Describe how a point mutation in the gyrA gene of Escherichia coli confers resistance to ciprofloxacin. Mention a specific mutation and its effect on the drug target.
Answer
A serine to leucine substitution at codon 83 (Ser83Leu) alters the quinolone‑binding pocket in DNA gyrase, reducing ciprofloxacin affinity and conferring resistance.
Step-by-step solution
- Explain that gyrA encodes a subunit of DNA gyrase, the target of fluoroquinolones.
- Describe a point mutation that replaces serine at position 83 with leucine (Ser83Leu).
- Show how this amino‑acid change alters the structure of the drug‑binding pocket.
- Conclude that the altered pocket lowers ciprofloxacin binding, resulting in resistance.
Common mistake: Mentioning mutation in rpoB instead of gyrA
Concept tested: Antibiotic resistance via point mutation
Published · How this solution was prepared and checked
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