7. A Pathway to the First Organism

Life is characterized by a collection of molecules that interact in such a way as to self-sustain and regenerate. An important aspect of this is the presence of a catalytic feedback loop linked to an information storage system. The catalytic feedback results in production of life components and replication of the information storage system, implying both “organismal” growth and (re)production of offspring. The DNA-RNA-protein system of extant life satisfies this requirement, but is clearly rather complex. The RNA world, which eliminates DNA by having RNA as the information storage molecule, appears to be an important simplification, but it is still a rather complex system. A further simplification is possible if the key translating molecule(s), transfer RNA, can also serve as the carrier(s) of genetic information. Using polynucleotide and polypeptide databases, and software to search for matches, it is possible to 1) determine possible “ancestral” sequences of tRNA, 2) translate the tRNA sequences into possible small polypeptides, and 3) compare these short (25+ amino acid) polypeptides to sequences of modern proteins. Interestingly, this process leads to several striking matches between the short sequences from tRNA and parts of the much longer sequences in modern proteins. Using the same procedure on randomly generated 75 nucleotide pseudo-tRNA produces no significant matches. This suggests the very real possibility that tRNA was not only the necessary molecule for making polypeptides according to a “recipe”, but that the tRNA itself was the source of the recipe. This is a major simplification of the feedback system since a separate information storage molecule is unnecessary. How an appropriate assemblage of tRNA necessary for translation could be packaged into a coherent cluster is a further vital point.