BIBC HW 1 Sol - Metabolic Biochemistry Summer Session 2010...

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Metabolic Biochemistry KEY Summer Session 2010 Homework 1 (40 pts.) 1) (5 pts.) How does enzymatic catalysis affect the rate constant (k) for the reaction being catalyzed? Explain. How does this affect the velocity of the catalyzed reaction? Enzymatic catalysis decreases the activation energy for the reaction. A small decrease in the activation energy produces a large increase in the rate constant, and therefore a large increase in the reaction velocity. 2) (5 pts.) How does enzymatic catalysis affect the equilibrium constant for the reaction being catalyzed? Explain. How does this affect the velocity of the catalyzed reaction? Enzymatic catalysis has no effect on the standard free energy change for the reaction. The standard free energy change determines the equilibrium constant, and the enzyme does not affect the standard free energy change. Even if the equilibrium constant for a reaction were to change (and this is physically impossible), the reaction velocity would be unaffected unless the forward and reverse rate constants changed relative to eachother. More explanation for 1 and 2 above: Catalysis does not change the equilibrium constant for a reaction, because there is a direct but inverse relationship between K eq and the overall standard free energy change, G°. Since the catalytic activity of the enzyme cannot affect G°, the catalytic activity also does not change K eq . The enzymatic catalysis does decrease the activation energy, , required for the reaction to proceed. This will increase the forward and reverse reaction rates and their rate constants, k 1 and k -1 , by the same amount. Therefore, since K eq = k 1 /k -1 , K eq cannot change because the ratio remains constant. Intuitively, we know that the enzyme will speed up the reaction rate, but we also know that the concentrations of reactant and product at equilibrium is dictated solely by their starting concentrations, and the standard free energy change between the two. The enzyme only speeds up how fast you get there.
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3) (5 pts.) The following chemical reaction was set up and allowed to proceed to equilibrium: compound X compound Y + compound Z
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