How the Krebs cycle powers life and death – with Nick Lane

thank you, thank you very much, it's a real pleasure to be here and it's amazing to see so many people you know, this is a talk about the

krebs

cycle

, isn't it? It's hard to know how you're trying to do it. make

krebs

cycle

s attractive to people um and I've done my best to ask a sort of Douglas Adams question here um you know his famous question about

life

and the universe and everything uh and this is my question, do you know? What does it bring to earth? to

life

and our own lives to an end and maybe it can make us aware too uh so the answer, I'm sorry to tell you, it's not 42, it's not 41 or 43, it's not that either and it's quite complicated, isn't it?

What I think we could probably all agree on is that metabolism is scary and this is a metabolic map of our own metabolism and all the little dots, the circles are molecules, different types of molecules and the lines that connect them are enzymes. -catalyzed reactions and these are the metabolic pathways and the flow goes through all of these things, all of this is what makes us alive and it's enormously complicated, so how can we start to deconstruct it and make it simple so that I can understand it, it's That's why I write books. I try to understand these things myself and if I can make it clear then I think all of you will be able to understand it very easily too, so one thing to note about this is what All biochemists immediately notice that in these types of graphs is right on the middle, there you'll notice there's a blue circle that stands out and says, I'm different, that's the Krebs cycle and you have to say what the heck.

Is it working there? Why is it like this? If you look very carefully, you will see that on the right side there is a yellow one. There is another cycle there that is almost hidden and was actually also discovered by Krebs. That is the urea cycle. but that's a little less central to the whole metabolism, so biochemists as a rule don't like to ask why they perceive it as speculation. Until relatively recently, you weren't allowed to ask why you would never get a job if you asked. How does that work mechanistically? What's going on? An evolutionary biologist asks why and I'm a biochemist who loves evolutionary biology and I look at that and I say why oh why oh why it's so complicated how can we deconstruct?

Well, you start by looking at the bits and this is the Krebs cycle as it is normally presented in textbooks and there really is nothing better, right? I mean, you look at the molecules themselves and they appear to be rearrangements of fragments of carbon, hydrogen and oxygen and then there are all these details of the different types of enzymes that do these different jobs and you look at it and you think, well, I'm not going to become a biochemist. , I'll go and do something else, um krebs. He himself is, of course, famous. This is a painting by Hans Krebs that was done for the Krebs festival in Sheffield in 2015, so this would have been 80 years after he went to Sheffield and discovered the Krebs cycle in 1937 when he was in Sheffield. and that is his drawing on the blackboard of the cycle that he discovered back then.

It's very difficult to convey how little we knew and how difficult it is, you know, you look at a cell with a microscope and you can see really soft things and now we can see. proteins down to atomic levels of structure it's extraordinary what we can see now, but we still can't see the metabolism as it's happening, we still can't see these molecules as they go through a cell, they're actually too small to see them that way. And then we have to imagine it and that's a very difficult thing again about biochemistry. You never actually see anything.

You have to try to rebuild it. It's a bit like detective work. So what do these molecules look like? Well, I have set. Some here look a bit like a collection of beetles, and you know, I think it was JBS Haldane who was asked what all this studying biology had taught him about God, and he said, Well, God had an excessive love for beetles. . I think God has an even greater love for carboxylic acids. These are everywhere in cells. This is basically if you believe that life is based on carbon. This phrase is based on carbon.

These are the carbon skeletons that life is made of. really central, I didn't bring my glasses and in any case you probably don't want to know that there are slight differences between these molecules, these are molecules in the Krebs cycle and it says roughly 2 h, there are two hydrogen atoms. have been extracted or added between those molecules and you can think why you would want to do it so well, I'll get to that, although this is what most people come to the conclusion: medical students, biochemistry students, this is basically it what they can remember. about the Krebs cycle and everything they want to know about the Krebs cycle, so we tend to gently mock him and sometimes Professor Krebs himself, who occasionally set himself as a target, this is what it's all about, um .

I'm going to spend a minute or two on this because we're going to see this kind of thing several times in this talk. This is my attempt to simplify it. Everyone should know this and it is taught in schools. Seeing down here at the bottom it says glucose, it doesn't have to be glucose, it can be food of any description and it breaks down into smaller pieces and I just marked a bit there called pyruvate and pyruvate is it breaks down a little bit more and enters the Krebs cycle. I am not going to try to explain what happens in the Krebs cycle step by step.

I do it in the book and try to make it as attractive as possible. but essentially you go around the Krebs cycle and what comes out is carbon dioxide and hydrogen comes out, it doesn't come out as hydrogen gas, it doesn't bubble out of there. I've written 2h and that 2h is attached to another molecule called nad nadh nicotinamide adenosine nicotinamide adenine dinucleotide um, this is another problem with biochemistry, it's all these difficult names, but really all it does is pass two hydrogen atoms, a where it passes them, to the surrounding membrane, how you can think of this. like a mitochondria or like a bacterial cell or like none of your cells because mitochondria are inside your cells, but they take 2 hours of division.

