Did life's bias come from space? More evidence
Monday, March 16, 2009 | 05:56 PM ET
by Emily Chung
CBCNews.ca
Like a pairs of gloves, the building blocks of proteins come in left-handed and right-handed versions that are exact mirror images of one another.
Just as your left foot only fits properly into a left shoe, living things interact with and produce only the "left-handed" version of those building blocks, which are called amino acids.
But if you make amino acids from scratch in a lab using their chemical components, you inevitably get half of the right-handed version and half of the left handed version.
So it might be expected that if nature makes amino acids in space using similar chemistry, you'd also get a fifty-fifty mixture.
Studies of individual meteorites have found that surprisingly, sometimes there can be quite a lot of "extra" left-handed amino acids on a meteorite. A new study published Monday in the Proceedings of the National Academy of Sciences confirms that's no fluke and suggests how that bias may have arisen.
The authors of the paper, Daniel Glavin and Jason Dworkin of the National Aeronautics and Space Administration Goddard Space Flight Center in Greenbelt, Maryland, found that three out the six meteorites that landed in Antarctica and that they studied, had significantly larger quantities of the left-handed version of the amino acids than the right-handed version. In fact, one had a whopping 18 per cent more of one particular amino acid.
Glavin and Dworkin suggested that such meteorites, asteroids, comets and their fragments may have delivered extra left-handed amino acids to the earth before life began and "biased" the Earth's inventory of organic compounds, encouraging living things to build themselves using the more readily available left-handed version.
The study used a different analysis technique than had been used by other studies, independently backing up the results of those previous studies.
The researchers also noticed a pattern -- only meteorites that were extensively altered by water while still attached to their parent asteroid have the large excess in left-handed amino acids.
"Therefore, water played a very important role in the bias of left over right handed amino acids in meteorites," Glavin said in an email.
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Comments
Uncle Al
There is no credible explanation for biological homochirality: chiral L-protein amino acids and chiral D-sugars. Weak interaction arguments (Mendeleev Commun. 13(3) 129 (2003), Angew. Chem. Int. Ed. 41(24) 4618 (2002)) are woefully insufficient (maximum 8x10^(-12) eV PVED versus ambient kT = 0.0257 eV. An obvious source is a chiral vacuum background in the massed sector (not interactive with EM), consistent with teleparallel gravitation, testable on a lab bench.
Crystallographic space groups P3(1)21 and P3(2)21 are enantiomorphic. All formula units configure into homochiral 3-fold helices (right-handed and left-handed, respectively). There are no conflicting or racemic screw axes. Quartz, berlinite and analogues, tellurium, selenium... single crystals thus furnish atomic-scale left and right "shoes" to test for a vacuum left "foot". P3(1)21 versus P3(2)21 quartz is particularly good for its commercial production and a control "sock" - amorphous fused silica.
Load an Eotvos balance with macroscopically and chemically indistinguishable single crystal quartz test masses, space group P3(1)21 opposing P3(2)21. 90 days later the net output is either zero (as with all Equivalence Principle tests since Galileo and Stevin in the late 1500s) or non-zero. Observation trumps dialectic. Somebody should look. A non-zero output is followed by each space group run against fused silica. A quartz enantiomorph homochiral to the vacuum background gives a smaller net signal. The two hemiparity experiments' outputs sum to the full parity experiment's output as a final validation.
Posted March 17, 2009 12:19 PM