1. Gene stability and DNA repair… Presented by Minakshisaikia 2nd semester, 23rdFebruary 2010 1

2. “Mutation” 2

3. Mutation… Error in DNA replication. Damaging effects of mutagens(chemicals and radiations). CHEMICALS: Alkylating agents like nitrosoguanidine, nitrosamine, etc. RADIATIONS: X-rays, U.V.rays, etc. 3

4. 1.ERROR IN REPLICATION… 4

5. 2.ONE POSSIBLE EFFECT OF MUTAGEN 5

6. “DNA repair system” 6

7. 7

8. DNA repair in a nut shell… 8

9. 1.PHOTOREACTIVATION /direct repair system… As the name suggests it acts directly on damaged nucleotides, converting each one back to its original structure. 9

10. Thymine dimerisation… 10

11. 2.EXCISION REPAIR SYSTEM… It involves excision of a segment of the polynucleotide containing a damaged site, followed by resynthesis of the correct nucleotide sequence by a DNA Polymerase. 11

12. ‘Excision repair system’ 12

13. 3.MISMATCH REPAIR SYSTEM… It corrects errors of replication, again by excising a stretch of single-stranded DNA containing the offending nucleotide and then repairing the resulting gap. 13

14. Methylation process… 14

15. ‘mismatch repair system’ 15

16. 4.SOS REPAIR SYSTEM… ‘Save Our Souls’ The SOS repair system is an emergency measure for copying with a damaged genome. This is error prone. 16

17. ‘SOS repair system’ 17

18. Conclusion: “A possible definition of mutation is therefore a deficiency in DNA repair…” 18

19. Bibliography… Genomes 3, T.A.Brown Genes vii, Benjamin Lewin Internet, Google Search 19

20. Thankyou… for your patience!!! 20