Now let us turn to the nucleic acids. Nucleotides are formed spontaneously in a Miller-type experiment. These nucleotides contain among them the allimportant one adenine triphosphate or ATP. Its importance ties in the role it plays in living cells as a source of energy as well as a precursor for DNA. The other nucleotides needed for DNA, which contain cytosine, guanine, and thymine, as well as uridine for RNA, are also formed spontaneously. Also simple sugars have been found in these experiments.
The next question is whether or not uninformed DNA and RNA are formed. The answer really is no. Short lengths of nucleotide polymers, called oligomers, do appear. But so far no RNA with molecular weights similar to those of transfer or ribosomal or messenger RNA has been found. (These are, of course, the three main categories of informed RNA.) And nothing approaching a high molecular weight double helix of DNA has appeared spontaneously. The researchers in this areaconclude, so far, there is no reason to suppose that nucleic acid molecules comparable in size to informed nucleic acids are formed spontaneously. It is always possible that tomorrow some researcher will find a way to effect the spontaneous formation of uninformed nucleic acids. And that may then provide the clue for the transition to informed molecules. But this is at present nowhere in sight. It forces us to think that perhaps informed nucleic acids did not arise spontaneously. That is, when they arose it was within living systems. Such living systems would have to be based on proteins. This, though somewhat implausible for the reasons given above, brings us back to a consideration of the origin of the first living system on the basis of proteins and, from that, the emergence of cellular life.