Glycogen Flashcards
Glycogenolysis in the liver can be allosterically regulated via substrate concentrations. How can glycogenolysis in muscles be regulated allosterically?
Ca2+ - Calmodulin & AMP
What enzyme is the regulatory point for glycogenesis?
Glycogen synthase
What enzyme is deficient in Type I: von Gierke glycogen storage disease?
Glucose-6-Phosphotase
What is the effect of cortisol and epinephrine on glycogen metabolism?
Cortisol and epinephrine activate the glycogen phosphorylase to breakdown glycogen and inhibit the glycogen synthase.
What symptoms are associated with a deficiency in the debranching enzyme?
Hypoglycemia & hepatomegaly
What is the effect of insulin on glycogenesis?
Hormones regulate regulatory enzymes via phosphorylation. When insulin is high, this stimulates dephosphorylation of the glycogen synthase to produce glycogen. Conversely, the glycogen phosphorylase is dephosphorylated and inactivated to prevent glycogen breakdown.
What is the effect of glucagon on glycogenolysis?
Glucagon promotes glycogen breakdown. The glycogen phosphorylase is phosphorylated and activated. Conversely, the glycogen synthase is phosphorylated and inactivated.
How is a new glycogen molecule created?
A glycogenin molecule forms a glycosidic bond with a glucose molecule via tyrosine. This process is called autoglycosylation
Where can glycogen be found?
In the liver and muscle tissues
What enzyme is deficienct in Type IV: Anderson glycogen storage disease?
Branching enzyeme
What enzyme is required to convert G1P to G6P?
Phosphoglucomutase
Describe the mechanism of glycogenolysis. Be sure to include all relevant substrates and enzymes.
The glycogen phosphorylase removes glycose molecules from glycogen one molecule at a time by breaking the a-1,4 linkages. This produces G1P.
When only four glucose molecules are remaining on a branch, the 4:4 transferase breaks the third a-1,4 bond and reattaches the three glucose molecules to an existing branch. The debranching enzyme then cleaves the remaining a-1,6 bond. This produces a glucose molecule that must be phosphorylated to enter glycolysis.
What glycogen storage disease is associated with a deficiency in the Lysosomal a-1,4 glucosidase? What are the symptoms?
Type II: Pompe
Cardiomegaly, muscle weakness, death
How does the use of glycogen in the liver and muscles differ?
The liver uses glycogen to maintain blood glucose levels. The muscles use glycogen to produce glucose for their own individual use.
What symptoms are associated with deficiency of glucose-6-phosphatase?
Hypoglycemia, lactic acidosis, hepatomegaly, hyperlipidemia, hyperuricemia, short stature, protruding abdomen
Glycogen is broken down to form G6P in the liver and muscles. How does the fate of G6P differ in each location?
In the liver, G6P is converted to glucose by the Glucose-6-Phosphatase. Glucose is then released into the blood.
In muscles, G6P enters directly into glycolysis.
Where are new glucose molecules added to glycogen?
At non-reducing ends of an existing glycogen
What glycogen storage disease is associated with a deficiency of the debranching enzyme? What are the symptoms?
Type III: Cori
Mild hypoglycemia, hepatomegaly
What types of bonds are present in a glycogen molecule?
a1-4 glycosidic bonds between glucose molecules
a1-6 glycosidic bonds at branching points
What glycogen storage disease is associated with a deficiency of the hepatic glycogen phosphorylase? What are the symptoms?
Type VI: Hers
Fasting hypoglycemia, hepatomegaly, cirrhosis
What is the target of the PKA for glycogenolysis?
The PKA phosphorylates the phosphorylase kinase. The phosphorylase kinase goes on to phosphorylate the glycogen phosphorylase for activation. Compared to glycogenesis, glycogenolysis requires two layers of activation for better precision.
What enzyme is required to convert G6P to glucose? Where is it located?t
Glucose-6-Phosphatase. The enzyme is located within the membrane of the liver ER. G6P must be transported into the ER lumen and glucose then transported out.
What symptoms are associated with McArdle disease?
Muscle cramps and weakness during exercise, myoglobinuria
How do high levels of G6P affect glycogenesis?
High levels of G6P indicate excess glucose. This G6P is diverted to glycogenesis and partially activates the (phosphorylated) glycogen synthase until insulin is produced.
