sp04-1 - Metabolic Biochemistry / BIBC 102 First Exam /...

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Metabolic Biochemistry / BIBC 102 First Exam / Spring 2004 I. (20 points) Fill in all of the enzyme catalyzed reactions which convert glycogen to lactate . Draw the correct structure for each intermediate molecule. (You do not need to give the correct name for each intermediate molecule or the correct name of the enzyme to receive full credit). Include the names or abbreviations of any other reactants and products (eg, ATP, ADP, Pi, NAD+, NADH, etc), and any required prosthetic groups (eg, biotin, TPP, etc.). Glycogen (draw the 2 terminal sugar subunits of the polymer only) lactate (draw structure)
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2 II. (15 points) When a muscle goes from rest to strenuous exertion, the primary source of ATP energy to drive muscle contraction is obtained from the conversion of glycogen to lactate. (A) Why is lactate produced from glycogen during strenuous exercise, not pyruvate or CO 2 ? (B) Two key regulatory enzymes are largely responsible for the increased production of lactate from glycogen during strenuous exercise. What are these enzymes, and how are they activated by strenuous exercise? III. (10 points) Phosphonacetyl-L-aspartate (PALA) is a potent inhibitor of ATCase because it mimics the two physiological substrates of this enzyme. However, low concentrations of this unreactive bisubstrate analogue actually increase the reaction velocity. On addition of PALA, the reaction rate increases until an average of three PALA are bound per enzyme molecule (see graph below). This maximal velocity is 17- fold greater than in the absence of PALA. The reaction rate then decreases to nearly zero on adding three more molecules of PALA per enzyme. Why do low concentrations of PALA activate ATCase?
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3 IV. (20 points) Consider the reaction X Y, a reaction for which G °′ = +17 kJ/mol. A. What is the equilibrium constant for this reaction? (show your work!) Keq = [Y]/[X] = B. In a typical cell this reaction is coupled to the hydrolysis of ATP: X + ATP Y + ADP + Pi Given that the G °′ for ATP hydrolysis is –30.5 kJ/mol, what is G °′ for the coupled reaction? (show your work!)
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sp04-1 - Metabolic Biochemistry / BIBC 102 First Exam /...

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