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19 Cards in this Set
- Front
- Back
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Where can glycogen be stored in the body?
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Most cells can store glycogen but liver and muscle are the main storage sites
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What tissues preferentially use glucose for energy?
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Brain, RBCs, kidney medulla, lens and cornea of eye, testes and exercising muscle
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At what point in fasting does gluconeogenesis take over as the main source of glycogen production?
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At 24 hr. This is when glycogen is depleted. However, it occurs as a minor source all along.
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In what tissue does glycogen degradation and glycolysis occur at the same time? Where does it not?
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Muscle. Liver.
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When do babies begin to make glycogen? How is this effected by Mom?
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In last 10 wk of pregnancy baby makes glycogen. If Mom is malnourished, baby may not make and can become severely hypoglycemic (after birth).
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What is glycogenin?
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It is the center of glycogen and is covalently bound through a tyrosine residue to glycogen
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What is the key (rate-limiting) enzyme in glycogen synthesis?
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Glycogen synthase. Generates alpha-1-4 glycosidic bonds.
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How are branches of glycogen synthesized?
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Generated every 8-10 glucose molecule by a branching enzyme (4:6 transferase) which creates a alpha-1-6 bond.
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What 2 pathways are involved in glycogen degradation?
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Minor route: in the lysosome by acid alpha-glucosidase. Major route: In cytoplasm by glycogen phosphorylase.
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What is the role of glucose-6-phosphatase? What tissue is it absent from?
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G6P can be converted to glucose in the ER and excreted into circulation. This is not present in skeletal muscle.
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What is Von Gierke Disease? How does it manifest?
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Def. in glucose-6-phosphatase. Hepatomegaly, renomegaly; inc. lactic acid, uric acid, lipids; dec. glucose during fasting; growth retardation and delayed puberty
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What is Pompe Disease? How does it manifest?
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Def. in acid-alpha-glucosidase. Cardiomegaly. Normal BG. Weak muscle tone.
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What is McArdie Syndorme?
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Def. in glycogen phosphorylase in skeletal muscle. Cramping after excercise, incr. myoglobin, no inc. in lactate after exercise. Temp. weakness after exercise.
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How does phosphorylation effect glycogen synthase? Glycogen phosphorylase.
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Inhibits. Activates (degradation).
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How does glucagon and Epi effect glycogen on a cellular level?
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G protein linked receptor --> activates cAMP --> Activates Protein Kinase A --> phophorylates phosphorylase kinase (active) & glycogen synthase (inactive). Glycogen is degraded.
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What hormones regulate glycogen metabolism?
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Glucagon (liver only), Epi and insulin
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On a cellular level, how does Epi binding to an alpha-1 receptor effect glycogen metabolism?
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G protein linked receptor activates phospholipase C --> 2nd messagers (such as Ca on Calmodulin) --> Glycogen degradation
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How does insulin work on a cellular level to effect glycogen metabolism?
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Works through tyrosine kinase pathway --> Activates protein phosphotases (dephosphorylates glycogen phorphorylase and glycogen synthase) --> Glycogen synthesis. Can also activate PDE which destroys cAMP.
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What allosteric regulators are involved in glycogen metabolism?
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Liver -- Decreased glucose cause degradation. Muscle -- Inc. AMP and Ca lead to glycogen degradation. Both -- Inc. G6P inc. synthesis and Dec. G6P and ATP leads to degradation.
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