I'll show you what happens in a moment, but eventually they react with the oxygen and that's what it creates. all our energy in the form of atp so that energy this reaction between hydrogen and oxygen you can think of it as rocket fuel really this is what drives us this is what makes us alive on this slide it is what makes us different from a corpse eh you I know that there is no difference in information between a living person or someone who died a moment ago, the content of the information is exactly the same, the difference is the flow of energy and the flow of matter that passes continuously and this is the core of all that, the krebs.

The cycle rotates continuously in all our cells. Notice that there's some kind of purple thing around the membrane itself and I have a lot more little h signs. These are the protons. These are the charged nuclei of hydrogen atoms. And? The energy released by this reaction between hydrogen and oxygen is used to pump protons across a membrane, so don't worry if you're a little scared by terms like protons, but basically now you have a charge on that membrane. there was an email sent by the r yesterday and it started about frankenstein uh and it said you know we all think life is about electricity and actually no it's not about

nick

lane

who will come and tell you everything it's about chemistry well, no, no, I mean, it's actually electricity, uh, not like Frankenstein, but this cycle, the Krebs cycle, is linked to the ignition of a membrane, so you have an electrical charge on the membrane and that electrical charge on the membrane.

It's small, it's 150 millivolts across the membrane, so it's not much, but if you were to shrink yourself down to the size of a molecule so that you were the size of, say, a carbon dioxide molecule or something like that, the electrical force What would you feel? field there are about 30 million volts per meter, that is the intensity of the field, so it is equivalent to lightning, which is what gave life to Frankenstein, so we have this Frankenstein monster, we have this happening everywhere our mitochondria, in all our cells. I've drawn this circle all along to simplify things.

This is what the mitochondria actually looked like and you can see that they have these very thin membranes, they are called Christine membranes and this is where all this proton pumping happens. If you were to iron all these membranes from one of your own body, it would be about four football pitchers of membrane that is charged like lightning, that's what makes us alive and that. The charge will flicker and die if it doesn't, if we don't keep spinning the Krebs cycle, that's why the Krebs cycle is so central to what's happening with life now, what I'm showing at the bottom is kind of a cartoon . of this process, so that in 2 h the two hydrogen atoms are divided into their components into electrons and protons, the electrons pass through a kind of wire inside the membrane, so that we have a current of electricity inside the membrane that flows into oxygen. of electricity drives the extrusion of protons through the membrane, so we have this electrical charge on the membrane and then they flow back through a turbine, in effect, the ATP synthase which is on the right side, so It's basically like a hydroelectric dam where the membrane is equivalent to the dam, the proton reservoir, if you like, is equivalent to the reservoir and the ATP synthase, well, it's a rotary motor, it's an extraordinary protein, this is another reason why the one that biochemists don't like to ask why, how? does something with that majesty, uh, evolve, it's simply a product of genes and natural selection, etc., but when I think about these questions, I wonder how it came about in the first place, it's a strange fact, but basically all life in the earth works. this way this way of generating electricity is conserved as universally as the genetic code itself this is how cells work bacteria work this way archaea work this way plants animals everything works this way so there is something profoundly important in how it works and yet it is very difficult In my opinion, these are two of the most important discoveries in the 20th century of science, one being that mitochondria themselves and bacteria work in the same way are basically cells electric fuel pumps. discovered by peter mitchell and i mean and jennifer moyle because jennifer moyle did all the experiments mitchell was a genius who thought things that no one else had thought before um but a lot of people thought he was a crazy nutcase uh and really he would practically walk out of the room if he came in , it really made people angry, it was jennifer moyle's experiments that made other people take mitchell seriously and it is a sad state of the world that mitchell himself got the nobel prize in 1978 but jennifer moyle was overlooked , which I think wouldn't happen to Dallas, let's put it that way, the other person there is Lynne Margulis, she really got the idea that mitochondria were once bacteria, so mitochondria, the energy packets in our cells themselves, were once free-living bacteria, um and and acquired two billion years ago, probably in the course of the evolution of complex cells, so these bundles of energy that we have were once free-living bacteria.

These are two of the most important discoveries that, again, I think everyone should know, but suddenly it gets a little messier and the Krebs cycle is not just about extracting hydrogen from food and burning it into oxygen, it is also used to produce the precursors for everything else, it provides the carbon skeletons for growth, it provides the carbon skeletons to make amino acids and to make fatty acids and to make sugars and from them to form nucleotides, the building blocks of DNA, etc. , so it is really fundamental for biosynthesis, as well as for energy, which is always recognized in textbooks, but it is a little complicated and awkward and put in a different chapter and we prefer not to talk too much about it, but there's a problem here because if you have a problem with breathing, it's not only affecting ATP synthesis, but it's also affecting the electrical charge on the membrane, if we can.

No, if we can't have the flow of electrons to the oxygen, then you don't have the electrical charge on the membrane, so the Krebs cycle can't turn and you can't produce anything, so if you have a problem with breathing, you have a problem not only with energy but with everything, with growth and development. Now fortunately this doesn't happen a lot and I will explain later in the talk why that is nothing more than the key to what is happening actually comes from cancer from cancer studies done in the last 10 to 15 years or so. , now it turns out that what you're seeing here is that you can.

