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ZieglerLecture6-EnzymeCatalysis-ppt1

ZieglerLecture6-EnzymeCatalysis-ppt1 - Lecture 6 Enzyme...

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Lecture 6: Lecture 6: Enzyme Catalysis Enzyme Catalysis BIOCHEMISTRY 100 Winter 2009 M. Ziegler
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Learning Objectives Learning Objectives 1. Terminology (explain/define; understand use of terms): catalyst, free energy diagram, activation energy, transition state, rate enhancement, free energy change, enzyme assay, hyperbola, allosteric (enzyme), steady state, Michaelis constant, turnover number, reversible inhibitor, irreversible inhibitor, competitive inhibitor, pure noncompetitive inhibitor 2. What parameter on the free energy profile of a reaction is altered by a catalyst such as an enzyme? 3. Calculate the rate enhancement due to the enzyme for a reaction whose uncatalyzed rate is 250 M•sec –1 and enzyme- catalyzed rate is 5 x 10 15 M•sec –1 . 4. Write a rate equation to express the forward velocity of a reaction such as A + B C , with a forward rate constant of k 1 . What is the order of the reaction with respect to A? With respect to B? What is the overall order of the forward reaction? 5. Explain in terms of a free energy diagram why it is important that the enzyme bind the transition state tightly, and not bind the subsrate too tightly.
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Learning Objectives, continued Learning Objectives, continued 6. What general types of reactions are catalyzed by chymotrypsin? 7. What is the shape of a plot of V vs. [S] for a chymotrypsin- catalyzed reaction? 8. What is the shape of a plot of V vs. [S] for an allosterically regulated enzyme like ATCase? 9. Write the kinetic mechanism for an enzyme that follows a simple Michaelis-Menten model. 10. Write the equation describing the “steady state” condition for an enzyme-catalyzed reaction, i.e., the equation relating rate of formation of the ES complex to rate of breakdown of the ES complex. 11. Write the Michaelis-Menten equation in its hyperbolic form. 12. Explain the parts of the hyperbolic plot of V vs. [S] for an enzyme - how does V relate to [S] when [S] = K M ? When [S] << K M ? When S >> K M ? 13. Explain the Lineweaver-Burk (double reciprocal) plot.
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Learning Objectives, continued Learning Objectives, continued 14. Given a double reciprocal plot for an enzyme, be able to calculate K M and V max for that enzyme and explain how you obtained them. How would you decide on the units for your values of K M and V max ? 15. Give an operational definition of K M . 16. Explain what the relative K M values indicate about how tightly an enzyme binds its substrate. If one enzyme can catalyze a reaction with two different substrates, A and B, and K M for A = 10 –3 M, whereas K M for B = 10 –4 M, which substrate binds more tightly to the enzyme? 17. Explain how a competitive inhibitor works, including its effects (if any) on the apparent K M and V max for an enzyme in the presence of such an inhibitor. 18. Explain how a pure noncompetitive inhibitor works, including its effects (if any) on the apparent K M and V max for an enzyme in the presence of such an inhibitor.
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