'Breakthrough' Could Explain Why Life Molecules Are Left- Or Right-Handed (science.org) 45
Researchers have proposed a new explanation for the origin of biological handedness or "homochirality," reports Science Magazine. "In three new papers, researchers suggest magnetic minerals common on early Earth could have caused key biomolecules to accumulate on their surface in just one mirror image form, setting off a positive feedback that continued to favor the same form." From the report: Chemical reactions are typically unbiased, yielding equal amounts of right- and left-handed molecules. But life requires selectivity: Only right-handed DNA, for example, has the correct twist to interact properly with other chiral molecules. To get life, "you've got to break the mirror, or you can't pull it off," says Gerald Joyce, an origin of life chemist and president of the Salk Institute for Biological Studies. Over the past century, researchers have proposed various mechanisms for skewing the first biomolecules, including cosmic rays and polarized light. Both can cause an initial bias favoring either right- or left-handed molecules, but they don't directly explain how this initial bias was amplified to create the large reservoirs of chiral molecules likely needed to make the first cells. An explanation that creates an initial bias is a good start, but "not sufficient," says Dimitar Sasselov, a physicist at Harvard University and a leader of the new work.
[...] Now, Sasselov and his colleagues have put these two pieces together. They wondered whether magnetic surfaces might favor a single RAO chiral form. To find out, they turned to magnetite, a magnetic mineral that is common in Earth's crust. They applied a strong external magnetic field, aligning electron spins in the magnetite and strengthening its magnetism. When they exposed the magnetite surface to a solution containing an equal mix of right- and left-handed RAO molecules, 60% of those that settled on top were of a single handedness. This created a crystalline seed that caused additional like-handed RAOs to bind, eventually forming pure single-handed RAO crystals, the researchers reported last week in Science Advances. When they flipped the field's orientation and repeated the experiment, crystals with the opposite handedness took shape. [...]
In a report accepted last week in The Journal of Chemical Physics they show that once an excess of chiral RNA is formed, known chemical reactions could pass on this chiral bias, templating amino acids and proteins with the opposite handedness and ultimately fostering other chiral molecules essential to cell metabolism. The quest that began with Pasteur isn't quite over, though. One loose end, Sasselov acknowledges, is that RAO has only been shown to lead to the synthesis of two of RNA's four nucleotides, cytosine and uracil. It isn't known to produce the other two, adenine and guanine, although Sasselov says there's a "big push" to search for RAO reactions that could do it. If they can, the mystery of biological handedness might be another step closer to being solved.
[...] Now, Sasselov and his colleagues have put these two pieces together. They wondered whether magnetic surfaces might favor a single RAO chiral form. To find out, they turned to magnetite, a magnetic mineral that is common in Earth's crust. They applied a strong external magnetic field, aligning electron spins in the magnetite and strengthening its magnetism. When they exposed the magnetite surface to a solution containing an equal mix of right- and left-handed RAO molecules, 60% of those that settled on top were of a single handedness. This created a crystalline seed that caused additional like-handed RAOs to bind, eventually forming pure single-handed RAO crystals, the researchers reported last week in Science Advances. When they flipped the field's orientation and repeated the experiment, crystals with the opposite handedness took shape. [...]
In a report accepted last week in The Journal of Chemical Physics they show that once an excess of chiral RNA is formed, known chemical reactions could pass on this chiral bias, templating amino acids and proteins with the opposite handedness and ultimately fostering other chiral molecules essential to cell metabolism. The quest that began with Pasteur isn't quite over, though. One loose end, Sasselov acknowledges, is that RAO has only been shown to lead to the synthesis of two of RNA's four nucleotides, cytosine and uracil. It isn't known to produce the other two, adenine and guanine, although Sasselov says there's a "big push" to search for RAO reactions that could do it. If they can, the mystery of biological handedness might be another step closer to being solved.
Easiest explanation (Score:1)
God is left handed so it's easier for him to design and create right handed molecules. Think about it, Michelango was right-handed so he sculpted David with his face turning left. It's also why right-handed Rodin sculpted The Thinker to be contemplating with his face turned leftward. Jeff Koons is left-handed so his Rabbit sculptures are always slightly right facing.
