Title:
Prebiotic photochemistry and its possible role in selecting the genetic alphabet

Abstract:
Recent experiments have shown that following UV light exposure, excited states of the canonical RNA and DNA bases (A, G, C, T, and U) generally decay orders of magnitude faster than in other heterocyclic compounds, endowing the nucleobases with high intrinsic photostability. These properties would have been highly advantageous for the first self-replicating molecules in prebiotic times before modern enzymatic repair and before the formation of the ozone layer that later attenuated the high levels of UV radiation on the early Earth. The photophysical properties of the bases thus appear to confirm the hypothesis, first proposed by Sagan, that UV light played a major role in early chemical evolution. The remarkably efficient dissipation of excess electronic energy by the RNA and DNA bases is functionality preserved from the prebiotic world, suggesting the possibility that the natural bases were selected in part due to their high intrinsic photostability or UV hardiness, and
that this is a vital property of the set of prebiotic molecules that could give rise to life on Earth or elsewhere in the universe.

We study the photoproperties of RNA bases as well as prebiotically plausible alternative bases in great detail by laser spectroscopy of nucleobases, isolated in a molecular beam. This talk will report on results and potential implications for modeling prebiotic chemistry and for the planetary conditions that could favor life as we know it.

Host in ELSI: Jim Cleaves