Question

The antibiotic that inhibits protein synthesis by premature chain termination and which structurally resembles aminoacyl tRNA is

• A. Tetracycline
• B. Chloramphenicol
• C. Puromycin
• D. Erythromycin

Hint:

Puromycin mimics the aminoacyl end of tRNA and causes premature release of the growing peptide chain.

Answer 1

The Correct Option is C

This question is testing the unique mechanism of puromycin, which is different from the other classic protein synthesis inhibitors because it works by disguising itself as a piece of the translation machinery rather than by blocking a step directly.

1. Tetracycline: Works by physically blocking the A site of the small ribosomal subunit, preventing any aminoacyl tRNA from docking there. It does not resemble tRNA itself, it just gets in the way of tRNA binding.
2. Chloramphenicol: Binds the 50S subunit and blocks the peptidyl transferase center, the enzyme site that links amino acids together. This stops chain growth but does not involve mimicking a tRNA structure.
3. Puromycin: Its structure closely copies the aminoacyl end of a real tRNA, so the ribosome mistakes it for one and lets it enter the A site and join the growing chain. Because puromycin cannot support further chain extension after that, the protein is released early and unfinished. This matches both parts of the question: tRNA mimicry and premature chain ending.
4. Erythromycin: Attaches to the 50S subunit and blocks translocation, the step where the ribosome shifts along the mRNA after each peptide bond. It does not act as a tRNA mimic.

Only puromycin fits both clues in the question: it looks like aminoacyl tRNA and it causes the chain to stop early once it is incorporated.

Let's summarize:

• Puromycin mimics aminoacyl tRNA and gets built into the growing peptide chain.
• Because it cannot extend the chain further, the protein is released prematurely and is non-functional.

So the antibiotic described in the question is puromycin.