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A new capillary electrophoresis technique could be much more sensitive to the presence of amino acids on other worlds in our solar system:
A simple chemistry method could vastly enhance how scientists search for signs of life on other planets. The test uses a liquid-based technique known as capillary electrophoresis to separate a mixture of organic molecules into its components. It was designed specifically to analyze for amino acids, the structural building blocks of all life on Earth. The method is 10,000 times more sensitive than current methods employed by spacecraft like NASA's Mars Curiosity rover, according to a new study published in Analytical Chemistry [open, DOI: 10.1021/acs.analchem.6b04338] [DX]. The study was carried out by researchers from NASA's Jet Propulsion Laboratory, Pasadena, California.
One of the key advantages of the authors' new way of using capillary electrophoresis is that the process is relatively simple and easy to automate for liquid samples expected on ocean world missions: it involves combining a liquid sample with a liquid reagent, followed by chemical analysis under conditions determined by the team. By shining a laser across the mixture -- a process known as laser-induced fluorescence detection -- specific molecules can be observed moving at different speeds. They get separated based on how quickly they respond to electric fields. While capillary electrophoresis has been around since the early 1980s, this is the first time it has been tailored specifically to detect extraterrestrial life on an ocean world, said lead author Jessica Creamer, a postdoctoral scholar at JPL.
Now we just need a robotic craft capable of drilling a hole through kilometers of crust in order to reach one of the possible subsurface water oceans on Ceres, Ganymede, Callisto, Europa, Enceladus, Titan, Dione, Titania, Oberon, Triton, Pluto, Eris, etc.
(Score: 3, Informative) by Immerman on Sunday January 29 2017, @04:58PM
I mean it's great that we can detect them more effectively, as they're certainly going to be present if life (as we know it) exists there.
But amino acids occur naturally through many different non-biological processes, that's why they're the building blocks of life - they were already there in massive quantities to be randomly mashed up until they formed early self-replicating proto-life structures and evolution could take over.
Still, it's a big step forward. Now, if we can also detect whether the chirality ("handedness") of the amino acids is biased in one direction, *then* we'd have a likely candidate for a life (as we know it) detector, as we have reason to believe that while non-biological processes will produce even amounts of left- and right-handed amino acids, biology will strongly prefer one or the other depending on which non-interchangeable version the dominant protolife happened to be based on.
(Score: 2) by butthurt on Sunday January 29 2017, @05:17PM
That is what we see on Earth, but it's conceivable (by me, anyway) that extraterrestrial life could make use of both enantiomers of a substance, or of various substances.
(Score: 2) by Immerman on Sunday January 29 2017, @11:55PM
Conceivable? Certainly. Likely? Not so much. Consider:
It is very unlikely that *any* viable protolife will spontaneously form, it's only through the application of large quantities of time and opportunities that it occurs at all. And at that initial point, it's extremely unlikely to be useful to employ both chiralities of all the molecules - you double the number of amino acids necessary for replication, as well as radically increasing the complexity of a cobbled-together, just barely capable of self-replication macromolecule, but are unlikely to get any functional advantage for doing so since the properties of left- and right-handed molecules are basically identical mirror-images of each other. And, even if by some miracle it happens to start that way, all it takes is some mutant sheding a redundant amino acid, with no loss of functionality, and it can now out-compete the original design.
And keep in mind as well that they would have to use both handednesses of *all* incorporated amino acids to avoid generating telltale chiral imbalances in the environment. Even if they happened to incorporate both for some molecules, it's very unlikely that they would do so for all of them. Especially considering that all the molecular mechanisms designed to work with a left-handed molecule will almost certainly be useless for working with the right-handed variant.
(Score: 3, Interesting) by butthurt on Monday January 30 2017, @03:40AM
It is very unlikely that *any* viable protolife will spontaneously form, it's only through the application of large quantities of time and opportunities that it occurs at all.
I agree. And all the living things we see on Earth—viruses too—appear to have a common ancestor. We should hesitate when generalising from what we see on Earth, some of which is likely to reflect the peculiarities of that ancestor.
> [...] at that initial point, it's extremely unlikely to be useful to employ both chiralities of all the molecules [...]
I wrote "make use of both enantiomers of a substance, or of various substances," not necessarily all of them. Not all molecules have chirality. You had written:
But amino acids occur naturally through many different non-biological processes [...] non-biological processes will produce even amounts of left- and right-handed amino acids [...]
