lecture6 - Enzyme Catalysis Enzyme Enzyme: a biological...

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Enzyme Catalysis Enzyme Catalysis Enzyme Enzyme : : a biological catalyst with the exception of some RNAs that catalyze their own splicing, all enzymes are proteins enzymes can increase the rate of a reaction by a factor of up to 10 20 compared to an uncatalyzed reaction some enzymes are so specific that they catalyze the reaction of only one stereoisomer; others catalyze a family of similar reactions The rate of a reaction depends on its activation energy, an enzyme lowers the lower activation energy with same start and end point
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Enzyme Catalysis Enzyme Catalysis For a reaction taking place at constant temperature and pressure, e.g., in the body the change in free energy is Represents the change in the energy between the reactants and products Determines whether a reaction will be exergonic or endergonic Enzymes don’t alter the change in free energy A B G¡ =  DH¡ -  TDS¡
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Activation Energy Profile Activation Energy Profile An enzyme alters the rate of a reaction and activation energy, but not its free energy change or position of equilibrium
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Enzyme Catalysis Enzyme Catalysis Consider the following reaction: H 2 O 2 H 2 O  +    O 2 No catalyst Platinum surface Catalase 75.2 18.0 48.9 11.7 23.0 5.5 Activation energy (kJ/mol) (kcal/mol) Relative rate* 1 2.77 x 10 4 6.51 x 10 8 Reaction Conditions * Rates are given in arbitrary units relative to  a value of 1 for the uncatalyzed reaction at 37¡C
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Enzyme Kinetics Enzyme Kinetics For the reaction the rate of reaction is given by rate equation loss loss gain where k is a proportionality constant called the specific rate constant specific rate constant order of reaction: order of reaction: the sum of the exponents in the the sum of the exponents in the rate equation, represents the number of molecules rate equation, represents the number of molecules A  +  B P Rate = ∆[Α] ∆τ ∆[Β] ∆τ ∆[Π] ∆τ _ _ = = Rate  =  k[A] f [B] g
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Enzyme Kinetics Enzyme Kinetics consider the reaction whose rate equation is given by the expression the reaction is said to be first order in A, first order in B, and second order overall For example: the reaction of glycogen with phosphate
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lecture6 - Enzyme Catalysis Enzyme Enzyme: a biological...

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