The Question is from neet-botany molecular-basis-of-inheritance , and it was created by the author NISHANTH

Question

A bacterial strain has a mutation in the gene encoding DNA gyrase.  Which antibiotic would likely be ineffective against this strain?

NISHANTH · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Mechanism of action of antibiotics
 **Related Topics**: Bacterial DNA replication, DNA gyrase function, antibiotic resistance
 **Prerequisites**: Understanding of bacterial genetics and the role of DNA gyrase in DNA replication.
## SOLUTION PATHWAY
**Given Information**:
A bacterial strain has a mutation in the gene encoding DNA gyrase.
**Method & Steps**:
1. Identify the function of DNA gyrase.
  Reasoning: DNA gyrase is a type II topoisomerase that introduces negative supercoils into DNA, relieving torsional strain during replication.  Antibiotics targeting DNA gyrase inhibit this process, preventing bacterial DNA replication and thus bacterial growth.
  Formula/Rule:  None directly applicable.
2. Determine which antibiotic targets DNA gyrase.
  Working: Ciprofloxacin is a fluoroquinolone antibiotic that specifically inhibits DNA gyrase and topoisomerase IV.  Penicillin inhibits cell wall synthesis, tetracycline inhibits protein synthesis, and erythromycin inhibits protein synthesis (by binding to the 50S ribosomal subunit).
  Key Point:  A mutation in the gene encoding DNA gyrase would render the bacteria resistant to antibiotics that target this enzyme.
3. Identify the ineffective antibiotic.
  Result: Ciprofloxacin would be ineffective because it targets DNA gyrase, which is mutated in this bacterial strain.
  Verification:  The mutation directly impacts the target of ciprofloxacin, making it ineffective.
 ## OPTION ANALYSIS
A :x: Penicillin inhibits cell wall synthesis, unrelated to the DNA gyrase mutation.
B :x: Tetracycline inhibits protein synthesis, unrelated to the DNA gyrase mutation.
C ✓: Ciprofloxacin inhibits DNA gyrase.  A mutation in the gyrase gene would confer resistance to this antibiotic.
D :x: Erythromycin inhibits protein synthesis, unrelated to the DNA gyrase mutation.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the mechanisms of different antibiotic classes: Understanding the specific target of each antibiotic is crucial.
  2.Assuming that all antibiotics target the same bacterial process:  Antibiotics have diverse mechanisms of action.
 **Quick Tips**:
  1.Memorize the key targets of common antibiotic classes (e.g., cell wall synthesis, protein synthesis, DNA replication).
  2.Relate antibiotic resistance mechanisms to the specific target of the antibiotic.

NISHANTH · Answer

Penicillin

NISHANTH · Answer

Tetracycline

NISHANTH · Answer

The correct Option is "Ciprofloxacin"

NISHANTH · Answer

Erythromycin

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