Which antibiotic class inhibits the 50S ribosomal subunit?

Which antibiotic class inhibits the 50S ribosomal subunit?

• A. Macrolides
• B. Aminoglycosides
• C. Tetracyclines
• D. Fluoroquinolones

Answer: (A)

Macrolides inhibit the 50S ribosomal subunit. They bind to the 23S rRNA within 50S and block the translocation step of protein synthesis, so the ribosome can’t move along the mRNA to add more amino acids. This stops elongation and often yields a bacteriostatic effect. Other classes act differently: aminoglycosides target the 30S subunit and cause misreading of the mRNA; tetracyclines bind the 30S to prevent tRNA from entering the A site; fluoroquinolones inhibit DNA gyrase and topoisomerase IV, affecting DNA replication rather than the ribosome.

Macrolides inhibit the 50S ribosomal subunit. They bind to the 23S rRNA within 50S and block the translocation step of protein synthesis, so the ribosome can’t move along the mRNA to add more amino acids. This stops elongation and often yields a bacteriostatic effect.

Other classes act differently: aminoglycosides target the 30S subunit and cause misreading of the mRNA; tetracyclines bind the 30S to prevent tRNA from entering the A site; fluoroquinolones inhibit DNA gyrase and topoisomerase IV, affecting DNA replication rather than the ribosome.