Answer to Question 2 from November, 2002
2. (7 points) Which specific repair pathway(s) is/are primarily responsible for repairing the following types of damage. In answering this question, you should consider non-excision pathways such as homologous recombination in addition to excision pathways such as BER.
- AP site
- uracil
- thymine glycol
- 3-methyl adenine
- cyclobutane pyrimidine dimers
- T-G mismatch
- double-strand break
- BER. Note: AP sites are generated and then repaired as part of the complete BER pathway. When AP sites are generated by spontaneous base loss, they can easily be repaired by the downstream portion of the BER pathway.
- BER. If the uracil in DNA is mismatched, it can also be repaired by the mismatch repair pathway.
- BER. Although the XPG protein (normally required for NER) participates in transcription-coupled repair of thymine glycols, the rest of the NER pathway does not participate. The only correct answer here is BER.
- BER. Many of you were confused by this question, because you recalled that 1-methyl adenine can also be repaired by a direct reversal process involving AlkB. But the question asked about 3-methyl adenine, not 1-methyl adenine.
- NER, and also direct reversal by CPD photolyase.
- T-G mismatches can be repaired by both MMR and BER.
- Homologous recombination (HR) and non-homologous end joining (NHEJ).
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