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Physicists Find Clue as To Why the DNA Double Helix Twists To the Right
New submitter Annanag writes Most organic molecules have left- or right-handed versions, mirror images of each other, just like gloves. For some reason, life always seems to favor one version over the other — the DNA double helix in its standard form always twists like a right-handed screw, for example. But why this preference for left or right happens has always been a mystery. Now, in an experiment that took 13 years to perfect, physicists have found hints that this asymmetry of life could have been caused by electrons from nuclear decay in the early days of evolution.
Nowadays it seems like almost everything is twisting to the right...
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Just flip it, it twist to the left, isn't it?
When will they find out why certain part of male anatomy seems to be twisting to the left for majority of us?
Mutations happen randomly. A mutation occurs in Right-Version that's beneficial and so the right version becomes the dominant version, nothing to do with right or left, its simply the version that got the beneficial mutation.
So evolution would drive nature to choose left or right versions of every little enzyme, molecule and so on, simply because it grows from benefitial branches and they are either left or right but not an even mix of both.
They forgot a simpler and perhaps more prominent selective force for one enantiomer over another: average experienced twist on the earliest nucleic acid chains from ocean currents. It should be slightly one way, due to Coriolis forces. Did life start North or South of the equator?
... before there was life?
Because there is a right way
TFA mentioned several possible scenario - spin-polarized electrons, circularly polarized light that is produced by the scattering of light in the atmosphere and in neutron stars, and so on - which should have been taking place in similar fashion all throughout the universe
Would this mean that if there are lifeforms elsewhere in the universe, would their physiology (whether or not they have DNA) be similarly affected by the polarized action of electron and/or photon around them?
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Here's my understanding of the article: In organic chemistry- molecules often have asymmetric shape. Even though their chemical composition is same, their selection of "which bond" about the carbon atom causes "twisted" molecules. So there can exist isomers of compounds (like glucose has, and particularly called as anomer). You can imagine the twisted molecule as a fat roll of putty twisted. So, some parts of putty will be observable from outside (exposed) and some, not that exposed.
In most of the reactions, one reactant comes near the other reactant to give/ take electron. But to come near that electron rich area (called reaction site), you need that area to be exposed. If the area is not exposed, no reaction would happen there. However, if the reaction happens, and the site is not well exposed (hence less room to accommodate a big fat molecule of reactant, then the bond (if made) will be very weak. A slight collision with anything- (forget an electron) even 5 photons will cause the reaction to happen, and the molecule to dissociate. ( a similar reaction happens in our eyes when as less as 5 photons hit our eyes and supply the energy to one stereo-isomer (cis on 11th carbon to be exact) retinal to convert to all trans retinal) Here's a wiki link: http://en.wikipedia.org/wiki/R...
Because of this twisting in proteins (Also known as a primary structure of protein), reaction sites are created, but are obfuscated because of secondary, and tertiary structure (too many amino acid units (group of arranged atoms), and their repeated patterns make a protein). Now, whenever a stabler structure is to be made, they can happen in one stable shape in space. for the other isomer, it wouldn't be stable, because of weak bond and less room.
My understanding is, the slow moving electrons hit the molecules in one of the reaction sites too obscure for regular ones, and this imparted the energy. It's a similar thing like UV rays or very strong electromagnetic radiations do. In case of electrons, when they come, they bring charge, which may throw the poor molecule off balance, and cause breaking due to the imbalance in electrical forces.
If it bent to the left, that'd be a bit...sinister.
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It's due to the rotation of the earth, duh! Those down-under rotate the other way, but they are upside down also, so it compensates.
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It's the Coriolis effect. Duh.
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The article is rather dubious really.
There's an underlying assumption that the symmetry braking of the solution requires an asymmetry in the starting condition.
If you place a pencil upright it is very unstable and it will fall over. In what direction it will fall depends on the 'background noise' disturbances which can be completely symmetrical - on average.
So you have a completely symmetrical situation but the outcome will be completely asymmetrical: the pencil falls over in one direction. It is not an interesting question to investigate why exactly the pencil fell in this specific direction.
So what's the deal here, if our dna pencil comes out oriented one way? That electroweak parity breaking causes the pencil to fall over in one direction? That the chances of the pencil falling over in a specific direction are slightly enhanced but the outcome can still be anything - as with a single roll of a dice with 17 'left' faces and 15 'right' faces? Or that the effect will just be drowned by the background noise?
I think the latter.
It reminds me of the claims that the bathtub always drains with a rotation that depends on the hemisphere, while in fact the impact of the coriolis effect is completely negligeable..
It's because we're all descendent from Derek Zoolander.
