## Mechanism of Action of Macrolides **Key Point:** Macrolides are protein synthesis inhibitors that bind reversibly to the bacterial 50S ribosomal subunit, preventing peptide bond formation and causing premature termination of translation. ### Ribosomal Binding Site Macrolides specifically target the 50S ribosomal subunit (large subunit in prokaryotes), which is structurally different from the eukaryotic 70S ribosome, conferring selective toxicity. ### Mechanism of Inhibition 1. Binding to 50S subunit blocks the translocation of peptides 2. Prevents elongation of the polypeptide chain 3. Results in bacteriostatic effect (not bactericidal) ### Comparison with Other Protein Synthesis Inhibitors | Drug Class | Ribosomal Target | Effect | |---|---|---| | Macrolides | 50S | Bacteriostatic | | Tetracyclines | 30S | Bacteriostatic | | Aminoglycosides | 30S | Bactericidal | | Chloramphenicol | 50S | Bacteriostatic | **High-Yield:** The 50S binding is the defining feature of macrolides and is tested frequently in pharmacology exams. This distinguishes them from tetracyclines (30S) and fluoroquinolones (DNA gyrase inhibitors).
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.