
Chiral Key Found to Origin of Life - softdev12
http://www.quantamagazine.org/20141126-why-rna-is-right-handed/
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daveloyall
> _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.

~~~
tjradcliffe
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.

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trendroid
> 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?

~~~
julienchastang
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...](http://www.lcg.unam.mx/frontiers/files/frontiers/Tuerk%20and%20Gold%201990.pdf)

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DSingularity
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.

~~~
refurb
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.

~~~
tiatia
"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.

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

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anateus
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"

~~~
andrewflnr
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.

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

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

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

~~~
fit2rule
The direction of light, from the perspective of the viewer, is the base. Its
not about up and down, but rather left or right ..

~~~
vanderZwan
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)

~~~
al2o3cr
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.

