Question

Which enzyme is responsible for relieving supercoiling during DNA replication?

• A. DNA ligase
• B. Helicase
• C. Topoisomerase
• D. Primase

Hint:

Topoisomerase = \textbf{Tension remover}. Cuts, relaxes, and rejoins DNA to prevent supercoiling.

Answer 1

The Correct Option is C

Concept: During DNA replication, the double helix must unwind to allow replication machinery to access the strands. This unwinding creates torsional strain ahead of the replication fork, leading to supercoiling of DNA. Different enzymes involved in DNA replication have specific roles:

• Helicase: Unwinds the DNA double helix.
• Topoisomerase: Relieves supercoiling by cutting and rejoining DNA strands.
• Primase: Synthesizes RNA primers.
• DNA ligase: Joins Okazaki fragments.

Step 1: Understand the problem of supercoiling.
As helicase unwinds DNA, the region ahead becomes overwound, creating tension and supercoils.
Step 2: Identify the enzyme that resolves this tension.
Topoisomerase cuts one or both strands of DNA, allowing it to rotate and relieve the stress, then reseals the strands.
Step 3: Differentiate from other enzymes.

• Helicase unwinds but does not relieve supercoiling.
• Ligase joins DNA fragments.
• Primase initiates synthesis.

Step 4: Conclude the answer.
Thus, topoisomerase is responsible for relieving supercoiling during DNA replication.