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How RNA formed on the early earth (Nature and SciAm report) May 17, 2009

Posted by rationalskeptic in Chemistry.
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(First paragraph is Scientific American’s report on the subject)

Cytosine

Cytosine

This week’s issue of Nature features a welcome discovery for those of us enthralled, mystified and frustrated by the study of the origins of life. John Sutherland, a chemist at the University of Manchester, and his colleagues claim to have figured out how ribose, phosphate and the nitrogenous (nitrogen-bearing) molecules known as nucleobases first came together to form nucleotides—the building blocks of the RNA world from which life is thought to have emerged. 

(The following is the free portion of the study provided by Nature)

Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions

Matthew W. Powner1, Béatrice Gerland1 & John D. Sutherland1

  1. School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, UK

Correspondence to: John D. Sutherland1 Correspondence and requests for materials should be addressed to J.D.S. (Email: john.sutherland@manchester.ac.uk).

 

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’ hypothesis1, 2, 3 this polymer was RNA, but attempts to provide experimental support for this have failed4, 5. In particular, although there has been some success demonstrating that ‘activated’ ribonucleotides can polymerize to form RNA6, 7, it is far from obvious how such ribonucleotides could have formed from their constituent parts (ribose and nucleobases). Ribose is difficult to form selectively8, 9, and the addition of nucleobases to ribose is inefficient in the case of purines10 and does not occur at all in the case of the canonical pyrimidines11. 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 molecules12, 13, 14, 15, 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 from the 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.