Name and briefly describe two major base damage repair pathways.

Name and briefly describe two major base damage repair pathways.

• A. Mismatch repair and homologous recombination.
• B. Base excision repair and nucleotide excision repair.
• C. Non-homologous end joining and transcription-coupled repair.
• D. Direct repair and error-prone repair.

Answer: (B)

Two major ways cells fix damaged DNA bases are base excision repair and nucleotide excision repair. Base excision repair targets small, non-helix-distorting lesions: a damaged base is removed by a DNA glycosylase, creating an abasic site; an AP endonuclease cuts the backbone, then DNA polymerase fills the gap and DNA ligase seals the final nick. Nucleotide excision repair handles bulky, helix-distorting damage: damage is recognized, the surrounding DNA is unwound, two incisions are made on either side of the lesion, a short DNA segment containing the damage is removed, and a replacement DNA strand is synthesized and sealed. Together, these pathways cover the common spectrum of base damage—BER for small changes and NER for larger, distortion-causing lesions. Other repair mechanisms listed address different problems, such as mismatches from replication or breaks in the DNA backbone, rather than base damage repair.

Two major ways cells fix damaged DNA bases are base excision repair and nucleotide excision repair. Base excision repair targets small, non-helix-distorting lesions: a damaged base is removed by a DNA glycosylase, creating an abasic site; an AP endonuclease cuts the backbone, then DNA polymerase fills the gap and DNA ligase seals the final nick. Nucleotide excision repair handles bulky, helix-distorting damage: damage is recognized, the surrounding DNA is unwound, two incisions are made on either side of the lesion, a short DNA segment containing the damage is removed, and a replacement DNA strand is synthesized and sealed. Together, these pathways cover the common spectrum of base damage—BER for small changes and NER for larger, distortion-causing lesions. Other repair mechanisms listed address different problems, such as mismatches from replication or breaks in the DNA backbone, rather than base damage repair.