198 | Nick Lane on Powering Biology

0:00:00.4 Sean Carroll: Hello, everyone. Welcome to the Mindscape Podcast. I'm your host, Sean Carroll. When I wrote "The Big Picture," that book that I wrote a few years ago, one of the most fun parts of the process to me was tracing what happens to the energy that we get from the sun through the atmosphere of the Earth, and then into life here on Earth. I always ask people when I give talks, "What good is the sun to us here on Earth?" with the idea that probably they're thinking, we get energy from the sun. Which is true, but what is most important about the energy is that it is in a low entropy form. It is useful energy. So that low entropy energy we get from the sun is captured by plants or unicellular organisms, and then it is basically bottled up in certain molecules, which then go on to be eaten, roughly speaking, by other organisms and used as fuel.

0:00:51.2 SC: So once that energy is in the right molecules and gets into animals and other aerobic organisms, it goes through what is called the Krebs Cycle or the citric acid cycle. The Krebs Cycle is kind of amazing. It's basically the way that we take the fuel stored in these molecules and turn them into useful energy in our bodies. And amazingly, it is really, really ubiquitous for life on Earth here, which maybe is a hint that there's something important about it. And not only is it, of course, important for metabolism and so forth, but it is perhaps uniquely important for metabolism.

0:01:24.3 SC: So today's guest is Nick Lane, a very well-known biochemist and writer, who is one of the world's experts on the origin of life. But we're talking mostly in this podcast not about the origin of life, but about how life uses energy in this Krebs Cycle, in this citric acid cycle. That's important for figuring out the origin of life because it is possible, it is conceivable, we don't know yet, that the Krebs Cycle predates life itself; that it has a non-biological origin. And coming into existence in a purely chemical way might have been one of the crucial steps into the origin of life. So this is fun stuff. Nick is an actual expert. When I was writing my book, I was not an expert, but I tried. I learned. I talked to people, etcetera. You'll learn a lot from his perspective on this stuff. And it's crucially important to tackling some of these big questions about why there is life at all. So Nick has a new book out called, "Transformer: The Deep Chemistry of Life and Death" which is about exactly this topic. And let me assure you, if you're not familiar, he is a brilliant writer, as well as scientist.

0:02:28.0 SC: Okay, occasional reminder that here at Mindscape, we have a website, preposterousuniverse.com/podcast, where you can get show notes and full transcripts for all of the episodes. And you can also support Mindscape by going and becoming a Patreon supporter at patreon.com/seanmcarroll. That's where you go. If you're a Patreon supporter, you get to ask the questions that we answer for the "Ask Me Anything" episodes, and you get ad-free versions of the podcast for a dollar a podcast. What better deal are you gonna find than that? That's pretty awesome. Okay, that's the occasional reminder of the commercial side of the venture. So with that, let's go.

[music]

0:03:21.3 SC: Nick Lane, welcome to the Mindscape Podcast.

0:03:23.8 Nick Lane: Pleasure. Thank you for the invitation.

0:03:25.3 SC: You know, we've had a couple of episodes recently learning about either life in general or human life in particular in the ancient world from modern DNA. And that's a very sensible thing to do. But what we're doing here is a little bit different. I mean, you're kind of like not talking about DNA and RNA as much as many other books on these subjects talk about. You wanna talk about energy and processes, and so forth. So I guess my first question is, should we even expect to be able to say anything about the origins of life just by studying the processes today? I mean, clearly they've changed a lot in the interim.

0:04:03.4 NL: Yeah, and it depends who you ask that question to, as to what kind of an answer you get. Yes, it's a good question. Can we use life as a guide to its own origin, or is there some kind of circularity to that? And I think for the last 50 or 60 years, people have avoided that question and used chemistry as a guide to life's origin. And if we use genes and we try and go back to the first cells that we can reconstruct from genes, it was already a complex cell with, well, with genes and with DNA and proteins, and this has got nothing to do with the origin of life. So it's a genuine question. But there's a really interesting thing about how do these complex metabolic pathways arise in the first place. And if they... There's one way of seeing... You could say, "Well, they evolve step-by-step." And if that's the case, then you have to have a gene for each step, and each intermediate has to do something useful for you. And it becomes enormously complicated very quickly. Whereas if what you assume is these pathways are more or less just spontaneous chemistry that should happen anyway in the right environment, then all the genes really need to do when they emerge, is just speed up processes that are happening anyway, in any which way you want it to do that. And so it basically... Thinking that the basic metabolic pathways of life is just spontaneous chemistry in the right environment, really solves a lot of problems.

0:05:29.8 SC: No, and that's actually a very interesting point. Even though I've talked to you and other people about this stuff many times before, that never quite sunk in. So whenever you have a process that is governed by evolution, it works incrementally, right? It starts with something, and then... So you ask a question like, "What good is half of a wing?" But the answer is [0:05:47.5] ____ how it evolved to something else, and then it made it there, so...

0:05:50.0 NL: Quarter of a wing. It is...

0:05:50.9 SC: Yeah, yeah. What good is that? So for these metabolic pathways, what you're saying is we can sort of sidestep that problem entirely 'cause maybe they just all happen spontaneously. It's not that you're building up the whole pathway piece by piece.

0:06:06.1 NL: If you start with chemistry, as the whole field has done for decades, and you're guided by the chemistry itself, what you end up with is a kind of a soup, the primordial soup, the famous primordial soup. And you got amino acids, and you got nucleotides; You got the building blocks of life floating around in this soup. And then what happens next? Well, somehow it polymerizes, and you end up with DNA or RNA or something. And then somehow information appears. [chuckle]

0:06:37.5 NL: There's a problem with the origin of information, if you see the origin of life this way, and then you have genes and they invent metabolism. And so, there's a lot... To my mind, there's a lot of jarring problems there. Whereas if... One of the biggest ones is, chemistry that actually has worked well over decades doesn't look anything like life's chemistry as we know it, and so it forces there to be this inventiveness of genes at an early stage because genes have to invent metabolism as we know it because the processes that gave rise to the building blocks were nothing like metabolism as we know it. Now, the alternative way is, as I say, you have this spontaneous pathways that just happen in the right environment, which give rise in the end to the building blocks of genes to the nucleotides, and eventually, they polymerize in that environment.

0:07:27.2 NL: Now, that's not been a popular view, and the reason it's not been a popular view is because the way that life does is, is it starts with CO2 and hydrogen, and they're just not very reactive with each other. [chuckle] And so for decades, nobody really ever succeeded in doing the experiments that show that this is really possible. But in the last five years, a lot of people have started to take it much more seriously, and these experiments are being done now, and what do we see? We see exactly the molecules of the central metabolic pathways, we see the Krebs Cycle intermediates, we see the amino acids, we see basically life's chemistry all just happening from CO2 and hydrogen, and it's just gobsmackingly beautiful to watch.

[laughter]

0:08:08.5 SC: So this is... Since I'm not a chemistry person at all, the idea here is that you have these molecules, CO2 and hydrogen, and in some sense they would like to combine or they would like to re-arrange, you know, put hydrogen onto the carbons, but there's no simple way to get there. But what chemistry can do is allow you to sort of catalyze it with the right conditions around.

0:08:38.4 NL: Yes. I mean, it's a physics problem really, [chuckle] it's just thermodynamics and kinetics.

0:08:43.6 SC: That's how I think about it, yes.

0:08:43.7 NL: So thermodynamically yes, they want to react and they want to make these organic molecules and they do in all kinds of different environments, but there are kinetic barriers to the reactions. And really, what life is doing is lowering the kinetic barriers to thermodynamically favored reactions. That's kind of all it does.

0:08:58.5 SC: Yeah. Good. And this is part of... Just to put it in the context for the people who are listening, there's a debate in origin of life circles, metabolism first versus replication first, is that a fair way to define the camps?

0:09:14.9 NL: Yes, I mean, it's exactly how a lot of the field has seen it. I think in recent years, people have been trying to get away from these slightly extreme camps [chuckle] and say, oh, co-evolution, they happened together.

0:09:25.7 SC: Sure.

0:09:26.8 NL: But yes, it's a kind of way of seeing the question, really.

0:09:31.7 SC: Yeah.

0:09:32.5 NL: And I suppose I would be in the metabolism first camp on the grounds that I want all this spontaneous chemistry to happen, but it's not really that I'm saying that life is about metabolism. Obviously, it needs genes and information, and I'm not sure that I would describe these proto-metabolic pathways that give rise to the building blocks of life. I wouldn't describe that as life, I would just describe it as a geochemistry in the right environment. And the people who say they want to have genes first, well, they've still got to make the nucleotides, they're still doing this prebiotic chemistry first. So it's really, where do you want to draw an arbitrary line across the continuum?

