Correct option is B
The correct answer is (b).
In long-patch base excision repair (BER) in humans, the process involves the following enzymes:
1. Glycosylase removes the damaged base, creating an abasic site.
2. AP endonuclease 1 cleaves the phosphodiester backbone at the abasic site.
3. DNA Polδ (or Polβ in some contexts) fills in the gap with new DNA, performing the repair synthesis.
4. Flap endonuclease 1 removes the displaced DNA flap generated during repair synthesis.
5. Finally, DNA Ligase 1 seals the nick in the DNA, completing the repair.
Incorrect options-
Option (a): Lyase activity is part of short-patch BER involving DNA Polβ’s lyase function, so this is not part of long-patch BER.
Option (c): Uses DNA Polβ and DNA Ligase 1, but DNA Polβ is primarily involved in short-patch repair.
Option (d): Combines DNA Polδ (correct for long-patch) with DNA Ligase 3 (correct for short-patch), which is inconsistent with the long-patch BER pathway.