I'm going to point this out, this shows one of the complexes. has gone the other way and we are taking the 2 hours instead of taking them from themitochondria, we are taking them from beyond the cytoplasm of the cell from outside the mitochondria we are feeding them somewhere else and that allows us to maintain this electrical charge, but look what else is happening, the Krebs cycle is going backwards, it has been reversed and now it is taking carbon dioxide and hydrogen from around them and converting them into um biosynthesis precursors cancer cells love this cancer cells want to make copies of themselves that's what they do they need to grow and divide you need to have all of this you need to have more fatty acids for membranes you need more nucleotides for DNA you need more amino acids for protein, so cancer cells do this and it's becoming increasingly clear that this happens quite frequently, so it becomes really very complicated.

This idea goes back to Warburg, Otto Warburg, a great German biochemist from the 1920s. He started talking about problems with mitochondria that he didn't understand and actually this photo of him looking a little like Dr. Frankenstein doesn't mean he was a very polarizing character a brilliant but extremely haughty biochemist uh and and um he In fact, Krebs was also a mentor, so these ideas that are now very popular in cancer known as Warburg change the idea that mitochondria effectively become biosynthetic instead of producing energy go back 80 years, 90 years to Warburg and suddenly they are fashionable again. and he wasn't right about everything, but he was right about a lot of things and I'll come back to that.

What I'm trying to say is that it's not a cycle, it's more like a roundabout, a magic roundabout with things coming and going from almost every junction, this is the magic roundabout in Swindon. I've noticed that when you try to find pictures of the magic roundabout in Swindon you always find the same picture and it's a pretty old picture, look at some of the cars there and you see those are pretty old cars so we're still reusing the same one image of the magic roundabout, probably because it is the only one where everyone drove correctly. I suspect I was there once and it's a scary place, it really is difficult to organise. that kind of flow to really work why would life organize a system where the same cycle is used to generate energy and make all the precursors for growth?

It seems crazy and if something goes wrong in any part of this because everything works in series then the whole system goes wrong, you know, this seems like a crazy way to do it now, when things go a little wrong, it changes the activity of the genes, there is an epigenetic switch, so literally thousands of genes are turned on or off when something goes wrong in the Krebs cycle and this is something that has been rediscovered in the last 10 years or so: if the concentration of intermediates increases or decreases, then genes are turned on or off, so it's you know, far from just being the energy packets of the cells, this is really the beating heart of what's happening with life, so why do we use the same cycle to create and destroy?

Not even a phoenix can do both at the same time. Well, this is not the answer, I put this slide because today was the last day of a postdoc in my lab, uh, gla in one and he's going to take a lecture in Thailand, he's Thai, uh, he's leaving this weekend of the week, um, etc. This is in Thailand, I have no idea where he really is, but my god, he looks good. I think this is probably the correct answer to almost every other question. This is the closest we're going to get to 42, but why? Why do I say it's not the right answer because plants have fooled us because plants, because of the way they do photosynthesis, they basically produce sugars that way and a lot of chemistry took a long time to discover and it was kind of of focused on the way that textbooks teach and the way that we are all taught biochemistry, you really know that I was, I was helping my youngest son, who is about to finish his general exams and he says in his textbooks that photosynthesis produces glucose, well, no, not really.

Actually, he took it to people who were trying to figure out the way that they couldn't understand why glucose wasn't being produced at all. It took them 10 years to figure out what was going on. Well, now we know, and that's why we've got the idea that photosynthesis makes sugars and respiration burns sugars and it all works as simple as this is the right answer and it's not that nice, it's definitely less than 42. This is um this is in Yellowstone and these are green sulfur bacteria and they grow completely, they are also photosynthetic, but they grow in a completely different way and they grow in a way that is much older, this is probably at least between one and two billion years before the origin of photosynthesis. we know this and this is what they do and this is the key to everything really what you've seen there is the Krebs cycle again, it's a slightly extended version of the Krebs cycle and what's happening is going backwards like it happens in cancer. cells and it's taking hydrogen, it's actually taking it from hydrogen sulfide in this case and it's taking co2 and it's putting them together to form organic molecules, so one turn of the cycle requires four molecules of carbon dioxide, this is about four times more effective than Calvin Benson's most familiar cycle, which is seen in most plants or all plants, was discovered in 1966 and the first author of that paper was Mike Evans and there he is in 1964, uh , with his car, and that car actually dates back to when I checked it and realized that the car was already old at that time, it's a 1950 model, so that gives us a slightly skewed version, but this is the cycle of inverse Krebs, first discovered in 1966 and it took literally 25 years before uh the field began to believe that Krebs himself never referred to Krebs.