0:10:12.4 SC: Yeah.

0:10:13.1 NL: And where you draw that line depends on which camp that you're in, but I think really there aren't camps, there are different ways of coming up with the requirements that biology has, and information is obviously one of the requirements, genes is obviously one of them. The question is, what's the easiest way to produce them so that they can do something useful for you, and if you have some kind of proto-metabolism, when genes are introduced into that, what do they do? They speed up the proto-metabolism, they make it better than it was before, and so, they have a purpose or use from the very beginning.

0:10:44.5 SC: Yeah, I think that... Again, this might be unfair, so correct me if I'm wrong, but the big picture message that seems to be coming across, in not just your most recent book, but your previous one as well, is about energy versus information. And information is something that is very exciting these days, lots of scientists, so my own colleagues love information theory and information, it's physical and things like that, and you're pushing back on that a little bit saying, okay, but let's not make it all bloodless and forget about the role of energy, [chuckle] because energy is kind of important here.

0:11:21.3 NL: I think there are some serious problems in biology, if we only focus on the information. I think we... It's not that I want to belittle it or anything, it is obviously... It's centrally important in biology, but it's not the only thing that is centrally important in biology, and I think if you think about the other things that make up life, which is basically turning gases into matter, that's what's going on very often, that's called growth. And it's a really simple question, but it's about physical chemistry, it's not something that we can... I mean, you probably can define it in informational terms, but it's easier just to think about it as chemistry. And that chemistry does again things which we can think about in informational terms, like self-organization, but it's much easier just to understand, you put oil on water and it's going to separate into two layers, the oily layer and the aqueous layer, and that's more or less how cell membranes work and you're getting order out of nothing, it's not out of nothing, it's about the thermodynamics of separation of two phases, depending on the molecular attractions between molecules.

0:12:30.8 SC: Right.

0:12:33.1 NL: Hydrophobic interactions or ionic bonds or whatever it may be, is there an informational way of seeing that? I'm sure there is, but it's less easy to understand than just the physical chemistry.

0:12:44.0 SC: Yeah. No, and I think that it's always good to have multiple perspectives on these things and we'll see, which actually leads us to the breakthroughs, but... Okay, I think this is enough for the big picture ground laying where we're coming from stuff, let's get our hands dirty a little bit. You've written a book about the Krebs Cycle, which I can just imagine the reaction of your publisher when you pitched this idea.

[laughter]

0:13:06.4 SC: Explain to us why the Krebs Cycle... Well, what is it, and why should we care right now?

0:13:12.0 NL: Okay, it was partly... Well, there's two reasons, one of them is, I am a biochemist and the Krebs Cycle is... It's probably the single most iconic pathway in all of biochemistry, and it's hated by almost all biochemists, especially medical students who have to do some biochemistry. It's a kind of the perfect circle right at the heart of all of metabolism, and nobody really understands. Some people are forced to memorize it, and this is one of the things that puts people off biology for life or biochemistry, it's just incredibly dull. And it's basically the rearrangements of bonds in molecules composed only of carbon and hydrogen and oxygen, and half of these rearrangements seem pointless.

0:14:06.6 NL: It really is a very, very difficult challenge. I could see why my publishers were bothered by it. Now, why then would I even write a book about it? There's two reasons really, and they're both ends of the book. One of them is... And I have two labs. One of the labs is working on the origin of life, and the other lab is working on fruit flies and mitochondria. Now, so the Krebs Cycle is basically what's happening in our mitochondria. It's where we are stripping down food to generate energy. We're stripping the electrons out of food, we're passing them into respiration, we're passing them on to oxygen to produce water as a waste product, and so we're basically burning hydrogen in oxygen, and that's what's powering us. And it's the Krebs Cycle which is doing that, but it goes through this strange cycle of lots of peculiar intermediate steps, which seem to be just a waste of time to try and understand, and lots of people did.

0:15:05.9 NL: It was discovered in the 1930s by Hans Krebs, it became dusty textbook biochemistry. People have have to learn it and don't want to know and forget it as soon as they can, but in the 60s, there was a really funky discovery at Berkeley that some bacteria living in deep sea hydrothermal vents do the Krebs Cycle backwards. So what we're really doing in the Krebs Cycle is we're taking these carbon skeletons, which are composed of carbon, hydrogen and oxygen, and we're stripping out the carbon and the oxygen and putting it out of CO2, and we're pulling out the hydrogen, and we're burning the hydrogen with oxygen, that's generating our energy, and we're releasing water as a waste product. Now, what these bacteria are doing in the deep sea hydrothermal vents, they're taking hydrogen that is bubbling out of the ground, and they're taking CO2 dissolved in the oceans, and they're running the Krebs Cycle backwards, putting in a bit of energy, and they're making these carbon skeletons. So this is the reverse Krebs Cycle, and it's basically turning gases into the core molecules of life, and it took 20 years before these ideas were really accepted, in part because people were looking for the genes for it, and it was not so obvious exactly how it worked, and so on.

0:16:29.9 NL: So now, moving forward another 20 or 30 years from when it was finally accepted, the chemistry at the origin of life, we start with hydrogen and CO2, and what do we get? We get these Krebs Cycle intermediates and we get almost all of them forming, and there are fairly simple set of conditions, and when you look at the mechanisms of the chemistry, basically... If you've got a carbon skeleton, you want to stick CO2 onto it, you get a Krebs Cycle intermediate, and you get another one and another one, and you're building longer and longer chains of these core molecules. You want to make an amino acids, you effectively just stick it straight on to that, the nitrogen straight on to where one of the oxygens used to be, and again, it happens spontaneously, and so the more we look at it, the more we realize that this end of the origin of life is starting with these gases that are definitely present in any hydrothermal system on the early earth, and you're making the core molecules of biochemistry very directly. And then the other end of this whole thing is to do with aging and cancer, and it turns out... And it's turned out over the last 10 years that often in cancer, the Krebs Cycle runs backwards. It doesn't do the normal thing...

0:17:41.7 SC: Really?

0:17:42.6 NL: It basically... Cancer cells, and sometimes our own bodies are basically fixing CO2, taking it out of the atmosphere and converting it into these carbon skeletons and using them for growth and powering growth that way. We're almost photosynthetic in that sense. No light involved, but we're taking CO2 from the atmosphere from our own bodies and converting it into the intermediates of metabolism. So this has been a big step change in what's going wrong with cancer, and in my own group working on mitochondria are looking at that, and so I've got two groups who are both trying in the lab to analyze these Krebs Cycle intermediates, both with completely different questions in their mind, and just for my own sanity, I have to try and put it all together and say, well, hang on a minute. They've gotta be related.

0:18:29.0 SC: But labs, unlike chemical pathways, do not grow up spontaneously. You must have had some inkling that there were similar things involved in these two projects.

0:18:37.6 NL: Yes, I have, and it's been building for a while, but it's really... The similar things is really to do with energy flow, in my own mind, at least, so this is why it is that cells generate energy by electrical charges on membranes, and that's what's happening in mitochondria, and actually, that's what is happening in some of these deep sea hydrothermal vents, is you have barriers with the natural electrical charge on them, and you ask the question, so what is this charge doing? And the answer is, in vents, well, it's powering the reaction between hydrogen and CO2 to make Krebs Cycle intermediate, and so the Krebs Cycle has come into it gradually through the back door, you might say.

0:19:18.5 SC: Yeah.

0:19:20.8 NL: My primary questions were to do with energy generation. But then you ask, well, what's the energy doing? And you end up thinking about the Krebs Cycle and it's very strange, the way that it's kind of infiltrated its way into my thinking, and not just me, there's plenty of people thinking along these lines around the world now as well, so it's quite exciting.

0:19:38.7 SC: So let me think about this as a physicist 'cause I'm trying to figure out why things are like this. When we talk about energy and how we use it, the most basic thing to do is have some fuel source and burn it, like in our car, we put in gasoline, and what's really happening there is that there's energy locked up in the fuel source and we're releasing it by some chemistry. That makes sense to me. But there's no cycles involved in that, so in a cycle, somehow you're taking various combinations of chemicals, as you said, carbon, hydrogen, oxygen, and by slightly changing the conditions, you're slightly raising and lowering the amount of energy that these guys have and sort of nudging the energy around the circle, so what's the point of that? Why are you doing something so complicated rather than just burning some fuel like my car does?

