One of the criticisms creationists make about the inorganic origin of life
scenarios is that when amino acids are made in the laboratory they are 50%
left handed and 50% right handed( a 50-50 ratio is called racemic). Since a
mixture of left and right handed amino acids make useless proteins and
living forms only have left handed proteins, the problem has been claimed to
be fatal tothe origin of life scenario. It has been known for a while that
non-racemic amino acids existed in the Murchison meteorite.
I had posted this somewhere several months ago.
***
Unless you are willing to believe in life in outer space, there is a mechanism
(unknown to us at this moment) which is quite capable of producing non-racemic
amino acids. Here is data from the Murchison meteorite in which non-racemic
amino acids were extracted.
amino acid d/l ratio in Murchison meteorite
GLU ASP PRO LEU ALA
H2O .322 .202 .342 .166 .682
H2O .30 .30 .30 nd .60
HCl .176 .126 .105 .029 .307
~Michael H. Engel and Bartholomew Nagy, "Distribution and
Enantiomeric Composition of Amino Acids in the Murchison
Meteorite", Nature , 296, April 29, 1982, p. 838.
Some of these results show that something in space was able to produce 70-90%
L amino acids. This concept that Christians propagate that nature can't
produce anything but racemic forms is flawed. I don't know the mechanism but
there is one. (See also Engel, Macko and Silfer, "Carbon Isotope Composition
of Individual amino acids in the Murchison Meteorite," Nature 348, Nov. 1.
1990, pp 47-48)
****
Some people still criticised these results as being due to left-handed amino
acid contamination. Cronin and Pizzarello provide strong evidence that the
chirality problem (handedness) may not be as severe as previously thought.
Peterson in an accompanying commentary notes,
"Now chemists have furnished intriguing evidence that
certain amino acids that formed in space 4.5 billion years ago
have a small, but significant, excess of the left-handed form.
John R. Cronin and Sandra Pizzarello of Arizona State University
in Tempe report their findings in the Feb. 14 SCIENCE.
"'This is the first convincing demonstration that there may
be some natural nonbiological process that results in a
slight...excess of the [left-handed] amino acids,' says Jeffrey
L. Bada of the Scripps Institution of Oceanography in La Jolla,
Calif.
"The observations suggest that extraterrestrial,
nonbiological organic matter could have played an essential role
in the origin of life on Earth by providing the initial asymmetry
from which a distinctive handedness developed, Cronin and
Pizzarello contend.
"Using sensitive analytical techniques, the researchers
extracted and studied in meticulous detail four amino acids found
int he carbon-rich Murchison meteorite, a type known as a
carbonaceous chondrite. They examined amino acids that were
relatively common in the meteorite but were not among the 20
amino acids found in terrestrial orangisms.
"By focussing on these particular amino acids, Cronin and
Pizzarello could avoid problems of contamination that would bias
the results. In each case, the researchers found an excess of
the left-handed form of the amino acid, ranging from 2 to 9
percent.
"The findings indicate that even amino acids that are never
found in known life-forms, and so could not result from
terrestrial biological evolution, display a lef-handed bias."~I.
Peterson, "Left-handed Excess in Meteorite Molecules", Science
News, Feb 22, 1997, p. 118
The article itself describes their procedure
"We initially targeted for study 2-amino-2,3-
dimethylpentanoic acid (2-a-2,3dmpa), an amino acid with two
chiral centers and, consequently, four steroisomers. This amino
acid meets two important criteria: (i) It is present in the
Murchison meteorite but has not been reported to occur in
terrestrial matter, and (ii) its two chiral centers are resistant
to epimerization because one 9C-2) lacks a hydrogen atom and the
other (C-3) has a methine hydrogen atom of low acidity.
Consequently, it is likely that the chiral centers retained their
original configurationsn through the aqueous and mild thermal
processing experienced by the meteorite parent body and that the
original enantiomer ratios have not been compromised by
contamination."~John R. Cronin and Sandra Pizzarello,
"Enantiomeric Excesses in Meteoritic Amino Acids," Science
275(February 14, 1997):951-955, p. 951
and
"Contamination of the 2-a-2,3-dmpa by a terrestrial source of the
L enantiomers seems improbable. A search of Chemical Abstracts
failed to produce a report of the natural occurrence of 2-a-2,3-
dmpa other than that in the Murchison meteorite."~John R. Cronin
and Sandra Pizzarello, "Enantiomeric Excesses in Meteoritic Amino
Acids," Science 275(February 14, 1997):951-955, p. 952
"The finding of enantiomeric excesses in amino acids
indigenous to the Murchison meteorite constitutes the first
natural evidence for the operation of an abiotic process for
enantiomeric enrichment. The observations suggest that organic
matter of extraterrestrial origin could have played an essential
role in the origin of terrestrial life as a provider of the
initial enantiomeric excesses from which homochirality
developed."~John R. Cronin and Sandra Pizzarello, "Enantiomeric
Excesses in Meteoritic Amino Acids," Science 275(February 14,
1997):951-955, p. 954
The creationist argument, that life could not arise spontaneously because
of the chirality problem, is beginning to look like a God of the Gaps argument.
glenn
Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm