Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response. There are two stages in this process:
- A signaling molecule activates a specific receptor protein on the cell membrane.
- A second messenger transmits the signal into the cell, eliciting a physiological response.
In either step, the signal can be amplified. Thus, one signalling molecule can cause many responses. A signal transduction functions much like a switch