mcb450-10s09 - Lecture 10 Enzymes: Kinetics, Specificity,...

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Lecture 10 Enzymes: Kinetics, Specificity, Regulation Office Hours - Noyes 208 Today (2/24/09) 2:00-3:00 PM
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Definition An enzyme is a biological catalyst. It accelerates the rate of a reaction, but does not affect free energy changes. Most enzymes are proteins, but some RNA’s also have catalytic activity.
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Relationship Between Kinetics and Thermodynamics An enzyme lowers the free energy of activation for the reaction which is another way of saying it increases the velocity. It does not affect the overall free energy change.
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Rate and Free Energy Change
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Some Properties of Enzymes Specificity Example: trypsin Regulation Coenzymes: Non-amino acid components necessary for the activity of some enzymes.
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A Multienzyme System This is the glycolytic pathway. Each of the ten reactions leading from glucose to pyruvate is enzyme-catalyzed. In the glycolytic pathway all the enzymes are soluble and present in the cytosol.
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Chemical Kinetics First-order reactions Rate is proportional to the concentration of [A]. v = k [A] First-order rate constant has units of t -1
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Chemical Kinetics Second-order reactions Rate is proportional to the product of the concentrations of [A] and [B]. v = k [A][B] Second-order rate constants have units of t -1 (conc) -1 If one reactant is present in large excess, the reaction can appear to be first-order, so called pseudo-first-order kinetics.
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First Rate Study Adrian J. Brown, over 100 years ago. Studied the hydrolysis of sucrose in living cultures of yeast. Yeast cells secrete an enzyme (invertase) into the medium that can cleave sucrose to glucose and fructose, which can enter the cell and be used as fuels. Made an unanticipated observation that the velocity of the reaction is not a linear function of sucrose concentration, but rather approached saturation.
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First Rate Study Rate [Sucrose] Predicted Observed
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Explained the behavior by postulating the existence of an enzyme-sucrose complex. At high concentrations of sucrose there will be
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This note was uploaded on 01/27/2010 for the course MCB 450 taught by Professor Mintel during the Fall '07 term at University of Illinois at Urbana–Champaign.

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mcb450-10s09 - Lecture 10 Enzymes: Kinetics, Specificity,...

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