Correct option is D
Explanation-
Statement A- DNA Pol I displays very limited processivity and possesses 3′→5′ exonuclease activity, allowing fidelity of DNA replication - Correct
DNA Pol I has low processivity (doesn’t stay on the DNA long). It has 3′→5′ exonuclease activity, allowing proofreading and error correction, hence supports fidelity.
Statement B - DNA Pol III is suitable for leading strand DNA synthesis due to its high processivity and 5′→3′ exonuclease activity that removes incorrect nucleotides - Incorrect
DNA Pol III does have high processivity, making it suitable for the leading strand. But it does not have 5′→3′ exonuclease activity. It has 3′→5′ exonuclease activity for proofreading. 5′→3′ exonuclease activity is a feature of DNA Pol I, not Pol III.
Statement C - DNA Pol I possesses 5′→3′ exonuclease activity which allows removal of the RNA primer while its 5′→3′ polymerase activity allows it to fill the gap created by removal of the RNA primer - Correct
This is the main role of DNA Pol I during lagging strand synthesis. It removes RNA primers with its 5′→3′ exonuclease activity and fills in the gaps using 5′→3′ polymerase activity.
Statement D - DNA Pol III is suitable for lagging strand DNA synthesis due to its low processivity and 5′→3′ exonuclease activity - Incorrect
DNA Pol III is actually highly processive, even in the lagging strand (with the help of the sliding clamp). Also, again, it does not have 5′→3′ exonuclease activity—that’s DNA Pol I's function.
So, the correct answer is Option d - A and C only
These two statements correctly describe the properties and roles of DNA Polymerase I and III.
