Question
Choose the correct sequence for how a type I topoisomerase relaxes DNA.
A. DNA release
B. Cleavage and opening of gate
C. Rejoining of cleaved strand
D. Strand passage
Choose the correct answer from the options given below :
This question was previously asked in
CUET PG 2026 Agri-Business Management Question Paper (25-Mar-2026) (Shift 2)
The correct answer is
B, D, C, A
Understanding Type I Topoisomerase DNA Relaxation Mechanism
Type I topoisomerases function to relax supercoiled DNA by transiently breaking and rejoining one DNA strand. This process involves several key steps performed in a specific order.
Sequence of DNA Relaxation
The mechanism proceeds as follows:
- B. Cleavage and opening of gate: The enzyme initially binds to the DNA and introduces a temporary single-strand break (nick). This cleavage event allows the enzyme to create an opening or 'gate' in the DNA backbone.
- D. Strand passage: Through this gate, the intact, opposite DNA strand passes. This passage alters the DNA's topological state.
- C. Rejoining of cleaved strand: Following the passage of the intact strand, the enzyme reseals the nicked DNA strand, restoring the phosphodiester backbone.
- A. DNA release: Finally, the type I topoisomerase detaches from the DNA molecule, leaving it in a relaxed state.
Therefore, the correct sequence representing the action of type I topoisomerase in DNA relaxation is B → D → C → A.
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