Which component do beta-lactam antibiotics target to exert their effect?

• A. Penicillin-binding proteins
• B. RNA polymerase
• C. DNA gyrase
• D. 30S ribosomal subunit

Answer: (A)

Beta-lactam antibiotics disrupt bacterial cell wall synthesis by targeting penicillin-binding proteins, the enzymes that cross-link peptidoglycan strands. The beta-lactam ring mimics the natural substrate (D-Ala-D-Ala) and binds to the active site serine of PBPs, inactivating them and blocking transpeptidation. Without proper cross-linking, the cell wall weakens and the bacterium eventually lyses as it grows. Other targets—RNA polymerase, DNA gyrase, or the 30S ribosomal subunit—are inhibited by different drug classes (rifamycins, fluoroquinolones, and aminoglycosides/tetracyclines, respectively), which is why those options do not produce the beta-lactam–specific effect.