bibc102COLEMANexam1key

- Metabolic Biochemistry Fall Quarter 2007 Midterm Exam 1(290 pts 1(15 pts For the following chemical reaction k1 CO2 H2O H2CO3 k-1 Name_KEY PID

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Metabolic Biochemistry Name__ KEY ________ Fall Quarter 2007 Midterm Exam 1 (290 pts.) PID__________________ 1) (15 pts.) For the following chemical reaction: k 1 CO 2 + H 2 O H 2 CO 3 k -1 Write two ways of expressing the equilibrium constant, K eq , for this reaction. K eq = k 1 / k -1 = [H 2 CO 3 ] eq / [CO 2 ] eq [H 2 O] eq Is this a first-order reaction or a second-order reaction? Two reactants, so second order reaction. 2) (15 pts.) For any chemical reaction, state whether the change in each parameter listed below would increase the forward reaction rate, decrease the forward reaction rate, or have no effect. a. Increase the reactant concentration _ Increase _ b. Increase the product concentration _ Decrease _ c. Increase the activation energy needed to reach transition state _ Decrease _ 3) (20 pts.) Sketch a plot of Gibbs Free Energy vs. the reaction coordinate for a generalized chemical reaction (do not include reaction intermediates). On your plot, show the standard free-energy change for the reaction, and show the standard energy of activation for the reaction (forward reaction only). Give the correct symbol for each of these, and indicate precisely where the change is on the plot. Finally, indicate which part or parts of the plot is affected by enzymatic catalysis. G Standard energy of activation; ΔG° Standard free energy change; ΔG° -----affected by enzyme 4 pts 4 pts 4 pts 4 pts 4 pts
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4) (30 pts.) In the catalytic reaction mechanism for chymotrypsin, describe the function of the ‘oxyanion hole.’ How does it participate in the catalysis? It serves to stabilize the oxyanion intermediate that is formed from the peptide bond (10 pts.) carbonyl of the substrate , following nucleophilic attack by Ser 195. Two hydrogen bonds are formed between hydrogens in the oxyanion hole (part of (5 pts.) amino groups of the peptide backbone of Gly 193 and Ser 195 of the enzyme), and the oxyanion. A mutant version of chymotrypsin is created that has amino acid substitutions in the active site of the enzyme that remove the oxyanion hole . All of the other key amino acids are still present, in the correct position. How would the standard free energy of activation (ΔG° ) change for the reaction catalyzed by this mutant version of chymotrypsin versus the normal version of chymotrypsin that contains an oxyanion
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This note was uploaded on 04/11/2008 for the course BIBC 102 taught by Professor Price during the Fall '02 term at UCSD.

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- Metabolic Biochemistry Fall Quarter 2007 Midterm Exam 1(290 pts 1(15 pts For the following chemical reaction k1 CO2 H2O H2CO3 k-1 Name_KEY PID

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