0:20:29.8 NL: Yeah, I mean, there's two answers to that. One of them is surprisingly the origin of life, it's everything's upside down, and we're not actually burning fuel, the fuel is being supplied by the planet, the fuel is the hydrogen gas bubbling straight out of the planet with a disequilibrium with CO2 in the ocean and now thermodynamically, they want to react together, and the question there is really more about the kinetic barriers that prevent them from reacting, but there is a physics question here as well that goes back to Harold Morowitz who... People have talked about the fourth law of thermodynamics, and I think his snappy phrase for it was energy flows in matter cycles because nothing... Energy transfer is never perfect and you're always going to increase entropy, and that means you can never do a perfect reverse of any specific reaction. And so photosynthesis and respiration are kind of opposite and equal processes, but not fully actually matter recycling through these two processes. I don't know if this is a profound insight or if it's kind of a statement to the obvious, I really can't tell, but it was beautifully put anyway, by Morowitz, and he saw the Krebs Cycle, this was back in the...

0:21:48.0 NL: Back in the late 60s, I think he saw the Krebs Cycle as kind of necessary thermodynamically that matter is going to cycle, and that's why he pulled it out as something important. And there were lots of protests at the time, and I think by the early 2000s, the ideas were beginning to die, mostly because nobody had succeeded in reproducing it in the lab, and now people have started reproducing it in the lab, and ironically not as a cycle that has kind of straight line pathways of a handful of intermediates. So I'm not sure his ideas are fully vindicated yet, but the kind of the thermodynamic drivers behind it, definitely yeah.

0:22:33.1 SC: Lets be more... A little bit more specific about that because I think this is crucial 'cause you've mentioned a couple of times, the hydrogen and the carbon dioxide, they want to burn and the specific... Maybe these are my words...

0:22:47.5 NL: Well, they wanna make organic molecules. They want to become Krebs Cycle intermediates, basically. That's thermodynamically the low energy state.

0:22:56.2 SC: I've gotten a lot of mileage out of our friend, Michael Russell's, line that the purpose of life is to hydrogenate carbon dioxide. And the way I interpret that is, there's a barrier, explain that... Maybe you should do this rather than me. Explain what you mean by a barrier? Why can't they just rearrange into a lower energy state?

0:23:17.9 NL: Well, I mean, you put them together in a test tube, hydrogen and CO2, and you warm up, let's say, you warm it up to 100 degrees centigrade and let's put a catalyst in there and shake it up and let it get on with it. And what happens, oh, nothing happens, and that's the problem. They're stable molecules, and they're just not easily going to react, and this is why chemists a long time ago dropped this problem. Now it's coming back, at least in part because we have serious problems with the climate emergency and CO2 and global warming and so on, and with energy security.

0:24:00.9 NL: So what happened if you were able to strip CO2 out of the atmosphere, split water to produce hydrogen, react the hydrogen with the CO2 and make synthetic gasoline, there is a nice solution, but that's basically what life is doing. And so there's been a big increase in the last few years in the chemistry of CO2 and hydrogen, and it's brought this problem, nothing to do with the origin of life, but it's made it more respectable again, to think about, well, how can we make them react and then you think, well, okay, life makes them react all the time, what is life actually doing, how is it making them less stable, more reactive? And the answer is, in my view, at least, well, life is not chemistry in a bucket, it's in a cell, and what's happening in the cell... Well, it's the difference between the inside and the outside of the cell is the difference between a living thing in the outside world, but if you're dealing with a single cell, what is the difference?

0:25:02.3 NL: You've got a membrane, it's five nanometre thick, say five millionths of a millimeter in thickness, and on one side of it, you've got one set of conditions, which is inside the cell, and the other side you've got the outside world, but really, all that membrane can tell is you've got some ions on this side and different ions on that side and... Well, what are they? What are they doing? Well, the answer is they're producing a charge on that membrane, an electric charge, and if you shrink yourself down to the size of a molecule, it's equivalent to a bolt of lightning, it's about 30 million volts per meter, is the field strength that you would experience if you were in that field.

0:25:40.3 NL: So what is that doing? Well, what it's doing in modern cells is all kinds of funky things with molecular machinery made from proteins and so on, and none of it's relevant to the origin of life, and you think, well actually, some hydrothermal systems mimic this thing where we've got a barrier. When we've got fluids with different compositions on opposite sides of the barrier, which generate a natural charge, what could that charge do for us? And the answer is, it can make hydrogen more reactive and it can make CO2 more reactive, so long as they are in separate phases, and if they can then be somehow brought together across the barrier, across the membrane, then you can make them react. And that's effectively what life is doing, and the question for me in a prebiotic chemistry point of view is if we don't have just bucket chemistry going on, but we've got some structure, can that structure and the charges involved in the two separate phases, can that drive this reaction between hydrogen and CO2 to make the organic molecules and drive in effect growth, your converting hydrogen and CO2 in the environment into more of you?

0:26:51.6 SC: Good, I think that's a good thing, not always a good thing, I suppose. There's too much of me already, but I wonder if we can chemist our way out of that, but... So at a very, very basic level in... Are all cells... What is the arrangement of charges, are they positively charged inside and there's a negative charge on the cell wall or is it not certain.

0:27:08.8 NL: It's usually positive outside.

0:27:11.8 SC: Okay.

0:27:11.9 NL: But the way that cells work now is by pumping protons. So protons are the nucleus of hydrogen atoms and they have a positive charge, and what we're doing in our own mitochondria, if we pump them out, and bacteria are doing exactly the same thing, they pump them from the inside of the cell to the outside, and so you have a positive charge on the outside of the cell and a relatively negative charge on the inside of the cell, and what we have in these hydrothermal vents is acidic oceans full of protons and alkaline fluids bubbling into these vents, which is lacking protons, and so it's not that there's really an overall electrical charge, it's that there's a difference in the proton concentration between the outside and the inside and they're going to flow in. And so it's really the pH gradient, which is potentially driving things at the origin of life.

0:28:08.0 SC: I mean, just as a physicist, I want charge to be conserved. So you can't pump out protons forever. Somehow, either you have to pump out an electron or a proton has to come back.

0:28:15.5 NL: Oh, yes. No, well, they flow back in again.

0:28:18.9 SC: Okay, good.

0:28:19.0 NL: So in modern cells, you pump them out and then they come through a turbine by the ATP synthase or something like that, and [0:28:24.6] ____ your powers work. So we're burning foods in our own mitochondria, the energy released pumps protons across the barrier to charge up the barrier, and then that charged barrier is propelling their flux back through machinery in the membrane through these turbines, like the ATP synthase, plenty of other proteins though, that they work through. So it's powering work.

0:28:47.0 SC: And in the modern biology, the modern cell, contemporary cells, this will be very, very complicated and intricate, but from everything you're saying, it does make sense how focusing on the energy flow gives you a similarity between what's happening at the cell wall and what might happen in a completely inorganic thing in chemistry underneath the ocean.

0:29:10.3 NL: Yeah, I think I misled myself for a long time because I was thinking... I think much more strictly in terms of energy, and what you think about with mitochondria in terms of energy is ATP is the universal energy currency people talk about in cells. And the ATP synthase is this amazing rotating motor that sits in the membrane and is powered by the flux of protons and it kind of cranks around and makes ATP, and it's an astonishing protein, amazingly sophisticated. And you think... Okay, so can I imagine you were saying... You were saying earlier on, what's was half an ATP synthase useful for? And the answer is, well, I can't imagine half an ATP synthase, I can't imagine the prebiotic version of it, it's plainly a product of genes and natural selection, in which case then you think, okay, well, what could a natural gradient have been useful for then, if you already need genes before you can use it? So is there something simpler that it might power that a kind of continuous influx of protons might power something?

0:30:21.0 NL: And it took me a long time to put ATP out of my mind and realize, well, hang on a minute, what we're really dealing with in growth, in turning gases in the environment into more of me, we're really trying to make more of me, we're trying to lower that [0:30:39.5] ____ kinetic barrier to the gases reacting to hydrogen and CO2 reacting with each other to make organic molecules. And in photosynthesis and in plenty of bacteria, the bacteria for example, that are doing this reverse version of the Krebs Cycle, well, they are using the electrical charge and the proton gradient, the inflow of protons directly to drive this reaction between CO2 and hydrogen. So you think, well, could that happen prebiotically? And here, we don't need a turbine and we don't need genes, we're dealing just with physical chemistry, and it's actually is to do with Nernst equation, but I won't go into that, but in effect, if you've got hydrogen in an alkaline environment and you want it to react, which means you want it to pass its electrons onto something else, what's left behind? The protons are left behind, and protons are acidic, and they're in an alkaline environment, they're gonna react with the hydroxide ions to form water, and so this is gonna be really favored in an alkaline environment. You're gonna have a... A lot of people might remember doing neutralization reactions, acid-based neutralization, even in your mouth, and it gets fizzing reaction going on in your mouth.

