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BIBC 102 Exam 1B KEY

BIBC 102 Exam 1B KEY - Metabolic Biochemistry Summer...

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Metabolic Biochemistry KEY Summer Session 2010 Midterm Exam (360 points) EXAM B Section 1—DO THIS PART OF THE EXAM FIRST 1) (12 pts.) Answer the following questions regarding this amino acid: a. What class of amino acids, based on its R-group, does this amino acid belong to: Nonpolar or hydrophobic b. Circle the alpha-carbon in this amino acid. 2) (6 pts.) For the chemical reaction: A + B C + D k 1 k 2 Define the forward velocity of the reaction in terms of the rate constant (assume the reverse velocity is negligible). V = k 1 [A][B] 3) (6 pts.) For the chemical reaction: A B Define the equilibrium constant in terms of equilibrium concentrations of reactant and product. k 2 k 1 K eq = [B]/[A] 4) (12 pts.) Enzymes affect which of the following for the reactions they catalyze (check all that apply: (3 pts. each checked or unchecked) a. the rate constant X b. the standard free energy change ( G’°) ____ c. the equilibrium constant ___ d. the standard free energy of activation ( ) X 5) (15 pts.) For a chemical reaction, K eq = 1000. For each item below, indicate whether they are true (T) or false (F) for this reaction. a. The reaction is exergonic T b. The reaction is endergonic F c. G’° is neg. T d. G’° = 0 F e. The reaction is favorable T
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6) (12 pts.) It is common for amino acids that form the active site of an enzyme to have side chains that participate in the reaction mechanism. List one amino acid whose R-group commonly participates in reaction mechanisms and draw the structure of the R-group only. (6 pts. each for amino acid and R-structure) Most common: serine --CH 2 OH Other good answers cysteine –CH 2 SH histidine, glutamic acid, aspartic acid (see text for structure) Not acceptable any hydrophobic, non-polar amino acid 7) (6 pts. each) Tell whether each statement below regarding enzyme reaction mechanisms is true (T) for false (F). a. The reaction mechanism of triose phosphate isomerase is an example of acid-base catalysis. T b. The stable, longer-lived intermediate that occurs during the reaction mechanism of chymotrypsin is referred to as the tetrahedral-enzyme intermediate. F c. The substrate or intermediates never actually become covalently bonded to the active site of the enzyme during a catalytic reaction mechanism. F d. When cleavage of ATP is used to power an endergonic reaction, the -phosphate of ATP may become transferred to the substrate to form a high-energy intermediate. T e. Amino acid substitutions that disrupt the reaction mechanism of an enzyme will decrease . F 8) (25 pts.) Which of the following describe an irreversible inhibitor? Check all that apply. ( 5 pts. each checked or unchecked) a. Binds reversibly ___ b. Often forms a covalent bond with the active site X c. Affects the substrate concentration required to reach ½ V max ___ d. Changes the V max value for a given amount of enzyme X e. The enzyme molecule that binds to the inhibitor is usually destroyed and rendered completely inactive X
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9) (6 pts.) Hexokinsase belongs to which class of enzyme based on the reaction it catalyzes?
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