The system is also available on the Internet. Each cell in a multicellular animal is receiving chemical signals that come from other cells. Hormones and neurotrasmitters are well known examples of such chemical signals. Some chemical signals come also from outside of the animals. Drugs and toxic substances are such examples.
Mutated animals have different receptor proteins and signal molecules.
For example the so called oncogenes encode many cell signal proteins which distribute from the surface of the cell to the intracellular cytoplasm and nucleus. When mutated these oncogene products disturb normal signal transduction which may eventually transform the cell into a carcinogenic states. Before 1980 few such cell signal molecules were known. In 1980s however many signal molecules had been discovered. It was also discovered that many of these molecules belong to a special family of enzyme protein called proteins kinase that phosphorylates other proteins.