Which repair pathway fixes base damage by removing a single base and is initiated by a DNA glycosylase?

Which repair pathway fixes base damage by removing a single base and is initiated by a DNA glycosylase?

• A. Nucleotide excision repair
• B. Mismatch repair
• C. Homologous recombination
• D. Base excision repair

Answer: (D)

Base excision repair handles small base-level damage. It begins when a DNA glycosylase recognizes a damaged or inappropriate base and removes it by cleaving the N-glycosidic bond, leaving an apurinic/apyrimidinic (AP) site. This creates a nickable site in the backbone, which an AP endonuclease then cleaves. A DNA polymerase fills the resulting gap, and DNA ligase seals the strand. This sequence specifically addresses single-base lesions, exactly what the question describes. In contrast, nucleotide excision repair targets bulky, helix-distorting lesions by removing a short oligonucleotide around the damage; mismatch repair fixes mispaired bases after replication; homologous recombination repairs double-strand breaks using a sister chromatid as a template. Thus the described mechanism aligns with base excision repair.

Base excision repair handles small base-level damage. It begins when a DNA glycosylase recognizes a damaged or inappropriate base and removes it by cleaving the N-glycosidic bond, leaving an apurinic/apyrimidinic (AP) site. This creates a nickable site in the backbone, which an AP endonuclease then cleaves. A DNA polymerase fills the resulting gap, and DNA ligase seals the strand. This sequence specifically addresses single-base lesions, exactly what the question describes.

In contrast, nucleotide excision repair targets bulky, helix-distorting lesions by removing a short oligonucleotide around the damage; mismatch repair fixes mispaired bases after replication; homologous recombination repairs double-strand breaks using a sister chromatid as a template. Thus the described mechanism aligns with base excision repair.