INHIBITOR of BACTERIAL PROTEIN SYNTHESIS. BACTERIAL PROTEIN SYNTHESIS The selectivity for bacterial…

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Bacterial protein synthesis and sites of drug action. The bacterial ribosome is composed of a 30S subunit and a 50S subunit. The steps in protein synthesis and translation of messenger RNA (mRNA) include the binding of aminoacyl transfer RNA (tRNA) to the ribosome, the formation of a peptide bond, and translocation. (A) Under normal circumstances, the nascent peptide is attached to the ribosome at the peptidyl site (P site), and the next aminoacyl tRNA binds to the acceptor or aminoacyl site (A site). Tetracyclines block aminoacyl tRNA from binding to the A site. Aminoglycosides and spectinomycin cause misreading of the genetic code, which leads to binding of the wrong aminoacyl tRNA and insertion of the wrong amino acid into the nascent peptide. (B) Macrolides, chloramphenicol, and dalfopristin block peptidyl transferase, the enzyme that catalyzes the formation of a peptide bond between the nascent peptide and the amino acid attached to the A site. (C) Macrolides and clindamycin block the translocation step in which the nascent peptide is transferred from the A site to the P site following the formation of a new peptide bond.