Glycogen Metabolism and Glycogen Storage Disorders MCQs

Patients with type I GSD may present in the neonatal period with hypoglycemia and lactic acidosis These children often have doll-like faces with fat cheeks, relatively thin extremities, short stature, and a protuberant abdomen that is due to massive hepatomegaly; the kidneys are also enlarged, whereas the spleen and heart are normal The biochemical hallmarks of type 1 GSD (von Gierke's disease) are hypoglycemia, lactic acidosis, hyperuricemia, and hyperlipidemia. Reference: Harper's Illustrated Biochemistry, 32 nd Edition, Page Number-538.

Explanation: Glucagon helps maintain blood glucose levels during starvation by stimulating gluconeogenesis and glycogenolysis. During starvation, insulin levels decrease and counterregulatory hormones increase. (Option B ruled out) Hormones are released based on their glycemic threshold in the order: Glucagon→Epinephrine→Cortisol & GH. (Option C & D ruled out) Glucagon acts on liver, stimulating gluconeogenesis and glycogenolysis. Thus, maintaining blood glucose levels during fasting and starvation. Key Takeaway: During starvation, glucagon is the primary hormone released in response to hypoglycemia. It maintains blood glucose levels by stimulating heapatic gluconeogenesis and glycogenolysis.

Ans. is 'c' i.e., Increased gluconeogenesis [Ref Vasudevan &hie p. 85, 86, Harper 28th/e p. 240, 241] In overnight fasting glucose level is maintained due to glycogenolysis and gluconeogenesis. FFA and ketone bodies (p-hydroxybutyrate) starts rising after 2-3 days, i.e. in later part of initial stage of prolonged starving

Glucose 6-phosphate is an important compound at the junction of several metabolic pathways: glycolysis, gluconeogenesis, the pentose phosphate pathway glycogenesis, and glycogenolysis. Reference : Harper's 32 nd edition, Page no.170

Between meals, the liver acts to maintain the blood glucose concentration by breaking down glycogen (glycogenolysis) and, together with the kidney, by converting noncarbohydrate metabolites such as lactate, glycerol, and amino acids to glucose (gluconeogenesis). The maintenance of an adequate blood concentration of glucose is essential for those tissues for which it is either the major fuel (the brain) or the only fuel (erythrocytes). Reference: Harper's 32 nd edition, page no. 170

Glucose-6 phosphatase deficiency leads to hypoglycaemia. This enzyme is required for both glycogenolysis and gluconeogenesis, the two pathways by which blood glucose levels are maintained. Pyruvate and lactate are converted to oxaloacetate for gluconeogenesis. Due to hypoglycaemia, there is high mobilisation of fatty acid from adipose tissue. Hypoglycaemia lowers blood insulin levels, which is an inhibitor of hormone sensitive lipase (HSL); low insulin levels result in loss of this inhibition, and TG stores in adipocytes are broken down by the action of HSL. Reference : Harper's 32 nd edition, Page no.179

Ans. is C. i.e., Hormone sensitive lipase Enzymes /Pathways activated by insulin Glycolysis : PFK-1, Pyruvate kinase, glucokinase, PDH. Glycogenesis : Glycogen synthase. Lipogenesis : Acetyl-Co-carboxylase, Fatty acid synthase. Cholesterol synthesis : HMG - CoA reductase. Triglyceride synthesis : Acyl - CoA glycerol-3-P transferase, glycerol kinase. Lipoprotein degradation : Lipoprotein lipase

Ans. is 'a' i.e., Muscle [Ref : Harper 250 le p. 178-179] Glucose-6-phosphatase is absent in muscles therefore, glucose-6- phosphate cannot be degraded to free glucose in muscles. Moreover, glucose-6-phosphate cannot diffuse out of the muscles. Therefore, muscle cannot provide glucose to maintain blood glucose level. Rather, muscle glycogen acts as a source of energy; the glucose-6-phosphate enters the glycolysis to produce energy.