So I'm a chemist who lapsed into biology and that magic number 35 years ago comes up again.
And when I became interested in where biology gets its energy from and how it handles it.
And of course the biological energy comes from the sun.
But there is another source of biological energy and that's geothermal energy
which the biological world at the bottom of the oceans receives from the thermal vents.
I won't discuss that.
So you're familiar with the idea of harvesting solar energy through solar panels and also through hydroelectric power stations
because they also are harvesting solar energy.
That the sun evaporates the oceans, it makes the clouds, rain falls on mountains and then it's collected in dams.
And the potential energy of the water stored in the dams drives turbines to generate electricity.
And that's actually quite a useful analogue for what happens in biology as you'll see in a moment.
This process by which biology harvests energy is photosynthesis.
And it's an incredibly complex process but consists of 2 separate reactions,
the so-called light reaction where solar energy is used to split water and generate oxygen and reducing equivalents.
And of course without this reaction there would be no life on Earth.
So this is where the oxygen that we respire comes from.
And then the reducing equivalents are used in the so-called dark reaction
to fix carbon dioxide and generate high energy organic molecules which we consume as food stuffs.
And so we harvest the products of photosynthesis on an industrial scale through agriculture
and then consume the high energy compounds,
the carbohydrates that are generated here in the form of corn which we then either consume directly or we feed to animals
and then consume the energy in the form of fats and proteins from the animals.
And the question I want to address is: Where do we convert energy in our bodies?
So here you are on the left with your organs and each of these organs is made of cells.
So here's a typical human cell.
So all human cells look like this apart from red blood cells.
They contain a nucleus where all the genetic, almost all the genetic information is kept.
The cell is bounded by a hydrophobic membrane to contain the contents of the cell.
And besides the nucleus in the cytoplasm of the cell are organelles,
the Golgi apparatus which is kind of post office,
the endoplasmic reticulum where proteins are made,
lysosomes which are effectively recycling stations and the mitochondria.
So it's the mitochondria I'm going to be talking about.
They're the power stations of cells.
And they have quite complex structures.
So they actually have 2 membranes, not 1.
So there's an outer membrane depicted in blue.
And inside there's the inner membrane which you can see is highly folded.
And it's in those highly folded membranes that the key steps in biological energy conversion in our bodies take place.
Now the process as you'll see is complex but at the heart of it lies a very simple piece of chemistry.
So if the sphere represents those highly folded membranes, the chemical energy
that is being released from the food stuffs that you ingest by oxidative process effectively by controlled burning,
that chemical energy is being used simply to transfer protons from the inside space to the outside space.
And this builds up an excess of protons in the outside space.
And this excess of protons is a source of potential energy.
And it's referred to in bioenergetics as the proton motif force by analogy with the electron motif force in electricity.
And effectively it is a voltage.
And we generate across our inner membranes by this process a voltage of approximately -200 millivolts.
And that energy store, that potential energy, can be coupled to other processes and made to do work.
And so as I'll show you in a moment the packages of biological energy that come out of mitochondria.
So this is the molecule adenosine triphosphate.
It's a high energy molecule.
It's produced by machines.
And so there are the proton pumps that I've just depicted
that harvest the energy and generate the proton motif force
which is analogous to the dam of water in a hydroelectric power station.
And then there's a turbine that converts this energy and uses it to drive the production of this useful fuel adenosine triphosphate.
And then there has to be a transport system because the energy packets are being produced inside the mitochondrion.
There has to be a transport system to deliver those energy packets to the cell,
to supply the cell with the energy that it needs to do everything that it does,
to produce proteins, to replicate DNA and so forth.
So in a simplified form now this is...the grey box represents the inner membrane of the mitochondrion
and embedded in that membrane are 3 proton pumps and they're called complexes 1, 3 and 4.
And so the products of oxidative metabolism, the burning of sugars and fats,
which I'm not going to describe produces redox energy in the form of the molecule NADH.,
nicotinamide adenine dinucleotide in its reduced form.
And the reducing equivalents of electrons are fed into this extra-membranous arm of this huge complex here.
So this is a protein complex built of 45 different proteins.
They have a combined molecular mass of about 1 MDa.
And the electrons are transferred through this membrane arm by quantum electron tunnelling events.
And they arrive at a quinone that is bound in this region here.
The quinone is bound in the oxidised form.
It becomes reduced.
So here's the reduced quinone.
And then equilibrates into the hydrophobic membrane.
And concomitant with this process of reduction of the quinone protons are ejected from the inside space to the outside space.
This is a matter of very active research at the moment.
