Signal amplification

A principle of signal transduction is the signal amplification. The binding of one or a few neurotransmitter molecules can enable the entry of millions of ions. The binding of one or just a few hormone molecules can induce an enzymatic reaction that affect many substrates. The amplification can occur at several points of the signal pathway.

A receptor that has been activated by a hormone can activate many downstream effector proteins. For example, a rhodopsin molecule in the plasma membrane of a retina cell in the eye that was activated by a photon can activate up to 2000 effector molecules (in this case, transducin) per second. The total strength of signal amplification by a receptor is determined by:
- The lifetime of the hormone-receptor-complex. The more stable the hormone-receptor-complex is, the less likely the hormone dissociates from the receptor, the longer the receptor will remain active, thus activate more effector proteins.
- The amount and lifetime of the receptor-effector protein-complex. The more effector protein is available to be activated by the receptor, and the faster the activated effector protein can dissociate from the receptor, the more effector protein will be activates in the same amount of time.
- Deactivation of the activated receptor. A receptor that is engaged in a hormone-receptor-complex can be deactivated, either by covalent modification (for example, phosphorylation), or by internalization.

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