(A)–(II); (B)–(III); (C)–(I); (D)–(IV)
Tetracycline, fusidic acid, macrolides, and kasugamycin are antibiotics that target bacterial protein synthesis at specific ribosomal stages. The correct matching pairs each with its precise mode of action for accurate exam preparation.
Correct Answer
The right option is (A)–(II); (B)–(IV); (C)–(I); (D)–(III). This aligns with established mechanisms: Tetracycline prevents ternary complex binding to the ribosome, fusidic acid blocks EF-G dissociation, macrolides stop amino-acyl tRNA binding initiation, and kasugamycin inhibits polypeptide exit.
Tetracycline (A) – (II)
Tetracycline binds the 30S ribosomal subunit, blocking the A-site to prevent the ternary complex (aminoacyl-tRNA, EF-Tu, GTP) from binding during elongation. This halts peptide chain growth early.
Fusidic Acid (B) – (IV)
Fusidic acid stabilizes EF-G on the ribosome post-GTP hydrolysis, preventing its dissociation and thus inhibiting translocation of peptidyl-tRNA from A to P site. It locks the ribosome in a stalled state.
Macrolides (C) – (I)
Macrolides like erythromycin bind the 50S subunit’s exit tunnel, preventing initiation of aminoacyl-tRNA binding and causing premature chain termination. They disrupt nascent peptide exit.
Kasugamycin (D) – (III)
Kasugamycin targets the 30S subunit to block formation of the initiation complex, specifically preventing aminoacyl-tRNA binding at the start and inhibiting polypeptide exit from the ribosome.
Option Analysis
| Option |
A |
B |
C |
D |
Status |
| 1st |
II |
IV |
I |
III |
✅ Correct |
| 2nd |
II |
IV |
III |
I |
❌ Wrong (swaps C & D) |
| 3rd |
II |
III |
IV |
I |
❌ Wrong (misplaces B, C, D) |
| 4th |
II |
III |
I |
IV |
❌ Wrong (misplaces B & D) |
