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Re: Great Siberian Explosion
almitt wrote:
>
> Now I can't recall the specifics, but I believe a study by
> Miller and Urey (UCLA?) created "life" by interacting an electrical charge
> with the amino acids in a lab. This is the basis of the "primordial soup",
> out of which life crawled, wherelightening was the electrical charge. Maybe
> some of our biologists can shed way more light than I can.....
>
> Hi Matt and all,
>
> I believe that Carl Sagan might have first done something like that at Berkley
> but who knows if other studies were also conducted later by others. My 2 cents
> worth anyway.
>
> --AL
>
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Well, here's where a biochemist can contribute something to the list!
So far, no one's definitely "created life" in a test tube, at least not
from scratch! Most high school biologists could probably recite
Miller's early experiment in Urey's lab with electrical discharges
inside sealed glass enclosures containing a gaseous mixture of methane,
ammonia, and hydrogen, along with water, thought at that time to be
representative of the primordial Earth's atmosphere. Imagine Miller's
delight when he saw the pinkish red tinge of the mixture after a few
days, especially when the analysis showed the presence of several amino
acids and other organic molecules typically considered "organic." This
was an experiment to attempt to simulate "prebiotic" conditions. The
limited amino acids produced were in equal numbers of optical isomers,
in other words, a racemic mixture.
Ironically, the conditions and mixture that Miller first contrived are
now felt not to be respresentative of the prebiotic atmosphere, which
was probably much less rich with hydrogen. Instead of methane, more
carbon dioxide is felt to have been present, and instead of ammonia,
molecular nitrogen was felt to be present. Under these conditions, the
yield of organic substances fall practically to zero!
Nevertheless, his experiments showed how relatively easy it is to
assemble organic compounds from prebiotic precursors. Dissimilar
conditions as occurred in the outer reaches of our primordial solar
nebula, given any number of sources of energy, could have formed many
organics readily. The precise pathways for their formations have been
well studied. As all of us on this meteorite list know, organic
compounds are found in meteorites, especially our carbonaceous
chondrites. The Murchison contained a number of amino acids remarkably
similar to those generated by Miller. The Murchison actually contained
more than 300 amino acids, not counting their enantiomers. Spectroscopic
studies of interstellar dust clouds strongly suggest the existence of
highly reactive combinations of carbon, hydrogen, oxygen, nitrogen, and
sulfur ...(and silicon)...that suggest similar organic compounds and
their immediate precursors, like formaldehyde, ammonia, isocyanic acid,
hydrogen isocyanide, etc., etc. Reflectant spectrometry of asteroids
and the moons of our gas giants support the red organic albedo's.
Interestingly, there are no aromatic or unsaturated amoino acids in
meteorites. No benzene rings as in phenylalanine. Even carboxylic
groups are relatively rare. There's a paucity of sulphur-containing
amino acids, too. No cysteines or methionines...
Nevertheless, it's been put forth by Armand Delsemme and others that
virtually all the basic building blocks of life were transported onto a
sterile degassed Earth by comets.
How these primeval amino acids might have joined together into peptides
under prebiotic conditions remains a great mystery. In 1951 Theodor
Wieland discovered how amino acids could be condensed to form simple
peptides from from amino-acid thioesters, which could themselves form
spontaneously under reasonable primordial conditions.
Still, it's a huge quantum leap from short peptides to catalyzing
self-replicating peptides, to a tRNA world, and eventually to
life...just an incredible miracle! That's the holy grail of
biochemistry.
As biologist, we've been incredibly fortunate to reverse engineer the
mechanisms of biology, genetics. And as bioengineers, we've been able
to "hack" into the machinations of life and attain useful consequences,
like synthesizing antivirals or cloning or engineering monoclonal
antibodies. But except for being able to hyjack existing biological
systems and adapting the principles to our end, we're still light years
away from manufacturing life from inorganics, not without loading the
dice by applying advanced organic catalysts to do specific biddings...
So, no one's created life from dust...not yet...
Oh boy, I'd better get some sleep...
Joseph
Of interest to me was the revelation that there was a L-isomer biase in
the amino acid make-up of the Murchison.
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