The Origin of Life: RNA?

So says John D. Sutherland, chemist at the University of Manchester.

Scientists have long suspected that the first forms of life carried their biological information not in DNA but in RNA, its close chemical cousin. Though DNA is better known because of its storage of genetic information, RNA performs many of the trickiest operations in living cells. RNA seems to have delegated the chore of data storage to the chemically more stable DNA eons ago. If the first forms of life were based on RNA, then the issue is to explain how the first RNA molecules were formed.

So how did they (Matthew W. Powner (lead author) and Beatrice Gerland co-author)) do it?

Instead of making the starting chemicals form a sugar and a base, they mixed them in a different order, in which the chemicals naturally formed a compound that is half-sugar and half-base. When another half-sugar and half-base are added, the RNA nucleotide called ribocytidine phosphate emerges.

A second nucleotide is created if ultraviolet light is shined on the mixture. Dr. Sutherland said he had not yet found natural ways to generate the other two types of nucleotides found in RNA molecules, but synthesis of the first two was thought to be harder to achieve.

Article is here. (PDF, 4 pages, Subscription Required). The abstract:

At some stage in the origin of life, an informational polymer must have arisen by purely chemical means. According to one version of the ‘RNA world’ hypothesis this polymer was RNA, but attempts to provide experimental support for this have failed. In particular, although there has been some success demonstrating that ‘activated’ ribonucleotides can polymerize to form RNA it is far from obvious how such ribonucleotides could have formedfrom their constituent parts (ribose and nucleobases). Ribose is difficult to form selectively and the addition of nucleobases to ribose is inefficient in the case of purines and does not occur at all in the case of the canonical pyrimidines. Here we show that activated pyrimidine ribonucleotides can be formed in a short sequence that bypasses free ribose and the nucleobases, and instead proceeds through arabinose amino-oxazoline and anhydronucleoside intermediates. The starting materials for the synthesis—cyanamide, cyanoacetylene, glycolaldehyde, glyceraldehyde and inorganic phosphate—are plausible prebiotic feedstock molecules, and the conditions of the synthesis are consistent with potential early-Earth geochemical models. Although inorganic phosphate is only incorporated into the nucleotides at a late stage of the sequence, its presence fromthe start is essential as it controls three reactions in the earlier stages by acting as a general acid/base catalyst, a nucleophilic catalyst, a pH buffer and a chemical buffer. For prebiotic reaction sequences, our results highlight the importance of working with mixed chemical systems in which reactants for a particular reaction step can also control other steps.

Cool work. As the Times article states, a lot of people figured that RNA was the first organic molecule formed that started the "chain reaction" called "life", there just was very little evidence that it was possible. This article changes all that.

I smell a Nobel.

Reference
Powner, M., Gerland, B., & Sutherland, J. (2009). Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions Nature, 459 (7244), 239-242 DOI: 10.1038/nature08013