Biologist Nick Lane’s latest theory has created a splash, by throwing a great spanner in the primordial soup - a big splash indeed – it involves the view that proton power is no late innovation but evolved much earlier in the tree of life than we first thought. He claims the tree of life supports his theory, which is ironic because the tree of life may not be so solid a theory anymore (although it remains a good approximation, just as Newtonian mechanics remains a good approximation to the theories propounded by Einstein, Schrödinger and Heisenberg).
The first branch in the tree is between the two great groups of simple cells, bacteria and archaea, and Lane reminds us (rightly) that both of these groups have proton pumps and both generate ATP from proton currents, using a similar protein. It seems very likely indeed that both inherited this machinery from a common ancestor, and that this source was the progenitor of all life on earth, including you, me and the oak tree down the road.
It must be said though that although traits found in both the archaea and bacteria are most likely inherited from the common ancestor of all life, a few must have been acquired later by gene exchange, thus giving credence to our belief that ‘distinct’ means in many cases ‘evolved independently’. We know that this common ancestor possessed DNA, RNA and proteins, a universal genetic code, ribosomes (which are protein-building mechanisms), ATP and a proton-powered enzyme for making ATP. Some IDists contest with the (what I believe to be mistaken) view that the detailed mechanisms for reading off DNA and converting genes into proteins could not have been in place at that time, but given that this structure was, as far as we know, rather like a modern cell, I think they are clutching at a very thin straw..
Yet there are nuanced differences as well - in particular, the detailed mechanics of DNA replication would have been quite different. Moreover, it looks as if DNA replication evolved independently in bacteria and archaea; that is, most scientists seem to agree that the defining boundaries of cells evolved independently in bacteria and archaea.
So the question ‘what sort of a cell was this common ancestor?’ is, as Nick Lane concedes, a difficult question. Clearly not a cell with no boundaries, that would defy every known chemical law – but seemingly it was a very simple yet sophisticated entity in terms of its genes and proteins, and was powered by proton currents rather than fermentation, but with membranes that are no longer seen in cells today. To compound the point, back then the oceans were very different to what they are now; the primordial oceans were saturated with carbon dioxide, making them acidic, whereas the seas today have more alkaline. Also there was practically no oxygen, and without oxygen, iron dissolves readily – and we can see from our geological studies that the vast banded-iron formations around the world are a result of iron that once dissolved in oceans. As oxygen levels slowly rose, billions of tonnes of iron precipitated out as rust. This almost certainly means that the interface between the alkaline vents and the primordial seas would have been much more conducive to biochemistry than they are today – in fact scientists have found ancient vents with a similar structure and even reproduced them in the lab.
So the theory that ancient alkaline hydrothermal vents were the incubators for life looks very plausible, particularly if hydrogen and carbon dioxide did in fact react in those vents to form simple organic molecules and also release energy. But I see a problem. hydrogen with carbon dioxide may well be central to life, but energy is required in the first place to engender this process, so much so that it is probably nigh-on impossible for bacteria to grow by chemistry alone without the catalysing energy. Let me offer an analogy. Think of the energy stored by ATP as equivalent to £1. If it takes £1 to kick-start a reaction, which then releases £2, in theory a cell has gained £1. However, if the only way a cell has to store energy is to make ATP, it can make only one molecule; to make two new ATPs would cost £2. So one ATP would have been spent to gain one ATP, and the spare change wasted as heat. That's not consistent with being alive. Yet Nick Lane is suggesting that the hydrothermal vents would provide a good explanation to this problem, claiming that::
“The fluid from the vents would have contained reactive molecules such as methyl sulphide, which would generate acetyl phosphate, a molecule that some bacteria today still use interchangeably with ATP. What's more, the natural proton gradient would have supplemented this energy source by spontaneously generating another primitive form of ATP called pyrophosphate. Pyrophosphate also acts in much the same way as ATP and is still used alongside ATP by many bacteria and archaea. These bacteria speed up its production using a simple enzyme called pyrophosphatase”.
So the common ancestor of life could harness the natural proton gradient of ancient vents to produce energy, and by some reversing process store energy too, as this system seems to allow cells to save up small amounts of energy, much the same as we save up our loose change and buy something so it no longer becomes waste, which is equivalent to saying that the proton gradients enable cells to grow and then, by their accumulative energy, leave the vents. This means it may well be true that the last common ancestor of all life was not a frivolously spending cell at all, but a thrifty rock riddled with bubbly iron-sulphur membranes that engendered the energy for primordial biochemical reactions. This natural flow reactor, power-driven by hydrogen and proton gradients, catalysed organic chemicals and brought about proto-life (both bacteria and the archaea) that would become the first living cells – eventually producing you, me and the oak tree. Given the intractability of this subject and the vast domains of time, it may never be possible to know for sure whether or not life evolved by this mechanism, or whether the initial elemental organism with the properties of self-replication happened just once (maybe only once in the entire history of the universe) or several times. But a good case may have been made that hydrothermal vents had the answer.
