GATE BT 2026 • Q20 MCQ • 1 Mark

Section 3: Genetics, Cellular and Molecular Biology

DNA replication, transcription, translation

Subtopic: Fundamentals of DNA replication, transcription, translation

Question Statement:

Which one of the following antibiotics blocks protein chain elongation by preventing the action of peptidyl transferase ?

Options:

  • (A) Bleomycin
  • (B) Rifampicin
  • (C) Chloramphenicol
  • (D) Tetracycline

Official Answer Key:

C

Step-by-Step Solution & Explanation

### **Official Solution & Concept Analysis (GATE BT 2026 Q.20)** **1. Governing Concept**: - **Topic**: Molecular Biology & Antibiotic Mechanism of Action (Translation Inhibitors) - Antibiotics targeting bacterial translation elongation: - **Chloramphenicol**: Binds the 50S ribosomal subunit and specifically inhibits **peptidyl transferase**, preventing peptide bond formation between aminoacyl-tRNA in the A-site and peptidyl-tRNA in the P-site. - **Puromycin**: Tyrosyl-tRNA structural mimic causing premature chain termination. - **Tetracycline**: Binds the 30S subunit and blocks binding of aminoacyl-tRNA to the A-site. - **Erythromycin (Macrolides)**: Binds 50S and blocks ribosomal translocation / nascent peptide tunnel exit. - **Streptomycin (Aminoglycosides)**: Binds 30S, causes codon misreading, and blocks initiation. **2. Option Analysis**: - **Option (A) [Tetracycline] is INCORRECT**: Inhibits accommodation of incoming aminoacyl-tRNA into the A-site. - **Option (B) [Streptomycin] is INCORRECT**: Binds 30S subunit, altering codon-anticodon fidelity. - **Option (C) [Chloramphenicol] is CORRECT**: Directly binds the peptidyl transferase catalytic center on the 23S rRNA of the 50S ribosomal subunit, preventing peptide bond formation. - **Option (D) [Rifampicin] is INCORRECT**: Inhibits bacterial DNA-dependent RNA polymerase (transcription), not translation. **3. Final Answer**: - **Correct Choice**: **C**

Practice This in Real CBT Exam Interface

Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.

Launch CBT Mock Test