMINATION

11. REPLICATION FORK

12. INITIATION
• Helicase enzyme break the hydrogen bonds
between Nitrogenous bases (denaturation)
• SSB protein binds on ssDNA to prevent
renaturation

13. • Gyrase enzyme reduces tension on DNA
• Primase enzyme added primes on both strand
of DNA at 3’ end.
INITIATION

14. Elongation

16. On the leading strand, DNA synthesis occurs continuously.
On the lagging strand, DNA synthesis restarts many times as
the helix unwinds, resulting in many short fragments called
“Okazaki fragments.”
DNA ligase joins the Okazaki fragments together into a single
DNA molecule

18. Termination
• Termination of DNA replication occurs when the
two forks meet and fuse.