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24 Cards in this Set

  • Front
  • Back
In vertebrates, where is glycogen mainly stored?
-skeletal muscles
what are beta particles and alpha rosettes?
-beta particle is a glycogen particle that has 55,000 glucose molecules
-alpha rosette is a cluster of 20-40 beta particles
How many tiers of glucose does a mature glycogen particle have?
What effect does branching have on a glycogen particle?
-makes it more soluble
-increase number of reducing ends
-positions nonreducing ends on outside where they are more accessible to enzyme cleavage
What are the 3 enzymes involved in glycogenolysis?
-glycogen phosphorylase
-debranching enzyme (glucotransferase, glucosidase)
what is the activated form for glucose?
What enzyme catalyzes formation of UDP-glucose?
UPD-glucose pyrophosphorylase
What drives the reaction of UDP -glucose formation?
formation of pyrophosphate and pyrophosphate broken down to 2 Pi
What enzyme adds UDP-glucose to an existing chain of glucose?
glycogen synthase
What enzyme forms branches in glycogen?
glycogen branching enzyme brings 6-7 glucose resides from a terminal end and attaches to C6 of internal glucose
What are the steps in initiating glycogen formation?
-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
Glycogen phosphorylase isozyme exist in which 2 organs?
liver and muscles
Describe hormonal regulation of glycogen phosphorylase in muscles
-epinephrine activates phosphorylase b kinase (phosphorylates less active phosphorylase b to active phosphorylase a)
-phosphorylates serine residues
Describe allosteric regulation of glycogen phosphorylase in muscles
-AMP and Ca2+ are positive allosteric modulators of phosphorylase b kinase
-ATP blocks allosteric site on phosphorylase b kinase
Describe hormonal regulation of glycogen phosphorylase in the liver
-glucagon activates activity of phosphorylase b kinase
-insulin activates activity of phosphorylase a phosphatase
Describe allosteric regulation of glycogen phosphorylase in the liver
-glucose binds to allosteric sites on phosphorylase a, causes conformational change and exposes phosphorylated serine residues which are cleaved by phosphorylase a phosphatase
Describe hormonal regulation of glycogen synthase in the liver
-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
Describe allosteric regulation of glycogen synthase
-Glucose and glucose 6-phosphate are positive allosteric modulators of phosphoprotein phosphatase which promotes active glycogen synthase a
Describe hormonal regulation of glycogen synthase in muscles
-epinephrine blocks activity of phosphoprotein phosphatase, which inhibits activation of glycogen synthase a
What enzyme primes glycogen synthase kinase 3 for action?
casein kinase II
Describe type Ia glycogen storage disorder, von Gierke's disease
-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
Describe type III glycogen storage disease, Cori's disease
-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
Describe type IV glycogen storage disease, Andersen's disease
-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
Describe type V glycogen storage disorder, McArdle's disease
-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