Question

Sequence of action of a type II topoisomerase: A. Dissociation of gyrase, B. Translation of unbroken DNA strand, C. Gyrase-DNA complex, D. Ligation, E. Cleavage of DS-DNA.

• A. D, A, B, C, E
• B. C, E, B, D, A
• C. C, D, A, E, B
• D. B, A, D, E, C

Hint:

Type II topoisomerase works by binding DNA, cutting both strands, passing another DNA segment, ligating the break, and then dissociating.

Answer 1

The Correct Option is B

Concept:
Type II topoisomerase changes DNA topology by making transient double-stranded breaks, passing another DNA segment through the break, and then resealing the DNA.

Step 1: Formation of gyrase-DNA complex.
The enzyme first binds to DNA and forms a gyrase-DNA complex. \[ \text{First step} = C \]

Step 2: Cleavage of double-stranded DNA.
The enzyme cuts both strands of DNA temporarily. \[ \text{Second step} = E \]

Step 3: Passage of unbroken DNA strand.
An unbroken DNA segment is passed through the break. \[ \text{Third step} = B \]

Step 4: Ligation.
The broken DNA strands are resealed. \[ \text{Fourth step} = D \]

Step 5: Dissociation of gyrase.
Finally, the enzyme dissociates from DNA. \[ \text{Fifth step} = A \] Thus, the correct order is: \[ C,\ E,\ B,\ D,\ A \] \[ \therefore \text{Correct Answer is (B)} \]