On the origin of terrestrial homochirality for nucleosides and amino acids

Proc Natl Acad Sci U S A. 2009 Jun 9;106(23):9144-6. doi: 10.1073/pnas.0904350106. Epub 2009 May 28.

Abstract

Before life could start on earth, it was important that the amino acid building blocks be present in a predominant handedness called the L configuration and that the ribose of RNA be predominantly in the D configuration. Because ordinary chemical processes would produce them in equal L and D amounts, it has long been a puzzle how the needed selectivities could have arisen. Carbonaceous chondrites such as the Murchison meteorite, which landed in Australia in 1969, brought some unusual amino acids with a methyl group replacing their alpha hydrogen. They cannot racemize and have a small but real excess of those with the L configuration. We have shown that they can partake in a synthesis of normal L amino acids under credible prebiotic conditions. We and others showed that small preferences can be amplified into solutions with very high dominance of the L amino acids because of the higher solubility of the pure L form than of the more stable DL racemic compound crystal. Here, we show that such solubility-based amplification of small excesses of three D nucleosides, uridine, adenosine, and cytidine, can also occur to form solutions with very high D dominance under credible prebiotic conditions. Guanosine crystallizes as a conglomerate and does not amplify in this way. However, under prebiotic conditions it could have been formed from homochiral D ribose from the hydrolysis of amplified adenosine or cytidine.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acids / chemistry*
  • Australia
  • Evolution, Chemical
  • Meteoroids
  • Nucleosides / chemistry*
  • Ribose / chemistry
  • Solubility
  • Stereoisomerism

Substances

  • Amino Acids
  • Nucleosides
  • Ribose