Terms in this set (30)
What is glycogen?
The energy storage polysaccharide in animals
What are the major sites of synthesis and storage of glycogen?
Liver and skeletal muscle
What limits storage capacity of glycogen?
The number of glycogenin molecules
Describe the structure of glycogen
Core protein is glycogenin. Branched. Grows off of non reducing ends. Linked together by alpha 1,4. Branched using alpha 1,6.
What are the major tissues involved in glycogen storage?
Liver and Skeletal muscle
What does glycogen that is stored in the liver used for?
Supplies blood with glucose between meals
What is muscle glycogen used for?
Oxidizes glucose via glycolysis to supply muscle with ATP for contraction
What can't muscle release glucose into the blood?
It has no glucose 6 phosphatase
What is the general rationale in conversion of blood glucose to glycogen?
Trap glucose, form G1P isomer, activate G1P, elongate partially degraded glycogen, form branch points, further elongate, etc.
What are the three pathways that glucose 6 phosphate can take on the cell?
Fructose 6 Phosphate to Glycolysis
6-Phosphogluconate to Pentose Phosphate Pathway
Glucose-1-Phosphate to UDP Glucose into Glycogen
What is the first step in committing glucose 6 phosphate to glycogen synthesis?
Formation of glucose 1 phosphate by phosphoglucomutase
Describe the pathway from Glucose 1 phosphate to being part of glycogen.
Glucose 1 phosphate becomes activated by UDP glucose pyrophosphorylase. Elongation by glycogen synthase (rate limiting enzyme), transfers glucose from UDP-glu to 4-OH of glycogen.
What is the rate limiting step of glycogen synthesis?
How is glycogen branching achieved?
Alpha 1,4 Alpha 1,6 transferase takes long chain off and makes a new alpha 1,6 bond to make a branch
What is the first step of glycogen degradation?
Phosphorolytic cleavage across the bond, removing Glycogen 1 Phosphate off the glycogen. Achieved by glycogen phosphorylase.
What vitamin is necessary for proteolytic cleavage of glucose off of the glycogen?
Pyridoxal P is derived from vitamin B6
When is glycogen debranched?
When it gets within 4 glucose units from a branch point
What is the first step of debranching? What is the enzyme involved?
Unit of 3-5 glucose units tranferred to end of another chain. alpha 1,4 alpha 1,4 transferase
What is the second step of debranching?
The single glucose left at the branch point is released as free glucose. alpha 1,6 glucosidase
What happens to glucose 1 phosphate?
Isomerized to G6P by phosphoglucomutase
Liver: G6P hydrolyzed to glucose
Muscle: G6P proceeds through glycolysis or PPP, can't be hydrolyzed
What is the covalent regulation of glycogen synthesis?
Glycogen synthase active in dephos form and activated in the phosphorylated form.
What is the allosteric regulation of glycogen synthesis?
Covalently inactiveform (phosphorylated) can be allosterically activated if there is a lot of G6P. More of a fine tuning thing. Covalent regulation is primary.
What is the covalent regulation of glycogen degradation?
Glycogen phosphorylase is active in the phosphorylated form.
What is the allosteric effects on glycogen degradation?
Muscle phosphorylase kinase is activated by Ca2+ (so activates glycogen phosphorylase).
Muscle phosphorylase is activated by AMP (inhibits glycogen phosphorylase)
Von Gierke's disease
G6Pase deficiency. Glycogen accumulation in the blood
Lysosomal alpha 1,4 glucosidase. Glycogen accumulation in the lysosomes
Debranching enzyme deficiency
Branching enzyme deficiency
Muscle glycogen phosphorylase deficiency
Liver glycogen phosphorylase deficiency
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