02.29.08
Origins
Key To Life Before Its Origin On Earth May Have Been Discovered
ScienceDaily (Feb. 29, 2008) — An 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.
Dov Henis said,
April 16, 2008 at 10:56 am
Science Should Be Spared This Scientifically Unsound Conjecture!
Chirality In Life, The Earliest Surviving Darwinian Evolution Product
http://www.physforum.com/index.php?showtopic=14988&st=180&#entry327715
A. From “…key to life before its origin on Earth?”
http://www.physorg.com/news123440279.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. “In 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.org/cgi/reprint/97/22/12032.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”, 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 occurrence, 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 occurrence 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 thus started it could only evolve in more favorable energetic directions and towards stabler components. Survival was the direction. After all, this was already Earth-life’s evolution.
But this is also a conjecture , even if a scientifically sound one . Chirality in life still awaits elucidation…
Dov Henis
http://blog.360.yahoo.com/blog-P81pQcU1dLBbHgtjQjxG_Q–?cq=1