Klappa8.) Part 1 - Glycogen: reactions of glycogen synthesis and degradation, regulation (phosphorylation cascade, allosteric effectors, role of AMP and calcium ions)
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- FrontGlycogenBackStorage form of glucose in animals that is a branched polymer of glucose
- FrontMain chain bonds in glycogenBackα(1→4) glycosidic bonds
- FrontBranch point bonds in glycogenBackα(1→6) glycosidic bonds
- FrontWhy branching is important in glycogenBackIncreases solubility, increases rate of glucose mobilization, and increases rate of synthesis
- FrontLecture detail about glycogen branching frequencyBackBranching occurs about every 8–10 residues
- FrontWhy branching increases glycogen mobilizationBackIt creates multiple nonreducing ends so glucose can be released from many sites at once
- FrontTwo opposite processes of glycogen metabolismBackGlycogenesis and glycogenolysis
- FrontGlycogenesisBackGlycogen synthesis
- FrontGlycogenolysisBackGlycogen breakdown
- FrontKey regulatory enzymes of glycogen metabolismBackGlycogen synthase and glycogen phosphorylase
- FrontBasic structural unit of glycogenBackGlucose residues
- FrontImportant structural feature of glycogenBackMany nonreducing ends
- FrontMain sites of glycogen synthesis and degradationBackNonreducing ends
- FrontHigh-yield branching conceptBackMore branches create more nonreducing ends, allowing faster synthesis and faster degradation
- FrontOverall sequence of glycogen synthesisBackGlucose → glucose-6-phosphate → glucose-1-phosphate → UDP-glucose → glycogen with branching enzyme forming α(1→6) branches
- FrontStep 1 of glycogen synthesisBackGlucose is phosphorylated to glucose-6-phosphate
- FrontEnergy requirement for glucose to G6P in glycogen synthesisBackUses ATP
- FrontEnzymes that convert glucose to G6P for glycogen synthesisBackHexokinase or glucokinase depending on tissue
- FrontHigh-yield role of G6P in metabolismBackBranch point that can go toward glycolysis, pentose phosphate pathway, or glycogen synthesis
- FrontStep 2 of glycogen synthesisBackG6P is converted to G1P by phosphoglucomutase
- FrontEnzyme converting glucose-6-phosphate to glucose-1-phosphateBackPhosphoglucomutase
- FrontPurpose of the G6P to G1P step in glycogen synthesisBackPrepares glucose for activation as UDP-glucose
- FrontActivated form of glucose used in glycogen synthesisBackUDP-glucose
- FrontReaction forming UDP-glucoseBackGlucose-1-phosphate + UTP → UDP-glucose + PPi
- FrontEnergy requirement of glycogen synthesisBackGlycogen synthesis requires energy
- FrontHigh-yield fact about UDP-glucoseBackActivated glucose donor for glycogen synthesis
- FrontFunction of glycogen synthaseBackAdds glucose from UDP-glucose to the nonreducing end of an existing glycogen chain
- FrontBond formed by glycogen synthaseBackα(1→4) glycosidic bond
- FrontImportant limitation of glycogen synthaseBackIt cannot start a brand-new glycogen chain by itself
- FrontWhat glycogen synthase requires to functionBackAn already existing primer chain
- FrontProtein that starts a new glycogen moleculeBackGlycogenin
- FrontRole of glycogeninBackNew glycogen molecule is initiated by attaching glucose residues to glycogenin
- FrontHigh-yield primer conceptBackGlycogenin starts the chain and glycogen synthase elongates it
- FrontFunction of branching enzymeBackForms α(1→6) linkages in glycogen
- FrontRole of branching enzyme in glycogen structureBackCreates the branched structure of glycogen
- FrontName of branching enzyme given by LippincottBackAmylo-α(1→4)→α(1→6)-transglycosylase
- FrontHigh-yield bond distinction in glycogen synthesisBackGlycogen synthase makes α(1→4) bonds and branching enzyme makes α(1→6) bonds
- FrontOverall sequence of glycogen degradationBackGlycogen phosphorylase removes glucose residues from nonreducing ends, debranching enzyme handles branches, and product is mainly glucose-1-phosphate that becomes glucose-6-phosphate
- FrontFunction of glycogen phosphorylaseBackRemoves successive glucose residues from the nonreducing ends of glycogen
- FrontBond broken by glycogen phosphorylaseBackα(1→4) glycosidic bond
- FrontMechanism used by glycogen phosphorylaseBackPhosphorolysis rather than hydrolysis
- FrontMain product of glycogen phosphorylase actionBackGlucose-1-phosphate
- FrontCofactor used by glycogen phosphorylaseBackPLP (pyridoxal phosphate, vitamin B6)
- FrontHigh-yield fact about glycogen phosphorylase cleavageBackIt yields G1P rather than free glucose from α(1→4) cleavage
