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Author Topic:   The Recurrent Problem of Chirality
sidelined
Member (Idle past 6026 days)
Posts: 3435
From: Edmonton Alberta Canada
Joined: 08-30-2003


Message 10 of 81 (285819)
02-11-2006 9:21 AM
Reply to: Message 1 by Evopeach
02-09-2006 4:49 PM


ID is a hollow shell game.
Evopeach
Another demonstration of intelligent design.. inexplicable by evolutionary theory
You fail to establish here how the intelligent design is suffient and necessary for the amino acids chirality and why evolution will never be capable of explaining this.
Regardless, this is simply not the case.There are models which are capable of giving clues to the origin though none fully developed simce the standards required by science are, unlike the intelligent design hypothesis,subject to rigorous investigation and experimental verification.
Allow me to reference but 2 articles to show the possibilities for chirality on earth.Here is the first.
Requested Page Not Found | Institute of Astronomy
Chirality and the Origin of Life
The origin of the homochirality of biological molecules (the use in living organisms of only left-handed or L-amino acids and right-handed or D-sugars) has puzzled scientists since the chirality of molecules was discovered by Louis Pasteur more than 150 years ago. Recently it has been discovered that an excess of L-amino acids is present in the Murchison and Murray meteorites indicating that a preference for L-amino acids existed in solar system material before there was life on Earth. This supports an idea, first proposed by Rubenstein et al. (1983, Nature 306, 118), for an extraterrestrial origin for homochirality.
In this model the action of circular polarized light on interstellar chiral molecules introduced a left handed excess into molecules in the material from which the solar system formed. Some of this organic material then finds its way onto Earth via impacts of comets, meteorites and dust particles during the heavy bombardment phase in the first few hundred million years of the solar system. These molecules were then part of the prebiotic material available for the origin of life, and tipped the scales for life to develop with L-amino acids and D-sugars.
Rubenstein et al. originally proposed that synchrotron radiation from neutron stars in supernova remnants would be a suitable source of the required UV circularly polarized light. However, this interpretation is not supported by theory or observation which show that the circular polarization of these sources is very low. New observations with the Anglo-Australian Telescope (above) have shown suprisingly high circular polarizations (the red and white regions in the image) in the infrared light from reflection nebulae in the star forming regions Orion OMC1 (a region in the Orion nebula M42) and NGC 6334. Although we can only observe these regions at infrared wavelengths which can penetrate the thick dust clouds in which they are embedded, it is predicted that circular polarization should also be present at the ultraviolet wavelengths needed for asymmetric photolysis of molecules such as amino acids. If our own solar system formed in such a region of high circular polarization, it could have led to the excess of L-amino acids which we see in meteorites and to the homochirality of biological molecules. It is possible that without such a process operating it would not be possible for life to start. This may have implications for the frequency of occurrence of life in the universe.
And the second
http://www.sciencenews.org/articles/20010505/fob1.asp
Rocks May Have Given a Hand to Life
Jessica Gorman
A long-standing mystery about the origin of life has a new possible solution.
The puzzle is that amino acids, the constituents of proteins, occur in two chemically identical forms that have structures mirroring each other like two gloves. Most chemical processes yield left- and right-handed amino acids in equal amounts yet life forms contain left-handed amino acids almost exclusively. New findings show that a mineral common on the ancient Earth might have segregated the mirror-image versions.
Much speculation has focused on extraterrestrial influences behind early life. Some scientists suggest that extra left-handed amino acids arrived on meteorites as life was emerging on Earth (SN: 2/22/97, p. 118). In another theory, Earth formed from dust harboring a primordial excess of left-handed amino acids.
A yellowish calcite crystal.
