We call Signals all (physical or chemical) events able to transmit information to a cell. Signaling requires at least two components:
- a physical (e.g. sound) or chemical (e.g. hormone) event that it is released into the environment in specific conditions and that we can call a Sign (S)
- a cellular structure able to react with (S) modifying the cell behavior according to the concentration and direction of (S). These structures are called Receptors ®.
The information content of any Sign includes at least all the factors required for its synthesis
Segni e Segnali
Example1: BH4
Every cell is able to synthesize BH4 (tetrahydrobiopterin) from GTP.
BH4 is an essential cofactor for the synthesis of:
- dopamine
- noradrenaline and adrenaline
- serotonine
- NO (Nitric Oxide)
BH4 synthesis is stimulated by Ascorbic Acid (Vit. C)
Signs structure
Signs are classified as sound, light, hormones, cytokines, chemokines, growth factors, and so on, according to their major effect, but they share a common property: the ability to give information about the existence of specific environments or about the availability of one or more nutrients. The minimal information content carried by any sign is that all the conditions required for its synthesis are present. But also Receptors ® are synthesized in specific conditions and therefore carry the information that this conditions exist.
To make signal understandable to the cell a set of chemical events called signal transduction take place upon binding of the ligand (S) to its receptor.
Non-linearity of signal transduction: ST is a multi-step process with different checkpoints sensitive to different external factors (inositol NADH/NAD+ ethanol; oxygen, diet, G-proteis and miristoyl and farnesyl, etc)