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Unformatted text preview: - - 1PRACTICE SET 2 Glycolysis and glycogen breakdown1. 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 14C -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 14C -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 [1-14C] glucose (glucose labeled at C-1 with 14C) is used as a substrate, what is the location of 14C in the product ethanol? Explain. (b) Where would 14C have to be located in the starting glucose molecule in order to assure that all the 14C activity were liberated as 14CO2during fermentation to ethanol? Explain. 3. 14C-Labeled glyceraldehyde-3-phosphate was added to a yeast extract. After a short time, fructose-1,6-bisphosphate labeled with 14C 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 14C 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 + H2O + 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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