Was the emergence of life on earth a highly improbable fluke? (Part II of IV)

The Universal Life Force

Everybody that has lived in the past and the vast majority of people alive today, believe that what separates living from non-living things, is the presence of some sort of ‘life force‘ or ‘elan-vital’. Living things clearly have something that separates them from non-living things such as rocks and streams and mountains and clouds. And this something, they say; escapes from your body when you die, leaving behind an inert shell: your corpse. It’s easy to see why this idea took hold because it makes intuitive sense: one minute you’re alive and then the next you are dead. And people throughout the ages naturally asked what it was that had changed in that short space of time, and from this came the idea of the soul temporarily inhabiting the body and then departing after death.

And then people naturally asked when did the life-force first enter living things? When did life first start? These are questions posed by all human cultures. It is a uniquely human trait to ponder our origins. The question of the origin of life is a fundamental question of great importance because it underscores everything about us. It never ceases to surprise me that many philosophers and artists and writers and politicians – and many others grappling to understand life – fail to become scientifically literate in the theories and ideas that science puts forward to explain life’s origins on earth.

I’ve said this before – and I’ll say it again – to really understand life in terms of how to live, how to love – you must get to grips with the modern scientific viewpoint. It’s only through objective investigations of how life arose that we can understand what life is. And once you have a good idea of what life is – then you’ll have a much clearer idea of how to live.

We know the earth is 4.7 billion years old and we think that life began about 3.7 billion years ago – and possibly earlier. So life emerged about a billion years after the earth was formed.

How did it happen? What was the first life like? Can we find clues? Where do we look for clues?

We can’t look at fossils because the earliest life left few hard remains behind. Where else can we look for clues?

Answer: inside our bodies. All living things alive today are related to the first life. We are its distant descendants – cousins, and within us all – within our cells and within our biochemistry, are littered – here and there – clues. Clues from the unimaginable distant past, that whisper to us, and tell us, how it all began…3.8 billion years ago.

This series is about those clues and what they tell us.

The advantage of such a scheme of allowing ourselves to be gently guided by science, is that it will remove from our thinking falsities and untruths that contaminate and confuse. For example, once you know that there is probably no afterlife, you can devote your energies to the ONLY life you’ll ever have. This one!

I feel privileged that you have decided to spend a bit of the life you have, reading these words. But I am sure these words will do you good, and allow you to better utilize your time on earth.

Energy, respiration and life

In biology class you probably learnt that if you’re an animal you stay alive by consuming other animals or plants and breaking them down through the process of respiration to release energy. The energy released is used to do mechanical work (move your muscles, gut, repair etc) or chemical work (chemical reactions and generate heat).

But what actually happens when you respire?

Well, essentially (and we are interested in essentials here) electrons are removed from the food you eat and then shuttled along protein molecules embedded in membranes in your cells. This shuttling of electrons takes place in organelles within the cell called Mitochondria – these have been dubbed the powerhouse of the cell (see below).

Respiration occurs on the surface of the inner membrane of the mitochondria that are present in all our body cells.

I will explain the above diagram shortly, for now all you need to understand is that the above diagram shows the outer membrane of the mitochondria on top, and the membrane at the bottom (studded with the proteins) is the inner membrane. The mitochondria are located within our body cells; each of which contains hundreds of them. Beyond the outer membrane above lies the cytoplasm (which I’m sure you learnt at school!).

So, what happens during respiration?

Essentially what happens is that the food you eat is oxidised – it is stripped of electrons. These electrons then begin a journey. They move along the above ‘electron transport chain’ starting on the left hand side yellow coloured protein and them move along the chain from protein complex I – to – protein complex IV. You don’t need to worry about the details but suffice it is to say that the electrons at the beginning of their journey are unstable and have high energy. As they move from complex I to complex IV they become less unstable and lose some of that energy. The energy they lose is used to pump protons (H+) across the membrane to the other side. You can see this clearly in the diagram. Complex I, complex II and complex IV each pump a proton (H+) across the membrane for every electron that passes through.

It was Peter Mitchell who had first postulated this mechanism of pumping protons across the membrane. It was for this singular insight that he received the Nobel Prize. Mitchell suggested that cells are powered not by chemical reactions, but by a kind of electricity, specifically by a difference in the concentration of protons (the charged nuclei of hydrogen atoms) across a membrane.

You can imagine this process like pumping water into a dam. When the protons are pumped across the membrane, their high concentration on the other side of the membrane, gives them a lot of energy. And like a dam, if you were to open the floodgates, they will flow back down again and this can be used to generate energy. Because protons have a positive charge, the concentration difference produces an electrical potential difference between the two sides of the membrane of about 150 millivolts. It might not sound like much, but because it operates over only 5 millionths of a millimetre, the field strength over that tiny distance is enormous, around 30 million volts per metre.

