glycogen metabolism Flashcards
Q: What is glycogenesis?
A: Glycogenesis is the synthesis of glycogen from glucose, primarily occurring in the liver and muscles.
Q: What enzyme converts glucose to glucose-6-phosphate?
A: Hexokinase (muscle) or Glucokinase (liver).
Q: What is the role of phosphoglucomutase in glycogenesis?
A: It converts glucose-6-phosphate to glucose-1-phosphate.
Q: How is UDP-glucose formed in glycogenesis?
A: UDP-glucose pyrophosphorylase catalyzes the reaction between glucose-1-phosphate and UTP.
Q: What enzyme elongates the glycogen chain?
A: Glycogen synthase adds glucose units via α(1→4) glycosidic bonds.
Q: How are branches formed in glycogen?
A: The branching enzyme (glucosyl 4:6 transferase) creates α(1→6) linkages.
Q: What is glycogenolysis?
A: The breakdown of glycogen into glucose-1-phosphate and free glucose.
Q: What enzyme removes glucose from glycogen?
A: Glycogen phosphorylase cleaves α(1→4) bonds, releasing glucose-1-phosphate.
Q: How is glucose-6-phosphate formed in glycogenolysis?
A: Phosphoglucomutase converts glucose-1-phosphate to glucose-6-phosphate.
Q: What enzyme debranches glycogen?
A: Debranching enzyme (glucosyl 4:4 transferase and α(1→6) glucosidase).
Q: Where does glycogenolysis primarily occur?
A: In the liver (to maintain blood glucose) and muscle (for energy during contraction).
Q: What hormones regulate glycogen metabolism?
A: Insulin (stimulates glycogenesis), Glucagon & Epinephrine (stimulate glycogenolysis).
Q: How does insulin promote glycogenesis?
A: Insulin activates glycogen synthase via dephosphorylation.
Q: How does glucagon stimulate glycogenolysis?
A: Glucagon activates glycogen phosphorylase via cAMP and PKA signaling.
Q: Why does muscle glycogen not contribute to blood glucose?
A: Muscle lacks glucose-6-phosphatase, so glucose remains trapped.
Q: What is the key regulatory enzyme of glycogenesis?
A: Glycogen synthase.
Q: What is the key regulatory enzyme of glycogenolysis?
A: Glycogen phosphorylase.
Q: What is the role of cAMP in glycogen metabolism?
A: cAMP activates protein kinase A (PKA), which phosphorylates and activates glycogen phosphorylase.
Q: What is Von Gierke’s disease?
A: A glycogen storage disease (Type I) due to glucose-6-phosphatase deficiency, causing severe fasting hypoglycemia.
Q: What is McArdle’s disease?
A: A glycogen storage disease (Type V) due to muscle glycogen phosphorylase deficiency, leading to exercise-induced cramps.
