Chris Kempes
speaker
209 appearances
1 recordings
1 series
first heard Jan 2025
last heard Jan 2025
Chris Kempes’s voice in public audio — every appearance, attributed to the second.
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as Sean said, a byproduct of what we call an endosymbiotic event where one cell started living inside the other cell. And so you, in this case, have a bacteria likely living inside of an archaea.
And the bacteria inside the archaea becomes this metabolic structure known as the mitochondria, which many people sort of associate with how life gets big and why life gets big and how organisms like us can produce so much energy. There's lots of other reasons that you might want a mitochondria. It distributes many copies of the metabolic genome throughout the cell.
Nick Lane has written really nicely about that. It distributes certain sorts of metabolic processes throughout the cell in a structured way. All of this is sort of really beneficial. And we understand that it must be getting over limits that we saw out of bacteria. I think our perspective would be the main limits that you start to see are about transport, right?
And so I would almost say you likely need to solve transport before you solve these other packaging problems around different sorts of genomes and having lots of internal metabolism and so forth. I think it's actually, you just can't
get substrates, the stuff that you use, products, the wastes in and out of the cell fast enough with diffusion alone for large bacteria to make the metabolism function. So you have to start adding active transport inside the cell, ways to stir the cytoplasm, ways to move packages around in the cytoplasm just to overcome the sort of challenges of diffusion.
And I think you probably need to do that before you start to get things like the mitochondria and other sort of endosymbiotic events.
Exactly. And you could think of it as, you know, you can think of it as a drift process or a random walk process in evolution. And so if there is one of these walls, I think you expect an evolutionary time for a very long period of time. Things just keep hitting that wall and and be stuck in a certain size range. And then it's you're waiting for a chance event where some.
fairly big change to architecture happens for one reason or another, and that gets you just on the other side of the wall, and then you're off to the races in this other evolutionary trajectory. And then all of the physics of that region become a target for evolution, and then you may need to solve a bunch of problems successively.
But many people would say it was harder to get the eukaryote than it was to get cellular life in the first place. Took longer. Yeah. It took longer, right? And I find that really interesting and surprising, right? And I also don't necessarily agree with that because I think there's other factors involved.
But that sort of thinking I think is really important to say you can just stall out at one level of complexity for a long time. Nothing wants you to get more complex. It's just if you stumble upon the right solution – that gets you over that hump. Then you're into this new valley with no competitors. You've got a new niche and we know it happens there.
Things diversify and go in every direction and you get lots of new solutions. But you have to wait for that chance event to get you over the hump still.
Exactly. And I think one of the reasons for that is once you move into this new space, you see a bunch of new challenges that you never had to deal with before. And likely each of those challenges needs its own solution. And so it's not then surprising that you get a bunch of complexity all at once.
And maybe you don't get it all at once evolutionarily, but looking back from our current vantage of all of these well-adapted organisms a billion years later, we would say, oh, wow, there's many innovations. They're all really optimized and they all go together. Now, you know, one of the biggest debates in how eukaryotes came to be is the ordering of events.
I mean, it's countless papers written about what was first. I mean, it's even gotten to the point where we say, well, is that a mitochondria first? Yeah. Is that a phagocytosis first argument? And so people really are trying to work through the ordering and have big debates about the ordering. And we don't have any fossils to tell us because these things are goopy and don't preserve well.
And so whereas that debate gets resolved in dinosaurs about what happened first, it doesn't get resolved for the eukaryotes yet.
Exactly. Yeah. So one thing that we found was the way in which protein concentration scales with cell volume is preserved from bacteria into eukaryotes. And we think there's one optimization related to diffusion that really drives that uniformity in this one scaling relationship. And However, metabolic power scaling shifts between prokaryotes and eukaryotes. The growth rate scaling shifts.
The eukaryotes pick up a bunch of scalings that you obviously don't have in bacteria, like how many mitochondria they have. Jordan Oki has a really wonderful paper showing how many mitochondria you get as a function of cell volume. And so there's, you know, lots of things are changing and then some things are staying the same. And
And both of those angles help us understand if we're onto the right theory, if we're onto the right constraints. So, for example, if we think a dominant constraint comes with a limit that should imply a major shift at one scale and we look at prokaryotes on one side and eukaryotes on the other side and they have exactly the same scaling, then we were wrong about the constraint.
Luckily, that hasn't happened to us. But that's a nice way to say we could easily falsify our theory if we'd pick the wrong constraints because there are certain things we would predict that just wouldn't hold up. You would move across transitions and either see shifts that you didn't expect or not see shifts that you did expect. And we think that's a sort of secondary test of these theories.
Yeah, that's great. So what I mean by metabolic power is just the total energy available to a cell. So this is how it would be like the total food that you and I ate. For cells, it's the same. If they use sunlight, it's the total sunlight they're able to capture. If they eat other things, it's how much of that that they're able to eat per unit time.
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