Primordial coding of amino acids by adsorbed purine bases.

Scanning tunneling microscopy and chromatography experiments exploring the potential templating properties of nucleic acid bases adsorbed to the surface of crystalline graphite, revealed that the interactions of amino acids with the bare crystal surface are significantly modulated by the prior adsorption of adenine and hypoxanthine. These bases are the coding elements of a putative purine-only genetic alphabet and the observed effects are different for each of the bases. Such mapping between bases and amino acids provides a coding mechanism. These observations demonstrate that a simple pre-RNA amino acid discrimination mechanism could have existed on the prebiotic Earth providing critical functionality for the origin of life.

Life before RNA.

The hypothesis that life originated and evolved from linear informational molecules capable of facilitating their own catalytic replication is deeply entrenched. However, widespread acceptance of this paradigm seems oblivious to a lack of direct experimental support. Here, we outline the fundamental objections to the de novo appearance of linear, self-replicating polymers and examine an alternative hypothesis of template-directed coding of peptide catalysts by adsorbed purine bases. The bases (which encode biological information in modern nucleic acids) spontaneously self-organize into two-dimensional molecular solids adsorbed to the uncharged surfaces of crystalline minerals; their molecular arrangement is specified by hydrogen bonding rules between adjacent molecules and can possess the aperiodic complexity to encode putative protobiological information. The persistence of such information through self-reproduction, together with the capacity of adsorbed bases to exhibit enantiomorphism and effect amino acid discrimination, would seem to provide the necessary machinery for a primitive genetic coding mechanism.