Question

Pick the correct statement(s) with respect to the inter-conversion of the topoisomers of a circularly closed double stranded DNA.

• A. Only one strand needs to be cut
• B. Both strands have to be cut
• C. No strand needs to be cut
• D. ATP is required for inter-conversion

Hint:

Topoisomerases can catalyze the inter-conversion of topoisomers without requiring cuts in both DNA strands. ATP may be required for certain types of topoisomerases.

Answer 1

The Correct Option is A, B, D

Step 1: Understanding the topoisomerase mechanism.
Topoisomerases are enzymes that can interconvert the topoisomers of circularly closed DNA by introducing transient single- or double-strand breaks. In many cases, only one strand needs to be cut to facilitate the inter-conversion between different topoisomeric forms, although ATP is often required for the reaction.
Step 2: Analyzing the options.
(A) Only one strand needs to be cut: Incorrect — Although one strand may be cut, topoisomerase may also act without cutting both strands in certain cases.
(B) Both strands have to be cut: Incorrect — Cutting both strands is not typically required for topoisomerase action.
(C) No strand needs to be cut: Correct — Some topoisomerases do not require cuts to facilitate inter-conversion.
(D) ATP is required for inter-conversion: Incorrect — ATP may be required for certain topoisomerases, but not for all.
Step 3: Conclusion.
The correct answer is (C) No strand needs to be cut, as topoisomerase activity can occur without cutting strands in some instances.