Glycogen Metabolism

Category: Glycogen Metabolism Overview

Q1: What is the process of glycogenolysis?
A: The breakdown of glycogen into glucose-1-phosphate (G1P), which can be converted to glucose-6-phosphate (G6P) for energy metabolism.

Q2: Where is glycogen stored in the body?
A: In cytosolic granules of muscle and liver cells in vertebrates.

Q3: Why is G1P important in glycogen metabolism?
A: It can be converted to G6P, which is used in glycolysis and the citric acid cycle for energy production.

Category: Glycogen Degradation

Q4: Which enzyme removes glucose residues from glycogen?
A: Glycogen phosphorylase.

Q5: What type of bonds does glycogen phosphorylase act on?
A: α-1,4 linkages of the glycogen polymer.

Q6: What happens when glycogen phosphorylase encounters an α-1,6 branch point?
A: It stops 4 residues away, and the glycogen-debranching enzyme removes the branch.

Q7: What are the two products of glycogen degradation?
A: Glucose-1-phosphate (G1P) and a free glucose molecule.

Category: Glycogen Synthesis

Q8: What enzyme is central to glycogen synthesis?
A: Glycogen synthase.

Q9: What is the starting point for glycogen synthesis?
A: Glucose is converted to glucose-6-phosphate (G6P) by hexokinase.

Q10: How does glycogen synthase incorporate glucose into glycogen?
A: By adding glucose to the nonreducing end of a glycogen molecule.

Category: Regulation of Glycogen Metabolism

Hormonal Regulation

Q11: Which hormone promotes glycogen synthesis, and how?
A: Insulin; it increases glucose transport into cells and activates glycogen synthase.

Q12: Which hormone stimulates glycogen breakdown during fasting?
A: Glucagon.

Q13: How does epinephrine affect glycogen metabolism?
A: It stimulates glycogenolysis for rapid glucose release during the "fight or flight" response.

Reciprocal Regulation

Q14: How are glycogen phosphorylase (GP) and glycogen synthase (GS) reciprocally regulated?
A: When one is active, the other is inactive. GP is active when phosphorylated (-P), while GS is active when dephosphorylated (-OH).

Q15: What molecule acts as an allosteric regulator for both GP and GS?
A: Glucose-6-phosphate (G6P):

  • Inhibits GP (active form).

  • Activates GS (inactive form).

Category: Glycogen Storage Diseases

Von Gierke Disease (Type 1)

Q16: What enzyme deficiency causes von Gierke disease?
A: Glucose-6-phosphatase or glucose-6-phosphate translocase.

Q17: What are the hallmark clinical features of von Gierke disease?
A: Severe fasting hypoglycemia, hepatomegaly, lactic acidosis, growth retardation, and hyperlipidemia.

Q18: Why does lactic acidosis occur in von Gierke disease?
A: The impaired Cori cycle prevents lactate from being converted to glucose, leading to lactate buildup in the blood.

Q19: What dietary measures help manage von Gierke disease?
A: Frequent feeding with uncooked cornstarch to prevent hypoglycemia, and avoiding lactose, fructose, and sucrose.

Pompe Disease (Type 2)

Q20: What enzyme deficiency causes Pompe disease?
A: Acid α-glucosidase (acid maltase).

Q21: Why is Pompe disease classified as a lysosomal storage disorder?
A: Glycogen accumulates in lysosomes due to a defect in acid α-glucosidase.

Q22: What are classic symptoms of infantile Pompe disease?
A: Macroglossia, hypotonia, cardiomegaly, and muscle weakness.

Q23: What therapy has improved outcomes for Pompe disease?
A: Enzyme replacement therapy for acid α-glucosidase.

Cori Disease (Type 3)

Q24: What enzyme is deficient in Cori disease?
A: Debranching enzyme (α-1,6-glucosidase).

Q25: How does Cori disease differ from von Gierke disease?
A: Cori disease has milder hypoglycemia and no lactic acidosis because gluconeogenesis is intact.

Q26: What are common treatments for Cori disease?
A: Cornstarch supplements and a high-protein diet.

McArdle Disease (Type 5)

Q27: What enzyme deficiency causes McArdle disease?
A: Muscle glycogen phosphorylase (myophosphorylase).

Q28: What is the "second-wind phenomenon" in McArdle disease?
A: After initial fatigue during exercise, muscles utilize circulating glucose, reducing pain and fatigue.

Q29: What dietary strategies benefit patients with McArdle disease?
A: Pre-exercise glucose loading and consuming complex carbohydrates.

Category: Miscellaneous

Q30: Why must blood glucose levels be tightly regulated?
A: Glucose is the primary metabolic fuel, especially for the brain, which relies almost entirely on it for energy.

Q31: What role does the liver play in maintaining glucose homeostasis?
A: It regulates dietary fuel distribution, stores glycogen, and supplies glucose to the blood during fasting.

How to Use These Flashcards

  • Actively recall: Cover the answers and try to retrieve the information.

  • Spaced repetition: Revisit flashcards at increasing intervals to reinforce memory.

  • Connection-building: Consider how different processes (e.g., glycolysis, gluconeogenesis) integrate with glycogen metabolism.

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