glycogen Flashcards
Glycogen synthase is regulated by what
insulin (stimulates)
glucagon (inhibits)
in the liver and muscle
How does glucagon turn off glycogen synthase
- glucagon goes to the liver stimulates beta adrenergic rec
- Gs recepter
- adenylate cyclase
- cAMP
- protein kinase A
- phosporylates glycogen synthase
What is the major enzyme of glycogen breakdown
glycogen phosphorylase
glycogen phosphorylase is regulated by what
glucagon (liver)
epinephrine (liver, muscle)
AMP (muscle)
all stimulate it
Where is glucose-6-phosphatase
in the liver
-takes phosphate off so glucose can go into the blood
What enzyme is defective in Von Gierke disease (type I)
glucose-6-phosphatase in the liver
- hallmark is severe hypoglycemia
- lactic acidosis
- hepatomegaly
- hyperlipidemia
- hyperuricemia
- short stature
- doll like face
- protruding abdomen
- emaciated extremities
is glycogen synthesis normal in von gierke
yes
What will von gierke not affect
muscle
Glucose-6-phosphatase is only in liver
Why is there hyperlipidemia in von gierke
secondary to severe hypoglycemia
- turn on hormone sensitive lipase
- breakdown TG to FFA
Why is there hepatomegaly in von gierke
glucose cannot get out and backs up in cell
-glucose and glycogen are osmotic and bring in water
What defect is in Pompe disease (type II)
lysosomal alpha, 4-glucosidase
hallmark cardiomegaly
- muscle weakness
- death by 2 years
Cardiomegaly is associated with which glycogen storage disease
Pompe (type II)
lysosomal alpha, 4-glucosidase
What defect is in Cori disease (type III)
glycogen deb ranching enzyme
- mild hypoglycemia
- liver enlargement
what defect is in Andersen disease (type IV)
Branching enzyme
- hallmark infantile hypotonia
- cirrhosis
- death by 2 years old
which two glycogen storage disease have death by 2 years old
Pompe (type II) - lysosomal alpha, 4 glucosidase
Andersen (type IV) - branching enzyme
Which glycogen storage disease have abnormal glycogen structure
Cori (type III)
Andersen (type IV)
What is the glycogen structure in Cori disease
defect in glycogen deb ranching enzyme
-shorter outer branches with single glucose residue alpha 1, 6 at outer branch
What is the glycogen structure in Andersen disease
defect in branching enzyme
- very few branches especially toward peripherally
- very linear appearing
What defect is in McArdle disease (type V)
muscle glycogen phosphorylase
- elevated glycogen in muscle only
- muscle cramps and weakness w/exercise
- myoglobinuria
What defect is in Hers disease (type VI)
hepatic glycogen phosphorylase
- mild fasting hypoglycemia
- hepatomegaly
- cirrhosis
In which glycogen storage diseases is glycogen structure normal
Von gierke (type I) pompe (type II) McArdle (type V) Hers (type VI)
Why is there only mild hypoglycemia in Hers disease
hepatic glycogen phosphorylase breaks down glycogen to G-6-P
-glucose can still get into blood by gluconeogenesis
Why is there severe hypoglycemia in von gierke disease
glucose-6-phosphate is trapped in the liver without glucose-6-phosphatase
- need phosphatase to get G6P from gluconeogenesis too
- both paths are blocked
In starvation a small amount of glucose can be made in the
kidney
