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Unformatted text preview: 5-1Cell and Molecular Biology (Biol. Chem. 410A)Lecture #5Harry R. Matthews, Ph.D.October 2, 1996 10:00 a.m.Properties of Enzymes IClinical correlations:scurvypellagraberiberipernicious anemiaricketsLearning objectives:enzymes are catalystsactive siteenzyme mechanismsprosthetic groupsvitamins & cofactorsOptional reading:Stryer IV:Chapter 8.Alberts et al.:3rd Ed., Chapter 2, pages 66-66; Chapter 3, pages 128-135.n many cases, enzymes require cofactors or coenzymes that are either a non-pro-tein part of the enzyme or participate in the reaction. Cofactors and coenzymes are de-rived from vitamins which means that vitam-in deficiencies lead to reduced enzyme activit-ies and disease. The table illustrates the im-portance of enzymes and cofactors or coen-zymes.IChemical reactions in biological systems are almost always catalyzed, otherwise they would occur too slowly. The catalysts that are used are proteins (except for a few instances of catalysis by RNA) although other molecules (prosthetic groups, coenzymes) may also be re-quired. The main functional characteristics of enzymes compared with chemical catalysts are their high efficiency, their specificity and their capacity for regulation. Enzyme-cata-lyzed reactions can lead to the transformation of energy from one state to another. Enzyme-catalyzed reactions conform to the same laws of thermodynamics as chemical reactions and engines do.Some of the reactions catalyzed are very complex; others are very simple. All occur at very rapid rates. For example, nearly half the CO2 produced by tissues is carried to the lungs by dissolving in the blood stream (the rest is carried by hemoglobin). The rate of solution of CO2 in water is much too slow for this process and so it is catalyzed by an en-zyme called carbonic anhydrase. CO2 + H2O <=====> H2CO3Carbonic anhydrase raises the rate of this reaction by 10 million times. Notice that the enzyme itself does not appear as part of the chemical equilibrium although its name is sometimes written above the arrows. The en-zyme is released after one reaction and is free to catalyze another. In this way, one molecule of carbonic anhydrase can hydrate 100,000 molecules of CO2 per second.The cell operates through chemical reac-tions. However, much of the interaction of an organism with its environment involves types of energy that are not chemical. Enzymes and enzyme-like proteins can transform chemical energy into other forms of energy and vice versa. The easiest is to transform chemical en-ergy into heat for maintaining body temperat-disordertreatmentscurvyascorbic acid (vitamin C)...
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