There are now over half a dozen carbon-containing meteorites where a (small) excess of L-amino acids was found, and none where the opposite enantiomer was found to be in excess. Since these meteorites where never in contact with the earth's biosphere (the samples were of course not scraped from the surface), the chance of an evolution of isolated systems into a random chiral direction is already pretty slim.
when you change the direction from where you view it it changes direction to the left..... woa dude! Far out
Article:
The interaction of left-handed electrons with organic molecules is not the only potential explanation for the chiral asymmetry of life.. Meierhenrich favours an alternative â" the circularly polarized light that is produced by the scattering of light in the atmosphere and in neutron stars3. In 2011, Meierhenrich and colleages showed4 that such light could transfer its handedness to amino acids.
But even demonstrating how a common physical phenomenon would have favoured left-handed amino acids over right-handed ones would not tell us that this was how life evolved, adds Laurence Barron, a chemist at the University of Glasgow, UK. âoeThere are no clinchers. We may never know.â
The new work is interesting and important, but its primary significance is that it makes future work distinguishing the possible alternatives more challenging. It's also interesting because unlike the other two proposed mechanisms it is a result of the fundamental asymmetry in the weak force rather than an accidental boundary condition, so it implies that life everywhere is more likely than not to be right-handed, whereas the explanations involving magnetic fields will make a universe that's 50/50 right/left.
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That explains why in Star Trek all intelligent life can interbreed despite evolving separately for billions of years. ;)
Electrons are right handed and left brained.
Why "right-handed"? Shouldn't it be "clockwise"?
Twisting towards the right hand could be "over the top" (clockwise) or "around the bottom" (counterclockwise). Not to mention that unless you specify whether you're twisting down the strand towards or away from you (assuming the strands are pointed straight away from your body), means you end up with 4 ways to arrive at 2 possible orientations.
I suppose the scientific response is, "No, shut up; we just defined this confusing and nonstandard wording as X."
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Hopefully, somebody will read past all the political jokes to answer this. I understand why the physicists are hypothesizing as to why DNA twists to the right. My question is whether or not the right twist is required for life or could a left twisted DNA led to life? If DNA must twist right for life to exist, does that preclude life on many of the star systems that could support life because the same condition that led to our right twisting DNA was absent?
Okay, so if you look at it in the opposite direction, is it still to the right? Is there a standard starting point, like when we say the right side of a car, we're assuming the orientation is from the driver's point of view. Facing the vehicle from the front would reverse that.
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All life we know about came from a single origin since all life is based on DNA, RNA and proteins. whatever the origin was it would have had left or right handed DNA and thus so did everything that followed. there's no reason to suppose the need for a bias for one or the other. one of them was going to win. it's like vhs and betamax.
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As light passes by a sun it is subject to an asymmetric situation where the solar atmosphere is in a magnetice field closer to one pole than another, rotating and having a gradient both radially and with the azimuth. thus there's a strong symmetry breaking effect on this light. On average, for all light passing the sun it's an equal handed effect. But if your planet happens to be subject to light that cam from the left side of the sun versus the right, that light could have a net polarization.
this effect would likely be orders of magnitude greater than this weak force polarization effect.
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DNA is shown as a helix to make it more appealing to the eye.
The proles don't want to see "a mishmash of random looking scientifical crap".
Rendering DNA in the form of a double helix makes it purty and romantical and radio-friendly.
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It's also interesting because unlike the other two proposed mechanisms it is a result of the fundamental asymmetry in the weak force rather than an accidental boundary condition, so it implies that life everywhere is more likely than not to be right-handed, whereas the explanations involving magnetic fields will make a universe that's 50/50 right/left.
TFA goes too far with this idea; which I think is confusing the issue here. While the article focuses on DNA chirality, I think that is going too far up the chain of evolution.
There were most likely replicating molecules before DNA, and many of the building blocks for life were likely set long before DNA became the preferred genetic coding system.
What this study says, in the bigger picture, is that the chirality of many classes of molecules in early life may have been influenced by this mild bias in the weak nuclear force. What that would mean is that organisms using building blocks of the 'wrong' chirality were --over the long term-- more likely to become extinct than their peers using the same building blocks with a different chirality. Over a couple of billion years that selection pressure would weed out organisms using the 'wrong' chirality because those molecules are more likely to break when exposed to low energy beta-decay.
Now, whether this mechanism specifically influenced the chirality of DNA... there is probably no way to tell. This mechanism of chirality selection works up and down the entire evolutionary chain. And it doesn't just select for right or left... it selects the chirality that is least likely to break from this source of pressure.
We don't know that.
The magnitude of forces generated from this force is far below what is around in the environment from random motions.
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The general trope has been exercised in several SF short stories, if not longer ones. I don't know if that has happened in the Star Trek universe though (only having seen maybe 20% of the series).
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