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Science Daily is reporting on new research [abstract;full paper paywalled] by researchers at the University of Illinois at Urbana-Champaign. [Ed's Comment: A link to the Arxiv version of the paper.]
The researchers, Swanlund Professor of Physics Nigel Goldenfeld, graduate student Farshid Jafarpour, and postdoctoral researcher Tommaso Biancalani have made a breakthrough in one of the most central chemical quirks of life as we know it: homochirality, the uniform "handedness" of biological molecules.
From the artcle:
Life is quirky. Although the molecules that make up all living things obey physical and chemical laws, they do so with a puzzling twist. How did the distinctive molecular features of life emerge, and what can they tell us about life on Earth and elsewhere in the universe?
...
Many chemicals, organic or otherwise, are chiral; that is, if the structure of each was reflected in a mirror, its "looking-glass" copy could not be turned or flipped to match the original. Like a pair of gloves, the left-handed and right-handed versions of a chiral molecule are functionally equivalent, but their fundamental asymmetry makes them distinct.
Inorganic reactions produce and consume both versions of chiral molecules at equal rates. This is what makes the chirality of biological molecules, such as sugars produced by microbes and plants or the amino acids that make up proteins, so shocking. In every living thing on Earth, all amino acids are left-handed, and all sugars are right-handed. Goldenfeld highlighted the central mystery of this phenomenon.
"Imagine you've got a coin, and it's perfectly made, so it's not biased at all, and you start flipping the coin. Each time you flip it, it keeps coming up heads," he said. "So then you say, something must be operating that's causing this to happen . . . you get the same puzzle with these biological molecules, and that's the problem of homochirality."
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"There are other models, and they may be correct for the origin of homochirality on earth, if you can prove that those prerequisites existed during the emergence of life," said Jafarpour. "But whether those foundations exist or not, for life that emerged anywhere in the universe, you'd expect that it would have self-replication, and our model says that's enough to get homochirality."
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The work leads to a key conclusion: since homochirality depends only on the basic principles of life, it is expected to appear wherever life emerges, regardless of the surrounding conditions.
"For me, the most exciting thing is that this mechanism shows that homochirality is really a biosignature of life, a 100% signature, and should be expected anywhere life emerges," said Goldenfeld. "So for example, we just learned that there is a global ocean of liquid water under the ice of Enceladus ... I think that looking for homochirality in the organic molecules that have been detected there would be a fantastic way to look for life there."
Should this model be validated, it could be a big step forward in recognizing life in the universe -- even if it's not life "as we know it." Fascinating stuff!
(Score: 2) by Runaway1956 on Thursday October 22 2015, @02:34PM
So, we colonize a new world. On that world, the handedness is reversed. The flora and fauna are very much like that found on earth, it's just other handed. I don't suppose that would make it poisonous to us. Would we get the same nutrition from it?
(Score: 2, Informative) by Anonymous Coward on Thursday October 22 2015, @02:57PM
We couldn't use those reversed substances for our metabolism, so the nutritional value would be zero. BTW, I wouldn't bet on those wrong-chirality being harmless. See on this page [chirality.org] under "Chirality in life" on how different-handed substances can have very different effects.
(Score: 2) by Runaway1956 on Thursday October 22 2015, @03:41PM
Excellent, and I thank you, AC. I have read a few stories dealing with mankind's potential reactions to alien life forms. Sometimes the theories made less sense than other times. Thalidomyde sorta puts some of those ideas into perspective. I never realized that the problem had to do with mirror images of the more beneficial molecules.
(Score: 3, Insightful) by frojack on Thursday October 22 2015, @09:42PM
We couldn't use those reversed substances for our metabolism,
You say this with such conviction.
Yet its not necessarily so.
Chirality can be concentrated in a portion of a structure, while allowing normal gut bacteria to break down the rest of the molecular structure.
No, you are mistaken. I've always had this sig.
(Score: 2) by TrumpetPower! on Thursday October 22 2015, @03:00PM
Deliberately poisonous or not...your immune system will go absolutely haywire.
First, you'll be subjected to all sorts of small bits of chemically reactive alien life -- the alien equivalent of pollen spores and dandruff. You'll likely experience an insanely intense allergic reaction to all of that.
And then there'll be all sorts of alien life that'll just love to at least try to eat you and that will find various parts of your body very well suited to their life cycles...your lungs are moist and warm and dark, and there'll be alien equivalents of fungi that'll think they've died and gone to heaven...but your immune system won't have a clue that they're there or how to evict them.
Actual infectious agents aren't likely to be a problem; those are at least somewhat host-specific. But all the regular background stuff that grows on anything that doesn't try to kill it...will grow on you. Think moss and mushrooms and that sort of thing. Assuming you survive the allergic anaphylactic shock long enough to notice....
b&
All but God can prove this sentence true.
(Score: 0) by Anonymous Coward on Thursday October 22 2015, @03:22PM
You're contradicting yourself: Either the immune system will notice those wrong-handed substances as something to fight, then it will also notice and fight the fungi in your lung. Or it will not notice them, then you'll not get an allergic reaction on them.
(Score: 2) by TrumpetPower! on Thursday October 22 2015, @03:57PM
Different agents, different responses.
There will be harmless agents akin to terrestrial pollens that will trigger inordinate immune responses, just as they do here on Earth. But the immune system will find them even more confusingly alarming than ragweed or what-not simply because it hasn't had a chance to learn how to ignore such substances.
And there will be alien equivalents of athlete's foot that don't specifically target living organisms but just happen to like the sorts of environments that are found in human bodies. But, again, the immune system won't have evolved to recognize such threats or defenses against them. Indeed, it'll likely just cause another ineffective allergic reaction that doesn't actually do anything to repel the invader but does plenty to make the host miserable.
So I'm no more contradicting myself than I am when I observe that the same person can simultaneously be unsuccessfully fighting off valley fever and be suffering from hay fever.
b&
All but God can prove this sentence true.
(Score: 1) by WalksOnDirt on Thursday October 22 2015, @06:39PM
No, but you could get some. You should be able to use most of the sugars and carbohydrates. I think levulose and dextrose are equally fattening, for instance. You could even use some of the protein, but you'd be missing the essential amino acids. Most vitamins are chiral, so those would be missing. There would also likely be allergic reactions, as others have mentioned.
So you should be able to ingest enough calories, but in the long term you would suffer from malnourishment, and eventually die.