Question

The statements true for topoisomerase-I enzyme
(A). Transiently break one of the two DNA strands.
(B). Break both of the strand of double helix DNA.
(C). Change the linking number in increment of one.
(D). Change the linking number by decreasing one.
Choose the correct answer from the options given below:

• A. (A)and (B) only.
• B. (A) and (C) only.
• C. (B), and (C) only.
• D. (B) and (D) only.

Hint:

Remember the differences between topoisomerases:
- Topoisomerase I: Cuts one strand, changes linking number by 1, does not require ATP.
- Topoisomerase II: Cuts both strands, changes linking number by 2, requires ATP.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Topoisomerases are enzymes that regulate DNA supercoiling by transiently cutting the DNA backbone, allowing the strands to untangle or relax before resealing the cuts.

Step 2: Detailed Explanation:
- Statement A is correct: Type I topoisomerases catalyze the relaxation of supercoiled DNA by introducing a transient single-strand break in the phosphodiester backbone. Type II enzymes break both strands (making Statement B incorrect).
- Statement C is correct: By cutting one strand, passing the unbroken strand through the gap, and resealing the cut, Topoisomerase-I changes the topological linking number (\(Lk\)) of DNA in steps of 1 (i.e., \(\Delta Lk = \pm 1\)). Type II enzymes change the linking number in steps of 2 (making Statement D incorrect).
- Thus, statements (A) and (C) are correct.

Step 3: Final Answer:
The correct statements for Topoisomerase-I are (A) and (C) only.