0:31:48.9 NL: It's spontaneous chemistry, it's about... It's unstoppable. And so you have hydrogen in this alkaline environment, it passes its electrons onto something else, onto the barrier, let's say, and now you've got protons reacting with hydroxide ions with this unstoppable reaction.

0:32:03.3 NL: If you put the hydrogen in an acidic environment and try and do the same thing, well, now you're making acid inside an acid environment. It's not gonna work. So hydrogen is reactive in alkaline solution. CO2, if you want to make it react well, first it has to pick up an electron, and now it's gotten a negative charge, how does it balance the charge? Well, if there's a proton handy right next to you in an acidic environment, you pick that up, now you balance the charge, now you take another electron, now you take an other proton, it becomes much more reactive in an acidic environment. And so what you need is hydrogen in an alkaline phase and CO2 in a acidic phase, and there has to be... Those two phases have to be juxtaposed right next to each other so that there can be a transfer of stuff, and the stuff that has to be transferred is electrons from one phase to the other phase and a semi-conducting barrier will transfer those electrons from one phase to the other phase, and that's effectively what the cell membrane is today, and it's effectively what these barriers are in vents, they're separate... They're semi-conductors between two separate phases.

0:33:08.4 SC: Okay, let me see if I can reconstruct what's going on here 'cause it does sound... It makes sense when you say it. [laughter] So we have all this energy locked up in CO2 and hydrogen, but you just put them in a little bucket and they don't react, they're too stable, they're too happy all by themselves, but if we can segregate them a little bit, and put one in an acidic environment and one in an alkaline environment, then they become much more ready to release their energy, to react in the right way to let that energy go. And so you need that kind of separation, a kind of barrier, a kind of membrane, you need acid and alkaline and you need a proton gradient, as you said, and then the idea would be, I suppose, that these reactions that have been enabled by this simple set up keep going and maybe grow and become more sophisticated as they go from being some inorganic chemistry to being life.

0:34:05.2 NL: Yes, all I'm really trying to do is preserve the same topology as a cell. So what you have in these vents is really a labyrinth of pores, cell-like pores with a thin inorganic barrier surrounding them, and at least in my imagination is, a lot of these are down at the bottom of the ocean and not easy to get at, but we can do experiments in the lab using microfluidic chips and things like that, and show that this kind of thing is at least possible, that on the inside of the pore, you have your alkaline fluids on the outside, you have your acidic fluids, and the barrier between the two, let's say there's electrons or protons, can cross that barrier and that's been shown to happen, which means you have separate phases.

0:34:52.2 NL: Mike Russell uses the phrase frustration. The mixing is frustrated, it's slowed down, but it happens anyway, but the rate at which the fluids are replenished with hydrothermal flow or ocean waters percolating in is faster to [0:35:04.7] ____ lighten the rate of mixing, and so you've constantly kept your two phases. So the planet is doing the work, it's really, it's gravity. In the end, it takes the ion down and puts the hydrogen coming from the earth and the CO2 in, so the planet is a giant battery, it's like a giant cell where the inside is alkaline relative to the outside, and the way that the topology of cells is very similar to the topology of the planet and the way that they function is very similar to at a micro-level what you're seeing inside these vents, but it's a beautiful idea that really cells mimic the structure of the planet.

0:35:43.2 SC: And just to be again, clear to the non-experts here, this is in contrast with what has been, I guess, the dominant view, or at least sort of the default view almost since Darwin, where he talked about like a little warm pond and you would have just all these chemicals and they would be complicated enough and life would start. And what you're emphasizing is, you can't just put chemicals in a bucket, you need the separation of different phases across a membrane, and that kind of chemistry that we see in life can be mimicked in certain environments, but not a pond. Maybe an underwater alkaline vent.

0:36:20.3 NL: To my mind, an underwater alkaline vent. There are some of these vents on the surface as well, so it's possible, but it's much harder to have if you got a... Let's say, yellow stone or something like that, or there are... The Cedars, for example, in Northern California, that's a serpentinizating system, which is to say it's the same type of system as the deep sea vents, but it's on land, but it provides some interesting problems because what you see then is this process of serpentinization produces alkaline fluids. So alkaline fluids come bubbling up through the ground and they form a pool at the surface, and the pool is alkaline, and there are no proton gradients there because it's not going into an ocean, which is acidic on the early earth.

0:37:09.8 NL: Now, there's a guy called Ken Nielsen who's done some beautiful work on the Cedars, and he was perplexed because there are these bacteria that grow there. And he thought, "Well, how are they doing it?" They had a normal functional ATPase, so they were able to jet... But normally, it pumps protons. There aren't any protons in this environment because it's only alkaline, so how do they do it? He's well, "Perhaps, they pump sodium ions," but it's a fresh water environment, they don't pump sodium either. There's no sodium there. So he thought maybe it's something funky, maybe it's calcium ions that they're pumping or something really weird. No, it turns out they pump protons. Where do they get the protons from? They get them from the hydrogen gas that's bubbling straight out, so they're taking them from and they pump them out of the cell, but they're growing... Where do they get their CO2 from?

0:37:57.7 NL: CO2 doesn't dissolve in alkaline fluids, so there's really starved of carbon, but if you squirt acid onto carbonates, then you dissolve the carbonate, and you get your CO2 that way, so they take the protons from the hydrogen gas and they squirt them onto the carbonates surrounding and dissolve the carbonate and get the CO2 that way. So they actually function as completely normal cells, but they're doing it in quite a complicated way. So the reason I'm telling you those complications, is if you think about life starting in a terrestrial geothermal system, and these gradients are not easy to come by, the nice thing about having an ocean setting, even if it's a shallow ocean, is that we have gradients, we have alkaline water going into an acidic system. You don't really get that on land.

0:38:42.9 SC: And you can use the sort of reasoning on the basis of chemistry and energetics to predict exactly what kind of environment you need, and we've even found the environments in places like Lost city.

0:38:55.8 NL: Yeah, the strong counter-argument to it has been that it's all hypothetical, that none of those chemistry actually works and that the chemistry starting with cyanide and UV radiation really works, and we've done it in the lab, and that argument is getting weaker as time goes by because we and others, people like Joe Moran, Martina Preiner, and so on, have been doing this chemistry in the lab for the last five or six years, and it really works, you can start with hydrogen and CO2 and make the Krebs Cycle intermediates. People are trying to make nucleotides that way. Now, the building blocks of DNA, it's not so easy, but watch their spot within six months or a year, they will be paid for showing nucleotide synthesis starting that way.

0:39:38.3 SC: Wow, okay, that's very cool. Good, I wanna get there. Let's put a pin in that. But I wanna build up a little bit because I get the analogy or the similarities between the energetics inside cells and the energetic in these vents or similar things where there is some kind of membrane, some kind of gradient, some kind of acid alkaline division, but how does that become a cell? How does that evolve into something you would recognize as living? Where is the point at which you replace this inorganic barrier with something we would recognize as a cell membrane?

0:40:15.9 NL: Well, it's actually, in a way, surprisingly easy because what are we doing here? We're using the barrier and the gradients to drive the reaction between CO2 and hydrogen to make organic molecules. Some of the easiest organic molecules to make under those conditions are longish chain, meaning 10-15 carbons, fatty acids or fatty alcohols or simple hydrocarbons. And what do they do? Well, they go through a standard phase transition, and if you have the... Especially the fatty acids, they have a charged head group, and that charged head group means that they will form a membrane, very much like a bilayer membrane surrounding cells.

0:41:03.1 NL: And we've done some work that shows that you form what we kind of optimistically call proto-cells because they basically use the bilayer membranes surrounding an aqueous space, that aqueous space got nothing in it. It's not a cell in any meaningful sense of the word, except that it's got a barrier around it, which is very much like a cell membrane, except that it's only made from fatty acids and fatty alcohol, so long chain meaning 10-15 carbons in a chain. The kind of things that have been made in those environments spontaneously form cells. Now, what happens to those cells? Well, they like to just stick to the barrier, and if they just sit there and stick to the barrier, then whatever is crossing that barrier is going to go into the cells as well, and so the question then is, well, can you use the same gradients across the barrier and the cell to drive the growth of the cell? Can that cell now make two cells, and so on? We've not really shown that yet, but in principle, it should happen, and if it does, then you've effectively got the natural gradients driving the growth and replication of proto-cells just through converting gases into the fatty acids that you need.

