Penicillin is active against bacteria by which mechanism?

• A. Inhibition of nucleic acid function
• B. Reduction of dihydrofolic acid
• C. Inhibition of peptidoglycan synthesis
• D. Inhibition of protein synthesis at the 30S ribosomal subunit

Answer: (C)

Penicillin targets the bacterial cell wall by inhibiting the enzymes that form cross-links between peptidoglycan strands. It binds to penicillin-binding proteins, blocking transpeptidation, so the cell wall cannot be properly cross-linked during growth. The weakened wall leads to osmotic lysis, making penicillin bactericidal for actively dividing bacteria. This mechanism is distinct from drugs that inhibit nucleic acid synthesis, disrupt folate metabolism, or block protein synthesis at the 30S ribosomal subunit.