Question

Which of the following helps in opening of DNA double helix in front of replication fork?

• A. Topoisomerase
• B. DNA polymerase I
• C. DNA gyrase
• D. DNA ligase

Hint:

DNA gyrase, a type of topoisomerase, helps relieve supercoiling tension ahead of the replication fork and enables the DNA strands to unwind for replication.

Answer 1

The Correct Option is C

Let's analyze each option:
(1) Topoisomerase: Topoisomerase helps relieve the torsional strain in the DNA ahead of the replication fork by creating temporary single-strand breaks, but it does not directly open the double helix. Hence, this is not the correct answer.
(2) DNA polymerase I: DNA polymerase I is involved in removing RNA primers and filling the gaps with DNA. It does not help in opening the DNA double helix. Hence, this is not the correct answer.
(3) DNA gyrase: DNA gyrase is a type of topoisomerase that helps relieve the supercoiling tension ahead of the replication fork. It introduces negative supercoils, thus helping in opening the DNA double helix for replication. This is the correct answer.
(4) DNA ligase: DNA ligase is responsible for sealing the nicks in the DNA backbone after replication. It does not play a role in opening the DNA double helix. Hence, this is not the correct answer.
Conclusion: The correct answer is Option 3: DNA gyrase as it helps in opening the DNA double helix in front of the replication fork.