An antibiotic that mimics aminoacyl-tRNAs gets incorporated into the polypeptide chain and prematurely terminates elongation. The following statements are made based on this observation:
A. It enters the ribosome through the A-site.

B. It enters the ribosome through the P-site.

C. A part of its structure resembles the carboxy terminus of amino acids and is available for making a peptide bond.

D. A part of its structure resembles the amino terminus of amino acids and is available for making a peptide bond.
Which one of the following options represents all correct statements?

Correct option is B

Correct Answer:  (b)
Explanation: The antibiotic described is puromycin, which structurally resembles the 3′ end of an aminoacyl-tRNA. It enters the ribosome through the A-site and participates in peptide bond formation by providing a free amino group. Once incorporated, it causes premature termination of translation because it cannot support further elongation. Hence, statements A and D are correct.
Information Booster
· Puromycin mimics the aminoacyl end of tRNA rather than the entire tRNA molecule.
· It binds to the A-site of the ribosome during translation elongation.
· The free amino group of puromycin accepts the growing polypeptide chain.
· The resulting peptidyl-puromycin dissociates from the ribosome, stopping elongation.
· Puromycin is widely used experimentally to study translation and ribosome function.
Additional Knowledge
Puromycin does not enter through the P-site; therefore statement B is incorrect. It also does not resemble the carboxyl terminus of amino acids, but instead mimics the aminoacyl (amino-bearing) end responsible for peptide bond formation, making statement C incorrect. Its unique structure explains why it acts as a chain terminator rather than a true elongation substrate during protein synthesis.