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Practice Problem Set 2

# Practice Problem Set 2 - Practice Problem Set#2 BIS 103-001...

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Practice Problem Set #2 BIS 103-001 Spring 2010 - 1 - Problem Set #2- Glycolysis, Glycogen breakdown 1. In working skeletal muscle under anaerobic conditions, glyceraldehyde-3-phosphate is converted into pyruvate (the payoff phase of glycolysis), and pyruvate is reduced to lactate. Write balanced equations for all of the reactions in this process, with the standard free-energy change for each (obtain from text). Then write the overall or net equation for the payoff phase of glycolysis (with lactate as the end product), including the net standard free-energy change. 2. A “pulse-chase” experiment using 14 C -labeled carbon sources is carried out on a yeast extract maintained under strictly anaerobic conditions to produce ethanol. The experiment consists of incubating a small amount of 14 C -labeled substrate (the pulse) with the yeast extract just long enough for each intermediate in the pathway to become labeled. The label is then “chased” through the pathway by the addition of excess unlabeled glucose. The “chase” effectively prevents any further entry of labeled glucose into the pathway. (a) If [1- 14 C] glucose (glucose labeled at C-1 with 14 C) is used as a substrate, what is the location of 14 C in the product ethanol? Explain. (b) Where would 14 C have to be located in the starting glucose molecule in order to assure that all the 14 C activity were liberated as 14 CO 2 during fermentation to ethanol? Explain. 3. 14 C-Labeled glyceraldehyde-3-phosphate was added to a yeast extract. After a short time, fructose-1,6-bisphosphate labeled with 14 C at C-3 and C-4 was isolated. What was the location of the label in the starting glyceraldehyde-3-phosphate? Where did the second 14 C label in fructose-1,6-bisphosphate come from? Explain. 4. Suppose you discovered a mutant yeast whose glycolytic pathway was shorter because of the presence of a new enzyme catalyzing the reaction Glyceraldehyde-3-phosphate + H 2 O + NAD + 3-phosphoglycerate + NADH + H + Although this mutant enzyme shortens glycolysis by one step, how would it affect anaerobic ATP production? Aerobic ATP production?

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