Question

1.

A) Compare/contrast how insulin and glucagon signal different blood glucose levels and their effects on glycogen breakdown, glycogen synthesis and glycolysis.

B) Compare the fates of glucose 6-phosphate from glycogen breakdown in liver and muscle

Answer 1

A) Insulin is secreted in response to high blood glucose levels. Insulin increases glucose absorption by cells. Glucagon on the other hand, is released when blood glucose levels are low. It then signals the liver to release the stored glucose. Thus, insulin release would lead to increased glycogen synthesis and decreased glycogen breakdown. Exactly reverse effect is seen with glucagon. Glucagon signals the liver to release glucose via glycogen breakdown. Insulin thus accelerates glycolysis while glucagon shuts it down. This is done to increase glucose catabolism for energy needs by insulin, and inhibiting glucose catabolism by glucagon.

B) Glucose is released as glucose-1-phosphate on glycogen breakdown, which is then remodeled as glucose-6-phosphate (G6P) for further needs. G6P in muscle enters glycolysis and then leads to lactate formation via pyruvate. G6P in liver, is converted to glucose to be secreted in the bloodstream.