Which process involves mismatch repair after DNA replication?

Which process involves mismatch repair after DNA replication?

• A. Mismatch repair system
• B. Nucleotide excision repair
• C. Base excision repair
• D. Double-strand break repair

Answer: (A)

The concept here is how cells fix errors that slip past the proofreading done during DNA replication. After the DNA has been copied, the mismatch repair system scans the new strand for mispaired bases and small insertion/deletion loops that polymerase proofreading missed. It differentiates the newly synthesized strand from the template strand using strand-specific signals (in bacteria, differences in methylation; in eukaryotes, nicks in the lagging strand help identify the new strand). Once a mismatch is found, a section of the new strand containing the error is removed, and DNA polymerase fills in the gap followed by ligation, restoring correct base pairing. This targeted repair lowers the mutation rate and maintains genetic stability. Other pathways fix different problems: nucleotide excision repair removes bulky, helix-distorting lesions like thymine dimers; base excision repair fixes small, damaged bases; and double-strand break repair handles breaks in both DNA strands through mechanisms like homologous recombination or non-homologous end joining.

The concept here is how cells fix errors that slip past the proofreading done during DNA replication. After the DNA has been copied, the mismatch repair system scans the new strand for mispaired bases and small insertion/deletion loops that polymerase proofreading missed. It differentiates the newly synthesized strand from the template strand using strand-specific signals (in bacteria, differences in methylation; in eukaryotes, nicks in the lagging strand help identify the new strand). Once a mismatch is found, a section of the new strand containing the error is removed, and DNA polymerase fills in the gap followed by ligation, restoring correct base pairing. This targeted repair lowers the mutation rate and maintains genetic stability.

Other pathways fix different problems: nucleotide excision repair removes bulky, helix-distorting lesions like thymine dimers; base excision repair fixes small, damaged bases; and double-strand break repair handles breaks in both DNA strands through mechanisms like homologous recombination or non-homologous end joining.