Second Messenger Model
This lesson covers:
- The second messenger model
The second messenger model
The second messenger model of hormone action involves a hormone (the first messenger) triggering the formation of a second messenger (cAMP) inside the cell, which activates enzymes to carry out a function.
The action of adrenaline as an example of the second messenger model
An example of the second messenger model in cell signalling is shown through the action of adrenaline, which is vital during the fight or flight response. Among its many functions, adrenaline plays a crucial role in rapidly making glucose available using glycogenolysis, which is when liver cells convert glycogen to glucose and release it into the bloodstream.
Cell signalling pathway for adrenaline:
- Adrenaline binds to complementary receptor on the cell-surface membrane of a liver cell.
- The binding of adrenaline causes the protein to change shape, activating a G protein.
- This activates the enzyme adenylyl cyclase.
- The activated adenyl cyclase converts ATP into cAMP.
- cAMP acts as a second messenger, binding to and activating many protein kinases via phosphorylation, amplifying the signal from adrenaline.
- Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose.
- Glucose moves out of liver cells by facilitated diffusion and into the blood through channel proteins.
- This increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration.
The cascade effect in this process means that one hormone molecule can generate multiple cAMP molecules. This effect amplifies at each stage, increasing the number of molecules involved.