ppt6 - 2/23/2009 Enzymes protein catalysts have great...

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2/23/2009 1 1 Enzymes c protein catalysts - have great specificity for the reaction catalyzed and the molecules acted on c catalyst - substance that increases the rate of a reaction without being permanently altered c substrates - reacting molecules c products - substances formed by reaction 2 Structure and Classification of Enzymes c some enzymes are composed solely of one or more polypeptides c some enzymes are composed of one or more polypeptides and nonprotein components
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2/23/2009 2 3 Enzyme structure c apoenzyme - protein component of an enzyme c cofactor - nonprotein component of an enzyme c prosthetic group – firmly attached c coenzyme – loosely attached c holoenzyme = apoenzyme + cofactor 4
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2/23/2009 3 5 The Mechanism of Enzyme Reactions a typical exergonic reaction A + B AB t C + D transition-state complex – resembles both the substrates and the products Enzymes increase the rate of a reaction by lowering the activation energy Enzymes do not alter the equilibrium constant of a reaction 6 Interaction of enzyme and substrate Figure 8.15 lock-and-key model catalytic site
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2/23/2009 4 The Catalytic Cycle of an Enzyme Figure 5.7 8 Coenzymes c often act as carriers, transporting substances around the cell Figure 8.13
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2/23/2009 5 NAD+/NADH Cycling Figure 5.12 10 The Effect of Environment on Enzyme Activity c enzyme activity is significantly impacted by substrate concentration, pH, and temperature
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2/23/2009 6 11 Effect of [substrate] c rate increases as [substrate] increases c no further increase occurs after all enzyme molecules are saturated with substrate Figure 8.17 12 Effect of pH and temperature c each enzyme has specific pH and temperature optima c denaturation - loss of enzyme’s structure and activity when temperature and pH rises too much above optima
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2/23/2009 7 13 Figure 8.18 Regulation of Activity of Biosynthetic Enzymes c Two major modes of enzyme regulation s Amount c Regulation at the gene level s Activity c Temporary inactivation of the protein through either covalent or noncovalent changes in enzyme structure
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2/23/2009 8 Regulation of Activity of Biosynthetic Enzymes s Feedback Inhibition : mechanism for turning off the reactions in a biosynthetic pathway s End product of the pathway binds to the first enzyme in the pathway, thus inhibiting its activity s The inhibited enzyme is an allosteric enzyme s Two binding sites: active and allosteric - Reversible reaction Feedback Inhibition of Enzymatic Activity Figure 5.29
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2/23/2009 9 Allostery Figure 5.30 Regulation of Activity of Biosynthetic Enzymes s Some pathways controlled by feedback inhibition use isoenzymes s Isoenzymes s Different enzymes that catalyze the same reaction but are subject to different regulatory controls
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2/23/2009 10 Isoenzymes and Feedback Inhibition Figure 5.31 Regulation of Activity of Biosynthetic Enzymes c Biosynthetic enzymes can also be regulated by covalent modifications s Typically involves attachment or removal of a small molecule to
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This note was uploaded on 11/30/2010 for the course CEE CEE444 taught by Professor Wen-tsoliu during the Spring '10 term at University of Illinois, Urbana Champaign.

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ppt6 - 2/23/2009 Enzymes protein catalysts have great...

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