replication patterns
- 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