09 Carbohdrates - Glycogenesis_Glycogenolysis

09 Carbohdrates - Glycogenesis_Glycogenolysis -...

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Carbohydrates: Glycogenesis/Glycogenolysis HNFE 3025 Fall 2009
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Metabolic Fates of Monosaccharides Depends on energy demands at the time Regulatory hormones Insulin, glucagon, epinephrine, cortisol Covalent modification of enzymes Cellular concentrations of metabolites, ions and ATP Allosteric modification of enzymes 2
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Metabolic Fates of Monosaccharides 3 Fig. 3-12, p. 78
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Glycogenesis Process by which glucose is stored as glycogen Liver 7 % of wet weight is glycogen Important for blood glucose homoeostasis Skeletal muscle 1% of wet weight 75% of body’s storage due to contribution of body mass Energy source for that muscle fiber only 4
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Glycogen Content in Skeletal Muscle and Liver of a Representative Adult Male and Female Ingesting Diets with Different Carbohydrate Contents The CHO composition of the diet plays a huge role in determining the size of glycogen stores in both liver and skeletal muscle. 5
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Glycogen Granules (Glycosome) Found in cell cytosol of liver and skeletal muscle, particularly abundant near the SR Contains: The glycogen molecule with glycogenin Glycogen synthase Glycogen phosphorylase Branching enzyme Debranching enzyme Kinases Phosphatase 6 regulate synthesis and breakdown
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Glycogenin The protein that starts off the glycogen molecule Found at the very core of the particle Glycogenin has self glycosylating activity Able to add about 7 glucose units onto itself, end to end Glycogen synthase takes over adding more and branching enzyme creates the branches. 7
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Glycogen Molecule Glycogen synthase Creates long chains of glucose joined by α 1-4 bonds Branching enzyme creates the branches Branches formed using α 1-6 glycosidic bonds located roughly every 13 glucosyl units Creates a compact structure Creates multiple non-reducing ends to provide a large source of available energy 8 Fig. 3-14, p. 80
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Glycogen 9 Up to 12 tiers Glycogenin Huge, yet compact molecule that allows glucose storage without large osmotic effect
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Glycogenesis 10 Fig. 3-13a, p. 79 This reaction traps glucose within the cell
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Steps in Glycogenesis 11 PP i + H 2 O 2 P i Inorganic Pyrophosphatase
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Glycogenolysis 12 Fig. 3-15, p. 81
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Steps in Glycogenolysis 13
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Regulation of GS and GP Both GS and GP are part of the glycosome If both were to be active, nothing would be accomplished, except the loss of UTP (ATP) Therefore, one must be active while the other is inactive When GP is active, GS is inactive When GP is inactive, GS is active This is accomplished by protein phosphorylation 14
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09 Carbohdrates - Glycogenesis_Glycogenolysis -...

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