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  • Title: Arguments against the stereochemical theory of the origin of the genetic code.
    Author: Di Giulio M.
    Journal: Biosystems; 2022 Nov; 221():104750. PubMed ID: 35970477.
    Abstract:
    I support the hypothesis that stereochemical theory is unnatural because it is based on artificial and not simple mechanisms as required for a good theory. Indeed, for stereochemical theory the origin of the genetic code requires, in the first place, a primary interaction, for example, between a codon and an amino acid on a proto-tRNA. But this interaction is a necessary but not sufficient condition, because the evolution of the mRNA molecule, which would really define the genetic code, is still necessary for the complete origin of the genetic code. In other words, the need for two molecules, tRNA and mRNA, to define the genetic code, with their at least partial independence would testify to an artificial mechanism typical of stereochemical theory because it would not guarantee that amino acid-codon (or -anticodon) assignments realized in the first phase of the origin of the genetic code, would necessarily be maintained also in the second phase of its completion. Furthermore, the genetic code encodes for amino acids but amino acids are not the truly functional aspect, they are only intermediaries, of their final products, proteins, which are the only true entities actually coded by genes. Therefore, it would not be immediately clear from the point of view of stereochemical theory, to say why it is the amino acids and not the proteins that are involved in the primary stereochemical interactions that would have led to the origin of the genetic code. Hence, at least some of the stereochemical theory models would be not very credible, not being able to say much about the coding of proteins by genes. Finally, I inspected the genetic code table following the logic that more closely similar amino acids should - according to stereochemical theory - be coded by highly similar codons, finding that only a few pairs of amino acids actually satisfy this logic, further discretizing the stereochemical theory.
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