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Unformatted text preview: B iochemis ry E duca ion Department of iochemistry & Molecular iology University of New Mexico BIOC 423 Int oducto y Biochemist y Glycogen OBJECTIVES Be able to describe the physiological role of glycogen in regulating glucose homeostasis Be able to recognize, and draw the 1 4 and 1 6 glycosidic bonds present in glycogen. Know the reactions involved in glycogen synthesis from glucose 6- phosphate. Know the reactions involved in the breakdown of glycogen. Understand how glycogen metabolism is regulated by hormones. OUTLINE Metabolic/Physiological Role of Glycogen Fed state Starvation Glycogen/Starch Structure Breakdown (Glycogenolysis) Liberating Glucose Phosphorylase Debranching enzyme complex Glucose Activation Generic model for biopolymer synthesis (Trap - Activate - Transfer) UDP activation Glycogen Synthesis Glycogen synthetase Branching enzyme ( 1 4:: 1 6 transferase) Insulin / Glucagon regulation LECTURE To date we have discussed two different methods to produce the energy (ATP) we need. One method is glycolysis in which ATP is produced by substrate level phosphorylation using existing glucose. This is an extremely rapid method of ATP production that is totally independent of the need for oxygen. The second method of ATP production relies on oxidative phosphorylation which utilizes the NADH produced in the CAC and glycolysis. Whereas the oxidative phosphorylation method can efficiently produce significant amounts of ATP, it is much slower than glycolysis because it depends not only on oxygen availability, but it also depends of the initial production of acetyl-SCoA for oxidation by the CAC. The acetyl-SCoA is produced from glucose, fatty acid and amino acid oxidation, all of which requires several reactions and far more time. To complicate this picture further there are some tissues (brain and RBCs) that will only use glucose as fuel molecules and are totally dependent upon glucose availability in blood. In the event that there is an emergency need for glucose by all tissues (i.e., the fight or flight response), glucose needs to be synthesized by the liver and put into the blood at a sufficient rate to provide the glucose for the rapid ATP synthesis. Glycogen metabolism will solve this problem. There is a second physiological situation where glycogen metabolism is the perfect solution. This situation is important and often overlooked in textbooks and it relates to the non-enzymic reactivity of glucose. Glucose, an aldehyde, can chemically react with amino groups (Schiff base formation) and then rearrange the bonds of the Schiff base to form a permanent glycated structure. This reaction happens all the time and is of medical significance. By analyzing the amount of glucose modified hemoglobin (HbA1C) physicians are able to get some idea about an individuals past history in maintaining normal glucose levels....
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