RN Nursing · Penicillin and Cephalosporin Antibacterials · Practice question
How does penicillin work to destroy bacteria?
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✓
It interferes with cell wall synthesis.
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It binds irreversibly to the cell wall.
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It interrupts bacterial DNA processes.
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It interrupts bacterial RNA processes.
Answer & explanation
Correct: It interferes with cell wall synthesis.
Penicillin exerts its bactericidal effect by interfering with bacterial cell wall synthesis. Specifically, penicillin binds to penicillin-binding proteins (PBPs), which are enzymes involved in the cross-linking of peptidoglycan strands — the structural polymer that gives the bacterial cell wall its rigidity and integrity. When penicillin blocks these enzymes, the peptidoglycan layer cannot be properly assembled or maintained. As bacteria attempt to grow and divide, the weakened cell wall cannot withstand osmotic pressure, leading to cell lysis and death. This mechanism is effective primarily against actively growing bacteria. Option B is incorrect; penicillin does not bind irreversibly to the cell wall itself but rather to specific enzymatic proteins. Options C and D are incorrect because interference with DNA or RNA processes describes the mechanisms of fluoroquinolones and rifamycins, respectively — not penicillins. Understanding this mechanism is also clinically important because bacterial resistance often develops through the production of beta-lactamase enzymes, which cleave the beta-lactam ring of penicillin and render it inactive, highlighting why beta-lactamase inhibitor combinations are used to overcome resistance.
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