BIBC 102 Exam 1 Fall 11 KEY

BIBC 102 Exam 1 Fall 11 KEY - KEY BIBC 102 Metabolic...

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BIBC 102 Metabolic Biochemistry KEY Fall Quarter 2011 Midterm Exam (400 pts.) MWF Lecture Part 1—Do this part of the exam first: 1) (4 pts. each) Which of the following are affected (changed) by the catalytic activity of enzymes? ( Check all that apply ) a. ΔG’°____ b. ΔG° X c. The rate constant for the reaction X d. The standard free energy of activation for the reaction X e. The equilibrium constant for the reaction ____ f. The overall thermodynamic favorability of the reaction ____ g. The rate at which the reaction reaches equilibrium X 2) (10 pts.) During glycolysis, the enzyme aldolase splits fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). When this reaction is allowed to proceed to equilibrium in vitro (in a test tube) the following concentrations of each compound are found: Fructose 1,6-P: 3.0 mM G3P: 0.9 mM DHAP 3 mM What is the equilibrium constant for this reaction? (Show your work) Convert to molar concentration K eq = (9 x10 -4 M)(0.003 M) = 9 x10 -4 M 0.003 M Units not required; 5 pts. for correct set up, 5 pts. for correct answer 3) (12 pts.) Based on the equilibrium constant you calculated for question 2, calculate ΔG’° for the conversion of fructose 1,6 bisphosphate to G3P and DHAP. (Show your work) G°’ = -RT ln K eq 4 pts. G°’ = -(8.315 J/mol•K)(310 K)( ln 9 x10 -4 ) 4 pts. G°’ = (-2.578 kJ/mol)(-7.0) = 18 kJ/mol 4 pts.
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4) (5 pts.) Do the equilibrium constant and ΔG’° you calculated for questions 2 and 3 indicate that this reaction would proceed in the forward direction? Yes or no. NO 5) (12 pts.) Referring to questions 2 through 4, the cellular concentrations of fructose 1,6-P, G3P, and DHAP in the cytoplasm are: Fructose 1,6-P: 5.0 mM G3P: 0.08 mM DHAP 0.4 mM Based on these cellular concentrations, calculate the actual free energy change, ΔG. (Show your work.) Mass action ratio Q = (8 x10 -5 M)(4 x10 -4 M) = 6.4 x10 -6 (drop units) 4 pts. .005 M G = G°’ + RT ln Q G = 18 kJ/mol + (8.315 J/mol•K)(310 K)(-12) 4 pts. G = -13 kJ/mol 4 pts. (Q must be correct) 6) (5 pts.) Referring to question 5, will the reaction proceed in the forward direction under these cellular concentrations of substrate and products? Yes, it will proceed in the forward direction. 7) (5 pts. each) Which of the following occur in the catalytic mechanism for the enzyme triose phosphate isomerase? Check all that apply. a. Hydrogen ions (H + ) are transferred between the enzyme and the substrate/intermediate X b. Electrons are transferred between the enzyme and the substrate/intermediate _____ c. Covalent bonds are formed between the enzyme and intermediate _____ d. Part of the catalytic mechanism involves hydrolysis _____ 8) (5 pts. each) Which of the following occur in the catalytic mechanism for the chymotrypsin? Check all that apply.
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This note was uploaded on 11/27/2011 for the course BIBC 102 taught by Professor Price during the Fall '02 term at UCSD.

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BIBC 102 Exam 1 Fall 11 KEY - KEY BIBC 102 Metabolic...

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