DNA repair mechanisms _______________.

Question

BlackTom AI · Accepted Answer

DNA repair mechanisms repair damage and mismatches in genomes.

1) Relevant knowledge points and concepts
- DNA is constantly subject to damage (UV, chemical adducts, oxidative lesions) and replication errors (mismatched bases).  
- Cells have multiple repair pathways specialized for different lesions: direct repair, base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), and double-strand-break repair (homologous recombination and non-homologous end joining).  
- The overall role of these pathways is to recognize abnormal DNA, remove or reverse the lesion/mismatch, restore the correct sequence, and maintain genome integrity.

2) Step-by-step reasoning process
- Detection: Damage or mismatches are recognized by sensor proteins (e.g., MutS/MutL in MMR, XPC in NER).  
- Removal: The damaged base or oligonucleotide segment is excised (glycosylases in BER remove damaged bases; endonucleases cut out oligonucleotides in NER).  
- Resynthesis: DNA polymerase fills the resulting gap using the complementary strand as template.  
- Ligation: DNA ligase seals the backbone to restore a continuous, correct DNA molecule.  
These steps directly address damage and mismatches in the genome, lowering mutation rates.

3) (No numerical calculations required; process steps shown above.)

4) Why the correct answer is correct
The phrase “repair damage and mismatches in genomes” precisely describes the primary function of DNA repair pathways: to correct chemical damage and base-pairing errors in DNA so genomic information is preserved.

5) Why the other options are incorrect
- “Fix every mutation event”: Incorrect because repair reduces but does not eliminate mutations—some lesions escape repair or become fixed as mutations.  
- “Are needed for horizontal gene transfer”: Incorrect; horizontal gene transfer is a process of acquiring foreign DNA (conjugation, transformation, transduction) and does not require DNA repair mechanisms, although repair can act on incorporated DNA.  
- “Fix problems in replication, transcription, and translation”: Partly misleading—repair fixes DNA problems that affect replication/transcription, and transcription-coupled repair targets lesions encountered during transcription, but it does not fix translation errors (which are errors in mRNA/protein synthesis).

Conclusion: Therefore, the correct answer is “repair damage and mismatches in genomes,” which matches the provided answer.

DNA repair mechanisms _______________. Single choice

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