Linezolid is an oxazolidinone antibiotic active against VRE and MRSA. Its unique mechanism is:
- A Binds the 50S ribosomal subunit at the peptidyl transferase centre (domain V of 23S rRNA), uniquely blocking formation of the 70S initiation complex (not elongation) ✓
- B Binds the 30S ribosomal subunit at the A-site, blocking aminoacyl-tRNA entry
- C Inhibits translocase (EF-G), preventing translocation of the peptidyl-tRNA from A-site to P-site
- D Cross-links 30S and 50S subunits via the mRNA tunnel, locking the ribosome in a translocation-blocked state
Correct answer: A. Binds the 50S ribosomal subunit at the peptidyl transferase centre (domain V of 23S rRNA), uniquely blocking formation of the 70S initiation complex (not elongation)
Explanation
Linezolid binds to the V domain of 23S rRNA on the 50S subunit at the peptidyl transferase centre. Uniquely among protein synthesis inhibitors, it blocks the very first step of translation initiation — preventing assembly of the 70S initiation complex (30S + 50S + mRNA + fMet-tRNA) — rather than blocking elongation. This early-stage inhibition contributes to its bacteriostatic activity and its lack of cross-resistance with other ribosomal antibiotics.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.