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By R. Irhabar. University of Saint Thomas, Saint Paul.

Mutations in genes encoding the proteins or RNA of bacte- rial ribosomes can cause resistance cheap 50 mg imuran mastercard. Resistance also results when bacteria take up plasmids carrying genes for inactivation of the antibiotic buy cheap imuran 50mg on-line. Because of the wide- spread and often indiscriminate use of antibiotics, strains of bacteria are rapidly developing that are resistant to all known antibiotics. Streptomycin inhibits initiation by binding to three pro- teins and probably the 16S rRNA of the 30S ribosomal subunit of bacteria. Abnormal initiation complexes, known as streptomycin monosomes, accu- mulate. Streptomycin can also cause misreading of mRNA, resulting in premature termination of translation or in the incorporation of incorrect amino acids into polypeptide chains that already have been initiated. The use of this antibiotic is lim- ited because it causes ototoxicity that can result in loss of hearing. It also causes misreading of mRNA Tetracycline Binds to the 30S ribosomal subunit and inhibits binding of aminoacyl-tRNA to the A site Chloramphenicol Binds to the 50S ribosomal subunit and inhibits peptidyltransferase Erythromycin Binds to the 50S ribosomal subunit and prevents translocation 272 SECTION THREE / GENE EXPRESSION AND THE SYNTHESIS OF PROTEINS Tetracycline. Tetracycline binds to the 30S ribosomal subunit of bac- teria and prevents an aminoacyl-tRNA from binding to the A site on the ribosome. This effect of the drug is reversible; thus, when the drug is removed, bacteria resume protein synthesis and growth, resulting in a rekindling of the infection. Furthermore, tetracycline is not absorbed well from the intestine, and its concentration can become elevated in the contents of the gut, leading to changes in the intestinal flora. Because it has been used to treat human infections and added to animal feed to prevent animal infections, humans have had extensive exposure to tetracycline. As a result, resistant strains of bacteria have developed. Chloramphenicol binds to the 50S ribosomal sub- unit of bacteria and prevents binding of the amino acid portion of the aminoacyl-tRNA, effectively inhibiting peptidyltransferase action.

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The transmission across the synapse antiepileptic drug for many years order 50 mg imuran free shipping, but it was is completed by binding of the neurotransmitter to a receptor on the postsynaptic noted that a small percentage of patients on membrane (Fig cheap 50mg imuran visa. Animals treated with reserpine showed naptic terminal, uptake into glial cells, diffusion away from the synapse, or enzy- signs of lethargy and poor appetite, similar matic inactivation. The enzymatic inactivation may occur in the postsynaptic termi- to depression in humans. Thus, a link was nal, the presynaptic terminal or an adjacent astrocyte microglia cell, or in forged between monoamine release and endothelial cells in the brain capillaries. Action potential Presynaptic neuron Storage vesicles Ca2+ An action potential in the containing neuro- 2+ presynaptic neuron allows Ca transmitter to enter and stimulate exocytosis Ca2+ of the neurotransmitter Synaptic cleft Postsynaptic The neurotransmitter binds to neuron proteins in the membrane of the postsynaptic neuron, causing channels to open that allow the nerve impulse to be propagated The neurotransmitter is then rapidly degraded, or internalized by either the pre-synaptic cell or glial cells (reuptake) Fig. Nitric oxide, because it is a gas, is an exception to most of these generalities. Some neurotransmitters are syn- thesized and secreted by both neurons and other cells (e. SYNTHESIS OF THE CATECHOLAMINE NEUROTRANSMITTERS These three neurotransmitters are synthesized in a common pathway from the amino acid L-tyrosine. Tyrosine is supplied in the diet or is synthesized in the liver from the essential amino acid phenylalanine by phenylalanine hydroxylase (see Chapter 39). The pathway of catecholamine biosynthesis is shown in Figure 48. The first and rate-limiting step in the synthesis of these neurotransmitters from tyrosine is the hydroxylation of the tyrosine ring by tyrosine hydroxylase, a tetrahy- drobiopterin (BH4)-requiring enzyme. The product formed is dihydroxyphenylala- nine or DOPA. The phenyl ring with two adjacent OH groups is a catechol, and hence dopamine, norepinephrine, and epinephrine are called catecholamines.

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What physiological factors influence blood pressure? Describe three mechanisms that promote the return c cheap imuran 50mg line. What are some symptoms of arteriosclerosis and how 14 50 mg imuran sale. The stomach, spleen, and liver receive blood via are these produced? Kidney disease usually results in the loss of protein material within arterial walls is from the blood into the urine. Differentiate between the terms in each of the fol- Cliff’s doctor, what treatments might you discuss with lowing pairs: him? Donnelley & Sons-Willard Copyright © 2005 Lippincott Williams & Wilkins 351 West Camden Street Baltimore, MD 21201 530 Walnut Street Philadelphia, PA 19106 All rights reserved. No part of this book may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval sys- tem without written permission from the copyright owner. The publisher is not responsible (as a matter of product liability, negligence, or otherwise) for any injury resulting from any material contained herein. This publication contains information relating to general principles of medical care that should not be construed as specific instructions for individual patients. Manufacturers’ product information and package inserts should be reviewed for current information, including contraindications, dosages, and precautions. Printed in the United States of America Library of Congress Cataloging-in-Publication Data Cohen, Barbara J. Memmler’s The human body in health & disease / Barbara Janson Cohen.