Chris Kempes

So that's the sort of total energy budget the cell is the metabolic power. And then scaling is just this idea that if you look across orders of magnitude in one feature, you get a linear relationship in orders of magnitude of another feature. And those could have different exponents, which would be the slopes of those different curves in that log-log, order of magnitude, order of magnitude space.

So that's the sort of total energy budget the cell is the metabolic power. And then scaling is just this idea that if you look across orders of magnitude in one feature, you get a linear relationship in orders of magnitude of another feature. And those could have different exponents, which would be the slopes of those different curves in that log-log, order of magnitude, order of magnitude space.

Mm-hmm. And so when we say there's a shift in a scaling relationship of metabolic power, what I'm really saying is that as you go across this evolutionary divide, you see a change in the exponent from one class to the other. Specifically, in prokaryotes, the exponent is greater than one, meaning... if you double in cell volume, you more than double the total metabolic power.

Mm-hmm. And so when we say there's a shift in a scaling relationship of metabolic power, what I'm really saying is that as you go across this evolutionary divide, you see a change in the exponent from one class to the other. Specifically, in prokaryotes, the exponent is greater than one, meaning... if you double in cell volume, you more than double the total metabolic power.

If you go up by a power of 10 in cell volume, you go up by more than a power of 10 in metabolic power. In Unisar eukaryotes, the exponent is sublinear, meaning that if you go up by an order of magnitude in cell volume, you go up by less than an order of magnitude in in metabolic power. So the power per unit volume is increasing in prokaryotes and decreasing in unicellular eukaryotes.

If you go up by a power of 10 in cell volume, you go up by more than a power of 10 in metabolic power. In Unisar eukaryotes, the exponent is sublinear, meaning that if you go up by an order of magnitude in cell volume, you go up by less than an order of magnitude in in metabolic power. So the power per unit volume is increasing in prokaryotes and decreasing in unicellular eukaryotes.

And that's a really fundamental difference that drives all sorts of downstream things that we can observe, like the growth rates, like the requirements for the number of ribosomes in the cell, all sorts of different features.

And that's a really fundamental difference that drives all sorts of downstream things that we can observe, like the growth rates, like the requirements for the number of ribosomes in the cell, all sorts of different features.

Exactly, exactly. You still need more power, but in a sort of gained efficiency way.

Exactly, exactly. You still need more power, but in a sort of gained efficiency way.

Yeah. So it looks like the nucleus is a more complicated story because I think the nucleus is mostly about regulation and separating out certain parts of the genome from each other and protecting the genome from reactive parts of the cell. But the mitochondria seem to just come along for the ride of that. So there, I think there's a big debate about causality. People would say,

Yeah. So it looks like the nucleus is a more complicated story because I think the nucleus is mostly about regulation and separating out certain parts of the genome from each other and protecting the genome from reactive parts of the cell. But the mitochondria seem to just come along for the ride of that. So there, I think there's a big debate about causality. People would say,

Well, the number of mitochondria have the same scaling as the metabolic power. So are they driving the metabolic power? And I would say we don't quite know yet. We don't know what's being optimized because it could be that the number of mitochondria you have are just optimized according to some other constraint.

Well, the number of mitochondria have the same scaling as the metabolic power. So are they driving the metabolic power? And I would say we don't quite know yet. We don't know what's being optimized because it could be that the number of mitochondria you have are just optimized according to some other constraint.

And that constraint is what's driving metabolic power and mitochondria come along for the ride. Or it could be some fundamental constraint about the mitochondria that require the metabolic scaling to be what we observe. But yeah, I mean, in general, that's exactly the sort of connection we try to draw. We say we have a physical constraint. Maybe it predicts something like total metabolism.

And that constraint is what's driving metabolic power and mitochondria come along for the ride. Or it could be some fundamental constraint about the mitochondria that require the metabolic scaling to be what we observe. But yeah, I mean, in general, that's exactly the sort of connection we try to draw. We say we have a physical constraint. Maybe it predicts something like total metabolism.

And then once we know total metabolism, we can write down a cell model. You know, we can write down a model of cell physiology and ask what other components should scale in what way according to this metabolism. And in bacteria, that gives us a whole host of predictions and the same in unicellular eukaryotes. Yeah.

And then once we know total metabolism, we can write down a cell model. You know, we can write down a model of cell physiology and ask what other components should scale in what way according to this metabolism. And in bacteria, that gives us a whole host of predictions and the same in unicellular eukaryotes. Yeah.

Absolutely. Yeah. And I think, you know, I think that's something we're starting to run up against more and more recently. I mean, it's interesting that, you know, in the early days of computer science, a lot of the considerations were really about, well, how much resources will this need as we scale up? So how much time, how many CPUs, how will this scale up in a resource constraint?

Absolutely. Yeah. And I think, you know, I think that's something we're starting to run up against more and more recently. I mean, it's interesting that, you know, in the early days of computer science, a lot of the considerations were really about, well, how much resources will this need as we scale up? So how much time, how many CPUs, how will this scale up in a resource constraint?