0:42:13.9 SC: Good. So let me again try to summarize, and you can tell me where I'm wrong here 'cause I have... I've even written about this stuff in the big picture, so I have some vague recollection of what's going on, if we think of life as requiring compartmentalization, the cell wall metabolism as we talked about, and also information, the DNA or RNA, whatever, my impression is, that the compartmentalization, that cell wall, part of it, that's the easy part, which is basically what you just said.

0:42:41.3 NL: It's a cell membrane I'm talking about rather than the cell wall.

0:42:42.0 SC: Oh, I don't even know what is the difference between those two terms.

0:42:43.3 NL: So the cell membrane is really thin, and it's made of these oily things, the fatty acids and so on. The cell wall is much more robust, but it's not really compartmentalizing things, it's providing a kind of rigid structure.

0:42:57.5 SC: Cell membrane. Okay.

0:43:00.7 NL: Now, that's later, to my mind, to make a bilayer membrane is, turns out to be a bit like mixing oil and water. It's not necessarily any more difficult than that.

0:43:10.2 SC: Right.

0:43:11.6 NL: And so it will form spontaneously.

0:43:13.5 SC: And the very interesting thing that you just added to that is this idea that because these membranes do form spontaneously, if they're right there in this environment where you have these dis-equilibria, these differences between alkaline acid, they can kind of inherit them, they can pick that up pretty quickly and become places where that metabolism can happen.

0:43:36.4 NL: Yeah, I mean...

0:43:39.9 SC: That's the hope.

0:43:40.4 NL: You've touched on the kind of the key point, I think, in how do you go from a purely inorganic system to a cell which is basically doing the same thing?

0:43:49.0 SC: Yeah.

0:43:50.0 NL: And for that to happen, you need to have some kind of transition, where instead of having a big mineral surface which is driving this reaction, instead it's happening over the membrane itself, so what would you need to have sitting in that membrane for the same thing to be going on? And the answer is, well, what does it today? And the answer is iron-sulfur proteins. So what's an iron-sulfur protein? An iron-sulfur protein has got a little cluster of iron, ferric and ferrous iron, so iron II and iron III and sulfide, maybe four of them. Four irons and four sulfurs, or sometimes two or sometimes three, but they're very small clusters, and they're always... In proteins, they're always bound by an amino acid called cysteine, and we've shown relatively recently that if you just mix iron and sulfur and cysteine in water at alkaline pH, you spontaneously form these iron sulfur clusters and they have a structure which is quite similar to the mineral [0:44:55.2] ____ graphite, which is part of the composition of these barriers that are doing...

0:45:00.4 NL: So we've effectively, we've just sequestered a little bit of this mineral surface with a single amino acid. No, polymers here at the moment, so this entire system, all the membrane itself is not made of polymers, it's just made of fatty acids. We have iron sulfur clusters bound by cysteine, which in principle, could sit near the membrane and drive CO2 reduction. In practice, it's really hard to show that where it kind of [0:45:26.7] ____.

0:45:26.8 SC: Sure.

0:45:27.9 NL: Because I know you're trying to demonstrate, but in principle, you can imagine that, maybe they kind of stick to the membrane and then they can drive a CO2 fixation inside the proto-cells, and now you've got an auto-trophic proto-cell which is going to grow because it's gonna make new organics inside itself rather than collecting them from the environment. So there's a lot of gaps there that we need to fill in, but in principle, if you've got auto-trophic growing proto-cells, then you've got the perfect environment later on for introducing genes.

0:45:55.1 SC: And don't take this the wrong way, but you are absolutely reminding me of why I do not want to be a chemist or a biologist. It's just too many things, too many chemicals, too many atoms, I just like a small number of electrons and protons and neutrons, to keep me happy.

0:46:08.8 NL: It's a real problem with both biology and chemistry, and I think... I kind of learn that the physicists mindset is very opposed...

0:46:17.6 SC: Much yes.

0:46:19.3 NL: To chemistry and biology. And the other way around, most biologists really struggle with physics, and to my mind, the answer is between physics, chemistry and biology, and unless... Unless I attempt to wrestle with physics, I'm not a good physicist, but I love physics, and I struggle... [chuckle] I struggle with the physics, but unless I make the effort to do it, most of what I've been talking about is actually a problem in physics more than other a problem in biology.

0:46:52.4 SC: Yeah, yeah. Well, I mean...

0:46:54.3 NL: How do you structure matter?

0:46:55.6 SC: Exactly. That's what makes it fun because there are these general principles of energy flow and entropy increase and information, but in the context of these very, very specific properties of all the different atoms and molecules that we care about, that's why it's a... But they're not actually challenging, but rewarding when you figure it out. And I think, I do want to once again contrast/compare to what is maybe the more common view in origin of life research 'cause we have this paradigm we haven't even mentioned yet of the RNA world, where RNA is a wonderful molecule because it can hold information like DNA can, but it's not quite as stable, so it's easier to sort of make and break apart and it can do functional things like proteins, so a lot of people really focus on creating RNA as the first step towards really understanding life, and you haven't even mentioned RNA yet, so what...

0:47:47.8 NL: Well, that's... RNA is clearly important, and it's central in how cells work today, and I think some form of an RNA world certainly happened. It's a necessary intermediate step to get to DNA and to get to real informational systems, but there's different ways of imagining an RNA world, and it is imagination because nobody's really ever seen one. You can create one by injecting a whole load of nucleotides into a bottle, but where did all those nucleotides come from? So the problem has been kind of compartmentalized, and we have the synthetic chemists who say, right, you want to have an RNA worlds before you can make RNA, you need to make the building blocks, the nucleotides. So my job is to make you the nucleotides and I'm a chemist, I'll make you nucleotides. Here's the way that works best. We start with cyanide in a terrestrial geothermal system, we have UV radiation, I can make you bucket loads of nucleotides, and now you guys, you RNA world guys, you can come up with systems, auto-catalytic systems that are going to make copies of RNA, and once you've got a system which is capable of making copies of itself, then it's going to become more sophisticated and at some point it's gonna say, hey, well, if I can use this ingredient from the environment to help me make a copy of myself, I'm gonna go ahead and build on some metabolism to the way the whole thing works. So that's the kind of the mainstream concept at the moment, so you have...

0:49:23.6 NL: Prebiotic chemistry makes you nucleotides, the nucleotides polymerize in some favorite environment, wet dry cycles is the usual one that people talk about, now you've got RNA, the RNA does it's stuff and invents things and copies itself, and we've got natural selection and that invents all of metabolism. And to my mind, almost every step of that is backwards, so... Where would I introduce RNA? What does life do? Well, life starts with CO2 and hydrogen to make Krebs Cycle intermediates, from Krebs Cycle intermediates, it makes amino acids and it makes sugars, and all of that has been done in the lab. To make nucleotides, you take the amino acids, and you take sugar phosphates, and you go through a bunch of steps, 10 steps or something to get the nucleotide building blocks for RNA. So this is quite hard, it's a lot of steps and to propose that this is going to happen spontaneously as prebiotic chemistry takes a lot of belief, I grant you. I've had a PhD student working on these questions for a few years, he's making progress, but we've not done all of it, but we're talking problems that last potentially for decades. Let's say it's successful, we're already in a kind of proto-cell world here because we've got...

0:50:51.3 NL: We're making the fatty acids, we're making the Krebs Cycle intermediates, they are kind of like fatty acids, really. So we have the spontaneous organization, we've got growing auto-trophic proto-cells as this term that I was using before, but cell-like things that are growing by converting CO2 and hydrogen into more of themselves and there's a system over time...

0:51:14.0 SC: Can you define the word auto-tropic?

0:51:17.9 NL: Sorry, yes. So it just means growing from... Instead of eating other things, you grow from gases in the environment, you grow from inorganic molecules in the environment, like plants. Plants are auto-trophic, they're growing from water and from CO2, lots of bacteria are auto-trophic, and they can grow perhaps from hydrogen or the hydrogen sulfide or something, and carbon dioxide, it's very similar principles, but they're not growing from organic molecules. They're not eating things. So heterotrophic is eating stuff.

0:51:49.5 SC: Okay.

0:51:51.6 NL: So what these early systems are doing then is of turning inorganic gases into organic molecules and they're growing. And let's say they get better at doing it... I wanna go into how we think that they can get better at doing it, but we think there are basic physical mechanisms of heredity that can make them better at doing it, but basically, the positive feedback loops.