This is true. So when life first appears, whatever molecules are present can be expected to be available in both forms. If, when life first appears, it can make use of both forms, that could be advantageous for it, for the obvious reason that it would have twice as much material available for its purposes. If heterotrophs appear later which consume those initial forms, the heterotrophs would also be at an advantage if they could make use of all the molecules in the living things they eat—which in this scenario would include both left- and right-handed molecules. That could mean having two enzymes of complementary handedness, or one enzyme with two reaction sites of complementary handedness—perhaps a symmetrical molecule such as I described above. The extra cost of creating such an enzyme or enzyme, compared to having one that can only handle molecules of a particular handedness, would be offset by the extra nourishment the heterotroph would gain.
> [...] the properties of left- and right-handed molecules are basically identical mirror-images of each other [...]
I would express it as: the properties are the same, except that the shapes are mirror images. I think you understand. You don't see how that could be useful? Look at your hands--they are mirror images of each other. Would they be equally useful if they were identical in shape? On a molecular scale, structures with two symmetrical ends can be useful. For example, bidentate ligands:
https://www.chem.purdue.edu/gchelp/cchem/bis.html [purdue.edu]
The possibility of using two enantiomers to form such structures seems obvious to me.
https://en.wikipedia.org/wiki/Enantiomers [wikipedia.org]
Examples of biological ligands are heme and chlorophyll.
https://en.wikipedia.org/wiki/Chlorophyll [wikipedia.org]
https://en.wikipedia.org/wiki/Heme [wikipedia.org]
Note the parts of their structures that attach to the central metal ions: in both instances there's a four-way symmetry.
Ligands can act as catalysts; biological catalysts are termed enzymes. An enzyme with a symmetrical reaction site would have obvious usefulness for catalysing reactions of symmetrical molecules—water, carbon dioxide, acetone, glycerol, etc. The examples I've given are of importance to terrestrial life.
https://en.wikipedia.org/wiki/Acetone [wikipedia.org]
https://en.wikipedia.org/wiki/Glycerol [wikipedia.org]
Incorporating molecules of opposite handedness would, as I've tried to explain, lend itself to the construction of such enzymes.
And, even if by some miracle it happens to start that way, all it takes is some mutant shed[d]ing a redundant amino acid, with no loss of functionality, and it can now out-compete the original design.
I wrote about alien life using both forms of a molecule, so there would indeed be a loss of functionality.
And keep in mind as well that they would have to use both handednesses of *all* incorporated amino acids to avoid generating telltale chiral imbalances in the environment.
Why? The word "telltale" seems to hint that detection by interplanetary explorers would result, yet I doubt you're suggesting that we've sent polarimeters to all the places where extraterrestrial life could hide and it cunningly remained hidden by being non-stereospecific. I assume you don't mean that, but I don't know what you do mean.
(Score: 2) by Immerman on Monday January 30 2017, @06:18PM
I agree we should hesitate about generalising, but you seem to be skipping several steps in your own conjecture - chlorophyll, heme, etc. are extremely sophisticated molecules that didn't emerge until hundreds of millions of years after life had clearly "crossed the line" into something beyond chemistry and developed into extremely large, sophisticated things like bacteria that had dominated the planet. For a well-developed organism, having mirror-image components may indeed provide some advantage - but protolife is unlikely to be even remotely that sophisticated - after all it's initially going to be a cobbled-together mish-mash of molecules that just barely stumbled into the capacity for self-replication. And by the time it evolves into something well-organized enough that we might call it life, it will have likely transformed the chemical environment into something closely reflecting it's own biases.
In fact, I seem to recall some mathematical modeling results posted here and/or on the green site a while back that suggested that even assuming you had different protolife based on both chiralities, one or the other would tend to dominate as once random "noise" pushed one chirality into a slight dominance, the resulting imbalance in available amino acid distributions would tend to rapidly snowball and starve out chemistry based on the opposing one.
Of course that doesn't apply if the same proto-organism uses both chiralities, but in the early stages, when the ecosystem is flooded with both chiralities of free amino acids, it seems unlikely that being able to utilize both would provide a significant advantage. In fact, even as resources became more scarce, it would still likely be a disadvantage - we're talking about pseudo-organisms that are likely still millions of years away from being able to synthesize their own chemistry - we're not talking about being able to "eat" twice as many things, we're talking about requiring twice as many basic components to be able to duplicate yourself.
And just to be completely clear - I would freely concede that some protoorganism *might* find a use for using some amino acid in an opposing pair of chiralities - but that's largely irrelevant to my argument. To avoid creating a chiral imbalance in the environment, it would have to use *EVERY* amino acid in its makeup in equal quantities. If even one amino acid were used in only one chirality, then the ecosystem would rapidly reflect that imbalance.
