maintenance of genomes correcting replication errors repairing dna damage
TRANSCRIPT
Maintenance of genomes
• Correcting replication errors
• Repairing DNA damage
Maintenance of genomes
• Replication errors
Inserting a wrong nucleotidecausing a mismatch
Inserting or deleting nucleotidescausing helix distortion
Figure 16.3b Genomes 3 (© Garland Science 2007)
Figure 16.4 Genomes 3 (© Garland Science 2007)
An error in replication can cause a point mutation
Maintenance of genomes
• Replication errors
Inserting a wrong nucleotidecausing a mismatch
Inserting or deleting nucleotidescausing helix distortion
Figure 16.5 Genomes 3 (© Garland Science 2007)
Replication slippage in microsatellites
Table 16.1 Genomes 3 (© Garland Science 2007)
Mismatch repair in E. coli
Mismatch repair in E. coli
Maintenance of genomes
• DNA damage
Physical damage – radiation, heat
Hydrolytic damage
Chemical damage – base modifications, base analogs, intercalating agents
Crosslinks caused by UV light
Figure 16.9 Genomes 3 (© Garland Science 2007)
Cyclobutyl dimers and formation of a (6-4) photoproduct caused by UV light
(results in a deletion)
In some organisms photolyases repair crosslinks
In humans the damaged region is excised and re-synthesized
Maintenance of genomes
• DNA damage
Physical damage – radiation, heat
Hydrolytic damage
Chemical damage – base modifications, base analogs, intercalating agents
Hydrolytic damage to bases
Maintenance of genomes
• DNA damage
Physical damage – radiation, heat
Hydrolytic damage
Chemical damage – base modifications, base analogs, intercalating agents
Base analogs and intercalating agents can cause point mutations and insertions/deletions
Figure 16.6c Genomes 3 (© Garland Science 2007)
Various damages to bases
Direct repair of methylated bases
Figure 16.22a Genomes 3 (© Garland Science 2007)
Base excision repair
Base excision repair (removal of uracil)
Fail-safe glycosylases
Table 16.3 Genomes 3 (© Garland Science 2007)
Nucleotide excision repairin E. coli
Short patch repair
Transcription-linked repair
Double-strand break repair(Non-homologous endjoining)
Double-strand breaks arecaused by ionizing radiation
Figure 16.20 Genomes 3 (© Garland Science 2007)
DNA repair processes
Replication-linked repair
SOS repair in E. coli
Expression of Pol IV and Pol V isinduced by DNA damage.
Switching to translesion DNA polymerases
Figure 16.11 Genomes 3 (© Garland Science 2007)
Effect of mutations on gene expression