(A) DNA replication
(B) mRNA translation
(C) RNA polymerase
(D) active transport of nutrients into the cell
Quinolones like ciprofloxacin block bacterial DNA processes essential for growth. This SEO article explains Q.66 with the correct answer and breakdowns of all options for microbiology exams.
Correct Answer
The correct answer is (A) DNA replication.
Quinolones target bacterial type II topoisomerases—DNA gyrase and topoisomerase IV—stabilizing cleavage complexes that fragment DNA during replication. This halts unwinding needed for replication forks, causing lethal double-strand breaks.
Option Breakdowns
(A) DNA replication
Quinolones trap gyrase-DNA complexes, preventing religation and blocking supercoil relaxation for replication progression.
They kill bacteria by overwhelming repair systems with strand breaks.
(B) mRNA translation
mRNA translation involves ribosomes synthesizing proteins from mRNA.
Quinolones do not bind ribosomes or affect tRNA/amino acid processes.
(C) RNA polymerase
RNA polymerase transcribes DNA to RNA but relies on gyrase for supercoiling relief.
Quinolones indirectly impact transcription via DNA damage, not direct enzyme inhibition.
(D) Active transport of nutrients into the cell
Active transport uses membrane pumps/ATP for nutrient uptake against gradients.
Quinolones target cytoplasmic enzymes, not membrane transporters.
| Option | Target Process | Quinolone Mechanism | Matches Q.66? |
|---|---|---|---|
| (A) DNA replication | Gyrase/Topo IV inhibition | DNA breaks halt forks | Yes |
| (B) mRNA translation | Ribosomes | None | No |
| (C) RNA polymerase | Transcription | Indirect only | No |
| (D) Active transport | Membrane pumps | None | No |
