Viroids

Viroids

In the laboratory at Cornell University the scientists work on, among other things, prebiological organic chemistry, making some notes of the music of life. They mix together and spark the gases of the primitive Earth: hydrogen, water, ammonia, methane, hydrogen sulphide – all present, incidentally, on the planet Jupiter today and throughout the Cosmos. The sparks correspond to lighting – also present on the ancient Earth and on modern Jupiter.

The reaction vessel is initially transparent: the precursor gases are entirely invisible. But after ten minutes of sparking, we see a strange brown pigment slowly streaking the sides of the vessel. The interior gradually becomes opaque, covered with a thick brown tar. If we had used ultraviolet light – simulating the early Sun – the results would have been more or less the same. The tar is an extremely rich collection of complex organic molecules, including the constituent parts of proteins and nucleic acids. The stuff of life, it turns out, can be very easily made.

Life is certainly more than the amino acids and the nucleotides. Image: © Elena

Such experiments were first performed in the early 1950’s by Stanely Miller, then a graduate student of the chemist Harold Urey. Urey had argued compellingly that the early atmosphere of the Earth was hydrogen-rich, as is most of the Cosmos; that the hydrogen has since trickled away to space from Earth, but not from massive Jupiter; and that the origin of life occurred before the hydrogen was lost. After Urey suggested that such gases be sparked, someone asked his what he expected to make in such an experiment. Urey replied, “Beilstein”. Beilstein is the massive German compendium in 28 volumes, listing all the organic molecules known to chemists and mentioned in one’s of Isaac Asimov’s amazing stories.

Using only the most abundant gases that were present on the early Earth and almost any energy source that breaks chemical bonds, we can produce the essential building blocks of life. But in our vessel are only the notes of the music of life – not the music itself.

Viroids are composed exclusively of nucleic acid, unlike the viruses, which also have a protein coat. They are no more than a single strand of RNA with either a linear or a closed circular geometry. Viroids can be small and still thrive because they are thoroughgoing, unremitting parasites. Like viruses, they simply take over the molecular machinery of a much larger, well-functioning cell and change a from a factory for making more cells into a factory for making more viroids.