Which post-replication repair pathways fix replication errors?

• A. Mismatch repair
• B. Base excision repair
• C. All of the above
• D. Nucleotide excision repair

Answer: (C)

Replication errors can come in several forms, and the cell uses more than one repair route after the DNA has been duplicated to keep the genome accurate. Mismatch repair is the system that scans newly synthesized DNA for mispaired bases and small insertions or deletions that escaped the proofreading activity of DNA polymerase, correcting them to restore proper base pairing. In addition, base excision repair handles damaged or chemically modified bases that could cause mispairing or mutations if left in place—examples include deaminated or oxidized bases. These changes might arise during replication or as a result of damage that the replication machinery encounters. Nucleotide excision repair tackles bulky, helix-distorting lesions that block replication, such as thymine dimers from UV exposure or large chemical adducts; by removing a short single-stranded segment around the lesion and filling it in, it clears obstacles to accurate replication. Since each pathway addresses different kinds of errors or damage that can occur around the time of replication, all of them contribute to fixing replication-related issues.