**Core Concept**
Gentamicin is an aminoglycoside antibiotic that exerts its antibacterial action by inhibiting protein synthesis in bacteria. This class of antibiotics binds to the 30S subunit of the bacterial ribosome, causing misreading of mRNA and thereby preventing the formation of functional proteins essential for bacterial growth and survival.

**Why the Correct Answer is Right**
Gentamicin binds to the 30S subunit of the bacterial ribosome and causes misreading of mRNA by forming a complex with the ribosomal RNA. This leads to the incorporation of incorrect amino acids into the growing peptide chain, resulting in the formation of non-functional or aberrant proteins. The primary target of gentamicin is the bacterial ribosome, which is essential for protein synthesis. This mechanism of action is responsible for the bactericidal effects of gentamicin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because gentamicin does not act by inhibiting cell wall synthesis. Inhibitors of cell wall synthesis, such as beta-lactam antibiotics, prevent the formation of the bacterial cell wall, leading to cell lysis and death.
**Option B:** This option is incorrect because gentamicin does not act by inhibiting DNA replication. Inhibitors of DNA replication, such as quinolones, prevent the replication of bacterial DNA, leading to cell death.
**Option C:** This option is incorrect because gentamicin does not act by inhibiting protein synthesis in mammalian cells. Aminoglycosides, including gentamicin, have a high degree of specificity for bacterial ribosomes and do not affect protein synthesis in mammalian cells.

**Clinical Pearl / High-Yield Fact**
Aminoglycosides, including gentamicin, can cause nephrotoxicity and ototoxicity as side effects. These toxicities are thought to result from the accumulation of the antibiotic in renal and auditory tissues, leading to damage and dysfunction.

**Correct Answer: C. Gentamicin exerts its antibacterial action by inhibiting protein synthesis in bacteria, specifically by binding to the 30S subunit of the bacterial ribosome.**

✓ Correct Answer: B. Gentamicin continues to exert antibacterial effects even after plasma levels decrease below detectable range