He died in 1981. He wrote a paper in 1981 on the evolution of metabolic pathways and never once mentioned the reverse Krebs cycle. I have no idea why not, but this really explains a lot. Here was the original figure showing how it works in that 1966 paper on the left side and you'll see it says reduced paradoxin, ferradoxin, it's the red protein and you can see right at the top, these are X-rays, uh. Crystal graphs showing electron density. They are really beautiful. These figures no longer look like this. That's how they used to make them. This was an article from 1972 and you can see the structure from which they emerged. the electron density now, can you make out that there are some squares and you can see those little kind of cubic lattices there, those are iron and sulfur clusters, so there are four iron atoms or ions and there are four sulfur ions there and It's a little bit it's a little cubic structure like a mineral in effect and that's the part of this molecule that does the work.

There are two places in the Krebs cycle where it's really difficult to make this chemistry happen and it's ferrodoxin that drives it. and then the whole cycle can go backwards and it's not involved in energy it's really involved in growth in doing things in making all the precursors that you need for life now this uh this too 1966 was another document um and this is perhaps one of the most important ones i have read and probably margaret dehoff has someone. Can we raise our hands? Who knows Margaret Dalhoff's name. margaret oakley day half of us here know it, john allen, but i know he knows it, but it's a real shame. because because she is really, she was described as the father and mother of bioinformatics and this was an article, she founded this whole field where now we all compare genetic sequences, letter by letter, to say well, this, this from this. bacteria are compared to this of that bacteria, etc., we can reconstruct a complete tree of life.

It all goes back to Margaret Dayhoff and this is an absolutely amazing article. I don't know if you can read the summary, but what she says there. I can't read the summary because I forgot my glasses, but what she says is that ferradoxin, this molecule that makes the Krebs cycle go backwards, has a structure that is made up of smaller repeating units and is ultimately reduced to four amino acids. . that repeat and repeat and repeat and they became more complex and these are some of the oldest amino acids and she says there, the part that I have highlighted in red says that maybe this goes back to a time at the origin of life before there was even a genetic code or before the genetic code was fully formed, which is one of the most exciting lines I've ever read in a scientific paper and what she did there is kind of a piece of detective work. to look at the modern sequences, deconstruct what makes them up, realize the whole context and I'm taking it back to the very origin of life, it's exciting, it's one of the best things about science? and and that's a challenge, so how could that work at the origin of life?

She had also pointed out some of the older clostridia bacteria and things like that that grow from carbon dioxide and hydrogen pretty much the same way they do. They don't actually use the reverse Krebs cycle, but they use something very similar, so the reverse Krebs cycle uses hydrogen and co2, it uses ferrodox in this iron protein and they also need to have the electrical charge on the membrane that they can. They don't grow without this electrical charge, so what they're doing is really simple chemistry and this is a tree of life built by, you could say Bill would probably describe himself.

Bill Martin here would probably describe himself as a disciple of Margaret Dayhoff and he has a very similar vision that he is incorporating real biochemistry and combining it with genetics and this tree of life that he has here goes backwards, you can see below , at the bottom we have the bacteria in archaea that appear to emerge independently from a hydrothermal vent at the bottom. This was a radical radical view when he presented that in 1999, that's this document, um and surprisingly it has become, I won't say mainstream, but it has become much more accepted now, probably, than before. certainly it was when he turned it off, the bacteria in the archaea that are there at the bottom are growing from carbon dioxide and hydrogen and the vents were discovered the year after that paper, the type of vent that I was talking about by deborah .

Kelly, who was captain of the submersible Alvin, the submersible Alvin had discovered black smokers in 1978, so this was brought forward to the year 2000 and she discovered a whole new type of vent system known as alkaline hydrothermal vents, and they're not. They are not like black smokers with smoke coming out of a chimney. They are actually active vents, but you don't see much happening. They're more like some kind of gothic cathedral or something. They are really beautiful things. They are really rich in hydrogen gas. Hydrogen gas is bubbling out of these vents and they were predicted to exist ten years before their discovery by a guy called Mike Russell, who is a geologist, and he had found something in the ground, sort of a fossil version, and figured out what should be happening. in the oceans and linked it to the origin of life.

Such a surprisingly lateral thought and the key to how Mike Russell thought about this is that he was saying that these vents have a kind of mineralized sponge texture. for them it is a kind of labyrinth of interconnected micropores uh and the walls between them today in the ocean in the lost city discovered by deb kelly uh today it is calcium carbonate aragonite but four billion years ago when there was no oxygen in the atmosphere They were probably made of other things the chemistry of the ocean was very different and there were probably a lot of iron and sulfur minerals there with a structure that is very similar to the iron and sulfur clusters that Margaret Oakley was talking about and was involved in. the reverse krebs cycle they bubble hydrogen out of the soil the early oceans were rich in co2 we have these groups of sulfur ions and because they are alkaline vents that go to an acidic early ocean we also have ph gradients so we have effectively electric charges We charge these barriers, so I really think that you know, the perfect set of circumstances is almost too perfect to be believable.

