Glycogen Metabolism Flashcards by Tarrah Miller

What is the stored form of carbs in animals and plants?

-Glycogen
-Starch

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Which bonds are seen in glycogen?

alpha-1,4 and alpha-1,6

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Where is the site of storage of glycogen and their significance?

1) Cytosol of liver
-Liver is the short term reserve used via glycogenolysis, works for 12-18hrs in fasting state, releases free glucose
2) Muscle, (brain minimal)
-lacks glucose-6-phospatase, so no free glucose is formed but glucose-6-phosphate is obtained, which is fuel for muscle contraction
-Glycogenin produces the first few glucose molecules

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When does glycogenesis start?

After 18hrs

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Why is liver “kind” and muscle “selfish”?

Muscle uses glycogen for itself but liver uses glycogen for the entire body

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Which enzyme converts glucose to glucose-6-phosphate?

Hexokinase/glucokinase

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Which hormone acts in glycogenesis?

Insulin

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What enzyme converts Glucose-1-phos. to UDP-glucose?

UDP-glucose pyrophosphorylase

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What is the enzyme that converts UDP glucose to alpha-1,4-linkage?

Glycogen Synthase

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What is the rate limiting step of glycogenesis?

Glycogen synthase

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Is alpha 1,4-linkage branched or unbranched?

Unbranched

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What does glycogenesis do to Gs pathway?

Inactive it

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What is glycogenin?

protein that form glycogen primer

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Is alpha 1,6-linkage branched or unbranched?

Branched

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What is the name of the branching enzyme and what step does it convert?

Amylo-1,4 to 1,6 transglucosidase
alpha-1,4-linkage to alpha 1,6-linkage

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A deficiency of branching enzyme leads to which glycogen storage disease?

Anderson’s disease

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Which hormone favors glycogenolysis?

Glucagon or epinephrine

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Under what conditions does glycogenolysis occur?

Fasting state

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What is the name of the enzyme that converts glycogen (unbranched) to glucose-1-phosphate?

Glycogen phosphorylase with PLP

What is the name of the enzyme that converts [a-1,6- linkage] to unbranched glycogen?

Debranching enzyme (Glucotransferase)

Some times [a-1,4- linkage] is broken down to glucose directly. Which enzyme catalyze this reaction?

a-1,4- Glucosidase which is found in lyzosomes

What two organs does Glucose-6-phosphate go to and what is its role?

Liver: breaks down to glucose and enters blood stream
and Muscle: it remains the same and is used for lactate/pyruvate for muscle energy

What are the two important enzymes in glycogenesis?

Glycogen Synthase
Amylo-1,4 to 1,6- transglucosidase (branching enzyme)

What is the rate limiting enzyme of glycogenolysis?

Glycogen Phosphorylase

What activates and inactivates Glycogen phosphorylase?

Activate: AMP Inactivate: Glucose-6-phosphate ATP Free glucose

What inhibits and what activates Glycogen synthase?

inhibits: PKA activates: Glucose-6-phosphate

Phosphodiesterase is broken down by ____ during ____ pathway

Insulin and Glycogenesis

When glycogenesis is activated by insulin it is?

Dephosphorylated

When glycogenesis is inactivated by glucagon it is?

Phosphorylated

Name the glycogen storage diseases (Vice President Can't Accept Money Here Today)

Type 1: Von Gierke's disease Type 2: Pompe's disease, Type 3: Cori's disease, Type 4: Anderson's disease Type 5: Mc'Ardle disease, Type 6: Her's disease, Type 7: Tauri disease

Vitamin B6 is involved in ____

Glycogen phosphorylation

Types 1-5 are autosomal ____ and they cause ___ of glycogen

Recessive and Accumulation

The cause in Anderson and Cori disease is a defect in ____ and _____ (Mnemonic: ABCD)

Anderson--> Branching enzyme Cori---> Debranching enzyme

What defective enzyme causes Von Gierke's disease , organ is affected, and what does it cause?

Glucose-6-phosphate and liver Leads to hypoglycemia and hyperlipidemia

What defective enzyme causes Pompe's (pump: heart) disease ?

Lysosomal acid alpha glucosidase or acid maltase/alpha-glucosidase Excess glycogen stored in heart, liver and muscle

What defective enzyme causes Mc'Ardle disease and affects which organ? High yield

muscle glycogen phosphorylase

A 24-year-old medical student experiences fatigue and muscular weakness when he does short durations of exercise. He develops muscle cramps if continues the exercise. The boy is suffering from which glycogen storage disorder? A. Cori's disease B. McArdle's Disease C. Anderson’s Disease D. Tauri’s Disease E. Pompe’s Disease What would her blood glucose levels be?

A Her glucose is unaffected

A 7-month-old male infant is brought to the physician because of a 2-month history of fatigue and weakness. His mother reports that he has difficulty feeding. He is at the 20th percentile for height and 3rd percentile for weight. Physical examination shows an enlarged tongue. Crackles are heard at both lung bases. The liver is palpated 1 cm below the right costal margin. Neurologic examination shows decreased muscle tone in the extremities. Serum glucose is 95 mg/dL. An x-ray of the chest shows cardiomegaly. The patient most likely has a deficiency of which of the following enzymes? A. Acid maltase B. Myophosphorylase C. Iduroate sulfatase D. Glucose-6-phosphatase

A 52-year-old man undergoes an exercise stress test for a 1-week history of squeezing substernal chest pain that is aggravated by exercise and relieved by rest. During the test, there is a substantial increase in the breakdown of glycogen in the muscle cells. Which of the following changes best explains this intracellular finding? A. Decrease in protein kinase A B. Activation of phosphorylase kinase C. Increase in glucose-6-phosphate D. Activation of protein phosphatase E. Inactivation of glycogen synthase kinase

A clinical trial is conducted to investigate the efficiency of a new glucagon receptor antagonist in the treatment of type 2 diabetes mellitus. After 12 weeks of treatment with this drug, all participants in the study achieved statistically significant reductions in fasting and postprandial serum glucose. Three individuals reported symptoms of hypoglycemia while exercising. The activity of which of the following cellular enzymes is most likely to be decreased in response to treatment with this drug? A. Mitogen-activated protein kinase B. Janus kinase C. Guanylate cyclase D. Protein kinase A E. Phospholipase C F. Protein kinase B

A 60-year-old patient is suffering from diabetes mellitus. This condition affects the stimulation of which enzyme of the glycogenolysis regulation cascade A. Adenylate cyclase B. cAMP dependent protein kinase C. Glycogen synthase D. Active glycogen phosphorylase E. Protein phosphatase-1

E ( directly stimulated by insulin)

Andersen’s disease is characterized by hepatosplenomegaly, cirrhosis of the liver and hepatic failure. This is caused by a defect in the formation of which of the following? A. Alpha-1,4-O-glycosidic linkages B. Alpha-1,6-O-glycosidic linkages C. Alpha, Beta-2-1,4-O-glycosidic linkages D. Beta-1,4-O-glycosidic linkage E. Beta-1,6 O-glycosidic linkages

What is the rate limiting step of glycogenolysis?

Glycogen phosphorylase

What coenzyme does glycogen phosphoryalase require?

Pyridoxal phosphate (vitamin B6)

What is the debranching enzyme called in glycogenolysis and what does it remove?

4:4 transferase - a-1,4 1:6 glucosidase- a-1,6

What limits gycogen phosphorylase?

Limiting dextrines