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Glycogen stored in:
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Liver & skeletal muscle
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Glycogen lowest when:Greatest when:
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>48 hours of a fast 4 hours after a meal
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McArdle's disease
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High muscle glycogen made but cannot be mobilized, decreased muscle glycogen phosphorylase
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Type O glycogen storage disease
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Liver deficient in glycogen, lack of glycogen synthetase
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Glycogenolysis
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Glycogen breakdown (catabolism), involves 3 enzymes
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Glycogen phosphorylaseglycogen debranching enzymephosphoglucomutase
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Cleaves glc off non-reducing endstakes out glucose at branch via hydrolysisconverts glucose-1-P-->glucose-6-P
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Rate determining step of glycogenolysisphosphorylysis
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Glycogen phosphorylasephosphate breaks glycosidic bond
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Glycogenesisenzymes
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Glycogen synthesisUDP-glucose pyrophosphorylase, glycogen synthase, glycogen branching enzyme
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UDP-glucose phosphorylase
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Substrate is glucose-1-P, drives unfavorable rxns & driven by PPi
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Glycogen synthase
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Makes alpha-1,4 linkages & extends glycogen chain
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Glycogen branching enzyme
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Makes alpha-1,6 bond & increases # of reactive ends
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Glycogenin
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Makes primers for glycogen synthase & provides scaffold
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Allosteric regulation of glycogen metabolism
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Glycogen phosphorylase & glycogen synthase
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Glycogen phosphorylase2 conformations
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2 catalytic sites, 2 allosteric sites, dimer T & R state
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T stateR state
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Less active, buried active site, low substrate affinity more active, accessible active site, high substrate affinity
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