The evolutionary stages of the complexity of biological catalysts mark and clarify the phases of the origin of the genetic code: A model for the origin of the reading frame with codons from proto-mRNAs with different frames

Abstract

I analyse the origin of the genetic code in the light of the evolution of biological catalysts. I discuss the rudimentary forms that the genetic code assumed in the presence of a catalysis performed by ions or by low molecular weight molecules, such as nucleotide coenzymes. However, it is only with the advent of a mixed polymer made of RNA and peptides - covalently linked - that the genetic code took on a clearer form. Indeed, the first true form of coding appeared. Furthermore, interacting peptidated RNAs promoted an extremely rudimentary form of protein synthesis. This stage evolved into a stage in which proto-mRNAs guided interactions among peptidated RNAs aimed at the synthesis of peptidated RNAs having an active catalytic function. Finally, the invasion of aminoacylated proto-tRNAs with specific amino acids, coming from amino acid metabolism, and recognising only three bases on these proto-mRNAs with reading frames larger than three bases, would have triggered the birth of actual mRNAs, i.e. the origin of codons. All this would have linked the metabolism of amino acids to the origin of mRNAs and therefore to the origin of the organization of the genetic code, as maintained by the coevolution theory of the genetic code.