It's Life, Jim, But Not as We Know It
Origin-of-life theorizing is beset by chicken-and-egg enigmas. Now some clever scientists say they've got a new solution to a longstanding problem that focuses on RNA as the hypothetical forebear of DNA-based life, the famous RNA World hypothesis. Their report is in the Journal of the American Chemical Society ("Efficient Self-Assembly in Water of Long Noncovalent Polymers by Nucleobase Analogues").
The problem in need of a resolution, as Science Daily summarizes ("Molecules Assemble in Water, Hint at Origins of Life"):
RNA bases don't form base pairs in water unless they are connected to a polymer backbone, a trait that has baffled origin-of-life scientists for decades. If the bases don't pair before they are part of polymers, how would the bases have been selected out from the many molecules in the "prebiotic soup" so that RNA polymers could be formed?Good question. The answer please?
Researchers at the Georgia Institute of Technology are exploring an alternate theory for the origin of RNA: they think the RNA bases may have evolved from a pair of molecules distinct from the bases we have today. This theory looks increasingly attractive, as the Georgia Tech group was able to achieve efficient, highly ordered self-assembly in water with small molecules that are similar to the bases of RNA. These "proto-RNA bases" spontaneously assemble into gene-length linear stacks, suggesting that the genes of life could have gotten started from these or similar molecules.Note that the authors published their results before taking what would seem to be the obvious next step: Showing that their linear stacks of "proto-RNA bases" could either (1) serve as the missing "polymer backbone" needed to connect real RNA bases, or (2) evolve undirectedly into real RNA polymers.
As it is, the relevance of their work to the origin of life is questionable, at best. Its premature publication may instead highlight the urgency felt by origin-of-life researchers to find some justification, however tenuous, for continued funding -- much of that at taxpayer expense.
Co-author Nicholas Hud muses:
"Thinking about the origin of RNA reminds me of the paradox of your grandfather's ax," said Hud, a professor in the School of Chemistry and Biochemistry. "If your father changed the handle and you changed the head, is it the same ax? We see RNA the same way. Its chemical structure might have changed over time, but it was in continual use so we can consider it to be the same molecule."There's only one drawback to this appealing homespun analogy. If you change the handle and the head, it's not the same ax.