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24 Cards in this Set
- Front
- Back
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In vertebrates, where is glycogen mainly stored?
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-liver
-skeletal muscles |
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what are beta particles and alpha rosettes?
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-beta particle is a glycogen particle that has 55,000 glucose molecules
-alpha rosette is a cluster of 20-40 beta particles |
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How many tiers of glucose does a mature glycogen particle have?
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12
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What effect does branching have on a glycogen particle?
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-makes it more soluble
-increase number of reducing ends -positions nonreducing ends on outside where they are more accessible to enzyme cleavage |
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What are the 3 enzymes involved in glycogenolysis?
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-glycogen phosphorylase
-debranching enzyme (glucotransferase, glucosidase) -phosphoglucomutase |
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what is the activated form for glucose?
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UDP-glucose
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What enzyme catalyzes formation of UDP-glucose?
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UPD-glucose pyrophosphorylase
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What drives the reaction of UDP -glucose formation?
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formation of pyrophosphate and pyrophosphate broken down to 2 Pi
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What enzyme adds UDP-glucose to an existing chain of glucose?
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glycogen synthase
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What enzyme forms branches in glycogen?
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glycogen branching enzyme brings 6-7 glucose resides from a terminal end and attaches to C6 of internal glucose
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What are the steps in initiating glycogen formation?
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-Make UDP-glucose
-glycogenin is primer with reactive Tyr which attacks C1 of UPD-glucose via glucotransferase activity, so that UDP is released and have glucose attached to glycogenin -glycogenin catalyzes addition of 7 more glucose residues (chain-extending activity) -glycogen synthase continues additional synthesis |
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Glycogen phosphorylase isozyme exist in which 2 organs?
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liver and muscles
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Describe hormonal regulation of glycogen phosphorylase in muscles
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-epinephrine activates phosphorylase b kinase (phosphorylates less active phosphorylase b to active phosphorylase a)
-phosphorylates serine residues |
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Describe allosteric regulation of glycogen phosphorylase in muscles
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-AMP and Ca2+ are positive allosteric modulators of phosphorylase b kinase
-ATP blocks allosteric site on phosphorylase b kinase |
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Describe hormonal regulation of glycogen phosphorylase in the liver
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-glucagon activates activity of phosphorylase b kinase
-insulin activates activity of phosphorylase a phosphatase |
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Describe allosteric regulation of glycogen phosphorylase in the liver
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-glucose binds to allosteric sites on phosphorylase a, causes conformational change and exposes phosphorylated serine residues which are cleaved by phosphorylase a phosphatase
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Describe hormonal regulation of glycogen synthase in the liver
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-glycogen synthase a is active
-phosphorylated glycogen synthase b is inactive -insulin blocks glycogen synthase kinase 3 (GSK3) from phosphorylating glycogen synthase and sitmulates phosphoprotein phosphatase -glucagon inhibits activity of phosphoprotein phosphatase |
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Describe allosteric regulation of glycogen synthase
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-Glucose and glucose 6-phosphate are positive allosteric modulators of phosphoprotein phosphatase which promotes active glycogen synthase a
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Describe hormonal regulation of glycogen synthase in muscles
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-epinephrine blocks activity of phosphoprotein phosphatase, which inhibits activation of glycogen synthase a
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What enzyme primes glycogen synthase kinase 3 for action?
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casein kinase II
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Describe type Ia glycogen storage disorder, von Gierke's disease
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-glucose 6-phosphatase deficiency, so liver can't mobilize glucose
-affects the liver -accumulation of normal glycogen in liver (enlarged liver), hypoglycemia, weakness -treated with glucose infusion -severe disease, but most patients survive -most common GSD |
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Describe type III glycogen storage disease, Cori's disease
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-debranching enzyme deficiency
-affects liver and cardiac and skeletal muscle -glycogen with short branches -similar symptoms as type Ia (hypoglycemia, weakness, enlarged liver), but milder than type Ia -treated with glucose infusion |
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Describe type IV glycogen storage disease, Andersen's disease
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-branching enzyme deficiency
-abnormally long unbranched chains of glycogen -affects liver and skeletal muscles -glycogen accumulation in liver and liver enlargement -kills within first year of life |
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Describe type V glycogen storage disorder, McArdle's disease
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-muscle glycogen phosphorylase deficiency
-affects skeletal muscles -not life-threatening, shows that liver glycogen is necessary for activity more so than muscle glycogen -muscles can't mobilize glucose well, so get muscle cramping -moderate increase in normal glycogen |
