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newlecture10 - Glycogen long-term storage form for glucose...

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15-1 Glycogen Breakdown Glycogen Breakdown Glycogen : long-term storage form for glucose. glucose. (reserves for glycolysis) (reserves for glycolysis) Primarily in liver and muscle Primarily in liver and muscle Glycogen is formed when we have Glycogen is formed when we have an excess of glucose intake -it is a highly branched structure -this allows it to be quickly broken down when glucose is needed for energy production glycogen molecule glycogen molecule
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15-2 Glycogen Breakdown Glycogen Breakdown Glycogen is cleaved ( α (1->4) linkage) by addition of phosphate to give α -D-glucose-1-phosphate no ATP is involved in this phosphorylation! therefore, this process can produce one more ATP than glycolysis that starts with free glucose HO(Glucose) n O H HO- PO 3 2 - + HO(Glucose) n-1 OH glycogen phosphorylase + OPO 3 2 - OH HO HO CH 2 OH O Glycogen α-∆-Γλυχοσε-1-πηοσπηατ + Η 2 Ο
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15-3 Glycogen Breakdown Glycogen Breakdown Enzyme-catalyzed isomerization converts glucose-1-phosphate to glucose-6-phosphate Glucose-6-phosphate can now enter glycolysis for ATP production But what about the branch points on glycogen? O PO 3 2 - OH HO HO CH 2 OH O α -D-Glucose-1-phosphate phospho- glucomutase OH OH HO HO CH 2 O PO 3 2 - O a -D-Glucose-6-phosphate
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15-4 Glycogen Breakdown Glycogen Breakdown Figure 15.2 The action of glycogen debranching enzyme 3 glucose residues glycogen debranching enzyme then hydrolyzes enzyme then hydrolyzes α α (1->6) glycosidic bond (1->6) glycosidic bond
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15-5 Glycogen from Glucose Glycogen from Glucose Glucose 1-phosphate reacts with uridine triphosphate to give UDPG and pyrophosphate Glucose- 1-phosphate + UTP UDPG + PP i UDP-glucose pyrophosphorylase O -P- O-P OH HO HO CH 2 OH O O OH OH H H H CH 2 H O HN N O O O - O O - Uridine diphosphate glucose (UDPG) O Occurs when high glucose and high ATP Occurs when high glucose and high ATP this is hydrolyzed this is hydrolyzed to drive the rxn. high high energy bond! bond!
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15-6 Glycogen from Glucose Glycogen from Glucose Coupling of UDPG formation with hydrolysis of pyrophosphate (PP i ) drives formation of UDPG to completion Glucose-1-phosphate + UTP 2P i ∆Γϒ220d (κϑ∞μολ -1 29 Υ∆ΠΓ + ΠΠ ι ΠΠ ι + Η 2 Ο -30.5 -30.5 Γλυχοσε-1-πηοσπηατε + ΥΤΠ Υ∆ΠΓ + ι ⊕0 + Η 2 Ο neutral neutral exergonic exergonic
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15-7 Glycogen from Glucose Glycogen from Glucose uridine diphosphate glucose (UDPG) then adds its glucose unit to the growing glycogen chain exchange of phosphate with ATP regenerates UTP HO(Glucose) n OH + Glycogen UDP G glycogen synthase HO-Glucose- O(Glucose) n OH + UDP new glucose unit added UDP + ATP UTP + ADP nucleoside phosphate kinase forms forms α α (1->4) glycosidic linkages (1->4) glycosidic linkages
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15-8 Which comes first?
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