This is the conclusion of modern biology, but it is a weak one, because in the past twenty years, as we will see, many other biological processes have turned out to have the distinctive signs of the codes. And since they are processes between organic molecules, we can rightly call them organic codes. Before examining these natural conventions, however, let us first discuss a criterion that allows us to recognize the existence of organic codes in nature.

The organic codes’ fingerprints

The genetic code is the only organic code which is officially recognized by modern biology, but is also a model where we find characteristics that must belong to all organic codes. To start with, we can clearly appreciate the difference that exists, at the molecular level, between informatic and semantic processes. In biology, the seminal examples of these processes are, respectively, DNA trascription and RNA translation (Figure 4-2).
In transcription, an RNA chain is assembled from the linear information of a DNA chain, and for such assemby a normal biological catalyst (an RNA polymerase) is sufficient, because each step requires a single recognition process (a DNA-RNA coupling). In translation, instead, two independent recognition processes must be performed at each step, and the catalyst of the reaction (the ribosome) needs special molecules – first called adaptors and then transfer RNAs – in order to link the two processes (Figures 4-2 and 4-3).
Briefly, an amino acid is attached to a tRNA by an enzyme (an aminoacyltransferase) which specifically recognizes a region of the tRNA, while a different region (the anticodon) interacts with a messenger RNA. With appropriate mutations, in fact, it has been possible to change independently the anticodon and the amino acid regions, thus changing the code’s correspondence rules. These code changes have been artificially produced in the laboratory, but have also been found in nature. Mitochondria and some micro-organisms, for example, do have codes which differ from the universal one, which again shows that there is no necessary link between anticodons and amino acids.