SEQ’S : 1st priority    How is synthesized in the ? Outline the steps of breakdown of glycogen.  Enlist different glycogen storage diseases with  deficient, How glycogen synthesis is regulated? How glycogen breakdown is regulated? 2nd priority 

Why muscles cant form free formed from glycogen  degradation and provide glucose for maintaining blood glucose level? What is the role of Ca and AMP in glycogen metabolism?

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 The main stores of glycogen in the body are found in skeletal muscle and liver The function of muscle glycogen is to serve as a fuel reserve for  the synthesis of adenosine triphosphate (ATP) during muscle contraction.  Function of liver glycogen is to maintain the blood glucose concentration, particularly during the early stages of a fast  Approximately 400 g of glycogen in muscle make up 1–2% of the fresh weight of resting muscle  Approximately 100 g of glycogen make up to 10% of the fresh weight of a well-fed adult liver.  Glycogen is a branched-chain polysaccharide made exclusively  from α-D-glucose. The primary glycosidic bond in glycogen is an α(1→4) linkage.  After an average of eight to ten glucosyl residues, there is a branch containing an α(1→6) linkage  Liver glycogen stores increase during the well-fed state and are depleted during a fast.  Muscle glycogen is depleted during strenuous exercise and is  resynthesized to replenish muscle stores  Glycogen synthesis occurs in cytosol Energy for Glycogen synthesis is derived from ATP and UTP α-D-Glucose attached to uridine diphosphate (UDP) is the source of all the glucosyl residues that are added to the growing glycogen molecule.

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 UDP-glucose is synthesized from glucose 1-phosphate and UTP by UDP-glucose pyrophosphorylase  Glucose 6-phosphate is converted to glucose 1phosphate by phosphoglucomutase. A , serve as first acceptor of glucose residues  from UDP-glucose. The reaction is catalyzed by glycogenin itself via autoglucosylation. Glycogenin then catalyzes the transfer of the next few  molecules of glucose from UDP-glucose, producing a short,  α(1→4)linked glucosyl chain. Elongation of glycogen chains by  Branches are made by the action of the branching enzyme, amylo-α(1→4) → α(1→6)-transglucosidase or 4;6 the primary product of glycogen breakdown is glucose 1-  phosphate. in addition, free glucose is released from each α(1→6)-linked glucosyl residue. Glycogen shorten the chain at the nonreducing  ends of the glycogen chains until four glucosyl units remain on each chain before a branch point  (PLP) is a coenzyme for glycogen  phosphorylase. forms limit dextrin. oligo-α(1→4)→α(1→4)-glucan transferase activity of  debranching enzyme removes the outer three of the four glucosyl residues attached at a branch (4-4 transeferase). the remaining single glucose residue attached in an α(1→6) linkage is removed hydrolytically by amylo-α(1→6)-

www.themedicalglobe.com / www.mgElearning.net Page 3 of 6  glucosidase activity of debranching enzyme, releasing free glucose. In the liver, glucose 6-phosphate is transported into the  endoplasmic reticulum (ER) by glucose 6-phosphate .  In ER, glucose 6-phosphate is converted to glucose by glucose 6-phosphatase  Lysosomal degradation of glycogen by lysosomal enzyme, α(1→4)-glucosidase (acid maltase) TYPE V: McARDLE SYNDROME (SKELETAL MUSCLE  GLYCOGEN PHOSPHORYLASE) OR MYOPHOSPHORYLASE DEFICIENCY  Deficiency of the liver isozyme of glycogen phosphorylase causes Type VI: Hers disease  TYPE II: POMPE DISEASE (LYSOSOMAL α(1→4)-GLUCOSIDASE  DEFICIENCY) Pompe dieases is Lysosomal storage disease  TYPE III: CORI DISEASE (4:4 TRANSFERASE and/or 1:6  GLUCOSIDASE DEFICIENCY) In Cori Disease, Glycogen has abnormal structure  TYPE Ia: VON GIERKE DISEASE (GLUCOSE 6-PHOSPHATASE  DEFICIENCY) TYPE Ib: GLUCOSE 6-PHOSPHATE TRANSLOCASE DEFICIENCY  Hyperlacticacidemia, hyperlipidemia, and hyperuricemia occurs in Tyoe Ia and IIb Glycogen phosphorylase in dephosphorylated form is inactive and the phosphorylated, active form

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 glycogen synthase, the active form is dephosphorylated and inactivated form is phosphorylated  In the well-fed state, glycogen synthase in both liver and muscle is allosterically activated by glucose 6-phosphate  glycogen phosphorylase is allosterically inhibited by glucose 6phosphate and ATP,  In liver free glucose is an allosteric inhibitor of glycogen phosphorylase FiAgcutirvea:tion of glycogen degradation by calcium and AMP (in muscle):    11.5  11.8  11.9 11.10 11.11

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