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Gene stability and DNA repair…

Presented by Minakshi saikia2nd semester, 23rd February 2010

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“Mutation”

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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.

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1.ERROR IN REPLICATION…

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2.ONE POSSIBLE EFFECT OF MUTAGEN

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“DNA repair system”

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PhotoreactivationOrDirect repair system

SOS repair system

DNA REPAIR

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DNA repair in a nut shell…

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1.PHOTOREACTIVATION /direct repair system…

As the name suggests it acts directly on damaged nucleotides, converting each one back to its original structure.

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Thymine dimerisation…

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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.

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‘Excision repair system’

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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.

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Methylation process…

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‘mismatch repair system’

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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.

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‘SOS repair system’

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Conclusion:

“A possible definition of mutation is therefore a deficiency in DNA repair…”

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Bibliography…Genomes 3, T.A.BrownGenes vii, Benjamin LewinInternet, Google Search

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Thankyou… for your patience!!!