BIO 226T - Lecture 21 Study Questions (last half)

BIO 226T - Lecture 21 Study Questions (last half) - Lecture...

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Lecture 21 Study Questions (7-10) 7. Probiotics – live, nonpathogenic bacteria that may be effective in the treatment or prevention of certain human diseases. Possible beneficial effects lie either in: Providing colonization resistance by which the nonpathogen excludes the pathogen from binding site on the mucosa, in enhancing the immune response against the pathogen Reducing the inflammatory response against the pathogen Ex. Oral administration of live Lactobacillus rhamnosus strain GG significantly reduces the number of cases of nosocomial diarrhea in young children. 8. B lactam antibiotics – penicillins and cephalosporins a. What is the mechanism of action of penicillin and other B lactam antibiotics? 1. Inhibit cell wall ( peptidoglycan ) synthesis in growing bacterial cells by binding to receptors in the bacterial cell membrane called “penicillin binding proteins (PBP’s)” some PBP’s in cell membrane are transpeptidases enzymes that catalyze transpeptidation (last step in cross-linking of bacterial cell wall) B lactam antibiotics bind to these transpeptidases inhibit cross-linking of peptidoglycan and stopping the wall from growing leads to cell lysis 2. Activate autolytic enzymes (murine hydrolases) which normally degrade peptidoglycan so that the cell wall can grow B lactam antibiotics inactivate the inhibitors of these enzymes lysis of the cell b. How do penicillin-treated cells die? Penicillin-treated cells die by rupture as a result of the influx of water into the high- osmotic-pressure interior of the bacterial cell Note: exposure of the bacterial cell to lysozyme (present in human tears) results in degradation of the peptidoglycan and osmotic rupture similar to that caused by penicillin c. Are these drugs always bactericidal? Penicillin is bactericidal, but it kills cells only when they are growing when cells are growing, new peptidoglycan is being synthesized and transpeptidation occurs BUT in nongrowing cells, no new cross-linkages are required and penicillin is inactive Penicillins are more active during the log phase of bacterial cell growth than during the stationary phase d. What is the importance of the B lactam ring in penicillin? Cleavage of the ring by penicillinases (β-lactamases) inactivates the drug, therefore an intact ring is required for activity e. What has been gained by modifying penicillin G? Modification of the side chain adjacent to the β-lactam ring endows these drugs with new
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This note was uploaded on 03/19/2008 for the course BIO 226T taught by Professor Field during the Fall '06 term at University of Texas at Austin.

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BIO 226T - Lecture 21 Study Questions (last half) - Lecture...

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