activate
Meaning of activate: To flip something in the body from standing by to working, whether a cell, an enzyme or a swallowed drug.
Definition of activate
To activate is to switch a cell, protein or other biological component from an inactive or resting state into a working one. The change is usually triggered by a specific signal and brings measurable consequences: the component alters shape, starts a chemical reaction, multiplies, or releases something it was holding. Much of biology is arranged this way, with machinery built in advance and held ready.
Why keep things switched off?
Building a protein takes time the body often does not have. An enzyme that digests tissue, a clotting factor, or an immune cell capable of destroying infected cells would all be dangerous if permanently on. The solution is to manufacture them in a disabled form and store them, then remove the block when they are needed. Activation can be a chemical tag added or taken away, a piece of the molecule cut off, a change in the surrounding acidity, or the arrival of a signal at a receptor. Once the signal stops, most systems have an equally deliberate route back to the resting state.
What does it look like in practice?
| What is activated | Trigger | Result |
|---|---|---|
| A T lymphocyte | Recognition of a foreign fragment | The cell multiplies and attacks |
| A digestive enzyme | Acid or another enzyme cuts it | It begins breaking down food |
| A platelet | Contact with a damaged vessel wall | It becomes sticky and helps form a clot |
| A prodrug | Processing by the liver | The medicine becomes effective |
Why does it matter in treatment?
Whole classes of medicine work by pushing this switch one way or the other. Some drugs are given deliberately in an inactive form so that the body converts them where they are wanted, or simply so they survive the journey through the stomach. Others block activation: anticoagulants work by preventing clotting factors from being switched on, and several cancer treatments target signals that keep growth machinery permanently activated. Immune treatments run the other way, aiming to activate cells against a tumor, an approach seen in cell preparations such as the lymphokine activated killer cell, in which lymphocytes are stimulated outside the body before being returned.
What goes wrong when the switch sticks?
Faults in the off position leave a system unable to respond, as in some inherited immune and clotting disorders. Faults in the on position are the more common problem. A gene mutation that leaves a growth signal permanently activated is one of the ordinary ways a cancer begins. Autoimmune disease reflects immune cells activated against the body's own tissue. Uncontrolled activation of clotting throughout the circulation is a recognized emergency.
Also known as
Used in a sentence
The assay measured how quickly the receptor was able to activate the downstream signaling pathway.
Good to know
Much biological machinery is manufactured in an inactive form and held ready, so both failure to activate and failure to switch off again produce recognized disease.