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Glycogen Metabolism

Glycogen Metabolism. C483 Spring 2013. 1. Why does glycolysis produce more energy (more ATP) from glucose units released by glycogen degradation than from free glucose? A) Limit dextrin contains additional molecules. B) The debranching enzyme releases free glucose.

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Glycogen Metabolism

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  1. Glycogen Metabolism C483 Spring 2013

  2. 1. Why does glycolysis produce more energy (more ATP) from glucose units released by glycogen degradation than from free glucose? A) Limit dextrin contains additional molecules. B) The debranching enzyme releases free glucose. C) The glucose is already phosphorylated after glycogen phosphorylase action. D) The glucose from glycogen degradation bypasses glycolysis. E) All of the above. 2. What is the driving force for the reaction catalyzed by UDP-glucose pyrophosphorylase that converts glucose 1-phosphate to UDP-glucose? A) The subsequent hydrolysis of pyrophosphate. B) The formation of an energy-rich product. C) Its large negative free energy change. D) The change in concentration of UTP. 3. Glycogen phosphorylase is ________ (more, less) active when not phosphorylated, and it is ________ (activated, inhibited) by glucose 6-phosphate. A) more; activated B) less; activated C) more; inhibited D) less; inhibited

  3. Glucose Metabolism Overview • Keep the main pathway purposes distinct • But learn details of chemistry and regulation based on similarities

  4. Glycogen • Storage molecule • Primer necessary • Very large! • Multiple ends allow for quick synthesis and degradation

  5. Chemistry of Synthesis • Step 1 • Near equilibrium • The link to glucose-6-phophate, our central molecule

  6. Chemistry of Synthesis • Step 2 • Count high energy bonds • Pyrophosphatase • UDP-glucose: activated for incorporation

  7. Chemistry of Synthesis • Step 3 • Growing end is non-reducing • UDP released

  8. Energetics of Synthesis • Total cost: one ATP equivalent

  9. Chemistry of Degradation • Inorganic phosphate as a nucleophile

  10. Overall Energetics

  11. Key Enzymes

  12. Regulation of Glycogen Phosphorylase b • Prototype of Allosteric regulation • Happens in muscle exertion

  13. Hormone Regulation • Glucagon • Signal Transduction • Covalent Modification • Glycogen phosphorylaseb becomes glycogen phosphorylasea

  14. Regulation of Glycogen Phosphorylasea • Relaxed state now favored • No allosteric effects except glucose deactivation in the liver

  15. Glucagon and Insulin • Act Reciprocally on Glycogen synthase and Glycogen phosphorylase

  16. Maintenance of Blood Sugar

  17. Answers • C • A • D

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