ProblemSet1

# ProblemSet1 - PRACTICE PROBLEM Set 1-Questions and Answers...

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PRACTICE PROBLEM Set 1-Questions and Answers BIS 103-001 Spring 2010 - 1 - Free energy changes and equilibrium constants 1. Calculate the standard free-energy changes of the following metabolically important enzyme- catalyzed reactions at 25°C and pH 7.0 from the equilibrium constants given. (a) Glutamate + oxaloacetate aspartate + α -ketoglutarate K’ eq = 6.8 (b) Dihydroxyacetone phosphate glyceraldehyde-3-phosphate K’ eq = 0.0475 (c) Fructose-6-phosphate + ATP F-1,6-bisphosphate + ADP K’ eq = 254 2. Calculate the equilibrium constants K’ eq for each of the following reactions at pH 7.0 and 25 o C, using the Δ G o ’ values given: (a) Glucose-6-phosphate + H 2 O glucose + P I Δ G o ’= -13.8 kJ/mol (b) Lactose + H 2 O glucose + galactose Δ G o ’= -15.9 kJ/mol (c) Malate fumarate + H 2 O Δ G o ’= +3.1 kJ/mol 3. If a 0.1 M solution of glucose-1-phosphate is incubated with a catalytic amount of the enzyme phosphoglucomutase, the glucose-1-phosphate is transformed to glucose-6-phosphate until equilibrium is established. The equilibrium concentrations are: Glucose-1-phosphate 4.5 x 10 -3 M Glucose-6-phosphate 9.6 x 10 -2 M Calculate K’ eq and Δ G o ’ for this reaction at 25 o C: Glucose-1-phosphate Glucose-6-phosphate 4. A direct measurement of the standard free-energy change associated with the hydrolysis of ATP is technically demanding because the minute amount of ATP remaining at equilibrium is difficult to measure accurately. The value of Δ G o ’ can be calculated indirectly, however, from the equilibrium constants of two other enzymatic reactions having less favorable equilibrium constants: Glucose-6-phosphate + H 2 O glucose + Pi K’ eq = 270 ATP + glucose ADP + glucose-6-phosphate K’ eq = 890 Using this information, calculate the standard free energy of hydrolysis of ATP. T= 25 o C. 5. Consider the following interconversion, which occurs in glycolysis: Fructose-6-phosphate glucose-6-phosphate K’ eq = 1.97 (a) What is Δ G o ’ for the reaction (assuming that the temperature is 25 o C)?

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PRACTICE PROBLEM Set 1-Questions and Answers BIS 103-001 Spring 2010 - 2 - (b) If the concentration of fructose-6-phosphate is adjusted to 1.5 M and that of glucose-6-phosphate is adjusted to 0.5M, what is Δ G? 6. Glucose-1-phosphate is converted into fructose-6-phosphate in two successive reactions: Glucose-1-phosphate glucose-6-phosphate Δ G o ’= -7.3 Glucose-6-phosphate fructose-6-phosphate Δ G o ’= +1.7 Calculate the equilibrium constant, K’ eq , for the sum of the two reactions at 25
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ProblemSet1 - PRACTICE PROBLEM Set 1-Questions and Answers...

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