And scientists would have to be skeptical and say, "Well, am I seeing faces in the clouds or something? This is what I'm excited about. This is on the left. You're seeing kind of a poor sketch of a pore in one of these vents. It's alkaline on the inside, it's acidic on the outside, there's a barrier around it. It's a pretty thick barrier compared to. And it has these iron and sulfur minerals and on the right side we have a bacterial cell, It's acidic on the outside and alkaline on the inside. We have a membrane and it has a protein that pumps protons, so topologically it's actually very similar and that's how I imagine it at least, so what I'm doing here is drawing it exactly how I drew the ones. other things just to show you how the topology works, on the left side that you're seeing.The pore with the iron-sulfur barrier surrounding it is causing hydrogen to react with CO2 in something that is equivalent to the reverse Krebs cycle.

It may not be a complete cycle, but it's basically driving this reaction and it's where the amino acids and fatty acids come from. those are the easiest things to do, the fatty acids will form together to form a membrane and on the right side you see that this membrane has formed around it and now everything isAlthough the concentrations are a little higher, the driving forces are the same This is probably the most complex slide I'm going to show you show this afternoon and I'm not going to analyze it in detail, but the one thing I really want you to take home from this. it's in I can't see it correctly but in green if I remember correctly it says h2 and in brown it says co2 maybe it's in maybe co2 in green okay these are the steps that start with carbon dioxide and continue up to the metabolism. we know it in the Krebs cycle as we know it and it's hydrogen hydrogen hydrogen carbon dioxide carbon dioxide hydro it's just one after another it's exactly the same thing repeating the chemistry and you think well why is it doing this chemistry again?

I'm going to slightly skip over this is doing this chemistry because you can't really do anything else when you think about what happens with CO2 binding near a surface to a mineral surface or to a cell membrane, maybe or to a group of metals or something in what electrons are being emitted. transferred from hydrogen, where do they go? I'm not going to go step by step, but what I would like you to remember from this is that all I am doing is transferring electrons in the presence of protons and I am going from carbon dioxide in each step until the end of this slide, I got to methanol, so we're transferring electrons to it and then we take a proton and we end up with a hydrogen more electrons transferring in this is the electron pair is moving towards the oxygen it binds to a proton it binds to a proton we end up with methanol and we can continue it's the same chemistry if you want to know more well I explain it more in the book but we We just saw it here in a few simple steps, wow, pyruvate itself, which I showed you at the beginning, is the beginning of the Krebs cycle in our own Krebs cycle, but these are all the intermediaries, these are the building blocks of life. and it is almost inevitable chemistry and now it is being done in the laboratory.

Pretty much everything I just showed you in the last five years, five to seven years, has been done in the lab and actually works, so I've been doing it. I've been talking about these ideas for a long time for more than 10 to 15 years or so and for a long time it's a little embarrassing because I would say well, in theory, all of this should happen. It is very difficult to make it work. in the lab and now not only in my lab but also in other labs around the world, people are doing this chemistry, it really works, it's fantastic, it's a very exciting time, so this is possible, it's not proven, but it is possible.

I'm just going to say one more thing before we move on to the origin of life, which is good to go beyond there. This is a completely chemical system driven by the environment itself to go beyond there. While you need genes, you need to be a proper cell, this is not a proper cell, it is a type of proton cell with an uncoded metabolism, where do the genes come from? Well, there are known interactions and I don't really know how they work and I just really drew some things here for fun, but there are known interactions between the bases and the nucleotides in RNA, so the letters, if you like, of RNA and amino acids, it is mainly about hydrophobicity, so if the hydrophobic amino acid will interact with a hydrophobic base. so water hates amino acids and bases that harm water and size also matters and what this means is that if we have these interactions, if we have a high enough concentration inside the protocells, then we can introduce a random sequence of RNA just any old letter you want doesn't make sense, it doesn't contain any information, but yes, yes, that will somehow create a non-random sequence of amino acids to form a peptide and it's not random because biophysical interactions say that whenever you get this type of hydrophobic base.

You will get this type of hydrophobic amino acid, then you will have produced a non-random peptide that may have a function because it can make the protocell grow faster or slower and if it is effective, it is encoded by that sequence and that sequence when copied is can transmit, so I'm not going to say anything more about that. We can ask questions later if you want, but in effect, there is no problem with the origin of information in biology if we think that metabolism comes first. and that these types of protocells come first, everyone has to produce the building blocks, but if you have a pure rna world where rna invents everything, it's really difficult to determine where all this information is coming from.

There is no problem in this environment, so, skip ahead, they have abandoned these cells, now they have genes and they are gone, and it is interesting that they have preserved the cells, they have preserved a structure that is topologically similar to the p

lane

t itself, so, the The interior of the planet is the core and the mantle, if it is rich in iron and the iron is effectively saturated with electrons, you could say that it wants to get rid of those electrons and oxidize and the exterior is relatively oxidized, a lot of carbon dioxide and water, etc. ., and the carbon dioxide will be collected, uh, the electrons from the iron and these things that I'm showing in the membrane there is a membrane these are hydrothermal vents actually in the crust these are the connection between the mantle and the oceans and the atmosphere and Cells are basically exactly the same with a relatively negative charge on the inside and a relatively positive charge on the outside and they maintain that difference.

