Microbiology for COMLEX Level 1 Practice Test

Bacterial ribosomes have a small (30S) and a large (50S) subunit. Drugs used to treat tuberculosis include streptomycin, an aminoglycoside, which binds to the 16S rRNA in the 30S small subunit. This binding disrupts decoding of mRNA and can block initiation, causing misreading of the genetic code and production of faulty proteins. Because the 30S subunit is essential for accurate translation in bacteria, its disruption effectively halts protein synthesis and kills the bacteria.

Other TB drugs work through different targets: rifampin inhibits DNA-dependent RNA polymerase, isoniazid and ethambutol impair cell wall synthesis, and pyrazinamide disrupts membrane metabolism. The key idea is that the TB-relevant ribosomal interaction occurs at the small subunit, not the large subunit or other cellular targets.