Originally posted by ChaseNelson Rufus and Jerry,
Jerry, I cannot find lucaspa's quote on that thread, perhaps I'm just not looking hard enough. Could you provide the reference?
LOL!! The reference is the abstract of the Joyce article you referenced!! Which tells me that you didn't really read the article, but instead read a creationist misquote from it.
Nature 2002 Jul 11;418(6894):214-21
The antiquity of RNA-based evolution.
Joyce GF.
Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
gjoyce@scripps.edu
All life that is known to exist on Earth today and all life for which there is evidence in the geological record seems to be of the same form--one based on DNA genomes and protein enzymes. Yet there are strong reasons to conclude that DNA- and protein-based life was preceded by a simpler life form based primarily on RNA. This earlier era is referred to as the 'RNA world', during which the genetic information resided in the sequence of RNA molecules and the phenotype derived from the catalytic properties of RNA.
See? Sorry, Chase, busted!
"My question, and maybe you can help answer it, is this: is it possibly a mechanism in the process of catalysis used by the first self-replicators that is responsible for the selection of L-chiral amino acids in organics of biological origin?"
Nature 2001 Feb 15;409(6822):797-801
Comment in:
Nature. 2001 Feb 15;409(6822):777-8.
A chiroselective peptide replicator.
Saghatelian A, Yokobayashi Y, Soltani K, Ghadiri MR.
Department of Chemistry, and Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
The origin of homochirality in living systems is often attributed to the generation of enantiomeric differences in a pool of chiral prebiotic molecules, but none of the possible physiochemical processes considered can produce the significant imbalance required if homochiral biopolymers are to result from simple coupling of suitable precursor molecules. This implies a central role either for additional processes that can selectively amplify an initially minute enantiomeric difference in the starting material, or for a nonenzymatic process by which biopolymers undergo chiroselective molecular replication. Given that molecular self-replication and the capacity for selection are necessary conditions for the emergence of life, chiroselective replication of biopolymers seems a particularly attractive process for explaining homochirality in nature. Here we report that a 32-residue peptide replicator, designed according to our earlier principles, is capable of efficiently amplifying homochiral products from a racemic mixture of peptide fragments through a chiroselective autocatalytic cycle. The chiroselective amplification process discriminates between structures possessing even single stereochemical mutations within otherwise homochiral sequences. Moreover, the system exhibits a dynamic stereochemical 'editing' function; in contrast to the previously observed error correction, it makes use of heterochiral sequences that arise through uncatalysed background reactions to catalyse the production of the homochiral product. These results support the idea that self-replicating polypeptides could have played a key role in the origin of homochirality on Earth
And
FASEB J 1998 Apr;12(6):503-507
RNA-directed amino acid homochirality.
Martyn Bailey J
Department of Biochemistry and Molecular Biology, The George Washington
University School of Medicine and Health Sciences, Washington, DC 20037, USA.
The phenomenon of L-amino acid homochirality was analyzed on the basis that
protein synthesis evolved in an environment in which ribose nucleic acids
preceded proteins, so that selection of L-amino acids may have arisen as a
consequence of the properties of the RNA molecule. Aminoacylation of RNA is the
primary mechanism for selection of amino acids for protein synthesis, and
models of this reaction with both D- and L-amino acids have been constructed.
It was confirmed, as observed by others, that the aminoacylation of RNA by
amino acids in free solution is not predictably stereoselective. However, when
the RNA molecule is constrained on a surface (mimicking prebiotic surface
monolayers), it becomes automatically selective for the L-enantiomers.
Conversely, L-ribose RNA would have been selective for the D-isomers. Only the
2' aminoacylation of surface-bound RNA would have been stereoselective. This
finding may explain the origin of the redundant 2' aminoacylation still
undergone by a majority of today's amino acids before conversion to the 3'
species required for protein synthesis. It is concluded that L-amino acid
homochirality was predetermined by the prior evolution of D-ribose RNA and
probably was chirally directed by the orientation of early RNA molecules in
surface monolayers.