Penicillin acts by inhibiting which bacterial process?

• A. Inhibit DNA replication
• B. Inhibit protein synthesis at the 50S ribosome
• C. Inhibit RNA transcription
• D. Inhibit cell wall synthesis by binding to penicillin-binding proteins, blocking transpeptidation

Answer: (D)

Penicillin works by blocking the bacterial cell wall synthesis. It binds to penicillin-binding proteins, the enzymes that catalyze cross-linking of peptidoglycan strands (transpeptidation). By mimicking the normal peptidoglycan substrate, it inhibits these enzymes, preventing cross-link formation, which weakens the cell wall. Without a strong wall, actively growing bacteria can’t withstand osmotic pressure and burst, making penicillin bactericidal. This mechanism is distinct from antibiotics that target DNA replication, protein synthesis at the 50S ribosome, or RNA transcription.