Penicillin is described as bactericidal because it does what?

Penicillin is described as bactericidal because it does what?

• A. Disrupts cell wall synthesis and causes bacterial death
• B. Inhibits protein synthesis at the 50S ribosomal subunit
• C. Interferes with DNA replication by inhibiting gyrase
• D. Destroys cell membranes

Answer: (A)

Penicillin is bactericidal because it directly cripples the bacterial cell wall, which is crucial for survival as the cell grows. It binds to penicillin-binding proteins and blocks the transpeptidase enzymes that cross-link peptidoglycan strands. Without strong cross-links, the wall becomes weak and cannot withstand osmotic pressure, causing the cell to swell and burst — death of the bacterium. This lethal action happens specifically in actively dividing cells where the wall is being synthesized, which is why penicillin is effective against growing bacteria. Other mechanisms listed target different essential processes—blocking protein synthesis at the 50S subunit often halts growth rather than killing outright, inhibiting DNA gyrase disrupts DNA replication, and destroying membranes harms membrane integrity—but penicillin’s death-inducing effect comes from inhibiting cell wall synthesis.

Penicillin is bactericidal because it directly cripples the bacterial cell wall, which is crucial for survival as the cell grows. It binds to penicillin-binding proteins and blocks the transpeptidase enzymes that cross-link peptidoglycan strands. Without strong cross-links, the wall becomes weak and cannot withstand osmotic pressure, causing the cell to swell and burst — death of the bacterium. This lethal action happens specifically in actively dividing cells where the wall is being synthesized, which is why penicillin is effective against growing bacteria. Other mechanisms listed target different essential processes—blocking protein synthesis at the 50S subunit often halts growth rather than killing outright, inhibiting DNA gyrase disrupts DNA replication, and destroying membranes harms membrane integrity—but penicillin’s death-inducing effect comes from inhibiting cell wall synthesis.