Tetracycline acts by inhibiting which bacterial component?

• A. 30S ribosomal subunit, blocking protein synthesis
• B. 50S ribosomal subunit
• C. DNA gyrase
• D. RNA polymerase

Answer: (A)

Tetracyclines inhibit protein synthesis by binding reversibly to the bacterial 30S ribosomal subunit. This binding blocks the attachment of aminoacyl-tRNA to the A site on the ribosome, so no new amino acids can be added to the growing polypeptide chain. Translation is halted, which stops bacterial growth.

For context, the 50S subunit is the target of other antibiotics like macrolides and chloramphenicol, DNA gyrase is targeted by fluoroquinolones, and RNA polymerase is targeted by rifamycins. This helps explain why tetracyclines have their specific action and why the other targets listed correspond to different drug classes.