And the precise mechanism by which proton translocation occurs is not yet elucidated.
But we know that for each 2 electrons that pass one at a time through this extra-membranous arm transferred to the quinone,
we know that for each 2 electrons 4 protons are ejected from the mitochondrion.
And then the reduced quinone carries the electrons to the next proton pump.
This is called complex 3 or the cytochrome bc1 complex which is made of another 11 proteins.
It's actually a dimeric complex.
You can see there's a plain of symmetry running through the middle here.
And here we have a rather complete understanding of how the protons are pumped from the membrane to the quinone.
Reduced quinone binds, transfers energy into this complex.
I won't describe what happens in detail, there isn't time.
But oxidised cytochrome c binds in this region here.
So this is the space between the 2 membranes, the outside of the inner membrane.
So oxidised cytochrome c interacts here, becomes reduced.
It then loses its affinity for this complex and then carries the electrons to the third proton pump in this chain.
So this is the terminal oxidase that Hartmut Michel is going to talk about in the next talk.
And by the way this is the site at which cyanide would kill Schrödinger's cat.
It would actually inhibit or not as the case may be.
It would actually inhibit this complex.
And what happens at this enzyme is that almost all the oxygen that we breathe in becomes reduced back to water.
So oxygen is being produced by photosynthesis and in our mitochondria it's being converted back to water.
And again concomitant with these events more protons are ejected from the inside space of the mitochondrion.
And there's quite a complete understanding of how this enzyme works, but not a completely, not a totally complete understanding.
So this briefly is how redox energy generated by oxidation of sugars and fats is converted into the proton motif force.
So this is how the potential energy is built up.
And then the potential energy is used by this device here that I'm going to describe in detail,
which then generates adenosine triphosphate from adenosine diphosphate and inorganic phosphate.
So the ATP is made here inside the mitochondrion and is then shuttled out by this protein here which is called ADP/ATP translocase.
So it's exchanging internal ATP and taking it out and making fuel available in the cytoplasm
and bringing back the spent fuel ADP to be reconverted back into ATP.
And there's a related protein that brings back the phosphate.
And so there's a very active cycle of generation of ATP and mitochondria being taken out into the cell, used up
and then the spent fuel being back and regenerated.
And from the amount of oxygen that we breathe in daily we can calculate how much ATP each of us is making by this process.
And each of us makes about 60 kilograms of ATP in this way every day.
So let me describe the turbine, the enzyme that's making adenosine triphosphate.
These are pictures taken in the 1960s of inner membranes in mitochondria.
And if you look carefully you can see that there are kind of lollypops attached to the surface.
And this is the turbine, the ATP generating enzyme.
So over the years my colleagues and I have built up this structural model of the turbine.
So it's made of 30 proteins approximately.
And the part shown in balls we've resolved to atomic resolution using mainly x-ray crystallography but also nuclear magnetic resonance.
And so this is the catalytic part.
You can see the ADP and phosphate molecules going into that interface there and then something happens.
They're brought together.
Chemistry happens and then ATP emerges.
There are 3 such catalytic sites in that region.
And the chemistry is driven by the rotation of this central shaft.
This is going around at about 100 to 200 times a second driven by the proton motif force across the membrane.
So protons go back through the interface between the rotating ring and the green protein here.
This is a stator structure that's holding the catalytic part static relative to the rotation of the rotor.
So the rotor itself contains 9 different proteins.
And one of the things that I've been interested in recently is that this ring here in humans is made of 8 identical proteins.
And I'll show you in a moment.
It takes 8 protons to go through the membrane to generate 360 degrees of rotation.
But this region here is stepping through 120 degree steps.
And this is the stepping action.
Each step brings about the synthesis of one ATP molecule.
So how can this be that this has got 8-fold steps and this has got 3-fold steps?
And of course what it means is that energy has to be stored transiently.
It's somewhere in this structure and then released in a quantised fashion to bring about the 120 degree stepping action.
And so this rotor that's driven around by the proton motif force has a number of elements
that it's useful to think about derived from manmade machines.
So there's a spring, we think, that's responsible for the transient storage of energy.
And then there's a crank which you've just seen.
So the asymmetric structure turning around in the middle of the catalytic part.
This modulates the properties of the catalytic sites.
In one state the sites are able to bind ADP and phosphate.
In the second state they make ATP and in the third state they release the ATP.
And so the chemistry is dependent upon this asymmetrical crank.
And then there has to be a bearing which has friction in it in order to generate torque,
in order to generate the 120 degree stepping action.
So this is the way we think about this structure here.
So the blue part is the catalytic part that I'm not going to describe in detail today.