0:52:13.2 NL: And we end up with nucleotides that polymerize. Again, I'm hand waving here, we now have nucleotides inside our proto-cells and they're going to polymerize, so now we have RNA. We've introduced our RNA quite late in these proceedings, and it's been introduced into something which is growing anyway, what's that RNA going to do? Well, it's going to improve proto-cell growth one way or another. Its success depends on, how could it possibly do that? Well, it can do that by effectively templating peptides, proteins, nascent proteins. Why would it possibly do that? Well, there are patterns in the genetic code that suggests there are bio-physical interactions between the codons or the anti-codons, through the code itself, between the nucleotides and amino acids, and effectively, they'll buy into each other in one way or another, it depends on their hydrophobicity, how much they like or dislike water, their size, there's various principles, they are very difficult to show in the lab. Again, I have got people working on that and it's a slow business. Some people claim they've succeeded, other people don't believe them, I really don't know, but the patterns in the code suggest it's possible. So we get a small string of RNA and it templates a small peptide onto it.

0:53:41.0 NL: What does that peptide do? Well, it has properties which are physical properties. Either its hydrophobic or it's hydrophilic. It wants to be in the solution or it wants to be in the membrane of a growing proto-cell. It's got those two phases right there, what's it gonna do if it goes to the membrane? Well, it probably is going to improve the way that the protons come in and reduce CO2, so it's going to improve growth, what's it gonna do if it sits there in the cytosol? Chances are it's going to interact with ions, like magnesium, in which case, physical chemistry says it's going to come up with a structure which looks a bit like the active site of an enzyme, such as the RNA polymerase enzyme, which is what actually polymerizes RNA in modern cells. So we have functions right there, which depend only on physical chemistry, so all we need to do is copy the RNA and [0:54:35.9] ____ CO2. So this is where the RNA world is in my...

0:54:38.6 SC: I like it. Yeah, okay, so you're blowing my mind here, so I'm gonna try once again to repeat what you just said in words that I understand and you can fix me. Biologists, bless their hearts, they like to imagine that natural selection is the wonderful mechanism that improves things, improves functions and stuff, so forth, but there are other mechanisms by which things improve. There's sort of optimization procedures just purely physically or chemically or energetically. So what we're saying here is that you can start with these primitive chemical reactions, protons flying across gradients, etcetera, etcetera, this can sort of... There's a step here that I'm missing, which is a very basic one, how this grows into something like the Krebs Cycle, but it becomes a little bit more dramatic and the Krebs Cycle intermediaries, as you've mentioned, become involved, and one thing I think maybe we glossed over is that in addition to shuffling energy around, the Krebs Cycle is responsible for making amino acids. Is that a true statement?

0:55:46.8 NL: Yes, not exactly responsible for making them, but basically that they are... It's a single step to go from a carboxylic acid, which is to say a Krebs Cycle intermediate to an amino acid. All you have to do is replace one oxygen with ammonia or something similar to ammonia, and it's that oxygen that gets replaced, is a pretty reactive oxygen. It's an alpha-keto oxygen. We don't need to worry about the terms, so basically it's gonna react with ammonia very quickly. And so the first thing you get if you react CO2 and hydrogen as a Krebs Cycle intermediate, if you put ammonia into that mix, the next thing you get is an amino acid. If you effectively steepen... If what you're doing is you're relying on hydrogen reacting with CO2, and a very small proportion is gonna react, let's say, but it's tiny proportion does, and it's going to make a few things, including perhaps a couple of amino acids. What are those amino acids going to do? Well, they have physical properties of their own, they're going to interact with other things. I said already, they can interact with iron and sulfur, and to make iron-sulfur clusters, cysteine will do that.

0:57:03.0 NL: What's that going to do? It's gonna sit in the membrane and it's going to convert more hydrogen and CO2 into organic molecules. So we're effectively converting more of this environmental disequilibrium into more of me.

0:57:15.0 SC: Right, right.

0:57:15.9 NL: And because these pathways should happen spontaneously, stuff should happen right the way down the pathway, and the more you steepen that gradient, the more of central biochemistry you should get right the way through to nucleotide building blocks of DNA. So that's the basic idea is, it's really about steepening the driving force through all of proto-metabolism by lowering the barrier to the reaction between CO2 and hydrogen.

0:57:43.4 SC: Right. So starting from this original CO2 and hydrogen desire to release their energies, we figured out chemistry that makes that happen. There's sort of a by-product that is amino acids, which leads also to other organic molecules and eventually even to RNA, RNA bases, which can then gang up, and then there's this fun step, which I'm not quite sure I understand, where just having RNA around lets you optimize the rest of the energetics in some sense, right? The RNA can kind of organize things, and maybe...

0:58:18.1 NL: What you have with... Let's say what you'd have in... We've got a population of proto-cells that are all growing and making copies of themselves, and we put RNA, we have RNA now inside it, and we got a load of random sequences of RNA. So there is no information, it's just random sequences, but those random sequences are capable of plating peptides non-randomly. So this random sequence is going to have a non-random peptide on it because the peptide that you form on that sequence depends on the sequence, even though the sequence is random, it's going to define...

0:58:51.4 SC: True.

0:58:52.7 NL: The amino acids in that peptide, so it's a non-random interaction there. And now we've got a population of these things all producing random RNAs with non-random peptides that can do some form of work. What kind of work can they do in this environment? Well, the work which is gonna be useful for a proto-cell is to make more proto-cells.

0:59:16.0 SC: Okay.

0:59:17.2 NL: Convert more CO2 into more... And if all of this whole system is capable of regenerating itself because all it is, is just thermodynamics, and the entire system is going to happen spontaneously, so long as the catalysts are there, you will go right the way through and you'll make more copies of yourself.

0:59:34.7 SC: Right.

0:59:36.3 NL: So we have... As soon as you have a random sequence of RNA in a growing proto-cell world, then we've got information on meaning because the meaning is coming from the context, and the context is cell growth, so the genes are introduced into a world of growing cells from the very beginning, which is all they've ever done.

0:59:57.2 SC: Yeah, so the RNA was not... It's not like RNA came into existence and whipped up some cell membranes, etcetera, it's that RNA found itself in this environment with proto-cell membranes and started... I don't want to speak too teleologically here, but it started to optimize things, it started to fine-tune things in ways that were trying to make more of itself, trying to abet this reaction that is going on.

1:00:22.2 NL: But we've cut out all the problem about how is it going to invent information from nothing. The answer is it doesn't need to, or all it needs to do is be a non-random template for peptides, which have function in the context of growing proto-cells, and as soon as you've got all of that lot together, then the whole information problem in biology just evaporates.

1:00:42.6 SC: Yeah, no, I'm very, very sympathetic to that. I've been thinking along similar lines myself, but okay, we're a long way from modern day life, and we wanna get to cancer and aging at some point, so let's accelerate ourselves. Because none of this stuff that we're talking about right now in that proto-cells are the very, very earliest cells has anything that we would recognize as mitochondria. Mitochondria were swallowed up much later on.

1:01:08.9 NL: Two billions years later now.

1:01:12.0 SC: Yes. So where do mitochondria come in? 'Cause that's where the Krebs Cycle happens these days. Yeah.

1:01:15.5 NL: Well, the Krebs Cycle happens in our mitochondria, but mitochondria were bacteria ones. Bacteria have their own Krebs Cycle and bacterial Krebs Cycle in an oxygenated environment works exactly the same way that ours does, it's effectively burning hydrogen in oxygen to generate energy, but if you put this bacteria in a deep sea hydrothermal vent, then everything goes in the opposite direction and the Krebs Cycle is in reverse and it's actually taking hydrogen and CO2 and making organic molecules. So we've got a long history of the planet, which started out four billion years ago with no oxygen in the atmosphere, and ends up some time around the Cambrian explosion where animals first appear, where oxygen levels were approaching modern levels, almost certainly, and we've got all of this spontaneous chemistry going on, which is going to depend really on the environment that it's in. And so the direction, when the Krebs Cycle either goes backwards or forwards, or it depends on the environment, so ours goes more or less forwards from our own point of view, we're burning hydrogen in oxygen to generate energy, but if you have an anoxic environment or a hydrothermal system, it's doing exactly the opposite of that, it's taking hydrogen and CO2 to make organic molecules.

1:02:34.9 NL: And so you have this very interesting question about the history of life on earth about, well, what happens to those cells where it suddenly flips? And the answer is, well, it probably doesn't suddenly flip, there are various... The idea that it's a perfect circle is almost certainly wrong. There's all kinds of different ways that it can operate, including a two-pronged version of the Krebs Cycle, so it's not a cycle in some sense, just calling it a cycle is already misleading. There's something platonic [1:03:02.5] ____ imperfection about it, and it's really not. It's just doing these two jobs that it always did, is producing hydrogen to burn, and it's on the one hand, or it's taking hydrogen and sticking it on to CO2 to make organic molecules, and it can do either at any time, it just depends on the environment it's in.

