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Unformatted text preview: Stephen Spiro, Problem Set 4 1 NAME: Most of the following problems require only short answers; so you can write your answers in the space provided. For problems involving calculations, please show your working . Any questions should be directed to your TAs or email@example.com Please turn in your answers during class on Thursday April 28 th . 1. You are a doctor treating a patient who suffers from severe hypoglycemia after prolonged (&gt;24 hr.) fasting. Glucose is converted to lactate normally in the patients liver. You administer glucogon and find that blood glucose increases normally (the patient was in the well-fed state prior to this test). The patients liver shows normal activities of pyruvate carboxylase and PEP carboxykinase. Which enzyme may show a genetic defect that accounts for these findings? Briefly explain your reasoning. After 24 hours fasting, glycogen supplies would be exhausted, and gluconeogenesis would become important. Since problems appeared only after glycogen was depleted, it must be a problem in gluconeogenesis, and not glycogen utilization. Since the conversion of glucose to lactate was normal, it must be one of the 4 reactions peculiar to gluconeogenesis that is defective. Tests for PEPCK and pyruvate carboxylase are normal; glucose-6- phosphatase must be normal for glycogen utilization to occur during the first 24 hours. That leaves Fructose-1,6-bis- phosphatase as the most likely defective enzyme. 2. The conversion of glucose to L-malate is responsible for the tart flavor of some wines. This transformation occurs in yeast cultures growing anaerobically in the presence of dissolved carbon dioxide. Based on the metabolic pathways you are now familiar with, propose a metabolic route for the fermentative production of L-malate from glucose. Your pathway should be redox balanced (with respect to NAD + and NADH), should involve no net depletion of TCA cycle intermediates, but does not necessarily need to yield a net gain of ATP. Glucose is converted to 2 pyruvate by glycolysis (with the production of 2NADH and 2ATP). Then 2pyruvate is converted to 2oxaloacetate by the pyruvate carboxylase reaction (consuming 2CO 2 and 2ATP). Then 2oxaloacetate can be reduced to 2malate by malate dehydrogenase. This reaction oxidizes 2NADH, so the overall pathway is redox balanced. Note that the malate dehydrogenase reaction has a positive delta G in the direction of malate oxidation, so is readily reversible. Stephen Spiro, Problem Set 4 2 3. Fats are usually degraded to acetyl CoA, which enters the TCA cycle. Glucose can be synthesized from oxaloacetate, a TCA cycle intermediate, by gluconeogenesis. synthesized from oxaloacetate, a TCA cycle intermediate, by gluconeogenesis....
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