Which repair pathway removes a single damaged base and fills the gap?

Which repair pathway removes a single damaged base and fills the gap?

• A. Base excision repair removes bulky lesions.
• B. Nucleotide excision repair removes single damaged bases.
• C. Mismatch repair removes single damaged bases.
• D. Base excision repair removes single damaged bases via glycosylases and fills the gap.

Answer: (D)

Base excision repair targets small, damaged bases. It starts with a DNA glycosylase recognizing the altered base and removing just that base, creating an abasic site. The backbone is then nicked, and a DNA polymerase fills in the resulting single-nucleotide gap before ligase seals the strand. This sequence—removing a single damaged base and filling the small gap—is exactly what base excision repair does. In contrast, bulky, helix-distorting lesions are handled by nucleotide excision repair, and mismatches from replication are fixed by mismatch repair, so the described mechanism specifically matches base excision repair.

Base excision repair targets small, damaged bases. It starts with a DNA glycosylase recognizing the altered base and removing just that base, creating an abasic site. The backbone is then nicked, and a DNA polymerase fills in the resulting single-nucleotide gap before ligase seals the strand. This sequence—removing a single damaged base and filling the small gap—is exactly what base excision repair does. In contrast, bulky, helix-distorting lesions are handled by nucleotide excision repair, and mismatches from replication are fixed by mismatch repair, so the described mechanism specifically matches base excision repair.