Question

Error-free repair of double strand breaks in DNA is accomplished by

• A. Non-homologous end-joining
• B. Base excision repair
• C. Non-homologous recombination
• D. Mismatch repair

Hint:

Non-homologous end-joining is crucial for repairing double-strand breaks, especially in the absence of a homologous template, to prevent genomic instability.

Answer 1

The Correct Option is A

Non-homologous end-joining (NHEJ) is the primary mechanism used to repair double-strand breaks (DSBs) in DNA. NHEJ is considered an error-free repair process because it directly joins the broken ends of DNA without the need for a homologous template, thus preventing errors during DNA repair. This pathway is particularly active in the G1 phase of the cell cycle.

(1) Non-homologous End-Joining:
- NHEJ works by ligating the two ends of a double-strand break, often without requiring a template. This makes it a quick but highly efficient repair mechanism, especially in cells that are not in the S or G2 phase, where homologous recombination is more common.

(2) Why Other Options Are Incorrect:
- Base excision repair (Option 2) is a repair mechanism for single-strand breaks or modified bases, not double-strand breaks.
- Non-homologous recombination (Option 3) is not a typical term used for DNA repair. Homologous recombination (HR) is the process that involves a homologous template for error-free repair of double-strand breaks.
- Mismatch repair (Option 4) is involved in correcting mismatched nucleotides during DNA replication, not in repairing double-strand breaks.

Conclusion: The non-homologous end-joining pathway is the mechanism that facilitates the error-free repair of double-strand breaks in DNA.