1:03:24.5 SC: Let me just make a statement rather than asking a question, then you can react to the statement because we've been talking about energy flow, right? Part of me as a physicist, again, wants to say, but really it's not energy, its entropy that is doing the work here because energy is just conserved, it's the same amount, but you have free energy, you have energy locked up in some low entropy form, in this case, the CO2 in the hydrogen, and you're increasing entropy by... You're finding a way to increase the entropy to lower the free energy, and I just wanna make this statement because it is part of my [1:04:00.5] ____ to convince people.

1:04:01.2 NL: No, you're absolutely right. I use the term energy very loosely, and I mean free energy most of the time when I'm talking about energy. And as far as entropy is concerned, I think this is one potential difference between the kind of physical chemistry that I've talked about and Shannon entropy is informational type entropy. If you mix oil and water, then you get the two phases, which form spontaneously, that's some form of order that you're getting from that... Why is it happening spontaneously? Well, this is happening spontaneously because the oil is hydrophobic and doesn't like water and is effectively releasing... It's a more stable state if it's separated, and the energy difference is heat, which is increasing the entropy in the surroundings, so when oil and water separate, entropy increases. The overall entropy of the universe increases as a result of that separation. And if we think about cells, we see exactly the same things. The protein folds in on itself, so the hydrophobic bits that don't like water go on the inside and the hydrophilic bits that like water go on the outside. So it's actually a low energy state, it releases energy as it folds in that way, and so it increases entropy. So everything's being driven by entropy increasing in the universe.

1:05:18.7 NL: But it's really being driven by the physical chemistry of hydrophobic and hydrophilic interactions of things. Now, I don't know that there is really an equivalent in Shannon entropy to that in purely informational terms is, you tell me. I'm out of my depth with that one.

1:05:34.0 SC: I would say that there probably is, I would need to go through the details, but the point is that, that...

1:05:36.7 NL: I imagine there is.

1:05:39.0 SC: As long as you're generating heat, what's happening is you're not keeping track of all the degrees of freedom that you count as heat, right? The motions of molecules or even infrared photons that you're giving off and you're sort of carrying away information in those. So you're only paying attention to some subset of the whole system, so it looks like it's becoming more orderly. But as you already said, the universe is becoming less orderly, so the Shannon entropy is also going up, I think... The reason I like to emphasize this is because I'm always hearing people lamenting the second law of thermodynamics, Ah, everything's running down. Entropy is increasing. Isn't it sad? And I wanna emphasize that we are only here because entropy is increasing, like we should be celebrating the second law of thermodynamics, not limiting it.

1:06:25.1 NL: Yes. Well, there would be no life without it.

1:06:27.3 SC: Exactly, that's right. Okay, so the mitochondria, good, our cells. Maybe talk about... 'Cause this is always a crucial question for exobiology. It did take a while for different cells to symbiotically absorb other kinds of cells, and now we call the mitochondria, and it did take some time and we're not sure why, like roughly speaking, some proto-biotic chemistry happened pretty early, but this absorption took a lot longer and then the eukaryotic transition also.

1:07:03.0 NL: Yeah, so all the prebiotic chemistry we've been talking about so far is basically, it's just chemistry and it should happen spontaneously, and it should happen in nanoseconds. The time scale, is not millions of years, the time scale is nanoseconds or picoseconds or something, and it doesn't... I mean, there's a lot of complexity there, but it doesn't strike me as necessarily that difficult. You know, we've got as far as strands of RNA and now as soon as that can copy itself, we have natural selection and the world's your oyster, really. So I don't think the origin of life is necessarily that serious a problem on a planetary scale, and I suppose nobody will be working on it if it was because the idea is we can do it in the lab, we can solve this problem, or at least we can understand how it might happen. But then from a biologist or a geologist point of view, there is a long gap of more than two billion before we see complex eukaryotic cells, so that's our own type of cell, which we've got mitochondria and they've got a large nucleus with lots of DNA...

1:08:12.9 NL: And we are very closely related to plants and to mushrooms and other eukaryotic cells, so plainly, we share a common ancestor, and by definition, a common ancestor arises once. So you could say, well, maybe there were thousands of separate origins of complex things, and they all just disappeared, and that may be true, but it's also possible, it only happened once, and the only evidence we have is that all the complex life we see around us is closely related and shares a common ancestry and by definition, only happened once. So if it happened on thousands of occasions, then we ought to see something in the fossil record, we ought to see...

1:08:51.4 NL: If we look in strange environments, maybe we'll find something. We never have, we've been looking for a long time. So you can turn the question on its head and say, okay, well, let's say it did happen once. Why would it only happen once? What are the... The thing about, again, an informational context, it's basically from the genes and the information that we know that it happened once. So again, I'm not knocking genes, but if you think about the genetic variation in bacteria or in archaea, it dwarfs the amount of genetic variation in eukaryotes, they have explored genetic sequence space far more thoroughly than eukaryotes ever did, and yet in their morphology, they remain small and simple, and standard, they've got amazing molecular machines, but they are always at the level of the molecular machines, they don't have large bloated cells with lots of moving parts in them... Lots of membranes. Lots of structures inside.

1:09:46.4 NL: So why then would you have the step change. And I think the most beautiful answer, it may not be quite right, but the answer is, well, you had some cells, some bacterial cells getting inside an archaea host cell, basically something very similar to bacteria, and that changes the topology of what cells are instead of having a cell membrane, which is your interface with the outer world, which you're also using to power everything because that's where the charge is, now we've internalized the charge along with some genes which are needed to control that charge, and you can now use your outer membrane to do anything else. You no longer need it to be charged in the same way, you don't need to have genes next to it in the same way that bacteria do.

1:10:32.6 NL: So suddenly, you've got a new structure, and over time, without asking anything other than normal natural selection, the bacteria living inside are gonna get smaller and simpler and throw away stuff they don't need, they're gonna compete with each other and they're going to end up as basically little power stations, optimized power stations, and the host cell is gonna pick up all this superfluous DNA that's floating around from these bacteria, and it's got more power than it knows what to do with, it's got these pesky bacteria, parasitic bacteria living inside that are probably gonna eat it, if they have half a chance. So it's got to kind of make sure it's using them for something useful for itself, but not being eaten, and so we've got a kind of a power struggle going on. The conflicts of the interest between the host cell and the symbiont, and it's a very productive way of seeing selection to say, okay, well, number one, it's not that easy for one cell to get inside another cell, if these cells are tiny bacterial things with the cell wall surrounding them, so that's rare, but we know of examples, and then once it's happened, we've got this power struggle going on where it's more likely to end in failure and extinction than it is in a fancy eukaryotic amazing system.

1:11:50.1 NL: So this gives you a reason why it only happened rarely. It doesn't say it had to happen once, it just says it's not gonna happen all the time, and we only have evidence for it happening once, maybe it happened a few times and they disappeared. But it also says why bacteria do not become large and complex. Well, they don't become large and complex because they don't have endosymbiosis, they can't restructure their energy generation in the same way, they are basically stunted by their cell structure, and so we have this step change where cells get inside cells, and now we have a kind of Russian doll type set up where the whole relationship between genes and energy changes to a different format, and that changes everything that's possible. It effectively allows eukaryotic cells to have a massive genome of nuclear genes, which allows you to do... To become multi-cellular, it allows you to... All the cells in your body have got exactly the same genome, but your brain cells only use some of those genes and your kidney cells use different genes, but if you made your brain cell from bacteria with one type of DNA and your kidney cells from another bacterial cell with a different type of DNA, they'd fight whereas if they're the same DNA, they're the same cell type, they don't fight in the same way. This is standard evolutionary biology now.

1:13:10.3 NL: But to be able to do that, you need to have a large genome in the first place, that if these cells switch on, these genes and off those genes, and those ones switch off these genes and on those genes and so on, you need a large genome, and to do that, you need a power supply and mitochondria are the power supply. So as soon as you've got a system which is effectively capable of building sophisticated bricks, you can build a sophisticated multi-cellular organism then which is capable of using those bricks to make organs and whatever.

1:13:38.8 SC: So if we buy the chemistry story that you... That you laid out for the very origin of life, it's possible that that happened multiple times all over the place. You've said that it's actually kind of easy and the time scale is short, but in contrast, you're saying that there probably was literally one cell that was the first eukaryotic cell, and we were all descended from that.

