Aminoglycosides are bactericidal against aerobic Gram-negative bacilli. Their lethal effect is best explained by which action at the ribosome?

• A Blocking translocation of the peptidyl-tRNA from the A site to the P site
• B Preventing attachment of aminoacyl-tRNA to the acceptor site
• C Inhibiting peptide bond formation at the peptidyl transferase center of the 50S subunit
• D Binding the 30S subunit and causing misreading of mRNA codons, inserting wrong amino acids ✓

Explanation

Aminoglycosides bind irreversibly to the 30S ribosomal subunit, chiefly at the A site, and interfere with proofreading of the codon-anticodon match. The resulting mistranslation inserts incorrect amino acids into growing polypeptides, producing nonfunctional proteins and a bactericidal effect. Tetracyclines block aminoacyl-tRNA entry at the A site but are bacteriostatic, while macrolides, chloramphenicol and lincosamides act on the 50S subunit and inhibit elongation rather than causing misreading.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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