Re:Easiest explanation (Score:5, Funny)
God is sinister? That may explain a great deal.
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I'm left handed. You may be right.
RAO is "ribo-aminooxazoline" (Score:5, Informative)
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-1, performative
The article does write out in long form what RAO stands for on first use, in the sixth paragraph: "They were intrigued by a molecule called ribo-aminooxazoline (RAO), which they discovered could react to form two of RNA’s nucleotide building blocks." You are correcting an error that does not exist.
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I was referring to the summary and BeauHD's poor editing.
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That it could have gone either way is NOT the point.
After that it's self reinforcing.
The actual point is that the mechanisms in prior hypotheses was not self-reinforcing ENOUGH. Other hypotheses didn't produce enough and/or as strong and persistent a preference for anyone to dominate.
Learn to read the whole summary, dipshit.
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They're only ASSUMING
It's not an assumption. It's an open question. Yet another example of Slashdot's armchair experts that are against actual science - like asking questions to things that you think are already answered.
It's not a necessary assumption.
Irrelevant. They're proposing a mechanism that gives a greater bias towards any particular outcome. Whether or not that's necessary is beside the point.
Learn what a hypothesis is, dipshit.
This is what I said:
the mechanisms in prior hypotheses
Learn to read properly, you illiterate anonymous coward cunt.
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You're missing why only right-handed molecules are useful. It's not something inherent, it's environmental.
I know nothing about this (Score:5, Interesting)
RAO has only been shown to lead to the synthesis of two of RNA's four nucleotides, cytosine and uracil. It isn't known to produce the other two, adenine and guanine
If magnetism helps to synthesize the first two nucleotides, maybe electricity helps with at least one of the other two. Perhaps a climactic event like a lightning strike, or a drawn-out process initiated by an acid or a base contacting an ore rich in two dissimilar metals to create an electric current, might be responsible.
To be clear, I know next to nothing about biochemistry, and if these are possibilities I'm sure they've been explored. But I've learned not to censor myself when it comes to brainstorming - I have no problem with looking stupid or misinformed if there's even a small chance that it could lead to something worthwhile.
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Or if the thesis is true,should we see left-handed DNA dominant in about 300K years.
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Where do these magnetic materials get their magnetism from? The only place I can think of is the earth's magnetic field, which flips direction [nasa.gov] irregularly every 300K years. Wouldn't the tendency for left-handedness and right-handedness cancel each other out over the billions of years that this planet has existed?
The only thing I can think of is that some ferrous mineral deposits may have a combination of coercivity and hysteresis such that once the Earth's magnetic field magnetizes them they resist the de-magnetizing effect of pole reversal. Another thing occurs to me though. Perhaps a lightning strike passing through sufficiently conductive earth would develop an electromagnetic field which would strongly magnetize a deposit of, say, magnetite. That would have greater resistance to changes in Earth's magnetic fiel
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Where do these magnetic materials get their magnetism from? The only place I can think of is the earth's magnetic field, which flips direction [nasa.gov] irregularly every 300K years. Wouldn't the tendency for left-handedness and right-handedness cancel each other out over the billions of years that this planet has existed?
The direction of the Earth's magnetic poles does not create "left" or "right" handed magnetism. Either direction magnetizes stuff exactly the same. It is the same as simply turning a magnet around.
The preference of one chirality on magnetite presumably ultimately is due to the inherent parity of the Electro-Weak force, which is not symmetric.
And the large body of research on this topic emphasizes that once a predominant chirality is present many other processes act to reinforce it.
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It's not so sophisticated. One enantiomer is very weakly attracted to a surface with a particular magnetization while the other is repelled, so a seed crystal tends to start with a particular chirality. RAO is somewhat unusual in that it only forms crystals with uniform chirality, so once you've got a seed started, the crystal goes down that path.
It's a mechanism to produce concentrations with a particular chirality.
Don't care (Score:2)
Give us L-sugars and other no-calorie foods that pass our digestive system as is and enable us to eat as much as we want, as the degenerates we are.
Re:Don't care (Score:4, Informative)
Give us L-sugars and other no-calorie foods that pass our digestive system as is and enable us to eat as much as we want, as the degenerates we are.
