Here's how it works:
1. Signal molecule (ligand): A cell releases a signaling molecule (like a hormone or neurotransmitter) that acts as a message.
2. Receptor protein: The signaling molecule binds to a specific receptor protein on the surface or inside the target cell.
3. Signal transduction: This binding triggers a series of events inside the target cell, often involving a cascade of other proteins. This is known as signal transduction.
4. Cellular response: The signal transduction pathway ultimately leads to a change in the target cell's behavior, such as:
* Altering gene expression
* Changing enzyme activity
* Altering cell shape or movement
Types of receptor proteins:
* Cell surface receptors: These are embedded in the cell membrane and bind to signaling molecules outside the cell.
* Intracellular receptors: These are located inside the cell and bind to signaling molecules that can pass through the cell membrane.
Examples of receptor proteins:
* Insulin receptor: This receptor binds to insulin, triggering glucose uptake by cells.
* Estrogen receptor: This receptor binds to estrogen, influencing gene expression related to female development and reproduction.
* Acetylcholine receptor: This receptor binds to acetylcholine, a neurotransmitter, triggering muscle contraction.
By binding to specific signaling molecules, receptor proteins act as "gatekeepers" of communication between cells, ensuring that only the intended message is received and acted upon.