1:14:01.2 NL: Not literally one cell, but one population of things snuggling up to each other, probably some kind of trade going on in raw materials between cells that are snuggling up and one of them gets inside another one, it happens here, but it also happens in the guys over there. These are processes that are happening when dealing with populations, but it's two populations of cells that are interacting with each other in a particular environment at a particular time, and it's that that gives rise to these complex cells. So we're not dealing with this kind of singularity of one cell gets inside one other cell and there's an amazing explosion, we're dealing with processes and populations and the probability of these relationships happening. So it is kind of normal probabilistic science, we're not talking miracles here, but we are talking about improbabilities [1:14:51.7] ____ probabilities.

1:14:51.8 SC: No, absolutely. And it wouldn't be surprising if we found life ubiquitous in the galaxy, but most of it was... It's a simple, slimy celled organisms.

1:15:03.6 NL: That would be my best bet.

1:15:03.9 SC: Yeah.

1:15:04.0 NL: Which is a bit of a disappointing bet...

1:15:07.3 SC: We'll find out.

1:15:08.2 NL: I would like it to be like, Hitchhiker's Guide to the Galaxy out there, but my own science tells me it's not likely to be.

1:15:15.2 SC: Okay, so we're almost up to the present day. There was a big leap to become eukaryotic and get mitochondria, but for better or for worse, there's a still family resemblance between the energetics of the Krebs Cycle in our cells today and this early chemistry that you're talking about, but as biology does, biology is very opportunistic and it uses things for different things, and now the Krebs Cycle is playing all these different roles. So we're winding down, but say a little bit about where we are in terms of aging or cancer or things like that.

1:15:50.9 NL: Yeah, so there's basically, there's this paradox then about the Krebs Cycle, it does two things. It started out making the carbon skeletons for growth. So it was providing the precursors to make amino acids, to make nucleotides, whatever it is, it's basically biosynthetic, it's making stuff. But today, we're using it... If you read about it in textbooks, it's gonna say it's used for burning things, it's used for respiration, where it's stripping the hydrogen out of food and we're burning it with oxygen [1:16:23.6] ____ we're stripping it from food, we're stripping it from the Krebs Cycle intermediates themselves. But actually we're doing both. And that puts quite a pressure on how the mitochondria work... So if you've got good functional mitochondria, you can do both at the same time, but as things run down over time, it gets harder and harder to do both, and then instead of having a kind of continuous flux going through the cycle, it begins to wear down a little bit as well. You can get flux going in the opposite direction, like the bacteria, and this happens in cancer, it was discovered 10 years ago that where you are seeing reverse flux through parts of the Krebs Cycle.

1:17:03.8 NL: And the work that I've been doing on this is to do with fruit flies and how their mitochondria work, and what we found is that how well they grow and how fertile they are, and things like that, depends on how good their respiration is. If they respire well, then the Krebs Cycle goes turning along and everything's hunky-dory, and they are capable of providing enough energy that they need to power everything to do their courtship dances. They're great fun to watch, these fruit flies, but they're also capable of growing using the Krebs Cycle intermediates to make more cell membranes, to make more proteins, to make more DNA and RNA, and so on.

1:17:54.7 NL: So you need to do those two things, and what we know from cancer is that the ATP is perhaps the less important of the two things that you need to grow, is... If you wanna make two cells from one cell, you need some ATP, but actually, you also need a lot of proteins, you need a lot of DNA, you need a lot of cell membranes. There's a lot of materials that you need to make two cells from one cell, you're doubling your materials, and the Krebs Cycle is providing a lot of that material. So you've got this tension there between making the energy you need, not necessarily to double the cell content, but to live, to run around to do stuff, to do a courtship dance, in the case of these fruit flies, and so on. At the same time, you need to make stuff, you need to make more cells. And it depends on how good your respiration is in the end. And as we get older and respiration begins to run down a little bit...

1:18:51.1 SC: I noticed.

1:18:51.7 NL: We get less good at doing the two things at the same time, and you end up doing one or the other, and the problem here then is as we get older, the Krebs Cycle begins to swing into reverse and begins to... We get less energy and more growth in effect, we slow down and we put on weight, and it's all about flux through the Krebs Cycle. So the last chapters in the book are about, why is this happening? And again, it's thermodynamics. In the end, it's really just about... We're doing a billion reactions a second in every cell, more than up to 20 billion reactions a second in every cell, if some of them go wrong and are not repaired, we do this second after second after second after second, over time, proteins get damage. We know that. This is not a sexy theory for aging, but it's been around a long time. And what we found is that as respiration becomes slightly damaged, the Krebs Cycle starts to go the opposite into reverse, and that gives you a growth phenotype which is a little bit like what cancer cells are doing, which is to say it's making more stuff, it's making more fats, it's making more membranes, it's making more cells, we begin to put on weight, we begin to have less energy, we slow down.

1:20:04.1 NL: We don't wanna go for the run, which might help our Krebs Cycle kind of go back into the forwards direction and so on, and this becomes an epigenetic state. This flux state is reinforced in the activity of the genes, then effectively the Krebs Cycle intermediate is bleeding out of the mitochondria, or saying to the genes, don't worry about making lots of energy, worry about making more fatty acids, worry about bulking up, and it's not a sustainable situation in the end, so we run down.

1:20:42.5 SC: Does this set of insights suggest any solutions? Is there a Krebs Cycle diet that will be your next self-help book that will help run their Krebs cycles in the right way?

1:20:54.8 NL: It doesn't obviously. I think the only solutions that come to my mind, the things that people do anyway, and the things that I've started doing more, as I'm finding myself in my mid-50s, and I've... In my 40s, I was putting on weight and slowing down a bit and spending too much time at my desk, and I'm beginning to realize the only way to make my Krebs Cycle go forward, is eat less and run more, and that helps.

1:21:18.8 SC: You're not gonna make any money with this book. Sorry, this is not gonna...

1:21:24.6 NL: All the people out there who are doing that anyway are gonna love it, but they're already doing it, so they're not gonna learn anything, and the people who don't want to make their Krebs Cycle work in the right way, are gonna be angry with me.

1:21:35.6 SC: Alright, here's the final question. But [1:21:38.9] ____ we've been talking about... Perhaps this is your interest, but it's certainly also mine, the origin of life question, and how these things come in terribly unfair, but how close are we to figuring this out? Is this a matter of 100 years from now we'll hope to have a complete picture, or do you think that progress is coming along sufficiently rapidly that people will come together? I've noticed anecdotally that folks in the origin of life community, especially senior people, tend to disagree with each other quite energetically in various ways. We're not a consensus yet.

1:22:15.4 NL: We're a long, long way from a consensus and... Yeah, there's not much love lost in that field. It's hard actually, and I wish it wasn't like that, and I try not to be like that. But maybe some people will say I am like that, but I don't want to be, but anyway, the point is, we'll never know how life started on a... Which is to say, that's a historical question, and you can make your time machine and go back and then what are you gonna look for? Where are you gonna go? Are you gonna go to a terrestrial geothermal system or are you gonna go to a deep sea hydrothermal vent, and if you see some kind of slime on the walls of this thing, what are you gonna analyze? Is it live yet? Or is it not yet? Is this a failed experiment in the origin of life, or is this one that works? As a historical question, it makes no sense at all, it's pointless. What we can do is understand intellectually how a sterile, wet rocky planet is capable of giving rise to living things. And we can try and think through all of the steps and we can try and demonstrate each one that really it can happen, that each step can happen, the idea that we can then put all of those steps together and do a [1:23:29.7] ____ make life, I understand it because I can make it. I don't see that happening at all. Certainly no time soon.

1:23:39.9 NL: Now, there's some people out there saying we'll able to do it in five years time, or if you read the small print, we really... What they mean is, well, I can make some kind of prototype thing which is capable of copying itself, but it's not really life as we know it. What gave rise to life is a planet on a planetary scale? These vents that I talk about were probably across the entire sea-floor of the early earth. We're dealing with... I refer to the earth as a battery, it's a giant battery, and the flow of energy and matter through this battery what's animating cells today, and we're dealing with planetary forces, the idea that in the lab, with our poultry facilities, we will be capable of producing cells that a planet... I don't know how many nanoseconds it took the planet to do this, probably quite a lot, but maybe only a few million years, but the idea that we would be able to do it, I don't think it's realistic that we are ever going to create life, but I think that what we can do is understand and demonstrate the believability of the steps that it's possible that a planet gives rise to life in this way. And I think that's something to aspire to.

1:24:50.3 SC: Yeah, it sounds like an appropriately humble goal in what is after all a pretty hubristic pursuit overall. So Nick Lane, thanks so much for being on the Mindscape podcast. This is great.

1:25:01.5 NL: It's great pleasure. Thank you.