The Action of Antimicrobial Drugs Growing peptide Protein Tunnel chain synthesis Growing polypeptide site Chloramphenicol 50S Binds to 50S portion and inhibits formation of peptide bond 30S 50S portion mRNA (a)Three-dimensional detail of the protein Protein sythesis site synthesis site showing the 30S and 50S subunit portions of the 70S prokaryotic Erythromycin ribosome. RNA Binds to 50S portion,prevents translocation-movement of ribosome along mRNA Messenger RNA 30S portion 70S prokaryotic ribosome Tetracyclines Interfere with attachment of Streptomycin Translation tRNA to mRNA-ribosome complex Changes shape of 30S portion. causes code on mRNA to be read incorrectly Direction of ribosome movement (b)In the diagram the black arrows indicate the different points at which chloramphenicol, erythromycin,the tetracyclines,and streptomycin exert their activities. Figure 20.4The Action of Antimicrobial Drugs Figure 20.4