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Wed Nov 23, 2005 7:43 pm
recfreq wrote:This has zero chemical information in terms of mechanisms and structures. Are we even talking about the same chirality? Have you looked at what a chirality question usually involves?
What are you talking about? The question is clearly asking about situations where nature prefers one chirality over the other, and discussing some possible reasons why this might happen. I don't think there's anything confusing or misleading about it.
Wed Nov 23, 2005 7:57 pm
I'm sorry, but I have never heard chirality asked for it, and if you like current events science, perhaps it's good. Again, we're going back to what is canonical and what's not. This is not canonical.
Wed Nov 23, 2005 8:18 pm
[quote:7a29b4c6c3=\"solonqb\"]5) The European Space Agency’s Rosetta mission launched in 2003 was to search for this on Comet Wirtanen. Some of the leading theories as to why this phenomenon has come about have to do with the nuclear weak force, ranging from the effect of polarized electrons released by beta decay to the parity-violating energy difference that makes one “hand” more stable than the other, as its true mirror image is composed of antimatter. Alternate theories involves cosmic radiation or an analogue to the oscillation of the Belouzov-Zhabotinsky reaction caused by stirring-induced nucleation. Recently, however, simple mechanical grinding has been shown to yield what property, the fact that all natural amino acids polarize light in the same direction?[/quote:7a29b4c6c3]
1st of all, there\'s no l-chirality or d-chirality. There\'re l-enantiomers and d-enantiomers, which are chiral. Chirality is a property, it doesn\'t \"specify\" one of the two forms. I\'ve never heard of homo and hetero chirality, but may be it\'s just a confusing way to say something very plain.
Now, the question. I\'m sure a mission searching for chirality is all good, personally I\'d like to invite her out to dinner some time and cut her up with a sword. The nuclear weak force clue seem ok for a lead-in, but why you say \"hand\" in the same sentence is beyond me, as \"handedness\" is usually the giveaway on chirality. If that wasn\'t clear, let\'s just say \"mirror image\" in the very next phrase. Where\'re the chemistry clues? Then recently anything should not be in your FTP clue. But at least you told us what you were looking for at the end. Here\'s a chirality question from ACF for comparison (others like them can be found in the ACF archive):
\"Le Bel and van\'t Hoff took advantage of this property to help determine the tetrahedral structure of carbon compounds. It is critical in pharmacology as it explains why only some methyl-dopa and ibuprofen molecules are effective. It also occurs in simpler molecules such as 2-butanol. The S and R labels are applied to enantiomers, pairs of molecules that demonstrate this concept. FTP, identify this term that indicates the molecular version of left- and right- handedness.
Questions would be very good if you just look at an ACF equivalent before writing. You don\'t have to imitate everything, but your clues should be in that general spirit of mechanism, historical importance, and academically driven, instead of recent \"mechanical grinding.\" In general, these were the problems with those packets in Technophobia that I felt needed some work. For instance, the \"sonic hedgehog\" question identified Nusslein-Volhard in the 1st sentence then talks about a few development related vagueness. Where\'s the emphasis on ventral activity, and working with other factors like FGF and retinoic acid, and that it acts by creating a concentration gradient, and just the plain fact that it\'s a morphogen, the whole pt of asking it? There needs to be some chemistry clues with actual factors, names, specific molecules.
Matt, I can\'t believe you liked this question? You want to be told that a \"hand\" is more stable than its \"mirror image\" in the middle of the question? Peace.
Wed Nov 23, 2005 9:22 pm
recfreq wrote:Matt, I can't believe you liked this question? You want to be told that a "hand" is more stable than its "mirror image" in the middle of the question? Peace.
Don't put words in my mouth. I said nothing about whether it's a good question or not.
My point is that you are criticizing it as if it is a question asking for "chirality." It is not. It is a question asking for "homochirality." If your criticism is that this is too obscure a term to ask about, fine. (It's clearly not an obscure concept, but the term isn't something one often hears.) But that doesn't seem to be what you are saying.
Wed Nov 23, 2005 9:40 pm
Similarly, I never said it was "confusing or misleading." I'm glad we cleared this up. My point was that it wasn't very good. I also don't know what "homochirality" is, so may be you or someone else could enlighten us. But either way, the giveaway on this question implies that the answer is "chirality."
Wed Nov 23, 2005 9:48 pm
recfreq wrote:Similarly, I never said it was "confusing or misleading." I'm glad we cleared this up. My point was that it wasn't very good. I also don't know what "homochirality" is, so may be you or someone else could enlighten us. But either way, the giveaway on this question implies that the answer is "chirality."
I didn't think it was confusing, and yet you seemed confused. Hence my confusion.
Homochirality is the situation that for certain molecules, only one of the possible chiralities is found in nature. An example is provided by amino acids, of course. The origin of this asymmetry is still somewhat mysterious. The question describes a few possibilities. Of course at some level it has to be due to parity violation, but it's not clear whether it's due to the intrinsic parity violation of the weak interaction or due to spontaneous parity violation, that is, to some accident of initial conditions. Put another way, it's not clear (as far as I know) that there can't be some other part of the universe where one could find right-handed amino acids.
The giveaway to this question does not
imply that the answer is chirality. It implies it wants to know the term for the situation, as with amino acids, in which only one chirality exists. Thus, the giveaway is appropriate for the answer "homochirality."
This is why I said that I do not think the question is confusing. On the other hand, I don't think this is a very good topic for a tossup.
Wed Nov 23, 2005 10:08 pm
OK, so basically why only one enantiomer exists for, say, amino acids other than glycine, as opposed to the property. I guess that's why it said "this phenomenon." My bad.
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