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#thymine dimers

2 public questions tagged with this topic.

Repair Pathway

Which repair pathway directly reverses thymine dimers?

Pyrimidine dimers induced by UV form cyclobutane rings linking adjacent thymines distorting helix. Cells possess multiple repair strategies. Photoreactivation, also called direct reversal, utilizes DNA photolyase enzyme that specifically binds cyclobutane pyrimidine dimers and uses energy from visible blue light to break cyclobutane ring restoring intact pyrimidines in single step without excision or synthesis. This light-dependent direct repair differs from nucleotide excision repair which cuts and replaces damaged segment, base excision which removes single base, and mismatch repair which co

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Photoreactivation Direct Reversal of Thymine Dimers

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Mutation and Mutagenesis

UV radiation mainly causes formation of

Ultraviolet radiation at 254-280 nm causes adjacent pyrimidines on same strand to undergo photochemical cyclization forming cyclobutane pyrimidine dimers and 6-4 photoproducts, covalently linking C5-C6 double bonds and distorting double helix by kinking backbone about 30 degrees. Thymine-thymine dimers are most frequent due to sequence abundance, blocking transcription and replication leading to mutations if translesion polymerases bypass incorrectly. Nucleotide excision repair employs UvrABC in bacteria and XPC-Rad23 in humans to excise damaged oligonucleotide segment. This principle illustra

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: UV-Induced Pyrimidine Dimer Formation

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