Exobiology and Evolutionary Biology

Prebiotic Routes to Carbohydrates Involving Borate Minerals (2)

PI: Steven Benner

An emerging consensus believes that an early form of life on Earth used RNA as its only genetically encoded component for biological catalysts (the “RNA world”). However, a corresponding consensus is not found for the hypothesis that RNA supported genetics in the first form of life. This is because prebiotic chemistry has not generated a model for abiotic synthesis of oligomeric RNA under conditions that the community accepts as “plausible”. Plausibly prebiotic routes to some pieces of RNA are known, including nucleobases and phosphates, however, and various solutions are available to solve the “water problem” when assembling RNA. Accordingly, the limiting challenge today for the “RNA first” model for the origin of life is ribose, the “R” in “RNA”. Here, the instability of ribose under conditions where it might be formed has caused many to argue that neither ribose nor any other carbohydrate could have been components of the first genetic system. In the previous funding period, we showed that it is reasonable to hypothesize that borate-moderated carbohydrate synthesis generated ribose, other pentoses, pentuloses and threose on prebiotic Earth from compounds that were almost certainly present, via cycles reminiscent of biological metabolism. These carbohydrates were shown to be stable for 8 months under the same conditions where they are formed. The proposed research will test this hypothesis by developing quantitative kinetic and thermodynamic models for borate-moderated synthesis, assigning structures to its intermediates and products, and determining how these change with changing environmental conditions. These will be correlated with possible environments on early Earth and Mars. The deliverable after three years will be data that remove prebiotic ribose synthesis as the limiting obstacle to the RNA-first hypothesis, allowing attention to turn to other issues surrounding prebiotic generation of oligomeric RNA: hydrolytic cleavage and the origin of homochirality.