Chapter_05 - Principles of BIOCHEMISTRY Third Edition...

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Prentice Hall c2002 Chapter 5 1 Principles of Principles of BIOCHEMISTRY BIOCHEMISTRY Third Edition Third Edition HORTON MORAN OCHS RAWN SCRIMGEOUR
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Prentice Hall c2002 Chapter 5 2 Chapter 5 - Properties of Enzymes Catalyst - speeds up attainment of reaction equilibrium Enzymatic reactions -10 3 to 10 17 faster than the corresponding uncatalyzed reactions Substrates - highly specific reactants for enzymes
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Prentice Hall c2002 Chapter 5 3 Properties of enzymes (continued) Stereospecificity - many enzymes act upon only one stereoisomer of a substrate Reaction specificity - enzyme product yields are essentially 100% (there is no formation of wasteful byproducts) Active site - where enzyme reactions take place
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Prentice Hall c2002 Chapter 5 4 5.1 The Six Classes of Enzymes 1. Oxidoreductases ( dehydrogenases ) • Catalyze oxidation-reduction reactions
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Prentice Hall c2002 Chapter 5 5 2. Transferases • Catalyze group transfer reactions
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Prentice Hall c2002 Chapter 5 6 3. Hydrolases • Catalyze hydrolysis reactions where water is the acceptor of the transferred group
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Prentice Hall c2002 Chapter 5 7 4. Lyases • Catalyze lysis of a substrate, generating a double bond in a nonhydrolytic, nonoxidative elimination ( Synthases catalyze the addition to a double bond, the reverse reaction of a lyase)
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Prentice Hall c2002 Chapter 5 8 5. Isomerases • Catalyze isomerization reactions
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Prentice Hall c2002 Chapter 5 9 6. Ligases ( synthetases ) • Catalyze ligation, or joining of two substrates • Require chemical energy (e.g. ATP)
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Prentice Hall c2002 Chapter 5 10 5.2 Kinetic Experiments Reveal Enzyme Properties A. Chemical Kinetics • Experiments examine the amount of product ( P ) formed per unit of time ( Δ [P] / Δ t ) Velocity ( v ) - the rate of a reaction (varies with reactant concentration) Rate constant ( k ) - indicates the speed or efficiency of a reaction
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Prentice Hall c2002 Chapter 5 11 First order rate equation • Rate for nonenzymatic conversion of substrate (S) to product (P) in a first order reaction: ( k is expressed in reciprocal time units (s -1 )) Δ [P] / Δ t = v = k [S]
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Prentice Hall c2002 Chapter 5 12 Second order reaction • For reactions: S 1 + S 2 P 1 + P 2 • Rate is determined by the concentration of both substrates • Rate equation: v = k [S 1 ] 1 [S 2 ] 1
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Prentice Hall c2002 Chapter 5 13 Pseudo first order reaction • If the concentration of one reactant is so high that it remains essentially constant, reaction becomes zero order with respect to that reactant • Overall reaction is then pseudo first-order v = k [S 1 ] 1 [S 2 ] 0 = k’[S 1 ] 1
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Prentice Hall c2002 Chapter 5 14 B. Enzyme Kinetics • When [S] >> [E], every enzyme binds a molecule of substrate (enzyme is saturated with substrate) • Under these conditions the rate depends only upon [E], and the reaction is pseudo-first order Enzyme-substrate complex ( ES ) - complex formed when specific substrates fit into the enzyme active site E + S ES E + P
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This note was uploaded on 07/21/2011 for the course BIO 101 taught by Professor Staff during the Spring '08 term at Northern Virginia Community College.

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Chapter_05 - Principles of BIOCHEMISTRY Third Edition...

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