sp08%20First%20Exam

sp08%20First%20Exam - Metabolic Biochemistry / BIBC 102...

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Metabolic Biochemistry / BIBC 102 First Exam / Spring 2008 I. (25 points) Fill in all of the enzyme catalyzed reactions which convert glucose to ethanol . Draw the correct structure for each intermediate molecule, showing the correct position of the hydrogen atoms at each carbon atom. 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.). (Note:You do not need to give the correct name for each intermediate molecule or the correct name of the enzyme to receive full credit.) Glucose (draw structure) ethanol (draw structure)
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2 II. (15 points. (A) In the space below, please sketch the Vo versus [S] plot for an enzyme obeying Michaelis-Menten kinetics in the presence and absence of a competitive inhibitor that is present at a concentration of [I] = Ki. Label the X and Y axes and the two lines. Indicate on your graph Vmax and the substrate concentration required for half of Vmax (that is, [S] 0.5 ) for each condition. (B) In the space below, sketch the double reciprocal plot (Lineweaver-Burk plot) for an enzyme obeying Michaelis-Menten kinetics. Label the X and Y axes, and give the values of the x and y axis intercepts in terms of Km and Vmax. Also show on this plot what the graph would look like if you repeated the kinetic analysis in the presence of sufficient irreversible inhibitor to inactivate half of the enzyme.
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3 (C) In the space below, please sketch the Vo versus S plot for an enzyme which shows positive cooperativity in substrate binding, in the presence and absence of an allosteric inhibitor . L abel the X and Y axes as well as the two lines. Indicate on your graph Vmax and the substrate concentration required for half of Vmax (that is, [S] 0.5 ) for each condition. What form of the allosteric enzyme binds the allosteric inhibitor better, the R state or the T state ? III. (15 points) (A) Draw out the mechanism of lactate dehydrogenase reaction as shown in the lecture handout. The structure of the nicotinamide ring of NAD + is shown below. Lactate + NAD + Pyruvate + NADH + H +
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4 (B) Consider the reaction: phosphoenol pyruvate + ADP ATP + pyruvate Given that the G °′ for ATP hydrolysis is –30.5 kJ/mol, the G °′ for phosphoenolpyruvate hydrolysis is –61.9 kJ/mol, RT is 2.48 kJ/mol, and the concentrations are: [ATP] = 2.24 mM, [ADP] = 0.25mM, [pyruvate] = 5.1x10 -5 M, and [phosphoenolpyruvate] = = 2.3x10 -5 M, and [phosphate] = 8mM, what will the G be for this reaction? Do not calculate a numerical answer. Full credit will be given for correct set up of the final equation (that is, a mathematical expression with appropriate numbers that is sufficient information to come up with the correct answer with a calculator). G
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sp08%20First%20Exam - Metabolic Biochemistry / BIBC 102...

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