2/10/2016 The Action of Antimicrobial Drugs Protein synthesis Inhibiting protein synthesis Protein -Target bacterial 705 ribosomes -Eukaryotes have 80S ribosomes -Difference in ribosome structure accounts for selective toxicity -However,mitochondria have 70S ribosomes so some toxicity may occur -Chloramphenicol,erythromycin, mRNA 3 streptomycin,tetracyclines (a)Three-d ional detail ofth subunit portions of the 705 prokaryotic Inhibition of protein synthesis by antibiotics. The Action of Antimicrobial Drugs Growing polypeptide Injuring the plasma membrane -Polypeptide antibiotics change membrane permeability -Antifungal drugs combine with membrane -Protein synthesis site sterols ·Injury to the plasma Direction of ribosome movement st cell reptomycin Tetracyclines Interfere with on mRNA to be Translation antifungal drugs.2/10/2016 3 The Action of Antimicrobial Drugs • Inhibiting protein synthesis – Target bacterial 70S ribosomes – Eukaryotes have 80S ribosomes – Difference in ribosome structure accounts for selective toxicity – However, mitochondria have 70S ribosomes so t i it some toxicity may occur – Chloramphenicol, erythromycin, streptomycin, tetracyclines Protein synthesis Protein synthesis site Growing polypeptide Tunnel 5' 50S 30S mRNA 3' Three-dimensional detail of the protein synthesis site showing the 30S and 50S subunit portions of the 70S prokaryotic ribosome Inhibition of protein synthesis by antibiotics. Growing polypeptide 50S Chloramphenicol Binds to 50S portion and inhibits formation of tid b d Messenger RNA 50S portion tRNA Protein synthesis site peptide bond RNA Streptomycin Changes shape of 30S portion, causing code on mRNA to be read incorrectly 70S prokaryotic ribosome Translation 30S portion Direction of ribosome movement Tetracyclines Interfere with attachment of tRNA to mRNA– ribosome complex The Action of Antimicrobial Drugs • Injuring the plasma membrane – Polypeptide antibiotics change membrane p m bilit permeability – Antifungal drugs combine with membrane sterols • Injury to the plasma membrane of a yeast cell caused by an antifungal drug. • Cell releases its cytoplasmic contents as the plasma membrane is disrupted by antifungal drugs