Here is the rotor and the ring in the membrane.
So the ring driven by the proton motif force is responsible for torque generation.
We think that the energy is stored transiently in this lower red part here.
So it's like a fly wheel or a spring in this mechanical analogue, I've shown here on the right.
And then this part is the crank or the cam which is revolving and pushing the pistons in this part here to make the chemistry happen.
And here is the bearing with friction in it which has to hold at some point
in order to generate the torque and the 120 degree stepping action.
And so in this mechanical depiction here, here's the flywheel.
This is the cam.
And here are the pistons pushing against the catalytic parts of the enzyme to make the chemistry happen.
So I'll try and explain to you how rotation is generated.
So here is the ring in the membrane here, it's made of proteins.
They're called C proteins.
They're very simple proteins.
They just have 2 transmembrane alpha helices linked by a loop in this region here.
So the asymmetrical rotor is attached to the top of the ring.
And the catalytic part is up here in the ceiling space.
Now the most important property of this ring is that although this is a hydrophobic environment
-remember this whole structure is buried in a phospholipid bilayer-
nonetheless there are carboxyl groups on each of the C proteins.
And in this model here we've drawn it with 12 C proteins in the ring.
So there are 12 carboxyl groups disposed around the circumference of the ring.
And in this region here the green protein, the A protein, is closely associated with the blue ring.
And the idea is that the A protein provides a half channel that allows protons to access negative charges in this region here.
And once neutralised this negative charge is more hydrophobic
and so it will simply move to this position here via Brownian motion.
And that brings another negative charge here.
Another proton goes in and so forth.
And so the neutralised carboxyls carry the protons around the ring until they reach this point here
which has the properties of making the carboxyl re-ionise, regenerate the negative charge
and release the proton on the other side of the membrane.
And the reason that the rotation is unidirectional is that there is as it were a tremendous pressure of protons in this direction
because of the -200 millivolts across this structure.
And so that pushes the ring around in the direction shown.
Now one of the questions that I had been interested in is how many protons are required to make each ATP molecule.
And in the example if there were 12 C proteins in the ring each 360 degrees of rotation would therefore consume 12 protons.
That 360 degrees of rotation as I've mentioned briefly would generate 3 ATP molecules up here.
And so in this model the cost of making each ATP would be the translocation of 4 protons.
And so as it says here each 360 degrees generates 3 ATPs.
A full rotation requires 1 proton per C protein.
And therefore the proton-ATP ratio is the ring symmetry divided by 3.
Now people expected that there would be one ring symmetry throughout the whole of biology.
But biology is more complicated than that.
And the ring symmetries differ on the one hand between multicellular life and on the other hand between unicellular life.
And therefore this is not as people had supposed a universal number.
And these are the cross sections of rings from the human enzyme depicted here.
From saccharomyces cereviciae, brewer's yeast.
This is from a bacterium that's got 11-fold symmetry.
Here is 13-fold symmetry, this is the enzyme found in a bacterium.
14-fold symmetry, this is the enzyme found in the ATP synthesising enzyme in chloroplast and 15-fold symmetry in a blue green algae.
And so what this means is that the enzymes containing these different sizes of ring pay different energy costs.
So this bacterium is paying 5 protons to make each ATP molecule whereas we pay 2.7 protons to make each ATP.
So what these rings represent are different gears in the motor.
This is the lowest gear, this is the highest gear.
And the idea is that because we're able to generate -200 millivolts,
we're able to drive this high gear and operate with higher efficiency.
Whereas this organism lives in an energetically relatively deprived ecological niche, it is supposed
and therefore it's not able to generate the -200 millivolts.
It generates a lower potential and so the price it has to pay is then to drive a lower gear
costing more energy to make each ATP molecule.
Now I've been interested in the last 2 or 3 years to find out whether this C8 solution that we find in man persists throughout chordates.
And we've produced evidence now that the C8 solution is found in birds, reptiles, mammals of course,
amphibians, ray-finned fishes and cartilaginous fishes.
We've not looked at tunicates yet.
And so the C8 solution, 2.7 protons per ATP, obtains for 50,000 species of vertebrates.
And we've latterly been looking at invertebrates.
We looked at echinoderms, chordates I've mentioned, annelid worms, brachiopods, molluscs, crustaceans, insets and nematode worms.
And in all these cases the C8 solution also obtains.
We're currently looking at porifera, sponges.
And my bet is that the C8 solution will also apply to the whole of multicellular life.
And so this would be 2 million species in addition to the 50,000 species of vertebrates.
Whereas we know that in the unicellular world, in yeast for example, they pay 10 divided by 3 protons to make each ATP.
