Maintenance of genomes Correcting replication errors Repairing DNA damage.

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Presentation transcript:

Maintenance of genomes Correcting replication errors Repairing DNA damage

Maintenance of genomes Replication errors Inserting a wrong nucleotide causing a mismatch Inserting or deleting nucleotides causing 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 nucleotide causing a mismatch Inserting or deleting nucleotides causing 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

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 repair in E. coli Short patch repair

Transcription-linked repair

Double-strand break repair (Non-homologous end joining) Double-strand breaks are caused by ionizing radiation

Figure Genomes 3 (© Garland Science 2007) DNA repair processes

Replication-linked repair SOS repair in E. coli Expression of Pol IV and Pol V is induced by DNA damage.

Switching to translesion DNA polymerases

Figure Genomes 3 (© Garland Science 2007) Effect of mutations on gene expression

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