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Non-Racemic Amino Acid Production

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As the Urey-Miller model of abiogenesis has grown weaker with time, interest in extra-terrestrial sources of amino acids has increased. The phrase “building blocks of life” is well-used: in 2005, space.com referred to amino acid precursors formed “in the winds of dying stars and spread all over interstellar space”; in 2008, National Geographic used the phrase when reporting on the detection of a precursor of glycine in the galaxy Arp 220. In December 2010, Nasa reported the presence of 19 amino acids in a carbon-rich meteorite and commented: “Finding them in this type of meteorite suggests that there is more than one way to make amino acids in space, which increases the chance for finding life elsewhere in the Universe.” Clearly, these sources are promoting the idea that finding amino acids provides a significant part of an abiogenesis solution. This is also the message picked up by the world’s media, which dutifully (and uncritically) passes on the hype.

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Comments
Homochirality Through Photon-induced Melting Of Rna/dna: Thermodynamic Dissipation Theory Of The Origin Of Life:
The homochirality of the molecules of life has been a vexing problemwith no generally accepted solution to date. Since a racemic mixture of chiral nucleotides frustrates the extension and replication of RNA and DNA, understanding the origin of homochirality has important implications to the investigation of the origin of life. Theories on the origin of life have generally elected to presume an abiotic mechanism giving rise to a large prebiotic enantiomer enrichment. Although a number of such mechanism have been suggested, none has enjoyed sufficient plausibility or relevance to be generally accepted. Here we suggest a novel solution to the homochirality problem based on a recently proposed thermodynamic dissipation theory for the origin of life. The ultraviolet absorption and dissipation characteristics of RNA/DNA point to their origin as photoautorophs, their replication assisted by UV light and temperature, and acting as catalysts for the global water cycle. Homochirality is suggested to have been incorporated gradually into the emerging life as a result of asymmetric right- over left-handed photon-induced denaturation of RNA/DNA occurring when Archean sea surface temperatures became close to the denaturing temperatures of RNA/DNA. This differential denaturing success would have been promoted by the somewhat right-handed circularly polarized submarine light of the late afternoon when surface water temperatures are highest, and a negative circular dichroism band extending from 220 nm up to 260 nm for small segments of RNA/DNA. A numerical model is presented demonstrating the efficacy of such a mechanism in procuring 100% homochirality of RNA or DNA from an original racemic solution in less than 500 Archean years assuming a photon absorption threshold for replication representing the hydrogen bonding energy between complementary strands. Because cholesteric D-nucleic acids have greater affinity for L-amino acids due to a positive structural complementarity, and because D-RNA/DNA+L-amino acid complexes also have a negative circular dichroism band between 200 - 300 nm, the homochirality of amino acids can also be explained by the theory.
Joseph
February 11, 2011
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There is a recent article about how exposure to UV can explain homochirality. When I locate the paper I will post it.Joseph
February 11, 2011
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