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Lecture 2 Glycogen Degradation - Biochemistry415/515...

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Biochemistry 415/515 Glycogen Metabolism Chapter 21 Berg • Tymoczko • Stryer Part I: Glycogen Degradation
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Glucose is for “immediate consumption” Mobilizable Fuel Stores Fat Glycogen
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From Marks’ Basic Medical Biochemistry: A Clinical Approach (2005) Smith, Marks and Lieberman p.575 Sources of blood glucose differ in fed, fasting and starved states
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Glycogen: major storage form of glucose in animals Large polymer of glucose (up to 10 6 glucose/mcl) Granules of 10-40 nm in the cytosol of most cells
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In glycogen, glucose residues are linked by glycosidic bonds Most glucose residues linked by α -1,4-glycosidic bonds Branches created with α -1,6-linkages
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What is the significance of branching? 1) Increases the sites for synthesis and degradation 2) Enhances the solubility of the molecule Anderson’s disease
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Starch: major storage form of glucose in plants Cellulose: major structural component of plant cell walls Additional storage forms of glucose
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Glycogen metabolism : regulated release and storage of glucose Glycogen degradation : 1) Stepwise release of the terminal 1,4-linked glucose from glycogen (as glucose 1-phosphate ) Entry into metabolism via conversion to glucose 6- phosphate Remodeling of 1,6-branches to permit further degradation Glycogen synthesis : next lecture
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Major sites of glycogen storage: Liver and Muscle Community-oriented: liver Degradation and synthesis are regulated to maintain blood glucose homeostasis of the organism. Selfish: muscle Degradation and synthesis are regulated to meet the energy needs of the muscle. Smith, Marks and Lieberman (2005) Marks’ Basic Medical Biochemistry: A clinical approach pg. 513
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Glycogen Degradation 1) Release of Glucose 1-P Enzyme: Glycogen Phosphorylase
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Glycogen phosphorylase Catalyzes glucose release by phosphorolysis Readily reversible in vitro [glycosidic bond ~ phosphorylester bond] In vivo glycogen degradation is favored: [P i ]/[gluc 1-P] = 100/1
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Energetically advantageous: the released sugar is already phosphoryla
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