Which two pathways repair double-strand breaks in cells?

Which two pathways repair double-strand breaks in cells?

• A. Base excision repair and nucleotide excision repair
• B. Homologous recombination and non-homologous end joining
• C. Mismatch repair and base excision repair
• D. Translesion synthesis and nucleotide excision repair

Answer: (B)

A key point is how cells fix breaks that sever both strands of DNA. There are two main repair routes: homologous recombination uses a sister chromatid as a perfect template to restoring the original sequence accurately, which makes it high-fidelity and is favored when a sister chromatid is available (during S/G2 phases). The other route is non-homologous end joining, which simply mends the broken ends together, a quicker fix that can function anytime but is more error-prone because it doesn’t rely on a template. The other repair systems listed address different problems. Base excision repair and nucleotide excision repair fix lesions on a single DNA strand, not breaks across both strands. Mismatch repair corrects replication errors, not breaks. Translesion synthesis helps the replication machinery bypass damage, rather than rejoining double-strand breaks. So the two pathways that repair double-strand breaks are homologous recombination and non-homologous end joining.

A key point is how cells fix breaks that sever both strands of DNA. There are two main repair routes: homologous recombination uses a sister chromatid as a perfect template to restoring the original sequence accurately, which makes it high-fidelity and is favored when a sister chromatid is available (during S/G2 phases). The other route is non-homologous end joining, which simply mends the broken ends together, a quicker fix that can function anytime but is more error-prone because it doesn’t rely on a template.

The other repair systems listed address different problems. Base excision repair and nucleotide excision repair fix lesions on a single DNA strand, not breaks across both strands. Mismatch repair corrects replication errors, not breaks. Translesion synthesis helps the replication machinery bypass damage, rather than rejoining double-strand breaks. So the two pathways that repair double-strand breaks are homologous recombination and non-homologous end joining.