Answer:
A signal transduction occurs when an extracellular fluid signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response.1 There are two stages in this process:
A signaling molecule activates a specific receptor in the cell membrane.
A second messenger transmits the signal to the cell, causing a physiological response.
In any of the stages, the signal can be amplified. Therefore, a signaling molecule can cause many responses.
Transduction signals normally involve the union of extracellular signaling molecules or ligands with cell receptors located on the outer surface of the plasma membrane and that triggers events into the cell. These external signaling substances are located in a place of the receptor and cause a change in the surface or spatial conformation thereof; What happens when the signaling molecule binds to the receptor. Cellular receptors typically respond to a single specific molecule or ligand with which it has an affinity and molecules that are even scarcely different from ligands, do not usually have an effect or act at most as inhibitors.
There are many molecules that can function as extracellular carriers of information. They include:
Amino acids and amino acid derivatives. Examples include glutamate, glycine, acetylcholine (Ach), adrenaline, dopamine, and thyroid hormone. These molecules act as neurotransmitters and hormones.
Gases, such as NO and CO.
Steroids, which are derived from cholesterol. Steroid hormones regulate sexual differentiation, pregnancy, carbohydrate metabolism and excretion of sodium and potassium ions.
Eicosanoids, are non-polar molecules that contain 20 carbons derived from a fatty acid called arachidonic acid. Eicosanoids regulate various processes, such as pain, inflammation, blood pressure and blood clotting. There are several drugs that are available without a prescription and are used to treat headaches and inflammation, these inhibit the synthesis of eicosanoids.
A great variety of polypeptides and proteins. Some of these are found as transmembrane proteins on the surface of an interacting cell. Others are part of the extracellular matrix or are related to it. Finally, a large amount of protein is excreted into the extracellular environment, where they participate in the regulation of processes such as cell division, differentiation, immune reaction or cell death and survival.