ASU researcher may have discovered key to life before its origin on Earth
February 28, 2008An important discovery has been made with respect to the mystery of “handedness” in biomolecules. Researchers led by Sandra Pizzarello, a research professor at Arizona State University, found that some of the possible abiotic precursors to the origin of life on Earth have been shown to carry “handedness” in a larger number than previously thought.
The work is being published in this week’s Early Edition of the Proceedings of the National Academy of Sciences. The paper is titled, “Molecular asymmetry in extraterrestrial chemistry: Insights from a pristine meteorite,” and is co-authored by Pizzarello and Yongsong Huang and Marcelo Alexandre, of Brown University.
Pizzarello, in ASU’s Department of Chemistry and Biochemistry, worked with Huang and Alexandre in studying the organic materials of a special group of meteorites that contain among a variety of compounds, amino acids that have identical counterparts in terrestrial biomolecules. These meteorites are fragments of asteroids that are about the same age as the solar system (roughly 4.5 billion years.)
Scientists have long known that most compounds in living things exist in mirror-image forms. The two forms are like hands; one is a mirror reflection of the other. They are different, cannot be superimposed, yet identical in their parts.
When scientists synthesize these molecules in the laboratory, half of a sample turns out to be “left-handed” and the other half “right-handed.” But amino acids, which are the building blocks of terrestrial proteins, are all “left-handed,” while the sugars of DNA and RNA are “right-handed.” The mystery as to why this is the case, “parallels in many of its queries those that surround the origin of life,” said Pizzarello.
Years ago Pizzarello and ASU professor emeritus John Cronin analyzed amino acids from the Murchison meteorite (which landed in Australia in 1969) that were unknown on Earth, hence solving the problem of any contamination. They discovered a preponderance of “left-handed” amino acids over their “right-handed” form.
“The findings of Cronin and Pizzarello are probably the first demonstration that there may be natural processes in the cosmos that generate a preferred amino acid handedness,” Jeffrey Bada of the Scripps Institution of Oceanography, La Jolla, Calif., said at the time.
The new PNAS work was made possible by the finding in Antarctica of an exceptionally pristine meteorite. Antarctic ices are good “curators” of meteorites. After a meteorite falls -- and meteorites have been falling throughout the history of Earth -- it is quickly covered by snow and buried in the ice. Because these ices are in constant motion, when they come to a mountain, they will flow over the hill and bring meteorites to the surface.
“Thanks to the pristine nature of this meteorite, we were able to demonstrate that other extraterrestrial amino acids carry the left-handed excesses in meteorites and, above all, that these excesses appear to signify that their precursor molecules, the aldehydes, also carried such excesses,” Pizzarello said. “In other words, a molecular trait that defines life seems to have broader distribution as well as a long cosmic lineage.”
“This study may provide an important clue to the origin of molecular asymmetry,” added Brown associate professor and co-author Huang.
Source: Arizona State University
Sep 18, 2009 |
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A. From "...key to life before its origin on Earth?"
http://www.physor...html#tab
When scientists synthesize these molecules in the laboratory, half of a sample turns out to be left-handed and the other half right-handed. But the amino acids that are the building blocks of terrestrial proteins are all left-handed, while the sugars of DNA and RNA are right-handed. The mystery as to why this is the case, parallels in many of its queries those that surround the origin of life...
Thanks to the pristine nature of this meteorite, we were able to demonstrate that other extraterrestrial amino acids carry the left-handed excesses in meteorites and, above all, that these excesses appear to signify that their precursor molecules, the aldehydes, also carried such excesses, Pizzarello said. other words, a molecular trait that defines life seems to have broader distribution as well as a long cosmic lineage.
B. From "Allosteric, chiral-selective drug binding to DNA"
http://www.pnas.o...2032.pdf
(Allosteric: of, relating to, undergoing, or being a change in the shape and activity of a protein, as an enzyme, that results from combination with another substance at a point other than the chemically active site)
DNA is polymorphic and exists in a variety of distinct conformations. Duplex DNA can adopt a variety of sequence-dependent secondary structures that range from the canonical right-handed B form through the left-handed Z conformation. Multistranded triplex and tetraplex structures are now known to exist. All of these unique conformations may play important functional roles in gene expression.
