Glycogen Metabolism Flashcards
What is the bonding / branching pattern of lycogen?
storage form of carbohydrates in animals
alpha 1-4 glucose w/ alpha 1-6 branches
Where is glycogen found & what is its respective function in each of those places?
- liver (and kidney)
- provide glucose for circulation to other tissues
- skeletal muscle & heart
- provide glucose for muscle use
What enzyme adds new glucosyl residues to glycogen?
glycogen synthase
What primer is required for glycogen synthesis?
glycogenin
What enzyme adds branch points to glycogen?
branching enzyne
How are glycosyl residues added to glycogen?
one at a time to non-reducing end
In what form can glucose be added to glycogen?
How is this form produced?
UDP-glucose (activated glucose)
- Glu-6-P –> Glu-1-P
- phosphoglucomutase
- glu-1-P + UTP –> UDP-glucose
- UDP-glucose pyrophosphorylase
Whta is the numerical pattern for glycogenesis branch points?
- occurs after a minimum of 11 glycosyl residues have been added
- the terminal 6-7 are removed as a block & moved to a more interior site
- attached by alpha 1-6 linkage
How are glucose units removed from glycogen?
This process requires what cofactor?
removed one residue at a time from a non-reducing end of glycogen by glycogen phosphorylase
Requires pyridoxical phosphate
hydrolytic reaction – yields glucose NOT glu-P
Pyridoxical phosphate is a derivative of what vitamin?
vitamin B6
What enzymes are involved with glycogenolysis?
- Phosphorylase removes glycosyl residues until 4 units remain behind a branch point
-
Debranching enzyme moves a triose from branch point to another branch
- contains alpha 1-6 glucosidase activity (removes branched glucosyl residue)
What enzymes are reciprocally active due to the tightly regulated & coordinately controlled processes of glycogenesis and glycogenolysis?
glycogen synthase
phosphorylase
What hormones exert regulatory contorl over glycogen metabolism?
What are their effects?
- Insulin
- stimulates glycogenesis
- inhibits glycogenolysis in liver + muscle
- Glucagon
- inhibits glycogenesis
- stimulates glycogenolysis in liver
- Epinephrine
- stimulates glycogenolysis in liver and muscle
What are the two forms of glycogen phosphorylase & what is their differentiating factor?
- phosphorylase-a
- phosphoryated
- active
- phosphorylase-b
- dephosphorylated
- inactive
Phosphorylation of glycogen phosphorylase is controlled by what enzyme?
How is it regulated?
phosphorylase kinase
activated by Ca2+ & subsequent phosphorylation
What enzyme removes the phosphate from the glycogen phosphorylase?
phosphoprotein phosphatase
How is glycogen synthase enzyme regulated?
What is the active & inactive forms?
via phosphorylation
- glycogen synthase-a: active & dephosphorylated
- glycogen synthase-b: inactive and phosphorylated
How does glucagon impact cells?
increase [cAMP] levels in the liver
How does epinephrine impact cellular metabolism?
- increase [cAMP] in liver & muscle cells
- inhbits glycolysis & stimulates gluconeogenesis in liver
- stimulates lycolysis in muscle cells
- increae [Ca2+] in liver
How does insulin impact cellular metabolism?
- inhibits glycogenolysis and stimulates glycogenesis in both liver & muscle
- effects are opposite those of cAMP
Glycogen storage diseases are characterized by what features?
deposition of abnormal type or quantity of glycoen in tissue
OR
failure to mobilize glycogen
Identify the enzyme effected by the provided glycogen storage disorder:
GSD0a
liver isozyme of glycogen synthase
glycogen synthase-2 (GYS2)
Identify the enzyme affected & mutation associated with the following glycogen storage disease:
Cori / Forbes
liver and muscle debranching enzyme
GSD3
Identify the enzyme affected & mutation associated with the following glycogen storage disease:
Anderson
branching enzyme
GSD4
