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Homochiral fantasies and the design inference

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A post at PT (go here) claims that recent work supporting a naturalistic origin of single chiral forms for amino acids (as exist in extant organisms and presumably had to occur under prebiotic conditions) constitutes a false positive for the design inference. The post also cites a case of someone using my design inference apparatus to argue for design from homochirality, but I personally have never done so (to the best of my knowledge, you won’t find any mention of “chirality” in the papers on my designinference.com website). Even if this research were entirely successful at showing how to get high concentrations of single chiral forms (at this point the research merely shows a statistically significant bias), it would not challenge the design inference. The reason is that even though homochirality poses an obstacle to a materialistic account of chemical evolution, it’s easy to imagine a filtration mechanism leaving behind homochiral batches of amino acids. But the chirality problem pales in comparison to the problem of sequencing amino acids to form functional proteins. That’s where Steve Meyer and I have always focused our attention. Let the Thumbsmen at PT come up with a plausible mechanism for protein generation along with a detailed account for how this proposed mechanism could generate a modest sized 250-amino acid protein, and I’ll take notice. Until then, indulge your homochiral fantasies.

Wow... how fortuitous... I just read this article. I am not so convinced that this article 'solves' the problem of homochirality at all. While this is certainly not my area of expertise I do have some comments that I think are noteworthy. Firstly, ignoring the example of proline for the moment, when experiments were begun with a 100% enatiomeric excess (ee) of a five different AA's, S, L, A, V, and T, the best they were able to generate was an ee of 68%. I suppose that's not bad, but doesn't 'solve' the problem of homochirality. It is further noteworthy that 18 of the 20 biologically relevant AA's form 1:1 racemic mixtures naturally. The two that do form enantiopure conglomerates are R, and T. Curiously R wasn't investigated in this study, and T performed quite poorly in generation of ee; a 100% ee of T was only able to generate a product with 58% ee. When proline was present in ee, it was able to generate a product with 100% ee. However this is dependent on conditions that in reality don't mimic the prebiotic world. Firstly, is the issue of enantiopure proline... since proline forms a 1:1 racemic mixture naturally, what's the basis for starting with an enantiopure proline? It would appear that this is because it's capable of generating a 100% ee, not because there's any basis in reality for doing so. Additionally... these experiments relied on the solution being saturated with proline, ie: contained undissolved proline; typically this study employed proline concentrations of 100mM. They did report using concentrations as low as 30mM though. If I recall correctly... the prebiotic world isn't thought to have been a highly concentrated soup... and it is doubtful that the prebiotic world ever contained a saturating amount of an enantiopure AA. Finally... these reactions were all carried out in DMSO... apparently mostly dry DMSO was used, and some experiments were carried out in aqDMSO with 350mM water. As I mentioned this isn't my area of expertise, so I can't really comment on what effect DMSO will have on this chemistry, but we all know prebiotic oceans were not comprised of predominantly DMSO. So to summarize, under the most artificial conditions, conditions that don't mimic reality, that is a solution of DMSO saturated with enantiopure proline, a 100% excess of enantiopure product can be generated. However, when one considers reality... ie: AA's that actually form enantiopure conglomerates naturalistically, the results are not as encouraging. Enantiopure T, (one of the two AA's that form enantiopure conglomerates) demonstrated a poor ability to synthesize enantiopure compounds, in fact it was practically the worst performer... underdone only by S. While this paper may be interesting academically, and may have some practical value industrially, it's ability to answer the question of homochirality is dubious at best. mattison0922
This isn't a comment but I couldn't find a way to email the staff here, you may want to post this article from Pravda http://english.pravda.ru/science/earth/05-06-2006/81549-dinosaurs-0 mentok
...how much of a bias are we talking about here?
Oh, I think they are highly biased against ID. Well, I completed the Science Versus Intelligent Design book, and strangely enough none of the essays actually directly address anything written by Dembski, Behe, Meyer, etc. Mung
I don't have a membership with Nature so I have a question for anyone who does: how much of a bias are we talking about here? Patrick
I still think homochirality will remain a very significant problem for pre biotic chemistry. If we are to generate any protein from a mixture of Amino Acids, the contamination of the solution with any significant percentage of opposite chirality molecules will vastly decrease the chances of biologically useful protein or RNA formation. idnet.com.au

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