Base excision repair (BER) corrects small, non-helix-distorting base lesions such as deaminated, oxidized, or alkylated bases. Which enzyme initiates BER by recognizing and removing the damaged base?

• A DNA glycosylase ✓
• B AP endonuclease
• C DNA polymerase beta
• D DNA ligase

Explanation

DNA glycosylases are the initiating enzymes of BER. Each glycosylase recognizes a specific type of damaged base and cleaves the N-glycosidic bond between the base and deoxyribose, creating an abasic (AP) site. AP endonuclease then cleaves the phosphodiester backbone at the AP site, DNA polymerase beta fills the gap, and DNA ligase seals the nick. This contrasts with NER, which removes bulky lesions as an oligonucleotide fragment.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.