Chiral Key Found to Origin of Life | Hacker News Reader

Chiral Key Found to Origin of Life

quantamagazine.org

84 pointssoftdev1224 comments

> In addition, radioactive decays produce electrons that are slightly more likely to be left-handed.

Is this a mistake in the article? I was under the impression that all electrons are fundamentally identical to one another.

The handedness of an electron refers to the orientation of its spin relative to its direction of motion. The electrons are all the same but the state they are emitted into is different.

The weak nuclear force breaks chiral symmetry, so in beta decays--which are governed by the weak force--you tend to get neutrinos with their spin aligned with their direction of motion and electrons with their spin anti-aligned with their direction of motion, where "aligned" means if your right thumb is pointed in the direction of motion, the curling of your fingers gives the sense of rotation associated with the spin and "anti-aligned" is the same except that it's your left thumb pointing along the direction of motion.

In a system with strict chiral symmetry the two spins would always be opposed (which is required because angular momentum is conserved) but there would be no preference relative to each particle's direction of motion.

> They unleashed a pool of random right-handed RNA molecules and let them react in a test tube with left-handed building blocks. They hoped that within that random pool of RNA molecules was a ribozyme capable of stringing the building blocks together.

Can someone explain the mechanism behind the origin of that ribozyme from original RNA molecules?

The mechanism is chance. As I understand the article these are selection experiments which you can think of as fast evolution in a laboratory setting. I tried to find a good reference for you but this was the best I could find [1]. Essentially they start with a large randomized pool of RNA molecules. They are then able to select out the catalytic RNAs through some process possibly involving a column. At first the number of RNA molecules that exhibit catalytic behavior is infinitesimal. But through PCR they are able to iteratively amplify each generation for the qualities they are looking for, in this case catalytic behavior. At the end of a few generations you have a pool of RNA molecules that exhibit the behavior you want.

[1] http://www.lcg.unam.mx/frontiers/files/frontiers/Tuerk%20and...

Such a subtle property has such a large impact. One thing that has stuck with me since undergraduate chemistry is that if you take the aspirin molecule and flip its chirality what you end up with is toxic and nothing like aspirin! I miss organic chemistry.

Ummm.... aspirin has no chirality. Salicylic acid is planar and the acetyl group can freely rotate.

The best example of chirality and toxicity is thalidomide. One isomer has low toxicity and the other causes horrible birth defects. Unfortunately the two isomers can interconvert so it isn't possible to create a pure sample of just one of them.

"it isn't possible to create a pure sample of just one of them."

Oh, to create a pure sample is a trivial task. But unfortunately it racemizes in your body.

It is actually a very interesting compound. Would not be surprised about a come-back.

Sorry, poor wording on my part. You are correct. You can create a pure sample, but it doesn't stay pure in your body.

You do realise that what you have written makes no sense. How could it be possible to determine that one isomer has low toxicity unless it is possible to separate them?

I am not 100% up to date in this area, but the last time I looked into the isomer theory of thalidomide toxicity it was not well supported by the experimental evidence.

Likely the title of the article changed, and the title here should change with it, as it's pretty bad. The new title of the article is "New Twist Found in the Story of Life's Start"

That's a cute title if you're already definitely going to read it, but to me, deciding whether to skip it like all the others, it's important to know that chirality specifically is the topic.

Can someone explain the intended meaning of the "handshake" in the photo accompanying the article?

It is intended to demonstrate chiralty (aka handedness). Notice the mirror in the background that reverses the handedness of the handshake.

Chirality is where two otherwise identical molecules can't be superimposed when you rotate them in space. They are mirror images of each other. The best way to imagine such an arrangement is to think of your hands.

I have a silly question: how is it determined which side is up and down?

The direction of light, from the perspective of the viewer, is the base. Its not about up and down, but rather left or right ..

It's still a completely arbitrary mapping.

Well actually, I suspect that it isn't arbitrary at all: historically, people have considered left-handed as deviant, strange, sinister, so obviously the good molecules are right-handed.

(Disclaimer: I'm a slightly bitter left-handed designer who has seen one too many "more intuitive" designs that are optimised for right-handedpeople)

The "left" or "right" refer to the direction that the chemical (usually in solution) rotates the plane of polarized light passing through it, from the point of view of an observer that the light is traveling towards.

An experimental setup to demonstrate this is a light source, a linear polarizer oriented in some direction (say along the x-axis for definiteness), followed by the sample container, followed by another linear polarizer, followed by a detector.

With nothing in the sample container, the second polarizer is rotated around the light beam axis until no light passes through. This will be very close to a right angle with the first one (try it with polarizing sunglasses :) ). The sample is then added, and the change in angle of the second polarizer required to again allow no light through is observed.

Also, try reading the article. Naturally-produced RNA, etc are all left-handed. :)

I don't follow your question. A right-handed helix remains so regardless of its orientation, just like how I wouldn't become left-handed if I were suspended upside-down.

How can you distinguish between two chiral molecules and two identical molecules one of which has been rotated 180 degrees with respect to the other?

There's no way to rotate a clockwise screw that makes it a counter-clockwise screw. Try it.

That's the definition of chirality. If you have a tetrahedral orientation of four different atoms around a center atom (e.g. carbon), there will exist a "right handed" and "left handed" version.

You can rotate the "left handed" version any way you want, but you won't be able to superimposed it on the "right handed" version.

Looking down on a right-handed spiral stair case you have to go counter-clockwise to go down, or clockwise to go up.

Rotating the spiral along it's axis changes nothing.

Rotating the spiral 180 deg around any axis perpendicular to its own, will not change the above.

Only when you reflect the spiral does it change handedness.

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