Which statement lists antibiotics that affect translation at the ribosome level and their targets?

• A. Penicillin (cell wall)
• B. Rifampin (transcription)
• C. Tetracycline (A-site tRNA entry); Chloramphenicol (peptidyl transferase); Erythromycin (translocation at 50S)
• D. Ciprofloxacin (DNA gyrase)

Answer: (C)

Antibiotics that affect translation do so by targeting the ribosome and specific steps of protein synthesis. Tetracycline blocks aminoacyl-tRNA entry to the A site on the 30S subunit, preventing new amino acids from being added to the growing chain. Chloramphenicol inhibits the peptidyl transferase activity in the 50S subunit, stopping peptide bond formation. Erythromycin, a macrolide, binds the 50S subunit and prevents translocation, causing the ribosome to stall as it moves along the mRNA. Together, these actions disrupt translation at different stages on the ribosome.

The other drugs target processes outside ribosome-mediated translation: penicillin disrupts cell wall synthesis, rifampin blocks transcription by inhibiting RNA polymerase, and ciprofloxacin inhibits DNA gyrase, affecting DNA replication.