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
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
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
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