BRAINCAKESecond Messenger System
Peptide hormones, and amine hormones such as adrenaline, are water soluble and cannot cross the cell surface membrane. They act through a second messenger system. The hormone is the first messenger: it carries the signal to the cell. A molecule made inside the cell, the second messenger, carries the signal on within the cell.
Example: adrenaline acting on a liver cell
1. Adrenaline binds to a specific receptor on the cell surface membrane. The receptor has a shape complementary to the hormone.
2. Binding changes the shape of the receptor, which activates a G protein on the inner side of the membrane.
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Key terms in this lesson
- g protein
- A membrane protein activated when a hormone binds its receptor, which in turn activates an enzyme to produce a second messenger.
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