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Ch 6 Enz SAQ - Short Answer Questions(Chapter 6 Enzymes 1...

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Short Answer Questions (Chapter 6 Enzymes) 1. Define the terms “cofactor” and “coenzyme.” 2. Draw and label a reaction coordinate diagram for an uncatalyzed reaction, S P, and the same reaction catalyzed by an enzyme, E. 3. For a reaction that can take place with or without catalysis by an enzyme, what would be the effect of the enzyme on the: (a) standard free energy change of the reaction? (b) activation energy of the reaction? (c) initial velocity of the reaction? (d) equilibrium constant of the reaction? 4. Sometimes the difference in (standard) free-energy content, G' °, between a substrate S and a product P is very large, yet the rate of chemical conversion, S P, is quite slow. Why? 5.Write an equilibrium expression for the reaction S P and briefly explain the relationship between the value of the equilibrium constant and free energy. 6. What is the difference between general acid-base catalysis and specific acid-base catalysis? (Assume that the solvent is water.) Ans: Specific acid-base catalysis refers to catalysis by the constituents of water, i.e., the donation of a proton by the hydronium ion, H 3 O + or the acceptance of a proton by the hydroxyl ion OH - . General acid- base catalysis refers to the donation or acceptance of a proton by weak acids and bases other than water. 7. Michaelis-Menten kinetics is sometimes referred to as “saturation” kinetics. Why? 8.Two different enzymes are able to catalyze the same reaction, A B. They both have the same V max , but differ their K m the substrate A. For enzyme 1, the K m is 1.0 mM; for enzyme 2, the K m is 10 mM. When enzyme 1 was incubated with 0.1 mM A, it was observed that B was produced at a rate of 0.0020 mmoles/minute. a) What is the value of the V max of the enzymes? b) What will be the rate of production of B when enzyme 2 is incubated with 0.1 mM A? c) What will be the rate of production of B when enzyme 1 is incubated with 1 M (i.e., 1000 mM) A? 9.An enzyme can catalyze a reaction with either of two substrates, S 1 or S 2 . The K m for S 1 was found to be 2.0 mM, and the K m, for S 2 was found to be 20 mM. A student determined that the V max was the same for the two substrates. Unfortunately, he lost the page of his notebook and needed to know the value of V max .
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