S07-e3_key - EXAM III CH339K ( Dr. Robertus) Spring 2007...

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EXAM III CH339K ( Dr. Robertus) Spring 2007 Name:___________________ANSWER KEY___________________________ UTEID: ______________________________________________ SHOW WORK FOR ALL COMPUTATIONAL PROBLEMS OR NO CREDIT! 1 cal = 4.18 J and therefore: R= 8.314 J/mole K = 1.99 cal/mole K Avogadro‟s number = 6 x 10 23 ; F=96.5 kJ/mol*V = 23.1 Kcal/mol*V Assume T=25 C in all problems, unless otherwise stated. Problem values are shown in [x] 1. [3] Describe why the spontaneous decarboxylation of OAA is so fast compared to that for succinic acid. This was discussed at length in class to understand C-C bond chemistry. OAA is a -keto carboxylic acid. It can stabilize C-C bond cleavage by enolate resonance 2. [2] We described the mechanism of the key glycolytic enzyme glyceraldehyde-3- phosphate dehydrogenase at length. In that mechanism, what is the role of the substrate inorganic phosphate? Pi acts as a nucleophile to attack and release the thiol ester intermediate to the enzyme. 3 [6] a. How much energy, in ATP terms, is released from glycolysis, going from glucose to 2 pyr? Consider NADH = 3 ATP and FADH2 = 2 ATP. Prep. Phase = 2 ATP loss Payoff Phase = 4 ATP = 2 NADH = 6 ATP 8 ATP released going from glucose to 2 pyruvates b. How much energy does it cost to convert 2 pyr to glucose in gluconeogenesis? 6 ATP + 2 NADH = 12 ATP
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c. Why might an organism want to carry out this process? When other sources of glucose are depleted, glucose is synthesized via gluconeogenesis for export from the liver to the brain. 4. [4] Glycogen phosphorylase (GP) is a key enzyme in glucose regulation. It is a dimer that exists in a T state and an R state. T can be shifted to R by the equilibrium binding of what effector? _______ AMP ________ In mammals the major mechanism to shift T to R is what? __ Phosphorylation ___ What role can high concentrations of glucose play in the regulation of GP? High concentrations of glucose cause the shift of glycogen phosphorylase from the R state to the T state, preventing further breakdown of glycogen to glucose 5 [4] a. What is the function of the glyoxylate shunt? It converts lipid derived AcCoA to glycolytic intermediates for glucose synthesis b. This pathway largely overlaps with what other pathway? TCA cycle, Krebs cycle, Citric acid cycle
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This note was uploaded on 05/01/2011 for the course CH 53890 taught by Professor Raymonds during the Spring '09 term at University of Texas.

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S07-e3_key - EXAM III CH339K ( Dr. Robertus) Spring 2007...

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