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York University
BIOL 2020
K Wheaton

Major sites of glycogen storage Liver and skeletal , higher concentration in liver, but more in mass in skeletal Glycogen in cytoplasm As granules 10-40nm Describe glycogen phosphorylase Regulatory enzyme in glycogen breakdown, by adding inorganic phosphates to make glucose-1-phosphate, advantageous because released sugar has a phosphate, can only remove glycosyl residues 4 away from branched point. 1 in 10 residues are branched, stops after releasing 6 glucose molecules Describe Glycogen remodelling thru 2 Transferase: shifts blck of 3 glu molec from enzymes one branch to another and alpha 1-6 glucosidase: releases branch (hydrolyzes) at 1-6 glycosidic bond Phosphoglucomutase Takes glucose 1-phosphate and changes it to glucose 6-phosphate so it can enter metabolic stream, has phosphorylated serine residue in active site, intermediate is glucose 1,6-biphosphate Which enzyme absent from liver Glucose-6-phosphatase Phosphorylase Regulated by allosteric enzymes(response to energy states) , reversible phosphorylation (response to hormones), Phosphorylase a and b A=phosphorylated and in R state, b=not phosphorylated and in T state (open active site) Muscle phosphorylase b active?neg In muscles with high AMP levels, ATP, allosteric inhibitor competes with AMP , energy charge of the (competitive)..controlled by? What else cell, G6P (feedback inhibition) stabilizes it? Change from a to b Happens by phosphorylase kinase (PK), uses ATP, initiated by hormons, e.g. epinephrine does this, Which is inactive , when active B, because ATP inhibits G6P, but when exercising it increases B Phosphorylase a found in? Deactivated by? Liver, glucose (R to T), insensitive to AMP Opposite of kinase Phosphorylase Phosphorylase kinase activated by? Phosphorylation and calcium ions , either hormones first then Ca or vice versa goes to a or b What activates glycogen to be degraded Epinephrine and glucagon(liver), from into glucose ..fasting vs. Exercise muscles it goes to G6P Muscular activity releases? And Epinephrine , glucagon breakdown in the stimulates? liver, Liver more responsive to? Glucagon, from pancreas , both hormones initiate the cyclic AMP GOOD FOR FINAL SO LOOK AT THEN! Glysogen synthesized by? Uses UDP glucose, activated when OH is esterified, added to non reducing terminal of glycogen, forms alpha 1-4 glycosidic linkages Glycogen synthase Adds glycosyl only to polymer with already 4 units, Glycogenin Primer for glycogen catalyzes 8 glycosyl subunits to another unit, so this is present in the core of all polymers of glycogen Branching , rules, and why? Breaking 1-4 and forming 1-6, branch of 7 added to chain of 11 residues, branch must be 4 away from another branched point,
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