Clindamycin acts by inhibiting which bacterial ribosomal subunit?

• A. 50S ribosomal subunit
• B. 30S ribosomal subunit
• C. 70S ribosome
• D. 40S ribosomal subunit

Answer: (A)

Clindamycin binds to the 50S ribosomal subunit of bacteria, where it blocks the translocation step of protein synthesis, preventing elongation of the growing peptide chain. This large-subunit interaction disrupts the peptidyl transferase–related activity needed to form peptide bonds, so the ribosome can’t continue producing proteins. The 30S subunit is targeted by other antibiotic classes (like tetracyclines and aminoglycosides), the 40S subunit is the eukaryotic counterpart, and the 70S ribosome refers to the whole bacterial ribosome rather than a specific subunit.