KlappaGlycogen Metabolism: Liver vs Muscle
Tier 2 · #13 of 33 · high yield · topic 3.8 — every high-yield fact from the book chapter, exam-ready.
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- FrontWhat is the activated, "high-energy" glucose donor for all anabolic glycogen synthesis reactions?BackUDP-glucose
- FrontIn glycogen phosphorylase regulation, which form is ACTIVE — phosphorylase a (phosphorylated) or phosphorylase b (dephosphorylated)?BackPhosphorylase a (the phosphorylated form) is active
- FrontWhich type of glycosidic bond forms the linear backbone of glycogen?Backα(1→4) glycosidic bonds
- FrontSkeletal muscle lacks which enzyme , making it unable to release free glucose into the blood?BackGlucose-6-phosphatase
- FrontGlycogen synthase is active in which form — phosphorylated or dephosphorylated?BackDephosphorylated ( synthase a = active )
- FrontWhich type of glycosidic bond forms the branch points of glycogen?Backα(1→6) glycosidic bonds
- FrontWhich hormone receptor is ABSENT from skeletal muscle , so glucagon cannot directly stimulate muscle glycogenolysis?BackGlucagon receptor
- FrontGlycogen phosphorylase cleaves α(1→4) bonds by inserting inorganic phosphate (not water). What is this process called?BackPhosphorolysis
- FrontWhat is the primary product released when glycogen phosphorylase cleaves a terminal glucose residue?BackGlucose-1-phosphate (G-1-P)
- FrontGlucose-6-phosphatase deficiency causes which glycogen storage disease ?BackVon Gierke disease (Type Ia)
- FrontWhat enzyme isomerizes glucose-6-phosphate to glucose-1-phosphate (and reverses it during degradation)?BackPhosphoglucomutase
- FrontGlycogen synthase cannot start a chain from scratch . Which protein serves as the obligatory primer by self-glucosylating an ~8-residue oligosaccharide?BackGlycogenin
- FrontWhy is the classic ischemic forearm exercise test diagnostic for McArdle disease (Type V) ?BackNo rise in blood lactate (no muscle glycogenolysis → no glycolytic flux → no lactate)
- FrontWhich coenzyme (vitamin) does glycogen phosphorylase require?BackPyridoxal phosphate (PLP, from vitamin B6)
- FrontIn the liver , what is the metabolic fate of the G-6-P produced by glycogenolysis?BackHydrolyzed to free glucose by glucose-6-phosphatase and exported into the blood
- FrontMcArdle disease (Type V) results from deficiency of which enzyme ?BackMuscle glycogen phosphorylase (myophosphorylase)
- FrontIn skeletal muscle , what is the metabolic fate of the G-6-P produced by glycogenolysis?BackEnters glycolysis locally to produce ATP for contraction ( cannot be exported )
- FrontThe branching enzyme cleaves ~7 residues and forms a new branch. What linkage does it create at the branch point?Backα(1→6) bond (a new branch point)
- FrontPompe disease (Type II) is a deficiency of which enzyme ?BackLysosomal acid glucosidase (acid maltase)
- FrontCloze: G-1-P reacts with _____ to form UDP-glucose , releasing pyrophosphate.BackUTP (uridine triphosphate)
- FrontWhich enzyme interconverts phosphorylase b → phosphorylase a by phosphorylation?BackPhosphorylase kinase
- FrontWhy is Pompe disease (Type II) considered the "odd one out" among glycogen storage diseases?BackIt is a lysosomal storage defect , not a cytoplasmic pathway defect ( synthase / phosphorylase pathways are intact)
- FrontWhat thermodynamically drives UDP-glucose formation forward (making it irreversible)?BackHydrolysis of pyrophosphate (PPi) to 2 Pi by pyrophosphatase
- FrontIn MUSCLE only, which allosteric signal activates phosphorylase b (without phosphorylation) during intense exercise?BackAMP
- FrontHers disease (Type VI) is a deficiency of which enzyme ?BackHepatic glycogen phosphorylase
- FrontThe debranching enzyme has two activities. What does its transferase activity do?BackMoves the outer 3 of 4 branch-point residues to another chain end, re-forming an α(1→4) linkage
- FrontWhich two allosteric signals inhibit glycogen phosphorylase in BOTH liver and muscle ?BackATP and glucose-6-phosphate
- FrontThe debranching enzyme 's α(1→6)-glucosidase activity releases the single branch-point residue as what (and by what process)?BackFree glucose , by hydrolysis
- FrontWhy does Von Gierke disease (Ia) block BOTH glycogenolysis and gluconeogenesis from releasing glucose?BackGlucose-6-phosphatase is the shared final step of both pathways
- FrontIn LIVER only, which allosteric inhibitor of phosphorylase a promotes its dephosphorylation when blood glucose is high?BackFree glucose
- FrontWhich hormone acts on BOTH liver and muscle to stimulate glycogenolysis?BackEpinephrine (adrenaline)
- FrontIn the cAMP cascade, hormone binding activates adenylyl cyclase to produce which second messenger?BackcAMP
- FrontWhich kinase , activated by cAMP , simultaneously phosphorylates phosphorylase kinase ( ON ) and glycogen synthase ( OFF )?BackProtein kinase A (PKA)
