The bridge between genes and organisms

Between the genes and the final structure of a body there are, in all multicellular organisms, several levels of organization whose general features have been known for some time (Figure 4-4). Genes intervene only at the very beginning of the ladder, when they are copied into primary transcripts of RNA. From this point onward, all other body construction steps take place in the absence of genes, and are collectively known as epigenetic processes.
(1) The first epigenetic event is the processing of primary transcripts into messenger RNAs. (2) The second is protein synthesis, the translation of messenger RNAs into linear chains of amino acids. (3) The third is protein folding, the transformation of linear polypeptides into three-dimensional proteins. Some proteins are then assembled into organelles (4), these into cells (5), and cells aggregate to produce tissues (6), organs (7) and finally the whole organism (8).
The units of a level of organization are assembled into structures that become the units of the next level, thus giving origin to a hierarchy of assemblies, from proteins and organelles to cells, tissues and organs. All events of epigenesis, in short, are processes of assembly.
In living systems, assemblies usually require the presence of guiding factors that can be broadly called catalysts, and we can speak therefore of catalyzed assemblies, but in some cases catalysts are not enough.
The classic example is protein synthesis, the second epigenetic step of the scala naturae that builds a bridge between genes and organism.
Protein synthesis is definitely an assembly operation, because amino acids are assembled into polypeptides, but a catalyst is not enough to determine the order of the units, and what is needed is a code-based set of adaptors. We must distinguish therefore between two very different types of epigenetic processes:
(1) processes of catalyzed assembly, and
(2) processes of codified assembly.
The bridge between genes and organism, in conclusion, is realized by one genetic step and by at least eight types of epigenetic processes.