It's important because for these cells to grow they need to get their hydrogen, they always need hydrogen and they need to get it from hydrothermal systems and they can't get it from anywhere else, really at this stage they can get it as hydrogen gas or they can get it as hydrogen sulfide that comes out of these systems or even as a ferrous ion, so an ion charged with two plus that can um. that and it can be oxidized to ferric and it can be oxidized, indeed, uh, and the electrons and protons can produce hydrogen, so it works in all kinds of interesting ways, but life is limited by the availability of the 2h that I've been talking. to photosynthesis and what photosynthesis does, these are cyanobacteria, what photosynthesis does is take the 2 hours of water, it uses the power of the sun to extract from the water, it extracts the 2 hours and uses them to form organic molecules and the Oxygen is the waste product and If you think of the Earth as a battery, like a giant battery, then we are supercharging that battery, the outside, the atmosphere, etc., now it is oxidizing even more, with an even more positive charge on relationship with the interior, it really wants to extract electrons and those electrons now come from water, which led to a kind of catastrophic change in the history of the Earth at the time of what is known as the great oxidation event 2.2 billion years ago. years and this is just a beautiful picture of an iron banding formation.

I love these things, they're not really diagnostic of the big rust event, but they are beautiful to look at. The point is that although oxygen appeared in the atmosphere at that time, not much, I mean limited amounts and a lot of the oceans actually remained. very low oxygen yes there was probably zero oxygen for another billion years or so after that but the thing is when oxygen levels increase we go well think about what the Krebs cycle is doing for two billion of years, all these bacteria are simply growing by taking 2 hours. out of the environment and so on and making the krebs cycle go backwards and that's how they grow and then there's oxygen in the atmosphere and everything goes backwards forward which direction does it go I mean it changes direction and goes the other way direction, how do you think?

How can you avoid an accident when something like this is happening? Well the answer seems to come in part from the first animals so these are from about 560 million years ago and these are the first trace fossils that have been found so this is before the Cambrian explosion um and these are little worm like things um that crawl through the mud and the mud that we know was full of sulfur, it was sewage gas in real conditions and somehow they did it, they needed oxygen to do this, but they did it. to deal with these sewer gas type conditions and it was a time when the oxygen levels were going up and down and were quite unstable and so how did they actually do it so well?

It seems like they didn't necessarily use a Krebs cycle as we know it. They actually have a type of two-pronged Krebs cycle. Many bacteria do this too, so instead of running it as a cycle in either direction, they split it up and maintain a balance there, so I won't go into details. of that, but it's basically a way of preserving it. If you produce too much in 2 hours, then you become a little saturated and cannot work and if you do not have enough, you will be incapable. burn anything, so this is a way to maintain balance to have just the right amount.

Now the interesting thing about these early animals is probably the way they manage to do it. It took me a long time to realize this obvious thing. really, which took me a long time to see. Bacteria, if you change the conditions, they have to keep changing their state because you know if there's a lot of sulfur around, you have to deal with the sulfur, you turn these genes on, you turn those genes off. run your krebs cycle this way and you'll be fine and now it changes, now there's some oxygen, so you turn those genes off, you turn these genes on, you change the krebs cycle and you do what animals can do with different tissues is have this the tissue does one job that tissue does a different job this tissue supports that and so on, so we have different flow patterns that go in different ways to make the Krebs cycle work.

I think this was probably one of the things that really made the Cambrian explosion possible. In this tissue differentiation, we think of them doing different jobs, but all of those jobs are supported by the way the Krebs cycle works, so this is an image I've always liked that shows the Ediacaran fauna on the left side. , so these were We really don't know what they were. They are marine filter feeders attached to the ocean floor often 200 meters deep, so they are too deep to be photosynthetic. They look a lot like plants, but they are too deep. It is completely dark at 200 meters depth, so they are not plants and they are all extinct.

The reason we don't know much about them is that they became extinct just before the Cambrian explosion and they probably became extinct because we know there was a time. where the sulfur levels increased back then and they probably just suffocated and those first animals that I showed you crawling through the mud dealing with sulfur were effectively pre-adapted to those conditions, they got different tissues that did different jobs and they were able to survive. Those changing conditions and oxygen levels emerged around the time of the Cambrian explosion and all of a sudden what we're seeing there are predators and prey, we're seeing armored animals sneaking around and eating each other and you can't. do that without oxygen and the simple reason is that you can't have multiple trophic levels in the absence of oxygen because of efficiency, so aerobic respiration is about 40 percent efficient and what that means is that you get approximately 40 percent efficiency. 40 percent of the energy from lunch you eat and the rest is wasted and then another trophic level will extract 40 percent of the energy from that, so an aerobic ecosystem can support five or six trophic levels, while an anaerobic one It's more driven. per fermentation is about 10 percent efficient in comparison, so you can only have two, at most, three trophic levels and that means that predation doesn't really pay off, you never have large enough population sizes, so we know the Cambrian explosion from geological evidence and from the types of behavior that these Cambrian animals had, they were predators and they would have had a krebs cycle like ours and they would have had the same problems that we have, you can be pretty sure that they would have shown signs of aging and things like So I'm showing you here again the complete Krebs cycle that I showed you before, the complete system inthe one we eat glucose, whatever it is, we are spinning the cycle in an oxygenated atmosphere, we are charging the membrane you have an electrical charge on the membrane, the problem is you can't do that forever, you will end up with damage just with the change, the pace of life, you will get damaged proteins, you can replace damaged proteins, well, you can fix everything if you want, but this is the obsession of evolutionary biologists.

