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ZieglerLecture12-GlycogenMetab-GNG-PPP

ZieglerLecture12-GlycogenMetab-GNG-PPP - Lecture 12 Lecture...

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Lecture 12: Lecture 12: Glycogen Metabolism, Gluconeogenesis, and the Pentose Phosphate Pathway BIOCHEMISTRY 100 Winter 2011 M. Ziegler
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Learning Objectives Learning Objectives 1. Write the reaction catalyzed by glycogen phosphorylase. From which end of a glycogen chain does it remove glucose monomers, and what are the monomeric products? 2. Explain what glycogen debranching enzyme does. What is the monomer produced from an α (1 6) branch point compared with the products of phosphorolysis of α (1 4) linkages. 3. How is the glucose-1-phosphate produced by glycogen phosphorylase converted to a compound that can enter glycolysis (reaction and name of enzyme)? Why is it more efficient for the cell to use the phosphorylase reaction, generating glucose-1-P, than to hydrolyze glycogen? 4. What is UDP-glucose, how is it made, and why doesn’t glycogen synthase use glucose-1-P as a substrate instead of UDP-glucose? What aspect of the formation of UDP-glucose is exergonic enough to drive the reaction? 5. What is the reaction catalyzed by glycogen synthase? 6. How is glycogen synthesis initiated? What aspect of the activity of glycogen synthase makes it unable to initiate new chains? 7. How are the α (1 6) branches in glycogen made? 8. Explain the “downstream” effects of glucagon or epinephrine stimulation, and of insulin stimulation, on covalent regulation of glycogen phosphorylase. What are the physiological conditions that each of those hormones signals?
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Learning Objectives, continued 1. Describe the covalent regulation of glycogen phosphorylase, and how allosteric regulation (by ATP, G6P, AMP, and glucose) fits into the covalent regulatory scheme. 2. Describe the covalent regulation of glycogen synthase, and explain how the effects of hormonal control on covalent regulation of glycogen synthase are “reciprocal” to covalent regulation of phosphorylase. 3. Describe the 3 steps in glycolysis that are NOT reversible for use in gluconeogenesis, and how those steps are bypassed in gluconeogenesis (substrates, products, names of enzymes, and names of required coenzymes). Which steps require input of free energy? 4. Describe the reciprocal allosteric regulation of PFK-1 and FBPase-1 by F-2,6-BP, and by ATP and AMP or ADP. 5. Explain what the Cori Cycle is, and why it is helpful when muscles are using anaerobic glycolysis to supply ATP for contraction. 6. What are the two important products of the pentose phosphate pathway? 7. What are the 2 phases of the pathway? Which is irreversible and which is reversible? What is the regulated enzyme in the oxidative phase? 8. What “route” is taken by glucose carbons (glycolysis, oxidative phase of pentose phosphate, nonoxidative phase of pentose phosphate) if the cell needs ATP? If it needs both NADPH and ribose-5-P? If it needs NADPH but not ribose-5-P? If it needs ribose-5-P but not NADPH?
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Where we’ve been and where we’re going Where we’ve been and where we’re going glycogen UDP-glucose G-1-P G-6-P glycolysis (10 steps) gluconeogenesis (11 steps) (oxidative) ribulose-5-P ribose-5-P
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