- FrontBesides PKA phosphorylation, which ion directly activates phosphorylase kinase during muscle contraction?BackCa2+ (released from the sarcoplasmic reticulum )
- FrontWhich hormone activates phosphoprotein phosphatase-1 , turning glycogen synthesis ON and degradation OFF ?BackInsulin
- FrontWhy does branching massively increase the RATE of glycogen mobilization?BackIt creates many non-reducing ends , so many phosphorylase molecules can work simultaneously
- FrontWhich enzyme dephosphorylates (inactivates) glycogen phosphorylase a ?BackPhosphoprotein phosphatase-1
- FrontWhat is the classic lab triad of Von Gierke disease (Type Ia) ?BackFasting hypoglycemia, lactic acidosis, hepatomegaly
- FrontRoughly how much of glycogenolytic output comes off as free glucose (at branch points) rather than as G-1-P ?BackAbout 8–10%
- FrontWhich tissue stores more glycogen by absolute mass — liver or skeletal muscle ?BackSkeletal muscle (300–700 g, ~80% of body total) vs liver (80–160 g)
- FrontWhat distinguishes Hers disease (VI) from McArdle disease (V) on the exam?BackHers: hepatomegaly + mild hypoglycemia + NORMAL lactate exercise test (hepatic phosphorylase, muscle intact)
- FrontWhat organelle/membrane houses glucose-6-phosphatase in hepatocytes ?BackThe endoplasmic reticulum membrane
- FrontWhy must glucose be dephosphorylated before leaving the cell?BackPhosphorylated glucose cannot cross the plasma membrane via glucose transporters
- FrontPompe disease most severely affects which two tissues , causing hypotonia/dystrophy and cardiomegaly?BackSkeletal muscle and heart
- FrontWhy is glycogen phosphorolysis energetically efficient compared with hydrolysis?BackThe product ( G-1-P ) is already phosphorylated , so it costs no ATP to trap glucose in the cell
- FrontPhosphorylase and glycogen synthase are reciprocally regulated. What futile cycle does this prevent?BackSimultaneous synthesis and degradation of glycogen at full speed
- FrontHow often does a branch point ( α(1→6) linkage ) occur along a glycogen chain?BackEvery 8–10 glucose residues
- FrontHow close to a branch point does glycogen phosphorylase stop, requiring the debranching enzyme to take over?BackIt stops within 4 residues of the branch point
- FrontWhat bond does glycogen synthase form, and what molecule does it release, when it transfers glucose from UDP-glucose onto a non-reducing end?BackForms a new α(1→4) bond and releases UDP
- FrontThe growing glycogen chain must reach how many residues before the branching enzyme acts?Back11 or more residues
- FrontCloze: The first committed step of glycogen synthesis is phosphorylation of glucose to G-6-P by _____ (or _____ in the liver).Backhexokinase (or glucokinase in the liver)
- FrontBesides hepatomegaly, lactic acidosis, and fasting hypoglycemia, what two additional findings complete the Von Gierke (Ia) picture?BackKidneys engorged with glycogen (renal enlargement) and hyperlipemia
- FrontWhat is the approximate molecular weight of a glycogen molecule?Back~10^7–10^8 Da
- FrontWhen glycogen phosphorylase is switched ON , what simultaneously happens to glycogen synthase (the direction of reciprocal regulation)?BackGlycogen synthase is switched OFF (and vice versa)
- FrontBesides increasing the rate of mobilization, why else is branching functionally important (its hydration effect)?BackIt increases solubility — 1 g of glycogen binds 2–3 g of water
- FrontIn the synthesis pathway, which enzyme isomerizes G-6-P to G-1-P (the step before UTP activation)?BackPhosphoglucomutase
- FrontAfter the debranching transferase moves the outer 3 residues, how many residues remain at the branch point, and how are they removed?Back1 residue remains ; the α(1→6)-glucosidase activity hydrolyzes it to free glucose
- FrontWhat is the purpose of liver glycogen versus muscle glycogen?BackLiver : maintain blood glucose for the whole body . Muscle : local fuel for contraction
- FrontRoughly what fraction of total body glycogen is held in skeletal muscle ?Back~80% of body total
- FrontRoughly how much total glycogen does the body hold on average (the chapter's headline figure)?Back~600 g (about 80–160 g in liver + 300–700 g in muscle )
- FrontBesides the liver , which other tissue expresses glucose-6-phosphatase (and thus can release free glucose )?BackRenal cortex (kidney) cells
- FrontWhich hormonal ratio is the master switch that sets the direction of glycogen metabolism in the fed vs fasted state?BackThe insulin-to-glucagon ratio
- FrontIn the LIVER , by what additional second-messenger route does epinephrine (alpha-adrenergic) activate glycogenolysis, besides cAMP?BackCa2+ release via IP3
- FrontWhich glycogenolysis-stimulating hormone acts on the LIVER ONLY (and not on skeletal muscle)?BackGlucagon
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