Final answer:
Base excision repair involves DNA glycosylase ('flipping out'), AP endonuclease, and DNA ligase. All three enzymes are necessary for the successful repair of damaged DNA nucleotides, hence the correct answer is 'A, B, and C are correct'.
Step-by-step explanation:
The question 'Base excision involves?' refers to the steps of the base excision repair (BER) pathway. This DNA repair mechanism fixes damage to a single nucleotide caused by oxidation, alkylation, hydrolysis, or deamination.
- DNA glycosylase initiates the process by 'flipping out' and removing the altered base.
- An AP endonuclease then makes a cut (or 'nicks' the DNA) adjacent to the site of the removed base.
- DNA ligase seals the DNA strand after the gap is filled with the correct nucleotide by DNA polymerase.
Therefore, the correct answer to the question is '5) A, B, and C are correct', as all mentioned enzymes: endonuclease, glycosylase, and ligase are involved in the base excision repair process.