replication patterns

1. DNA REPLICATION
By,
SWATHILAKSHMI
OST-2021-20-26

2.  Rolling circle replication
 The Cairns model of replication

3. Introduction
 Process of producing 2 identical copies from one original DNA molecule
 3 basic steps
1. Initiation
2. Elongation
3. Termination
 In eukaryotes –linear structure
In prokaryotes – plasmid- “rolling circle replication”

4. ROLLING CIRCLE MODEL OF DNA REPLICATION

5.  Replication in eukaryotes is bidirectional, this type is unidirectional.
 Ideal example of this type is the circular plasmid of bacteria, as it happens
only in circular genomes.

6.  Circular dsDNA will be ‘nicked’
 3’ end is elongated
 5’ end is displaced
 Replication of both “uninicked” and displaced as ssDNA.
 Displaced DNA circulates and synthesis its own complementary strands.

7. INTIATION
 Cleave phosphate ends by action of:
1. Helicase
2. Topoisomerases
3. SSBPs

8. ELONGATION
 -OH group of broken strand.
 The polymerase will start to move in a circle for elongation
 End will be displaced
 It will grow like a waving thread

9. TERMINATION
 The linear DNA molecule is cleaved from the circular resulting in a:
a. Double stranded circular DNA molecule
b. Single stranded linear molecule.
 The linear single stranded molecule is circularized by the action of ligase and
then replication to double stranded circular plasmid molecule.

11. Ex: Conjugation of F+ and F- bacteria

12. Examples
 HHV-60
 Hepatitis delta virus

13. The cairns model of DNA replication
 Dr. J Cairns used autoradiography to demonstrate semi- conservative
model of replication
 He grew E. Coli on a medium contain 3H-thymine.
 The DNA was then extract and subjected to autoradiography

15.  The E. Coli DNA is circle.
 The DNA is replicated while maintaining the integrity of the circle.
 An intermediate theta structure forms.
 Replication of the DNA seems to be occuring at one or two moving junctionsin
the circle.
 The DNA is unwound at given point and replication proceed at y junction, in
semi conservative manner.

17. Thankyou