Lecture17 (1)

Lecture17 (1) - BIS101 12/2/10 Lecture17:ChromosomeMutation...

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BIS101 12/2/10 Lecture 17: Chromosome Mutation
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LECTURE 11: Outline Chromosome changes Chromosome rearrangements Changes in chromosome number Polyploidy Aneuploidy Cancer genetics
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Comparison of DNA Mutation Repair, Double-Stranded Break Repair & Recombination
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Homologous Recombination Used to repair DNA double-strand-breaks (DSBs) and to restart stalled or broken replication forks. Homologous recombination is a templated repair mechanism. A homologous chromosome is used as the repair template. Homologous recombination is conservative and repair occurs with a high degree of fidelity.
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One strand at the ends of the broken chromosome is degraded to form long single-strand tails with 3’- ends. The 3’-tail is bound by many molecules of a RecA- family protein (RecA in bacteria; Rad51 in mammals) to form a nucleoprotein filament. Rad51 nucleoprotein filaments can locate homologous sequences on another chromosome and then exchange base-pairs between the broken end and the intact “donor” duplex. This is called Strand Invasion
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Ends are first “trimmed” to create flush DSB-ends that can be ligated by a special DNA ligase called Lig4. NHEJ is a non-conservative repair mechanism, i.e. it is mutagenic because some nucleotides at the break site are lost. Non-Homologous End Joining
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the use of a homology-dependent repair system? a)Base excision repair
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Lecture17 (1) - BIS101 12/2/10 Lecture17:ChromosomeMutation...

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