X.3.3 The genetic code (and co-evolution of the protein-nucleic acid system) could have been at the beginning
This hypothesis assumes that the evolution of proteins and nucleic acids occurred together from the very beginning (Alberti 1997, Barbieri 2003).The gene hypothesis of the origin of life also assumed that, at least from a certain moment, there was some form of co-evolution of these two components of modern living systems.However, in contrast, the coevolution hypothesis (hypothesis of the genetic code) emphasizes the fact that proteosynthesis, based on the existence of a genetic code, is of central importance in life processes.
It is very difficult to explain the evolution and development of the proteosynthetic apparatus in the current complicated, or even in any simplified, form.The point from which the proteosynthetic apparatus was to begin is of little importance.Its formation is not much more probable if we assume that it was preceded by a period of biological evolution, during which organisms functioned on the basis of some other principle (e.g., cf. competition of oligonucleotides, described in the previous section) or if we assume that it began to develop in an abiotic environment.The evolution of the genetic code as, on the one hand, a set of rules for the translation of a sequence of nucleotides into a sequence of aminoacids and, on the other hand, as a specific molecular apparatus that provides for this translation, is a major problem both from the viewpoint of biochemistry and from the viewpoint of systems theory.The proteosynthetic apparatus, even in the most reduced form that we can imagine, must contain dozens of various components, enzymes and tRNA.It is thus “worthwhile” for a cell only if the number of proteins that it needs to synthesize is sufficiently large (hundreds, thousands?)It is hard to imagine that organisms existing prior to the evolution of the genetic code could be sufficiently complicated for the proteosynthetic apparatus to be “worthwhile” for them.
The aspect of the possibility of any sort of development of the genetic code is a similarly serious problem. Even the smallest modification of the rules for the translation of a sequence of nucleotides to a sequence of aminoacids usually renders worthless the information that is written in the nucleic acids using the original rules.Consequently, it is hard to imagine how, for example, a simpler doublet code could evolve into the present-day triplet code, coding twenty aminoacids.