The signal transduction codes

The transfer of information from environment to genes takes place therefore in two distinct steps one from first to second messengers, which is called signal transduction, and a second pathway from second 

The experimental results, in brief, have proved beyond doubt that outside signals do not have instructive effects. Cells use them to interpret the world, not to yield to it. Such a conclusion amounts to saying that signal transduction is based on organic codes, and this is in fact the only plausible explanation of the data, but of course we would also like a direct proof. As we have seen, the signature of an organic code is the presence of adaptors, and the molecules of signal transduction have indeed the typical characteristics of adaptors. 

In signal transduction, in short, we find the three characteristics of the organic codes  

In addition to growth factors, it has been shown that countless other molecules have multiple functions. Cholecystokinin, for example, is a peptide that acts as a hormone in the intestine, where it increases the bile flow during digestion, whereas in the nervous system it behaves as a neurotransmitter. Encephalins are sedatives in the brain, but in the digestive system are hormones that control the mechanical movements of food. Insulin is universally known for lowering the sugar levels in the blood, but it also controls fat metabolism and in other less known ways it affects almost every cell of the body. 

At the beginning of the twentieth century, Hans Spemann made one of the most important discoveries of embryology. He was able to prove that the differentiation of developing cells - i.e. the actual expression of specific proteins - is always preceded by a process that determines the fate of those cells. Spemann made the discovery by studying what 

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