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WWU CHEM 472 - First Exam

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Chem/Bio 472 First Exam January 28, 2010 Name________________________1. (15 points) a. A research student is attempting to sequence an oligosaccharride from a mutant cell line. From analysis, she finds the presence of sialic acid (N-acetylneuraminic acid), galactose and glucose. Treatment of the intact oligosaccharide with -galactosidase has no effect, but treatment with neuraminidase (which cleaves after sialic acid) produces N-acetylneuraminic acid and a disaccharide. What is the order of sugars in this molecule?Methylation followed by hydrolysis of the oligosaccharide produced 2,3,6 tri-O-methyl-galactose and 2,3,4-tri-O-methyl-glucose. Draw the disaccharide that produced these results. 2. (10 points) An enzyme catalyzing the following reaction was isolated from a marine diatom. Analysis disclosed that the enzyme contained a tightly bound NAD+. Suggest a reaction mechanism for the reaction. Name the enzyme.3. (12 points) Why is PEP so “peppy”? List at least 3 thermodynamic contributors to the large free energy release upon hydrolysis. Explain.CH2OHOHHOHHCH2O-PCH2OHHHOOHHCH2O-Pa.b.c.4. (20 points) 14C-Labeled glyceraldehyde-3-phosphate was added to a yeast extract containing all the glycolytic enzymes. After a short time, fructose 1,6 bis-phosphate labeled with 14C at C-3 and C-4 was isolated. What was the location of the 14C label in the starting glyceraldehyde-3-phosphate? Where did the second 14 C label in the fructose come from? Explain. Name the enzyme responsible for this reaction and draw the enzyme-substrate complex for GA3P on this enzyme.5. (15 points) Arsenate is structurally and chemically similar to inorganic phosphate and many enzymes that require phosphate will also use arsenate. Organic compounds of arsenate are less stable than analogous phosphate compounds. Which reaction of glycolysis would arsenate most directly affect? What would the product of this reaction bein the presence of arsenate? Why is arsenate so toxic? 6. (10 points) The concentration of glucose in human blood plasma is maintained at about 5 mM. The concentration of free glucose inside a monocyte is much lower. Glucose isadministered intravenously as a food source in certain clinical situations. Given that the transformation of glucose to G6P consumes ATP, why not administer intravenous G6P instead? Be specific about the chemical nature of the problem. 7. (18 points) The reaction catalyzed by phosphoglycerate kinase has a G’ of –18.8 kJ/mol. The intracellular steady state levels of the reaction components are listed below. Calculate the G for these conditions. R=8.3145 J/K.molG’ =-18.8 kJ/mol = -2.3RT log Keq’ G = G’ + 2.3RT log Q[1,3-BPG] =10-6 M [3-PG] = 5 x 10-4 M [ATP]/[ADP] =


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