You will never see an evolutionary biologist who is not obsessed with sex. So how much effort do we want to put into sex and what can you see behind this Pacific salmon that everyone puts in? their effort in sex and then suffer what is known as catastrophic senescence, immediately afterwards they drop dead in heaps, they put everything into it for the good of their offspring, in effect, now we all do the same thing to some extent, not in a catastrophic way , but we have to take some measures. type of evolutionary decision: how much repair do we want to do?

Because the more repair we do, the fewer offspring we will have because we have dedicated more resources to that instead of this. You have to choose to a certain extent and different animals make that decision in different ways, some put a lot more resources into extending their lifespan and others put a lot more resources into sex right away if you want it, the problem is, again, already You've seen it before, this just shows if we're racking up damage, if we have. We've made a decision, well, we're going to put most of our effort into sex and some into surviving a little longer.

You will take damage and part of that damage will be done in breathing and when you get the damage and breathing then you are going to have a problem with the whole system because it is all connected in series and I showed you this before also with Warburg now it turns out that this is not only specific to cancer cells, it's pretty much what's happening in a lot of our cells as we age and the reason is damage, so again you can see I'm painting it. I should have painted it blue, but anyway, if we have damage here and we have some Proton flow again, we are putting the Krebs cycle in reverse again.

I would like to call this a wiring diagram for being old because what you are seeing here is less energy because we are cutting off the first one, so instead of pumping out 10. protons or pumping out six protons, so for every 2 hours we have we get less energy so we're losing energy in comparison and we're spinning the krebs cycle backwards so we start gaining weight we're fixing co2 like we're plants or something we're gaining weight uh and and um and we are getting slower and that is the essence of aging now and it also makes us more vulnerable to cancer than diseases of old age, so instead of having a breakthrough operating the Krebs cycle, we get something much slower, so we don't necessarily pump it out that way, it's much more subtle than that and this can last for decades, this type of state, so there are some cells that can't do that.

These are pancreatic beta cells and this is surprising to me. They need to detect glucose and when glucose levels rise in the bloodstream they release insulin and that lowers glucose levels again. How do they detect glucose well? It senses glucose by effectively having a system of flux capacitors so that they allow the glucose to flow freely and allow the Krebs cycle to spin freely and that generates a membrane potential so that it charges the membrane electrically and if you have a highly charged membrane, that's the signal to produce insulin now, if you have respiratory damage and you can't load your membrane much, you get this signal from glucose and you can't just turn the Krebs cycle that way, so you can't do it. you don't get the insulin out, so you end up with hyperglycemia and you end up with diabetes.

Now it's not just those cells, it's also the neurons. Neurons love glucose, they can get by with ketones and things like that, but they were very reluctant to burn amino acids. acids or fatty acids or other things like that, well, they have the same thing, regardless of what the reason is, I'll get to that in a moment, they have the same problem as they get older, so you're going to be losing power. If you're not careful now, if you're faced with that situation, if you're left with glucose and you can't burn it off because you don't have a complete Krebs cycle, well, you won't be able to think, so what are they?

You're going to do it well, this is an idea that comes from um from uh from Eric Shone and Estella Aria Gomez, which is a very good idea, I don't know, it's not a very popular idea in the field, I have to say, but I think they We are on to something, what they are saying is that you increase the calcium because with the calcium you can you can increase the rate of respiration and the load on the membrane, so pump out a little more calcium if you don't have enough glucose, pump a little. more calcium in you can charge your membrane a little more and it works, except that calcium can be harmful and it is especially harmful to the place where the sources of calcium are, which are the membranes right next to the mitochondria called breasts, the membranes associated with mitochondria.

Now this is part of another membrane system called the endoplasmic reticulum and it's making proteins and processing proteins and many of the proteins that you'll be familiar with in Alzheimer's disease, so you know you're going to see plaques and tangles in the brain. of people with Alzheimer's disease the plaques are made of an amyloid protein and the amyloid protein is made is a small part of a processed precursor protein the amyloid precursor protein all that protein cutting and sorting is happening in mothers in these membranes right next to the mitochondria and they are damaged by calcium because the mitochondria themselves are not working properly you are right he is right she I don't know but it makes a lot of sense to me but the other reason I like this and I know that these are the last few minutes the other reason I like this is it says it's very important to have a high membrane potential when glucose floods an area of ​​the brain so you can see in pet scans and things like that the parts The brain lights up when glucose enters, so it closes, the capillaries open, the flow of glucose enters this part of the brain, it lights up, we are receiving a large electrical charge on the mitochondrial membranes and it seems that we really need Is that charge connected to things? maybe even more important than just thinking or just the mechanics of thinking is connected to consciousness itself this is a really beautiful idea by luca turin uh now luca turin is a biophysicist and he's had all kinds of interesting ideas uh I'm not going to talk about the most of them, but he came and visited me at UCL a few years ago.

