41. Glycogen Metabolism Flashcards
major storage cacrbohydrate in animals
glycogen
______ gram of glycogen
stored in muscle and liver
500 grams
where does glycogenesis occur
- liver and muscle
* cytosol
rate limiting step of glycogenesis
elongation of glycogen chains
alpha (1,4) glycosidic bonds
enzyme: glycogen synthase
protein that serves as a primer for glycogen synthesis when glycogen is completely depleted
glycogenin
synthesis of UDP-glucose requires this enzymes
phosphoglucomutase
UDP-glucose pyrophosphorylase
source of all glucosyl residues that are added to glycogen molecule
UDP-glucose
elongation of glycogen chains
enzyme
glycogen synthase
rate limiting step of glycogenesis
elongation of glycogen chain
•glycogen synthase
•bonds formed at non-reducing end (C4)
formation of branches in glycogen
enzyme ?
branching enzyme
•amylo alpha (1–>4) –> alpha (1–>6) transglucosidase
forms alpha (1–>6) bonds by transferring 5-8 glucosyl residues
branching enzyme
•amylo alpha (1–>4) –> alpha (1–>6) transglucosidase
forms alpha (1–>4) bonds between glucose residues
glycogen synthase
for mobilizing stored glycogen
glycogenolysis
where does glycogenolysis occur
- liver, muscle
* cytosol
what is the substrate of glycogenolysis
glycogen
what are products of glycogenolysis
- glucose - liver
* glucose-6-phosphate - muscle
rate limiting step of glycogenolysis
shortening of glycogen chains
enzyme : glycogen phosphorylase
- cleavage of alpha (1–>4) bonds
between glucosyl residues at non reducing ends of glycogen chains
co-enzyme: pyridoxal phosphate
when does shortening of glycogen chain stop
when 4 glucosyl units remain (limit dextrin)
removal of branches of glycogen
enzyme?
debranching enzyme :
•alpha (1–>4) -> alpha (1–>4) glucantransferae
•amylo-alpha (1–>6) glucosidase
- cleaves alpha (1–>4) and alpha (1–>6) bonds
debranchign enzyme yields free glucose from cleavage of ___ bond
alpha (1–>6) bonds
conversion of glucose-1-P to glucose -6-P or glucose
enzyme
phosphoglucomutase
and when present
glucose-6-phosphatase
lysosomal degradation of glycogen
alpha (1–>4) glucosidase (acid maltase)
degrades 1-3% of glycogen
lysosomal degradation of glycogen
deficiency of this enzyme leads to Pompe disease
alpha (1–>4) glucosidase (acid maltase)
glycogen synthase
pathway
glycogenesis
glycogen phosphorylase
pathway
glycogenolysis
Presence of glucose-6-P
effect on
glycogen synthase
activated
Presence of glucose-6-P
effect on
glycogen phosphorylase
inhibited
Presence of ATP
effect on
glycogen phosphorylase
inhibited
Presence of calcium (muscle)
effect on
glycogen phosphorylase
activated
Presence of glucagon and epinephrine
on
glycogen synthase
inhibited
Presence of insulin
effect on
glycogen synthase
activated
phosphorylation
effect on
glycogen synthase
inactive
Presence of glucagon and epinephrine
effect on
glycogen phosphorylase
activated
Presence of INSULIN
effect on
glycogen phosphorylase
Inhibited
PHOSPHORYLATION
effect on
glycogen phosphorylase
Active
group of inherited disorders characterized by deposition of abnormal type or quantity of glycogen in tissues
glycogen storage diseases
glucose-6-phosphatase deficiency
Type Ia
Von Gierke disease
lysosomal acid maltase deficiency
Type II Pompe disease
debranching enzyme deficiency
Type III a cori disease
branching enzyme deficiency
type IV Andersen disease
muscle phosphorylase deficiency
Type V McArdle syndrome
liver phosphorylase deficiency
Type VI
Hers disease
- ÎÎ glycogen in liver and renal tubule cells
- hypoglycemia
- lactic acidosis
- ketosis
- hyperlipidemia
Von Gierke disease
- ÎÎ glycogen in lysosomes
- Juvenile onset - hypotonia, death, heart failure
- adult onset - muscle dystrophy
Pompe disease
- fasting hypoglycemia , hepatomegaly in infancy
- ÎÎ limit dextrin
- muscle weakness
Type IIIa cori disease
- hepatosplenomegaly
- ÎÎ polysaccharide with few branch points
- death from heart or liver failure before age 5
Anderrsen disease
- poor exercise tolerance
- muscle cramps and myoglobinuria but no alctic acidosis
- ÎÎ muscle glycogen
McArdle syndroe
- Hepatomegaly
* mild hypoglycemia
Hers disease
