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newlecture10 - 15-1Glycogen BreakdownGlycogen...

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Unformatted text preview: 15-1Glycogen BreakdownGlycogen Breakdown•Glycogen: long-term storage form for glucose. glucose. (reserves for glycolysis)(reserves for glycolysis)•Primarily in liver and musclePrimarily in liver and muscle•Glycogen is formed when we haveGlycogen is formed when we havean excess of glucose intake-it is a highly branched structure-this allows it to be quickly broken down when glucose isneeded for energy productionglycogen moleculeglycogen molecule15-2Glycogen BreakdownGlycogen 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 onemoreATP than glycolysis that starts with free glucoseHO(Glucose)nOHHO-PO32 -+HO(Glucose)n-1OHglycogenphosphorylase+OPO32 -OHHOHOCH2OHOGlycogenα-∆-Γλυχοσε-1-πηοσπηατ+Η2Ο15-3Glycogen BreakdownGlycogen Breakdown•Enzyme-catalyzed isomerization converts glucose-1-phosphate to glucose-6-phosphate•Glucose-6-phosphate can now enter glycolysisfor ATP production•But what about the branch points on glycogen?OPO32 -OHHOHOCH2OHOα-D-Glucose-1-phosphatephospho-glucomutaseOHOHHOHOCH2OPO32 -Oa -D-Glucose-6-phosphate15-4Glycogen BreakdownGlycogen BreakdownFigure 15.2 The action of glycogen debranching enzyme3 glucose residues3 glucose residuesglycogen debranchingglycogen debranchingenzyme then hydrolyzes enzyme then hydrolyzes αα(1->6) glycosidic bond(1->6) glycosidic bond15-5Glycogen from GlucoseGlycogen from GlucoseGlucose 1-phosphate reacts with uridine triphosphate to give UDPG and pyrophosphateGlucose- 1-phosphate+UTPUDPG + PPiUDP-glucosepyrophosphorylaseO-P-O-POHHOHOCH2OHOOOHOHHHHCH2HOHNNOOO-OO-Uridine diphosphate glucose(UDPG)OOccurs when high glucose and high ATPOccurs when high glucose and high ATPthis is hydrolyzedthis is hydrolyzedto drive the rxn.to drive the rxn.high high energy energy bond!bond!15-6Glycogen from GlucoseGlycogen from Glucose•Coupling of UDPG formation with hydrolysis of pyrophosphate (PPi) drives formation of UDPG to completionGlucose-1-phosphate+UTP2Pi∆Γϒ220d(κϑ∞μολ-129Υ∆ΠΓ+ΠΠιΠΠι+Η2Ο-30.5-30.5Γλυχοσε-1-πηοσπηατε+ΥΤΠΥ∆ΠΓ+2Πι⊕0+Η2Οneutralneutralexergonicexergonic15-7Glycogen from GlucoseGlycogen from Glucose•uridine diphosphate glucose (UDPG) then adds its glucose unit to the growing glycogen chain•exchange of phosphate with ATP regenerates UTPHO(Glucose)nOH+GlycogenUDPGglycogensynthaseHO-Glucose-O(Glucose)nOH + UDPnew glucoseunit addedUDP+ATPUTP+ADPnucleosidephosphate kinaseforms forms αα(1->4) glycosidic linkages(1->4) glycosidic linkages15-8Which comes first?...
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newlecture10 - 15-1Glycogen BreakdownGlycogen...

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