Sarah Walker
speaker
510 appearances
1 recordings
1 series
first heard Jun 2024
last heard Jun 2024
Sarah Walker’s voice in public audio — every appearance, attributed to the second.
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I think it's a small space. But chemistry is very large. There might be a lot of them out there, but we don't know.
That's right.
Yeah. I mean, there's also all kinds of other weird properties that happen around this kind of phase boundary. So this other project that I have in my lab is focused on the origin of chirality, which is, you know, thinking about, so chirality is this property of molecules that they can come in mirror image forms. So like, just like chirality means hand. So you're
Your left and right hand are what's called non-superimposable because if you try to lay one on the other, you can't actually lay them directly on top of each other. And that's the property of being a mirror image.
So there's this sort of perplexing property of the chemistry of life that no one's been able to really adequately explain that all of the amino acids in proteins are left-handed and all of the bases in RNA and DNA are right-handed. And yet the chemistry of these proteins building block units, amino acids, and nucleobases is the same for left and right-handed.
So you have to have like some kind of symmetry breaking where you go from these chemistries that seem entirely equivalent to only having one chemistry take over as the dominant form. And for a long time, I had been really, I actually did my PhD on the origin of chirality. I was working on it as like a symmetry breaking problem in physics. This is how I got started in the origin of life.
And then I left it for a long time because I thought it was like one of the most boring problems in the original life, but I've come back to it because I think there's something really deep going on here related to this like combinatorial explosion of the space of possibilities. But just to get to that point, like this feature of this handedness has been the main focus, but...
people take for granted the existence of chiral molecules at all, that this property of having a handedness. And they just assume that it's just a generic feature of chemistry. But if you actually look at
molecules, if you look at chemical space, which is like the space of all possible molecules that people can generate, and you look at small molecules, things that have less than about 7 to 11 heavy atoms, so things that are not hydrogen, almost every single molecule in that space is achiral, like doesn't have a chiral center. So it would be like a spoon of
spoon doesn't have it like it's the same as its mirror image it's not like a hand that's different than its mirror image but if you get to like this threshold boundary above that boundary almost every single molecule is chiral so you go from a universe where almost nothing has a mirror image form there's no mirror image universe of possibilities to this one where every single structure has pretty much a mirror image version and what
we've been looking at in my lab is that it seems to be the case that the original life transition happens around the time when you start accumulating. You push your molecules to a large enough complexity that chiral molecules become very likely to form. And then there's a cascade of molecular recognition where chiral molecules can recognize each other.
And then you get this sort of autocatalytic feedback and things self-reinforcing.
No, it's a super interesting feature. I think chirality breaks symmetry in time, not space. So we think of it as a spatial property, like a left and right hand. But if I choose the left hand, I'm basically choosing the future of that system for all time because I've basically made a choice between the ways that that molecule can now react with every other object in its chemical universe.
Oh, I see. And so you're actually like, when you have this splitting of making a molecule that now has another form it could have had by the same exact atomic composition, but now it's just a mirror image isometry, you're basically splitting the universe of possibilities every time.
In two, but molecules can have more than one chiral center, and that's not the only stereosometry that they can have. So This is one of the reasons that Toxol fills 1.5 universes It's all of these spatial permutations that you do on these objects that actually makes the space so huge.
So the point of this sort of chiral transition that I'm putting out is chirality is actually a signature of being in a complex chemical space. And the fact that we think it's a really generic feature of chemistry and it's really prevalent is because most of the chemistry we study on Earth is a product already of life.
And it also has to do with this transition in assembly, this transition in possibility spaces. Because I think there's something really fundamental going on at this boundary that you don't really need to go that far into chemical space to actually see life in terms of this depth in time, this depth in symmetries of objects in terms of like chiral symmetries or this assembly structure.
But getting past this boundary that's not very deep in that space requires life. It's a really weird property, and it's really weird that so many abrupt things happen in chemistry at that same scale.
Well, it's efficient for things to eat other things that are already alive because they don't have to go all the way back to the, Base chemistry.
I actually think it's a gift that we don't have much time.
Showing 161–180 of 510 · page 9 of 26
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