Question

During a "fight or flight" response in mammals, the adrenal gland releases a hormone called epinephrine that stimulates liver cells to release glucose for emergency fuel. Describe and explain the signal transduction pathway that follows the release of epinephrine.

Answer 1

During the fight or flight response, epinephrine binds to receptors on liver cells, stimulating the production of cyclic AMP and activating protein kinase A. This leads to the activation of enzymes that break down glycogen into glucose and inhibit glycogen synthesis, resulting in increased blood glucose levels for a burst of energy.

Step-by-step explanation:

Signal Transduction Pathway of Epinephrine in Liver Cells

During a fight or flight response, the adrenal gland releases the hormone epinephrine, which mediates a complex signal transduction pathway in liver cells. Once epinephrine binds to its receptor on liver cells, a cascade of events is triggered, leading to the conversion of glycogen to glucose. The signaling pathway involves the activation of β-adrenergic receptors, increase in cyclic AMP (cAMP) levels, and activation of protein kinase A (PKA). PKA then phosphorylates enzymes which result in the breakdown of glycogen. Specifically, glycogen phosphorylase kinase (GPK) is activated, which in turn activates glycogen phosphorylase (GP) to catabolize glycogen into glucose. Concurrently, phosphorylation of glycogen synthase (GS) inhibits its activity, preventing glycogen synthesis. This regulated process efficiently increases blood glucose levels to meet the body's immediate energy needs.