Linezolid, an oxazolidinone antibiotic, inhibits bacterial protein synthesis at which specific step?
- A Blocks peptidyl transferase activity at the 50S subunit after 70S initiation complex formation
- B Prevents formation of the 70S initiation complex by binding 23S rRNA of the 50S subunit ✓
- C Blocks translocation of the ribosome along mRNA at the EF-G step
- D Causes misreading of mRNA by binding the 30S A-site
Correct answer: B. Prevents formation of the 70S initiation complex by binding 23S rRNA of the 50S subunit
Explanation
Linezolid binds to the 23S rRNA of the 50S ribosomal subunit and prevents assembly of the 70S initiation complex, thereby blocking the very first step of translation initiation. This unique mechanism distinguishes it from other 50S inhibitors (chloramphenicol, macrolides) that act after initiation complex formation. Aminoglycosides cause misreading at the 30S A-site (option D); fusidic acid blocks EF-G-mediated translocation (option C).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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