What are the two major sites of synthesis and storage of glycogen?
Liver and skeletal muscle
Storage capacity of glycogen is limited by the number of what molecule?
Glycogenin
What hormones are key players in the regulation of glycogen synthesis and degradation?
Insulin, glucagon, and epinephrine
Glycogen granules consists of a ____ core with a ___ coat.
Polysaccharide (glycogen) , protein coat containing enzymes necessary for glycogen breakdown and synthesis
Reactions occurring with glycogen take place at the reducing or nonreducing ends?
Nonreducing
Is glycogenin at the reducing or nonreducing end of glycogen?
reducing
What is the differency between liver and muscle glycogen?
Liver glycogen supplies the blood with glc between meals. Muscle glycogen oxidizes glc via glycolysis to supply muscle with ATP for cont'n.
T/F: Muscle has glucose-6-phosphatase and can release free glc into the blood.
False: the glycogen in muscle can only be used via glycolysis
What is the pathway from glc to glycogen?
1. Glucose is converted to G6P by hexokinase/glucokinase, 2. G6P converted to G1P by phosphoglucomutase 3. G1P converted to UDP~glc by UDP glc phosphorylase 4. UDP~glc adds to glycogen chain for elongation by glycogen synthase (forms a-1,4 bonds). When chain becomes 10-15 units long, an a-1,6 bond is created
What is the pathway for glycogen degradation?
Glycogen phosphorylase (uses pyridoxal-P) adds a phosphate and removes G1P. When chain is 4-6 units until a branch point, the debranching enzyme dissables the branch point by transfering a 3-5 glc unit to the end of a chan (a1,4, a1,6-transferase) and the single glc left at the branch point is released as free glc (a 1,6 glucosidase)
How many ATP does it take to store one G6P as glycogen?
1 ATP
Is glycogen synthase activated in the phos or dephos form? What phosphorylates/dephosphorylates glycogen synthase?
Activated in the dephos form. Protein phosphatase 1 dephosphorylates. PKA phosphorylates and inactivates the glycogen synthase.
What can allosterically activate glycogen synthase?
accumulation of G6P
Is glycogen phosphorylase activated in the phos or dephos form? What phosphoylates/dephosphorylates the glycogen phosphorylase?
Glycogen phosphorylase is activated in the phosphorylated form--phosphorylated by phosphorylase kinase (which is phosphorylated in PKA). It is deactivated by removing the phosphate by protein phosphatase-1.
What are allosteric activators/inhibitors of muscle phosphorylase?
Activators: AMP, Ca2+ (binds to phosphorylase kinase-calmodulin is a subunit of phosphorylase kinase)
Inhibitors: G6P and creatine-P
What allosterically inhibits liver glycogen phosphorylase?
Glucose
Both muscle and liver glycogen synthase are allosterically activated by what?
High G6P
What hormones will stimulate cAMP synthesis with respect to glycogen?
Glucagon and Epinephrine in the liver
Eprinephrine in the muscle
What hormone stimulates cAMP degradation?
Insulin
Insulin activates what two things to inactivate glycogen breakdown?
Protein phosphatase 1 and cAMP phosphodiesterase
What is the enzyme deficiency in von Gierke's disease (Type I glycogen storage disorder)? What are the characteristics?
G6Pase deficiency, glycogen accumulation in liver and kidney, lactic acidemia, hypoglycemia, hyperuricemia, hyperlipidemia, ketosis, normal glycogen structure
What is the enzyme deficiency in Pompe's disease (Type II glycogen storage disease)? What are the characteristics?
Lysosomal a-1,4-glucosidase deficiency. glycogen accumulation in lysosomes, early death, normal blood glc, normal glycogen structure, frequently heart is main organ involved
What is the enzyme deficiency in Cori's/Forbes' disease (Type III glycogen storage disease)? What are the characteristics?
Debranching enzyme, abnormal glycogen, having short outer chains; hypoglycemia
What is the enzyme deficiency in Anderson's disease (Type IV glycogen storage disease)? What are the characteristics?
Branching enzyme, abnormal glycogen, having long unbranched chains, early death due to cardiac or liver failute
What is the enzyme deficiency of McArdle's disease (Type V glycogen storage disease)? What are the characteristics?
Muscle glycogen phosphorylase-abnormally high content of muscle glycogen; weakness, cramping, and decreased serum lactace after exercise; normal glycogen structure
What is the enzyme deficiency of Hers' disease (Type VI glycogen storage disease)? What are the characteristics?
Liver glycogen phosphorylase-abnormally high content of liver glycogen; mild hypoglycemia and ketosis; normal glycogen structure