About the only way I could see to avoid creating an imbalance is if some protoorganism were capable of replicating both left- and right-handed versions of itself based on available resources. That would likely require something FAR more sophisticated than just making identical replicas though, and even then it's not clear that random biases wouldn't trigger a biased snowball effect. Perhaps though if left-handed chemistries could only create right-handed replicas, and vice-versa...
(Score: 2) by butthurt on Monday January 30 2017, @09:21PM
[...] you seem to be skipping several steps in your own conjecture - chlorophyll, heme, etc. are extremely sophisticated molecules [...]
They're just the examples that came to mind of biological molecules that have symmetry.
[...] we're talking about pseudo-organisms that are likely still millions of years away from being able to synthesize their own chemistry [...]
I was talking about alien life of any sort, not necessarily very simple forms.
And just to be completely clear - I would freely concede that some protoorganism *might* find a use for using some amino acid in an opposing pair of chiralities [...]
That's all I was saying (although I wanted to include other chiral molecules besides amino acids). I was unaware that life on Earth, including mammals, does use D-amino acids.
https://en.wikipedia.org/wiki/D-amino_acid [wikipedia.org]
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC18334/ [nih.gov]
To avoid creating a chiral imbalance in the environment, it would have to use *EVERY* amino acid in its makeup in equal quantities. If even one amino acid were used in only one chirality, then the ecosystem would rapidly reflect that imbalance.
I'm not entirely following you. You seem to be supposing life-forms that can interconvert amino acids, but which are unable to change the handedness of those amino acids. However, we can instead suppose that such interconversions could proceed through glycine, which lacks chirality.
https://en.wikipedia.org/wiki/Glycine [wikipedia.org]
There have been a couple of occasions on Earth that come to mind when one organism produced molecules that other organisms were unable to metabolise. When plants began to produce oxygen, the atmosphere became oxidising; eventually life-forms arose that tolerated, and even depended upon, the oxygen. When plants began to produce lignin, at first deposits of the stuff formed (coal), then the deposition lessened because organisms developed the ability to break the lignin down. Similar events might happen on other worlds. Even if they didn't, organic molecules can be degraded into simpler molecules not only by living things, but by light or oxidation.
(Score: 2) by Immerman on Wednesday February 01 2017, @12:40AM
All I'm assuming is you've got a crude self-replicating amino-acd based molecular automata which almost certainly had no ability to synthesize anything, but only to assemble existing environmental components into copies of itself. I am decidedly NOT considering life, as by the time you have that the available chemical ecosystem will have already been completely reworked by a few (hundred?) million years of molecular automata spreading across the planet.
I will concede that after life is established and controlled bio-chemical synthesis has begun, then yes, perhaps it could evolve the ability to use and synthesize the now near-absent alternate chiralities of its component amino acids - it just seems exceedingly unlikely as either one would likely require dramatic mutation, and be useless if not fatal without the other.
(Score: 2) by VLM on Sunday January 29 2017, @05:56PM
amino acids occur naturally through many different non-biological processes
Thats why its no lose. Say the ratio detected is qty 1:2:3:4:5:6:7 then you can generate theories about the peculiar non-life conditions resulting in that ratio, which is interesting. Or you end up with a paradox that can't be solved without life or life is the simplest explanation. Of course it'll be partial each not binary one or the other (probably).
Anyway in summary even if its used to prove theres absolutely no life, then whatever ratio is detected will still imply something interesting.
How the chirality separation works in CE is giant chiral glucose (or whatever) molecules get mixed in and that can be detected... nothing is every really new in chemistry or anything and I remember 20 years ago doing quant analysis using EDTA where EDTA is a big ole giant molecule that kinda wraps around metal ions in a highly predictable manner, this CE technique is similar in concept in that you're adding something to F with the molecules depending on chirality instead of being metal ions, whatever..
(Score: 2) by Immerman on Sunday January 29 2017, @11:38PM
Ratios of what, exactly? Different amino acids? I would think that, given the wide range of different processes that can create them, you'd be hard pressed to come up with *any* ratio of different kinds of amino acids that wouldn't have a plausible non-biological explanation.
I hadn't realized CE could be used for chiral separation, but Google confirms it. thanks for that tidbit.
And just for the sake of completeness, amino acid detection can't possibly be used to prove there's no life - just that there's no amino-acid based life.
(Score: 2) by VLM on Monday January 30 2017, @01:10PM
wouldn't have a plausible non-biological explanation.
Ah OK there is also the more opposite approach, whatever-ium is unstable at pH 8 and higher and 115C and higher so the presence of whatever-ium proves the local environment has not spent much time above pH 8 and 115C and somethingelseium being unstable above 100C with evidence that it was there but 90% of it being decayed away would imply temps spent some time between 100C and 115C.
It'll be fun data to theorize over.