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Re: H. C. Urey's work


     
     Hello Martin and Joseph,
     
     Interesting posts.  Can you give me some more information regarding this 
     "L-isomer biase", and its relationship to amino acids from living 
     organisms?  I think this topic is related to this recent finding:
     
     "
     "
     Subject: A Clue To The Origin Of Life 
     Author:  Ronald C Baalke at Gateway
     Date:    7/31/98 8:22 AM
     
     
     Anglo-Australian Observatory
     PO Box 296, Epping
     NSW 2121 Australia
     
     Friday, 31 July 1998
     
     A Clue to the Origin of Life
     
     Astronomers using the Anglo-Australian Telescope have found a possible 
     explanation for why life on earth almost exclusively uses left-handed 
     amino acids and right-handed sugars as the building blocks of proteins 
     and nucleic acids -- a mystery that has puzzled scientists for 150 
     years.
     
     They believe the asymmetry was imprinted in organic molecules in 
     interstellar space before the formation of the Solar System. These 
     molecules then found their way onto the Earth via the impacts of 
     comets and meteorites to provide the starting material for the origin 
     of life. This was revealed today in a paper in the international 
     journal 'Science' by Dr Jeremy Bailey, from the Anglo-Australian 
     Observatory, and his colleagues.
     
     In 1848, Louis Pasteur discovered that some molecules can exist in two 
     mirror image forms, right-handed or left handed. In living organisms, 
     molecules tend to be all one form, not a mixture of both. Amino acids 
     for example, the building blocks of protein, are always left-handed, 
     where as sugars (including deoxyribose, an important component of DNA) 
     are always right-handed. When these molecules are synthesised in a 
     laboratory, equal numbers of right and left are formed. The reason for 
     the imbalance puzzled scientists for decades.
     
     In 1930, scientists discovered a way of destroying molecules of one- 
     handedness, providing a partial solution to the problem. They used 
     circularly polarised light.* But this was only part of the story. When 
     life began on earth, there was no source of circularly polarised 
     light.
     
     Last year, scientists at Arizona State University discovered an excess 
     of left-handed amino acids in the Murchison meteorite. (The Murchison 
     metorite fell in 1969 near Murchison in Victoria, Australia and has 
     been found to contain an extraordinary variety of organic molecules.) 
     This remarkable discovery shows that the asymmetry already existed 
     before life began on Earth, and may well have been present in the 
     material from which the Solar System formed.
     
     Dr Bailey and his colleagues used the Anglo-Australian Telescope at 
     Siding Spring Mountain near Coonabarabran to show how the asymmetry 
     might have been generated.
     
     "We detected circularly polarized light (below right) in a region of 
     the Great Nebula in Orion called Orion Molecular Cloud 1 (OMC-1, 
     pictured left). We know that new stars are being formed here, and we 
     also know that organic molecules are present," Dr Bailey said.
     
     "This region may well be similar to the region in which our own solar 
     system formed," he added.
     
     The circularly polarized light in such a region could imprint a 
     preferred handedness on any organic molecules in the region, including 
     those in a cloud beginning to collapse to form a star and its planets.
     
     "We know that ultraviolet circularly polarised light is needed to 
     select handedness in molecules such as amino acids, but unfortunately 
     thick dust clouds prohibited observations at these wavelengths," Dr 
     Bailey said. "So we made the observations at infrared wavelengths. Our 
     calculations however, show that circular polarisation is present at 
     all wavelengths, from infrared to ultraviolet," he added.
     
     Many scientists believe that a preferred handedness in molecules must 
     have been present in order for the origin of life to be possible. 
     These results therefore suggest that the suitability of our planet for 
     life may be as much a consequence of the environment in which our 
     solar system formed as of the local conditions on the early Earth.
     
     Further information:
     
     Dr Jeremy Bailey
     Anglo-Australian Observatory
     phone 61 2 9372 4823
     email jab@aaoepp.aao.gov.au
     
     - End -
     
     Footnote:
     
     * Light is an electromagnetic wave consisting of oscillating electric 
     and magnetic fields. The direction of the electric field determines 
     the 'polarization' of the light. Many light sources such as the sun 
     and most artificial lights produce unpolarized light. The fields are 
     randomly oriented with no preferred direction.
     
     In 'linearly polarized' light, the electric field oscillates along a 
     fixed line. A familiar example is the light from the daylight sky. 
     Polarizing filters such as those used in some sunglasses, or for 
     mounting on cameras, filter out linearly polarized light and will 
     cause the sky to darken if rotated to the appropriate angle.
     
     In 'circularly polarized' light, the electric field direction rotates 
     in a circle rather than oscillating from side to side. Circularly 
     polarized light is rarely encountered in natural situations. Depending 
     on the direction of rotation (either clockwise or anticlockwise) 
     circular polarization can be either left-handed or right-handed.
     
     
     [NOTE: Images supporting this release are available at 
     http://www.aao.gov.au/press/life.html]
     "
     "
     
     Regards,
     Bob V.
     
______________________________ Reply Separator _________________________________
Subject: H. C. Urey's work
Author:  martinh@isu.edu at Internet 
Date:    9/22/98 6:33 AM
     
     
Hello All,
     
Herald Urey was one of the pioneers of meteorite research using both 
advanced chemical analysis, as well as exceptional insight. Although in the 
end, some of his theories were abandon by most scientists for more 
supported ideas, Urey is one of the pillars in meteorite research to which 
much of our current understanding has evolved.
     
Here is an excerpt discussing the work done in H. C. Urey's lab:
     
"In 1953, Stanley L. Miller, one of Urey's students at the University of 
Chicago, had synthesized in the laboratory several complex hydrocarbons, 
including amino acids, by means of an electrical discharge in a mixture of 
hydrogen, water vapor, methane, and ammonia. Urey, in fact, had proposed 
the occurrence of such an abiogenic process in the primordial nebula to 
account for the presence of organic compounds in meteorites."
     
--page 313, Cosmic Debris: Meteorites in History by John G. Burke (1986)
     
     
And one from Bob Dylan:
"Mothers and fathers throughout the land, don't criticize what you don't 
understand
The times they are a changing."
     
     
Also, Joseph wrote:
"Of interest to me was the revelation that there was a L-isomer biase in 
the amino acid make-up of the Murchison."
     
I agree Joseph. It seems the L-isomer biase may be a fingerprint for life 
as we know it. Or maybe, life is as we know it.
     
-Martin
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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