That’s equivalent to a bolt of lightning!

Mitchell called this electrical driving force the proton-motive force. It sounds like a term from Star Wars, and that’s not inappropriate.

So, what happens is that when the electrons are stripped from food, they travel along the electron transport chain, and as they do so, they shed energy and this energy is used to pump protons (H+) across the inner mitochondrial membrane. So what you have now is a large concentration of protons on the other side and like the reservoir in a dam they have a lot of energy that can be used to do work.

What happens next?

Because the protons are much more highly concentrated on one side they pass back through the membrane through a rotating molecular turbine called the ‘ATP Synthase’ (see above diagram). The analogy is the same as water passing through a rotating turbine to generate electricity. So in the case of the ATP Synthase, for every 3 protons that bind to it and that are passed through the ATP Synthase, a single molecule of ATP is produced, and if you remember, ATP is the universal energy currency of life.

It is the proton gradient that is generated across the membrane from the electrons stripped from food that powers life. And it was this that Peter Mitchell had discovered. He had discovered the life force.

This was an important discovery because it shows all cells and all life is powered by a force field as universal to life on Earth as the genetic code and DNA. This tremendous electrical potential in the proton gradient can be tapped directly, to drive the motion of flagella, for instance, or harnessed to make the energy-rich fuel ATP.

The key thing to remember is that the proton gradient is THE fundamental mechanism used by all all life on earth. Be it bacteria, algae, plant, animal, mammal, fungi – all life on earth uses this proton pumping method to generate ATP and thus energy.

So the first life on earth must have used this proton pumping method to – right?

But as you can see it is extremely complex. The ATP Synthase enzyme that makes ATP is a rotating motor powered by the inward flow of protons and it is composed of many parts. Another protein that helps to generate the membrane potential, NADH dehydrogenase, is like a steam engine, with a moving piston for pumping out protons. And the protein molecules embedded in the membrane that form complexes I – IV are highly complex consisting of many sub-units. The diagram above is a simplification and does not do justice to the complexity of the proteins involved!

The truth is that these amazing nanoscopic machines are very complex and therefore must be the product of prolonged evolution by natural selection. This means they could not have powered the first life on earth, because the first life had to be, by definition, simple enough to have come about by chance, luck and chemistry. This leaves us with a paradox.

Life guzzles energy, and inefficient primordial cells must have required much more energy, not less. These vast amounts of energy are most likely to have derived from a proton gradient, because the universality of this mechanism means it evolved early on.

But how did early life manage something that today requires very sophisticated machinery?

The answer was proposed 20 years ago by the geologist Michael Russell, who had been studying deep-sea hydrothermal vents…

[To be continued…]

Summary of part II

  • Once upon a time people believed that what kept us alive was some sort of mysterious ‘life-force’ or ‘elan vital’. Many people today; especially of a religious persuasion, still cling to this idea of a soul because it is intuitive
  • Modern science now tells us that there is no such thing as a ‘life force’ per se, but rather an energy conducting chain, that channels energy from food to our bodies to keep us alive. The process that keeps this electron transport chain moving is known as respiration.
  • All living things on earth generate energy through a process that is ESSENTIALLY the same. This occurs within the inner membrane of organelles present inside our bodily cells called Mitochondria
  • The process has remained unchanged for 4 billion years and is the same for all living things
  • Electrons are stripped from food and then shunted along an ‘electron transport chain’ on the inner mitochondrial membrane. At the beginning of the chain the electrons have high energy but as they move along the chain they lose energy and this energy is used to pump protons (H+) across the inner mitochondrial membrane.
  • Protons are positively charged and their higher concentration on one side of the membrane creates a large dam (or potential) of energy that can be utilised as an energy storage device
  • The protons then move back across the membrane through a rotating protein molecule called the ATP Synthase (like water rushing through a turbine that causes the turbine to spin)
  • As the ATP Synthase turbine spins it generates mechanical force that can be used to make ATP  – the universal currency of energy.
  • The proton pumping mechanism to create a H+ gradient is shared by all life on earth. It is very old and must have been used by the first life to generate energy
  • BUT, the process as it stands today is very complex, involving many protein molecules for the electron transport chain and for the ATP Synthase etc – so, since the first life on earth must have been simple it could not have had the system and components that are used today.They are far too complex.
  • What we need is a mechanism that can generate a proton gradient across a membrane but without having to use all the molecules and proteins used today
  • If we can find a simple way that this might have happened, it might shed light on how life first began on earth
  • Deep sea hydrothermal vents may provide the answer to the mystery of the origin of life…

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