THE ORIGINS OF LIFE
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AbioticSynthesis.html#Miller's_Experiment
1. Miller's Experiment
Stanley Miller, a graduate student in biochemistry, built the apparatus shown here. He filled it with
* water (H2O
* methane (CH4)
* ammonia (NH3) and
* hydrogen (H2)
* but no oxygen
He hypothesized that this mixture resembled the atmosphere of the early earth. (Some are not so sure.) The mixture was kept circulating by continuously boiling and then condensing the water.
The gases passed through a chamber containing two electrodes with a spark passing between them.
At the end of a week, Miller used paper chromatography to show that the flask now contained several amino acids as well as some other organic molecules.
In the years since Miller's work, many variants of his procedure have been tried. Virtually all the small molecules that are associated with life have been formed:
* 17 of the 20 amino acids used in protein synthesis, and
* all the purines and pyrimidines used in nucleic acid synthesis.
* But abiotic synthesis of ribose — and thus of nucleotides — has been much more difficult. However, success in synthesizing pyrimidine ribonucleotides under conditions that might have existed in the early earth has recently (Nature 14 May 2009) been reported.
2. Molecules from outer space?
The Murchison Meteorite
his meteorite, that fell near Murchison, Australia on 28 September 1969, turned out to contain a variety of organic molecules including:
* purines and pyrimidines
* polyols — compounds with hydroxyl groups on a backbone of 3 to 6 carbons such as glycerol and glyceric acid. Sugars are polyols.
* the amino acids listed here. The amino acids and their relative proportions were quite similar to the products formed in Miller's experiments.
The question is: were these molecules simply terrestrial contaminants that got into the meteorite after it fell to earth.
Probably not:
* Some of the samples were collected on the same day it fell and subsequently handled with great care to avoid contamination.
* The polyols contained the isotopes carbon-13 and hydrogen-2 (deuterium) in greater amounts than found here on earth.
* The samples lacked certain amino acids that are found in all earthly proteins.
* Only L amino acids occur in earthly proteins, but the amino acids in the meteorite contain both D and L forms (although L forms were slightly more prevalent).
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SO... it is very easy for the building blocks of life to form, and they also exist in outer space...