The Role of Adrenaline
- A hormone called adrenaline can affect blood glucose concentration
- When it is secreted it increases the concentration of blood glucose
- It does this by binding to different receptors on the surface of liver cells that activate the same enzyme cascade that occurs when glucagon binds to its specific receptors
The second messenger model
- Adrenaline binds to specific receptors on the membrane of liver cells
- This causes the enzyme adenylyl cyclase to change shape and become activated
- Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
- cAMP binds to protein kinase A enzymes, activating them
- Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
- Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
- Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose
- This process is known as glycogenolysis
- The enzyme cascade described above amplifies the original signal from adrenaline and results in the releasing of extra glucose by the liver to increase the blood glucose concentration back to a normal level
The effect of adrenaline is amplified so that each molecule can stimulate many molecules of cAMP, which in turn activate many enzymes molecules
- Adrenaline also stimulates the breakdown of glycogen stores in muscle during exercise
- The glucose produced remains in the muscle cells where it is needed for respiration
