Molbiol 2011-09-reparation-recombination
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Transcript of Molbiol 2011-09-reparation-recombination
DNA repair
Mutations
The Ames Test
The repair systems
• Mainly, the undamaged complementary strand acts as a template for the DNA polymerases involved in repair– Mismatch repair
– Base excision repair
– Nucleotide excision repair
– Direct repair
– Recombinational repair
– Error-prone repair
Mismatch repair
Mismatch mechanism
Mutations in mut proteins?
Base excision repair
Repairing apurinic and apyrimidinic
sites
Nucleotide excision
repair
Mutations in excision
repair systems
Direct repair
Methyltransferase
When both strands are damaged
SOS system
Recombination
Recombination• Three forms
– Homologous
– Site specific recombination
– Transposition
Recombinational repair
DNA replication stalled because of lesion
Replication continues
Repair
Recombination
Blockade
Replication following a break
Blockade
Recombination
Reseal
Meiotic recombination
Recombination between homologous a chromosomes
Recombination permits genetic
mappingIf each recombinant occurs at 2.5%, then the total map distance is 5% or 5 m.u.
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Generation
The simple minded
mechanism (incorrect) of
meiotic recombination
Gene conversion indicates that another mechanism must be operable
Gene conversion on a molecular level
The mechanism of homologous recombination
The topology
of the Holliday structure
Resolution of the Holliday structure
Non-identical sequences
The enzymes of recombination
Rec A
Site specific recombination
Site specific recombination within one molecule
Use of recombinase to
resolve a dimeric genome
Transposition
Direct transposition
Replicative transposition
Retroviruses