The latest question in the Clinico-Basic Pharmacology test is "What is the mechanism of action of penicillin?" Penicillin is a beta-lactam antibiotic that acts by inhibiting the synthesis of the bacterial cell wall. Clinico-Basic Pharmacology It does this by binding to the enzyme trans peptidase, which is responsible for cross-linking the peptidoglycan chains that make up the cell wall. This inhibits the growth of the bacteria and eventually leads to cell death.