100cps1s09

100cps1s09 - Biochemistry & Molecular Biology...

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Unformatted text preview: Biochemistry & Molecular Biology 100C Spring, 2009. Problem Set #1 due: April 13. 1. 3'-Phosphoadenosine-5'-phosphosulfate (PAPS) is an intermediate in the biosynthesis of sulfate esters. (a) Write a biologically relevant, balanced reaction for the hydrolysis of PAPS. (b) What is the standard free energy for this hydrolysis reaction (G' hydrolysis)? (c) Why is this reaction strongly exergonic or endergonic, as the case may be? 2. In glycolysis, the hydrolysis of phosphoenolpyruvate (PEP) is coupled to the synthesis of ATP from ADP and orthophosphate (HPO 4 2- ). (a) Using the information given below, calculate both the standard free-energy change and the equilibrium constant for the coupled reaction: ATP + H 2 O ADP + HPO 4 2- G' = -7.3 kcal mole-1 PEP + H 2 O pyruvate + HPO 4 2- G' = -14.2 kcal mole-1 (b) From thermodynamic principles, would you suspect pyruvate kinase (PK), the enzyme catalyst for this reaction, might be allosterically regulated by ATP? Why? (c) Sketch PK activity plots (initial velocity this reaction, might be allosterically regulated by ATP?...
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100cps1s09 - Biochemistry & Molecular Biology...

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