C. Chirality in life still awaits elucidation
First, reasearch findings should be stated scientifically correctly. In A above NOT "a molecular trait that defines life seems to have broader distribution as well as a long cosmic lineage%u201D, but YES "a molecular conformation dominant in Earth life may have broader distribution and additional cosmic presence.
Next, re in A above "the mystery as to why this is the case":
My conjecture about the probable reasons for the prevailing chirality:
Darwinian evolution started at life's day one, with the genesis of the first organisms, the replicating oligomers, pre-archaea genes. It started under yet-unknown energetic conditions, by a serendipitous accident, with oligomeric (RNA?) conformations, in a soup containing all their essential molecular progenitors. These Conformations happened to absorb the amounts of energy enabling their polymerization, to lengths precipitated as determined by the nature and conditions of the soup.
The sugars and the nitrogen-based compounds that, together with the phosphates, are the components of the genes-organisms, are chiral. There probably is an energetic advantage in homochirality and chiral homogeneity for the self-replication of biopolymers.
This serendipitous accident set up a matrix-field of energy with a potential extended between its source, the sun radiation and the precipitating organisms. This was the genesis of the ongoing formation and maintenance of Earth's biosphere.
And since the biosphere started it could only evolve in more favorable energetic directions and towards stabler components. Survival. After all this is evolution.
But this is a conjecture. Chirality in life still awaits elucidation...
Dov Henis
A. From "...key to life before its origin on Earth?"
http://www.physor...html#tab
When scientists synthesize these molecules in the laboratory, half of a sample turns out to be %u201Cleft-handed%u201D and the other half %u201Cright-handed.%u201D But the amino acids that are the building blocks of terrestrial proteins are all %u201Cleft-handed,%u201D while the sugars of DNA and RNA are %u201Cright-handed.%u201D The mystery as to why this is the case, %u201Cparallels in many of its queries those that surround the origin of life...%u201D
Thanks to the pristine nature of this meteorite, we were able to demonstrate that other extraterrestrial amino acids carry the left-handed excesses in meteorites and, above all, that these excesses appear to signify that their precursor molecules, the aldehydes, also carried such excesses,%u201D Pizzarello said. %u201CIn other words, a molecular trait that defines life seems to have broader distribution as well as a long cosmic lineage.%u201D
B. From "Allosteric, chiral-selective drug binding to DNA"
http://www.pnas.o...2032.pdf
(Allosteric: of, relating to, undergoing, or being a change in the shape and activity of a protein, as an enzyme, that results from combination with another substance at a point other than the chemically active site)
DNA is polymorphic and exists in a variety of distinct conformations. Duplex DNA can adopt a variety of sequence-dependent secondary structures that range from the canonical right-handed B form through the left-handed Z conformation. Multistranded triplex and tetraplex structures are now known to exist. All of these unique conformations may play important functional roles in gene expression.
C. Chirality in life still awaits elucidation
First, reasearch findings should be stated scientifically correctly. In A above NOT "a molecular trait that defines life seems to have broader distribution as well as a long cosmic lineage%u201D, but YES "a molecular conformation dominant in Earth life may have broader distribution and additional cosmic presence.%u201D
Next, re in A above "the mystery as to why this is the case":
My conjecture about the probable reasons for the prevailing chirality:
Darwinian evolution started at life's day one, with the genesis of the first organisms, the replicating oligomers, pre-archaea genes. It started under yet-unknown energetic conditions, by a serendipitous accident, with oligomeric (RNA?) conformations, in a soup containing all their essential molecular progenitors. These Conformations happened to absorb the amounts of energy enabling their polymerization, to lengths precipitated as determined by the nature and conditions of the soup.
The sugars and the nitrogen-based compounds that, together with the phosphates, are the components of the genes-organisms, are chiral. There probably is an energetic advantage in homochirality and chiral homogeneity for the self-replication of biopolymers.
This serendipitous accident set up a matrix-field of energy with a potential extended between its source, the sun radiation and the precipitating organisms. This was the genesis of the ongoing formation and maintenance of Earth's biosphere.
And since the biosphere started it could only evolve in more favorable energetic directions and towards stabler components. Survival. After all this is evolution.
But this is a conjecture. Chirality in life still awaits elucidation...
Dov Henis