Section 3: Genetics, Cellular and Molecular Biology
DNA replication, transcription, translation
Subtopic: Fundamentals of DNA replication, transcription, translation
Question Statement:
The antibiotic tetracycline inhibits bacterial protein synthesis by interfering with:
Options:
(A) interaction between tRNA and mRNA
(B) translocation of mRNA through ribosome
(C) peptidyl transferase activity
(D) binding of aminoacyl-tRNA to the ribosomal A-site
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2019 Q.13)**
**1. Governing Concept**:
- **Topic**: Molecular Pharmacology & Protein Synthesis Inhibition
- **Tetracycline** is a broad-spectrum polyketide antibiotic that binds specifically to the **30S small ribosomal subunit** of bacterial ribosomes (near the A site).
- Mechanistically, it sterically blocks the **binding of incoming aminoacyl-tRNA to the ribosomal A site**, thereby prematurely terminating translation elongation.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Does not inhibit base-pairing directly; sterically blocks entry.
- **Option (B) is INCORRECT**: Translocation is inhibited by macrolides (erythromycin) and fusidic acid.
- **Option (C) is INCORRECT**: Peptidyl transferase is inhibited by chloramphenicol.
- **Option (D) [binding of amino-acyl tRNA to ribosome] is CORRECT**: Precise biochemical mechanism of tetracycline action.
**3. Final Answer**:
- **Correct Choice**: **D**
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