The first branch in the tree is between the two great groups of simple cells, bacteria and archaea, and Lane reminds us (rightly) that both of these groups have proton pumps and both generate ATP from proton currents, using a similar protein. It seems very likely indeed that both inherited this machinery from a common ancestor, and that this source was the progenitor of all life on earth, including you, me and the oak tree down the road.
It must be said though that although traits found in both the archaea and bacteria are most likely inherited from the common ancestor of all life, a few must have been acquired later by gene exchange, thus giving credence to our belief that ‘distinct’ means in many cases ‘evolved independently’. We know that this common ancestor possessed DNA, RNA and proteins, a universal genetic code, ribosomes (which are protein-building mechanisms), ATP and a proton-powered enzyme for making ATP. Some IDists contest with the (what I believe to be mistaken) view that the detailed mechanisms for reading off DNA and converting genes into proteins could not have been in place at that time, but given that this structure was, as far as we know, rather like a modern cell, I think they are clutching at a very thin straw..
Yet there are nuanced differences as well - in particular, the detailed mechanics of DNA replication would have been quite different. Moreover, it looks as if DNA replication evolved independently in bacteria and archaea; that is, most scientists seem to agree that the defining boundaries of cells evolved independently in bacteria and archaea.
So the question ‘what sort of a cell was this common ancestor?’ is, as Nick Lane concedes, a difficult question. Clearly not a cell with no boundaries, that would defy every known chemical law – but seemingly it was a very simple yet sophisticated entity in terms of its genes and proteins, and was powered by proton currents rather than fermentation, but with membranes that are no longer seen in cells today. To compound the point, back then the oceans were very different to what they are now; the primordial oceans were saturated with carbon dioxide, making them acidic, whereas the seas today have more alkaline. Also there was practically no oxygen, and without oxygen, iron dissolves readily – and we can see from our geological studies that the vast banded-iron formations around the world are a result of iron that once dissolved in oceans. As oxygen levels slowly rose, billions of tonnes of iron precipitated out as rust. This almost certainly means that the interface between the alkaline vents and the primordial seas would have been much more conducive to biochemistry than they are today – in fact scientists have found ancient vents with a similar structure and even reproduced them in the lab.
So the theory that ancient alkaline hydrothermal vents were the incubators for life looks very plausible, particularly if hydrogen and carbon dioxide did in fact react in those vents to form simple organic molecules and also release energy. But I see a problem. hydrogen with carbon dioxide may well be central to life, but energy is required in the first place to engender this process, so much so that it is probably nigh-on impossible for bacteria to grow by chemistry alone without the catalysing energy. Let me offer an analogy. Think of the energy stored by ATP as equivalent to £1. If it takes £1 to kick-start a reaction, which then releases £2, in theory a cell has gained £1. However, if the only way a cell has to store energy is to make ATP, it can make only one molecule; to make two new ATPs would cost £2. So one ATP would have been spent to gain one ATP, and the spare change wasted as heat. That's not consistent with being alive. Yet Nick Lane is suggesting that the hydrothermal vents would provide a good explanation to this problem, claiming that::
“The fluid from the vents would have contained reactive molecules such as methyl sulphide, which would generate acetyl phosphate, a molecule that some bacteria today still use interchangeably with ATP. What's more, the natural proton gradient would have supplemented this energy source by spontaneously generating another primitive form of ATP called pyrophosphate. Pyrophosphate also acts in much the same way as ATP and is still used alongside ATP by many bacteria and archaea. These bacteria speed up its production using a simple enzyme called pyrophosphatase”.
So the common ancestor of life could harness the natural proton gradient of ancient vents to produce energy, and by some reversing process store energy too, as this system seems to allow cells to save up small amounts of energy, much the same as we save up our loose change and buy something so it no longer becomes waste, which is equivalent to saying that the proton gradients enable cells to grow and then, by their accumulative energy, leave the vents. This means it may well be true that the last common ancestor of all life was not a frivolously spending cell at all, but a thrifty rock riddled with bubbly iron-sulphur membranes that engendered the energy for primordial biochemical reactions. This natural flow reactor, power-driven by hydrogen and proton gradients, catalysed organic chemicals and brought about proto-life (both bacteria and the archaea) that would become the first living cells – eventually producing you, me and the oak tree. Given the intractability of this subject and the vast domains of time, it may never be possible to know for sure whether or not life evolved by this mechanism, or whether the initial elemental organism with the properties of self-replication happened just once (maybe only once in the entire history of the universe) or several times. But a good case may have been made that hydrothermal vents had the answer.
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