Following statements are made about DNA base excision repair (BER):
A. BER process begins with a DNA glycosylase, which extrudes a base in damaged base pair, then clips out the damaged base.
B. In bacteria, DNA polymerase III fills is the missing nucleotide in BER.
C. Eukaryotic apurinic/apyrimidinic (AP) endonuclease (APE1) performs proofreading activities.
D. APE1 possesses 5’→3’ exonuclease activity.
Which one of the following options shows combination of all correct statements?

Correct option is B

Explanation :Let's review each statement in detail:

• Statement A is correct: The BER process begins with a DNA glycosylase that recognizes and removes a damaged base by cleaving the glycosidic bond, leaving behind an abasic site.

• Statement B is incorrect: In bacteria, DNA polymerase III is not the primary enzyme involved in filling the missing nucleotide during BER. In bacterial BER, DNA polymerase I is usually responsible for filling the gap after base removal.

• Statement C is correct: Eukaryotic apurinic/apyrimidinic (AP) endonuclease (APE1) performs essential functions in BER, including cleaving the DNA backbone at the abasic site. APE1 also plays a role in DNA repair beyond just its endonuclease activity.

• Statement D is incorrect: APE1 does not possess 5' → 3' exonuclease activity, but rather 3' → 5' exonuclease activity, which is important for processing the abasic site in the repair process.

Information Booster:

1. DNA glycosylase initiates the BER process by recognizing and removing damaged bases, leaving behind an abasic site.

2. APE1 is crucial for processing the abasic site during BER. It cleaves the DNA backbone, allowing for the proper repair of the DNA strand.

3. APE1 does not perform proofreading activities but is involved in the excision of damaged bases during repair.

4. The role of APE1 in cleaving the DNA backbone at abasic sites is an essential part of the base excision repair pathway.

5. In bacteria, DNA polymerase I is the key polymerase responsible for filling the gap after the removal of the damaged base.

Additional Information:

• Statement A (Correct): The process of BER begins with DNA glycosylase, which identifies and removes the damaged base from the DNA strand.

• Statement B (Incorrect): In bacterial BER, DNA polymerase I is the primary polymerase involved in filling in the missing nucleotide, not DNA polymerase III.

• Statement C (Correct): APE1 is involved in cleaving the DNA backbone at the abasic site, an essential step in BER.

• Statement D (Incorrect): APE1 has 3' → 5' exonuclease activity, not 5' → 3' exonuclease activity, which makes the statement incorrect.