People already tried that. [wikipedia.org] In short, it's expensive as hell, and offers no advantages over other artificial sweeteners.
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Give us L-sugars and other no-calorie foods that pass our digestive system as is and enable us to eat as much as we want, as the degenerates we are.
People already tried that. [wikipedia.org] In short, it's expensive as hell, and offers no advantages over other artificial sweeteners.
From your source: l-Glucose is indistinguishable in taste from d-glucose
I'd say that's a considerable advantage (I hate the taste of other artificial sweeteners)!
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Well, if it's worth it to you, you can just order some off the Internet. It costs about $100/g.
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It turns out that glucose doesn't actually taste that sweet. [researchgate.net] Diabetics eating glucose tabs aren't enjoying it as much as you would think.
Most of the sugars we consume are disaccharides, meaning two sugars bound together. Sucrose is the table sugar variety, with a fructose and a glucose bound together, or lactose - milk sugar - with a galactose and glucose bound together.
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>In short, it's expensive as hell, and offers no advantages over other artificial sweeteners
It has a huge advantage over artificial sweeteners- the taste is identical.
The "expensive" part is the only reason it isn't used. That and the fact that in large quantities it seems to be a laxative, but it's not the only stupid thing like that.
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"The "expensive" part is the only reason it isn't used."
So it's reserved for people who have coconut-water coming out of all their taps.
Heard this Before! (Score:5, Interesting)
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Agreed. It seems like life requires positive feedback. The first life probably didn't require a very biased handedness of the surrounding chemicals - it caused an imbalance by having a chiral mechanism that made more of its own chirality.
I've also heard some folks say that the weak force in physics, being the only one that doesn't exhibit P symmetry, must have been involved. Give me a break - a handedness-breaking mechanism is neither necessary nor sufficient to jump start life.
So monopoles then? (Score:2)
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At the end of the day, both D and L chemistries work... as long as all of the chiral molecules involved are the same orientation. It is the racemic mixture of both D and L that poses the biggest theoretical hurdle to life's formation under the primordial conditions (or at least that is my understanding). Which one comes out on top in any biosystem is ultimately down to random chance. However, before that chance can occur
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I'm not sure that's quite right. ISTM that a rock embedded in the mud is likely to have one end nearer the surface than the other, and the orientation of the magnetic field could well determine which end was on top. You *would* see the opposite effect on the other side of the equator, of course, and there would be a question of which got started first, but it's not clear that it would really be chance...exactly. The ocean would likely be deeper an colder on one side than the other, which would give one s
Hey! (Score:2)
Alien life (Score:2)
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Aren't Archeobacteria left-chirality ?
This is not a meaningful statement. DNA/RNA are d-chiral in all life, while amino acids and proteins are l-chiral, in archaea also.
There is a minor archaea anomaly in the case of the chirality of the glycerol linkage between the phospholipid head and the side chain in the cell wall membrane - a single specialized situation, which is l-isometric in archaea, but d-isometric everywhere else.
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What would happen if we met and interacted with beings that had opposite chirality but similar molecules?
They might consider us low-calorie food.
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Welll....I'm not sure. The proteins would probably be indigestible, but I think the fats and carbohydrates are generally non-chiral.
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but I think the fats and carbohydrates are generally non-chiral.
I read about L-glucose as a low-kj sweetener. A left-handed isomer of glucose.
Is that a separate thing from chirality?
https://en.wikipedia.org/wiki/... [wikipedia.org]
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No...but we can digest both dextrose and levulose. So, yeah, they're chiral, but they aren't exclusive. OTOH, I've got no idea about L-glucose. My expectation is that it might digest more slowly or something, but not that it wouldn't digest. Still, it's a good point that SOME carbohydrates are chiral. Looking it up, even a simple thing like fructose has 3 chiral centers. Whether there's any distinction in how they are digested I couldn't find in a quick search, so my GUESS is that it doesn't make any
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You wouldn't know unless you ate them.
You might experience anal oily discharge: https://www.cracked.com/articl... [cracked.com]
The bacteria wouldn't be able to infect you.