He now he wanted to talk about general anesthetics and he didn't know anything about general anesthetics, but what he told me is that well, nobody knows anything about general anesthetics. I don't know how they work, they all have different shapes and they all have different charges and none of them interact in any significant way with the hand and glove type of receiving mechanism and that was what interested him even in Zen. he said an inert gas that is basically a sphere of electron density, it doesn't really have a shape, it doesn't really have chemistry, but it does have physics, he said, and this physics involves it in some way, I don't really know how it does it. is able to transfer electrons and what I had demonstrated using uh epr and techniques like that, so electron paramagnetic resonance is that oxygen is involved, the transfer of electrons to oxygen xenon accelerates it and that is associated with why you can get under control general.

Anesthesia short circuits your breathing, it can only do it very gently because if it did a lot of it it would kill you immediately, so it must be a very subtle effect, but you know, if you overdose on a medication general. anesthetic will kill you, so there is some subtlety, probably these things are actually pretty bad at doing it and therefore less likely to kill you, but somehow they do it anyway, now we also don't know a lot of things that really We are deeply ignorant. We do not know what the electroencephalogram is, we know that we can interpret it very well, but we do not know what structures in the brain produce the electric fields that give the EEG, we know that they are neurons and we know.

These are not just individual neurons, but networks of neurons because the signals are high enough that they come from networks, but the assumption in the field is that they come from the axonal membranes, from the plasma membranes themselves that depolarize as neuron. is firing, but inside the neurons there are mitochondria and there are many more mitochondria and the charge is at least twice the charge on the plasma membrane and we have these beautiful membranes that I showed you before in these beautiful Christie membranes, they are often parallel to each other and we have an oscillating current in them they generate electromagnetic fields it is really difficult to measure them I am trying to think of ways to do it other people are trying to think of ways to do it but it is very likely that it seems to me that the electromagnetic field The fields generated that We detect with the EEG are generated by the mitochondria within the cells rather than by the membranes themselves and that they interact with the fields in the plasma membrane and this is happening, so why mitochondria and why electromagnetic? fields and this is the final slide that I am going to leave you with and this is the first slide that I showed you as well.

This system now think of it as a bacteria and it has the Krebs cycle that generates amino acids. and everything needs all the precursors and it's burning things into oxygen and it's taking in glucose or whatever from the environment and it's charging the membrane and this system works in series so it's all connected in time and as time goes by as oxygen levels will drop then respiration will decrease the membrane potential will drop and so moment by moment in the life of a bacterial cell and I'm showing you a bacterial cell here um the stream of consciousness is in effect um the real time report on the State of the cell in relation to its environment.

I say nothing about human consciousness. I'm just saying what, from the point of view of biophysics, is a feeling if we feel in love or if we feel pain or if we feel hungry. or whatever it is what is what what is a feeling we don't know there's no there's no answer for that and there's actually two types of explanation for it, one of them is that it's some kind of concoction it's an emergent property of a complex enough central nervous system but it still does not say what it is and in reality what it says is that there is some deception that is not real, it is just a concoction to fool us and make us think that we are conscious.

I don't find it very attractive as an idea, the alternative idea is that well, it's a property of matter, that there is an unknown physical law and that the sun is conscious in one way or another and so is everything else, and that doesn't I find it very attractive. credible, it seems to me that consciousness is widespread at least throughout the animal kingdom. It seems to me that anyone who has a pet will recognize that they have feelings. And why where do we stop? So what is natural selection that acts to beautify consciousness from simpler animals?

In the end, the majesty of human consciousness, what is the simplest possible form of consciousness that we can imagine, what is it, if you want a little consolation, what is the simplest possible form, I think it is the electrical charges in the membranes generated by the spinning of the Krebs cycle in relation to the environment as a real-time report on the state of cells in relation to their environment. I'm going to stop there. I have to thank my group because they are doing an incredible job. I didn't present any data tonight. I usually give talks with a lot of data.

I have to say that these days they are brave and they are working on some of the most amazing questions in science, but they are not easy questions and they can take a long time to make a lot of progress and that can end a career and that's why I say you have to be brave. If you do a PhD and you don't know the articles and every result you get for three or four years is negative. Well that's not great, you know they may force you to leave science so it takes some bravery to do it and I'm very grateful to them for coming on this adventure and making this adventure for me much more exciting because we are I am making progress and I think we are starting to understand things.

I'll leave you alone with a reverse Krebs cycle painting by Audrey Noel as a book. I hope I did it in time. Yes. 8 o'clock. Fantastic.