- FrontWhy phosphorolysis is important in glycogen breakdownBackIt releases glucose-1-phosphate, which already contains phosphate and saves an ATP later
- FrontWhy glycogen is an efficient rapid fuel sourceBackPhosphorolysis releases G1P and saves energy compared with taking up free glucose and phosphorylating it
- FrontWhy glycogen phosphorylase stops near branch pointsBackIt cannot cleave indefinitely through a branch
- FrontDistance from a branch point where glycogen phosphorylase stopsBackFour glucosyl units before a branch point
- FrontName of the partially degraded glycogen structure near a branch pointBackLimit dextrin
- FrontNeed for debranching enzymeBackThe debranching enzyme is required when glycogen phosphorylase reaches a branch
- FrontActivities of the debranching enzymeBackTransferase activity and α(1→6)-glucosidase activity
- FrontFunction of debranching enzyme transferase activityBackTransfers a block of residues from the short branch to another chain
- FrontFunction of debranching enzyme α(1→6)-glucosidase activityBackHydrolyzes the remaining α(1→6)-linked glucose
- FrontProduct released by α(1→6)-glucosidase activityBackFree glucose
- FrontHigh-yield distinction in glycogen breakdownBackMost glycogen breakdown gives G1P, but branch removal by α(1→6)-glucosidase releases free glucose
- FrontStep after G1P formation in glycogenolysisBackG1P is converted to G6P by phosphoglucomutase
- FrontEnzyme converting glucose-1-phosphate to glucose-6-phosphateBackPhosphoglucomutase
- FrontImmediate cellular product after main glycogenolysis stepBackGlucose-6-phosphate
- FrontClean synthesis vs degradation comparisonBackGlycogen synthesis uses UDP-glucose and glycogen synthase to form α(1→4) bonds with branching enzyme creating α(1→6) bonds, whereas glycogen degradation uses glycogen phosphorylase to break α(1→4) bonds by phosphorolysis and debranching enzyme to handle α(1→6) branches
- FrontBig-picture regulation of glycogen metabolismBackRegulated by allosteric mechanisms and reversible phosphorylation in response to hormones
- FrontKey enzymes regulated in glycogen metabolismBackGlycogen phosphorylase and glycogen synthase
- FrontMaster rule of covalent regulation in glycogen metabolismBackPhosphorylation activates glycogen breakdown and inhibits glycogen synthesis
- FrontLess active form of glycogen phosphorylaseBackPhosphorylase b
- FrontMore active phosphorylated form of glycogen phosphorylaseBackPhosphorylase a
- FrontEnzyme that converts phosphorylase b to phosphorylase aBackPhosphorylase kinase
- FrontEnzyme that reverses phosphorylase a to bBackPhosphoprotein phosphatase
- FrontHigh-yield fact about phosphorylase kinaseBackActivates glycogen phosphorylase by phosphorylation
- FrontEffect of phosphorylation on glycogen synthaseBackInactivates glycogen synthase
- FrontHigh-yield comparison of phosphorylation effectsBackPhosphorylation activates glycogen phosphorylase but inhibits glycogen synthase
- FrontHormones that stimulate glycogen breakdownBackGlucagon and epinephrine (adrenaline)
- FrontSecond messenger increased by glucagon or epinephrine in glycogen breakdownBackcAMP
- FrontEffect of cAMP on glycogen regulationBackActivates protein kinase A (PKA)
- FrontEffect of PKA on glycogen breakdown pathwayBackActivates phosphorylase kinase
- FrontEffect of phosphorylase kinase on glycogen phosphorylaseBackConverts glycogen phosphorylase b to a
- FrontEffect of glucagon or epinephrine on glycogenolysisBackIncreases glycogenolysis
- FrontEffect of hormone-driven phosphorylation on glycogen synthaseBackGlycogen synthase is phosphorylated and becomes less active
- FrontNet effect of glucagon or epinephrine on glycogen metabolismBackTurns glycogen breakdown on and glycogen synthesis off
- FrontInsulin effect on glycogen regulationBackActivates hepatic protein phosphatase-1 (PP1)
- FrontEffect of PP1 on glycogen enzymesBackRemoves phosphate groups from key glycogen enzymes
- FrontEffect of insulin-activated PP1 on glycogen phosphorylaseBackGlycogen phosphorylase becomes less active
- FrontEffect of insulin-activated PP1 on glycogen synthaseBackGlycogen synthase becomes more active
- FrontNet effect of insulin on glycogen metabolismBackGlycogen synthesis is favored
- FrontHigh-yield hormone summary for glycogen metabolismBackInsulin causes dephosphorylation and glycogen synthesis, whereas glucagon or epinephrine cause phosphorylation and glycogen breakdown
- FrontMain allosteric activator of glycogen synthaseBackGlucose-6-phosphate