Rob Lavinsky
Researchers in Washington, D.C., now report that calcium carbonate, or calcite, can adsorb an excess of left-handed amino acids onto some of its crystal faces and of right-handed amino acids on other faces. Robert M. Hazen and Timothy R. Filley of the Carnegie Institution of Washington and Glenn A. Goodfriend of George Washington University report their results in the May 8 Proceedings of the National Academy of Sciences.
"It is very exciting," says Max Bernstein of NASA's Ames Research Center and the SETI (Search for Extraterrestrial Intelligence) Institute, both in Mountain View, Calif. "Such results provide a plausible scenario by which . . . amino acids could be separated from their mirror images, potentially solving a vexing problem of prebiotic chemistry."
In their analysis, the scientists focused on calcite because it was widely present on the early Earth and is compatible with biological molecules. For instance, it's the primary ingredient of sea shells.
The researchers placed each of four fist-size calcite crystals in a 50-50 solution of right- and left-handed aspartic acid, an amino acid. Two of the crystals had super-smooth surfaces, and two had microscopic terraces. The scientists found that the terraced crystals ended up with a 10 percent excess of right-handed amino acids on one type of face and a similar excess of left-handed amino acids on another. The smooth-faced crystals tended not to differentiate between the mirror-image forms of aspartic acid.
Hazen speculates that billions of years ago, amino acids might have lined up on crystals' terraces. They could have then combined into the first all-lefty peptides, or short protein segments.
The calcite results are "of special significance for origin-of-life researchers," says Noam Lahav of the Hebrew University in Jerusalem. But he cautions that the findings still do not point to a chemical mechanism by which southpaw amino acids overtook their right-handed siblings as life emerged.
John Cronin of Arizona State University in Tempe also remains puzzled. Since both the mirror forms become concentrated on crystal faces, "it would be necessary for life to have originated from a particular spatially isolated crystal surface, which seems rather improbable," he says.
Hazen suspects that, in fact, that's what happened. The left-handed amino acids in one place got the edge, he speculates, because by pure chance, these lefties bonded into peptides capable of self-replication.
References:
Hazen, R.M., T.R. Filley, and G.A. Goodfriend. 2001. Selective adsorption of L- and D-amino acids on calcite: Implications for biochemical homochirality. Proceedings of the National Academy of Sciences 98(May 8):5487.
Further Readings:
Peterson, I. 1997. Left-handed excess in meteorite molecules. Science News 151(Feb. 22):118.
Sources:
Max Bernstein
Astrophysics Branch
Mail Stop 245-6
NASA Ames Research Center
Moffett Field, CA 94035-1000
John R. Cronin
Department of Chemistry and Biochemistry
Arizona State University
Tempe, AZ 85287-1604
Robert M. Hazen
Geophysical Laboratory
5251 Broad Branch Road, N.W.
Washington, DC 20015-1305
Noam Lahav
Faculty of Agriculture
Hebrew University of Jerusalem
P.O. Box 12
Rehovot 76100
Israel
Your turn now evopeach. How does the intelligent design hypothesis explain chirality?It cannot since it merely heaps the problem onto a chimera used by those close minded individuals who refuse to investigate properly the mysteries of the world with due care and honesty.
ID holds no explanatory power because it is not an explanation but a shell game.You cannot assuage hunger by snapping at empty air with the hopes of gaining sustenance.
This message has been edited by sidelined, Sat, 2006-02-11 07:23 AM

But I realize now that these people were not in science; they didn’t understand it. They didn’t understand technology; they didn’t understand their time. R.P. Feynman

This message is a reply to:
 Message 1 by Evopeach, posted 02-09-2006 4:49 PM Evopeach has not replied

Replies to this message:
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sidelined
Member (Idle past 6026 days)
Posts: 3435
From: Edmonton Alberta Canada
Joined: 08-30-2003


Message 12 of 81 (286745)
02-15-2006 1:56 AM
Reply to: Message 1 by Evopeach
02-09-2006 4:49 PM


Evopeach
You intend on posting a rebuttal to post #10 soon?

This message is a reply to:
 Message 1 by Evopeach, posted 02-09-2006 4:49 PM Evopeach has not replied

  
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