So this seems to be a solution for multicellular life and other solutions apply to unicellular life
depending on the situation in which the animals live.
To my mind this leaves a lot of unanswered questions.
It opens up all kinds of other questions that I don't have time to discuss here.
But I find it very surprising that the whole of multicellular life, given the diversity of niches,
ecological niches in which those animals are found, that a single solution applies to all those animals.
So at the end I just wanted to say a few more general things about this field of bioenergetics.
About some of the...how we can apply our knowledge of bioenergetics to solve some of the challenges that you will be faced with.
As we know we have an aging population
and the process of aging itself is certainly related to processes that are linked to energy conversion in mitochondria.
And as we age also there's an increase in the incidence of neurodegenerative diseases in the population.
And again there's a link to the energy converting processes in mitochondria.
I'll say a little bit more about this in a moment.
We're also trying to use up knowledge of bioenergetics to generate new drug targets
to combat this problem of drug resistance in relation to infectious disease.
And in fact the only drug to be introduced against tuberculosis in the last 30 years
is in fact an inhibitor of the ATP synthesising turbine in that microorganism.
So, one can make drugs which will affect the ATP generating machine in the microorganism
without affecting the ATP generating machine in our bodies.
And then I also want to say 1 or 2 words about increasing demand for energy.
So, I said at the beginning that almost all genetic information is in the nucleus of the cell.
And the reason for that qualification is that the mitochondrion also contains a small amount of DNA,
certainly 17 kilobases of DNA and 32 genes.
Now that DNA molecule differs from the DNA in your nucleus in so far
as it's derived entirely from your mother, there is no paternal component in there.
And so any mutation in the mitochondrial DNA that leads to disease will be inherited in a matrilineal fashion, in a non-Mendelian fashion.
And this is a characteristic of the so called mitochondrial diseases.
They almost inevitably lead to neuromuscular disease.
And these are diseases of early life.
And in the western world about 1 in 6,000 of the population are affected by these diseases.
But there's also, as I said a few moments ago,
increasing evidence for the involvement of the dysfunctional mitochondria in Parkinson's disease, Alzheimer's disease and Huntington's disease,
these scourges that are increasing in our population.
In the case of familial Parkinson's disease where the disease is inherited
there's no doubt whatever that that arises from dysfunction in the mitochondria.
In the case of sporadic Parkinson's disease which is a more common form of it the links are not so clear yet.
But there clearly are links.
There's also, apart from the involvement of mitochondrial dysfunction in neurodegenerative disease,
there's also involvement in cancer and involvement in aging.
I don't have time to go into those topics.
Now, you may have noticed in the last few days that the mitochondria have been in the headlines.
And so I took this from the Daily Telegraph: "Britain could create the first "3-parent baby" through IVF."
And then the same newspaper said: "Three parents: Sorry, but this is science gone mad."
So this is the way of correcting those diseases where the mutations are in the human mitochondrial DNA.
So what one does is to take a mother who is carrying the mutation, you fertilise the egg,
you then take the nucleus from the fertilised egg and transfer it into a cellular background
where you've removed the nucleus where the mitochondria still exist from a donor that is not carrying the mutation.
And so that's where the third parent comes in.
The 2 normal parents to make the fertilised egg.
The third parent to provide the mitochondria.
And this is a therapy that's been developed at Newcastle University in Britain.
And there is now permission to go ahead with this and use it in a clinical setting.
So finally I want to just mention something about the energy crisis.
So, in 1950 the population of the world was 2.5 billion.
Today it's 7 billion.
And the population is increasing by a billion every 13 years.
And not only is there a problem with the increase in the population but as this index, the human development index,
that's defined here, it contains life expectancy, adult literacy, school enrolment and GDP per capita,
as this index goes up so does the demand for energy.
So it's not just a question of the population increasing,
it's a question of demands from developing nations increasing as their development index goes up.
And at the moment 85% of our energy comes from fossil fuels, mostly from oil and gas and coal.
We require 15 terawatts of electricity.
So that's 150 billion 100 watt bulbs, light bulbs burning continuously.
And by 2050 that will have doubled to 30 terawatts.
And you'll notice the United States consumes currently 3.5 terawatts.
And alongside that increasing demand for energy is this relentless rise in atmospheric carbon dioxide.
So this shows figures up to 2004.
But it continues in the same fashion up to the current day.
So, all that I was going to say at the end is
that we can use our knowledge of bioenergetics to contribute to producing greener forms of energy.
And that topic will be discussed here at this conference.
So I end there and thank you very much.
Applause.