First messenger

Definition

A first messenger is a hormone or signaling molecule that binds to a cell surface receptor, initiating a cascade of intracellular events. It is the initial signal in the communication process between cells.

5 Must Know Facts For Your Next Test

1. First messengers are usually hydrophilic and cannot cross the cell membrane.
2. They bind to specific receptors on the surface of target cells.
3. The binding of a first messenger typically activates a second messenger inside the cell.
4. Examples include hormones like insulin and adrenaline.
5. First messengers play a crucial role in transmitting signals from the extracellular environment to the intracellular machinery.

Review Questions

• What is the primary function of a first messenger?
• Why can't first messengers cross the cell membrane?
• Give two examples of molecules that act as first messengers.

Related terms

secondMessenger: A molecule that relays signals received by receptors on the cell surface to target molecules inside the cell.

receptorProtein: A protein on or in a cell that binds to specific molecules such as hormones, triggering a response in the cell.

signalTransduction: The process by which a chemical or physical signal is transmitted through a cell as a series of molecular events.