Final answer:
Glucagon modulates the activity of enzymes involved in glucose metabolism by upregulating those that promote glycogen breakdown and gluconeogenesis, and downregulating those involved in glycogen synthesis. It works through a second messenger system to phosphorylate enzymes, which activates some and deactivates others.
Step-by-step explanation:
Glucagon is a hormone released by the pancreas that plays a crucial role in glucose metabolism, particularly in elevating blood glucose levels. When blood glucose levels decline, glucagon is secreted and modulates the activity of various enzymes. It stimulates glycogenolysis by converting glycogen into glucose in the liver and muscle cells. Moreover, it promotes gluconeogenesis, or the formation of glucose from non-carbohydrate sources within the liver. Additionally, glucagon impacts cellular reactions by inhibiting the uptake of glucose for cellular respiration, which in turn helps maintain blood glucose levels.
Hormonal action on enzymes is often complex, involving upregulation and downregulation based on the body's needs. Specifically, glucagon upregulates the activity of enzymes responsible for breaking down glycogen and downregulates enzymes involved in the synthesis of glycogen. Through the action of adenyl cyclase and the second messenger cAMP, glucagon activates protein kinases that result in the phosphorylation and alteration of enzyme activity; some enzymes become active while others become inactive in response to glucagon.