- FrontMain allosteric inhibitors of glycogen phosphorylaseBackATP and glucose-6-phosphate
- FrontAdditional inhibitor of glycogen phosphorylase in liverBackGlucose
- FrontAllosteric activator of glycogen phosphorylase in muscleBackAMP
- FrontRole of AMP in glycogen regulationBackAMP is a low-energy signal that allosterically activates glycogen phosphorylase in muscle
- FrontTissue specificity of AMP activation of glycogen phosphorylaseBackMuscle only
- FrontWhy AMP activation of glycogen phosphorylase makes sense in muscleBackLow ATP signals that muscle needs more fuel, so glycogen breakdown increases and G6P enters glycolysis
- FrontReaction linking falling ATP to rising AMPBack2 ADP → ATP + AMP by adenylate kinase
- FrontVery high-yield AMP factBackAMP directly activates muscle glycogen phosphorylase even without phosphorylation
- FrontRole of Ca2+ in glycogen metabolismBackDuring muscle contraction, increased intracellular Ca2+ activates phosphorylase kinase
- FrontHow Ca2+ activates phosphorylase kinaseBackBinds to the calmodulin subunit of phosphorylase kinase
- FrontEffect of Ca2+ activation on glycogen breakdownBackActivates glycogen phosphorylase and increases glycogenolysis
- FrontWhy Ca2+ regulation is useful in muscleBackIt increases glycogen breakdown during contraction even before ATP is severely depleted
- FrontLecture phrase for muscle glycogenolysis regulation during contractionBackRole of AMP, Ca2+, and adrenaline
- FrontMeaning of ATP as a glycogen regulatory signalBackHigh-energy signal that reduces glycogen breakdown
- FrontMeaning of G6P as a glycogen regulatory signalBackSignals good glucose availability and reduces glycogen breakdown
- FrontLecture statement about ATP and G6P on phosphorylaseBackLiver and muscle phosphorylase are allosterically inhibited by ATP and G6P
- FrontHigh-yield ATP and G6P conceptBackHigh ATP or high G6P means glycogen should not be broken down aggressively
- FrontReciprocal role of G6P in glycogen metabolismBackG6P activates glycogen synthase and inhibits glycogen phosphorylase
- FrontWhen glycogenolysis should increaseBackGlucagon or epinephrine, cAMP, PKA, phosphorylase kinase, glycogen phosphorylase a, AMP in muscle, and Ca2+ in contracting muscle
- FrontWhen glycogenesis should increaseBackInsulin, PP1, dephosphorylation, active glycogen synthase, and high G6P
- FrontSuper high-yield bond fact in glycogen synthesisBackGlycogen synthase makes α(1→4) bonds
- FrontSuper high-yield branch fact in glycogen synthesisBackBranching enzyme makes α(1→6) branches
- FrontSuper high-yield glycogenolysis factBackGlycogen phosphorylase breaks α(1→4) bonds by phosphorolysis to yield G1P
- FrontSuper high-yield debranching enzyme factBackDebranching enzyme has transferase and α(1→6)-glucosidase activities
- FrontSuper high-yield phosphorylation rule in glycogen metabolismBackPhosphorylation activates glycogen phosphorylase and inhibits glycogen synthase
- FrontSuper high-yield AMP fact in glycogen metabolismBackAMP activates glycogen phosphorylase in muscle only
- FrontSuper high-yield Ca2+ fact in glycogen metabolismBackCa2+ activates phosphorylase kinase via calmodulin
- FrontSuper high-yield G6P fact in glycogen metabolismBackG6P activates glycogen synthase and inhibits glycogen phosphorylase
- FrontCheat-sheet glycogen synthesis pathwayBackGlucose → G6P → G1P → UDP-glucose → glycogen
- FrontCheat-sheet enzymes for glycogen synthesisBackGlycogen synthase adds glucose in α(1→4), branching enzyme makes α(1→6), and glycogenin starts a new chain
- FrontCheat-sheet glycogen degradation pathwayBackGlycogen is degraded mainly to G1P
- FrontCheat-sheet glycogen phosphorylase functionBackRemoves glucose from nonreducing ends, breaks α(1→4) by phosphorolysis, and uses PLP (B6)
- FrontCheat-sheet debranching enzyme functionBackHandles α(1→6) branches and releases some free glucose
- FrontCheat-sheet covalent regulation of glycogen metabolismBackGlucagon or epinephrine → cAMP → PKA → phosphorylase kinase → phosphorylase active; phosphorylation activates phosphorylase and inhibits glycogen synthase; insulin → PP1 → dephosphorylation → synthesis favored
- FrontCheat-sheet allosteric regulation of glycogen metabolismBackG6P activates glycogen synthase, ATP and G6P inhibit glycogen phosphorylase, glucose inhibits liver phosphorylase, AMP activates muscle phosphorylase, and Ca2+ activates phosphorylase kinase via calmodulin
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