Peptide nucleic acids rather than RNA may have been the first genetic molecule

Abstract

Numerous problems exist with the current thinking of RNA as the first genetic material. No plausible prebiotic processes have yet been demonstrated to produce the nucleosides or nucleotides or for efficient two-way nonenzymatic replication. Peptide nucleic acid (PNA) is a promising precursor to RNA, consisting of N-(2-aminoethyl)glycine (AEG) and the adenine, uracil, guanine, and cytosine-N-acetic acids. However, PNA has not yet been demonstrated to be prebiotic. We show here that AEG is produced directly in electric discharge reactions from CH₄, N₂, NH₃, and H₂O. Electric discharges also produce ethylenediamine, as do NH₄CN polymerizations. AEG is produced from the robust Strecker synthesis with ethylenediamine. The NH₄CN polymerization in the presence of glycine leads to the adenine and guanine-N⁹-acetic acids, and the cytosine and uracil-N¹-acetic acids are produced in high yield from the reaction of cyanoacetaldehyde with hydantoic acid, rather than urea. Preliminary experiments suggest that AEG may polymerize rapidly at 100°C to give the polypeptide backbone of PNA. The ease of synthesis of the components of PNA and possibility of polymerization of AEG reinforce the possibility that PNA may have been the first genetic material.