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Chemists show life on Earth was not a fluke

How life came about from inanimate sets of chemicals is still a mystery. While we may never be certain which chemicals existed on prebiotic Earth, we can study the biomolecules we have today to give us…

In them, began life. University of Utah

How life came about from inanimate sets of chemicals is still a mystery. While we may never be certain which chemicals existed on prebiotic Earth, we can study the biomolecules we have today to give us clues about what happened three billion years ago.

Now scientists have used a set of these biomolecules to show one way in which life might have started. They found that these molecular machines, which exist in living cells today, don’t do much on their own. But as soon as they add fatty chemicals, which form a primitive version of a cell membrane, it got the chemicals close enough to react in a highly specific manner.

This form of self-organisation is remarkable, and figuring out how it happens may hold the key to understanding life on earth formed and perhaps how it might form on other planets.

The 1987 Nobel Prize in Chemistry was given to chemists for showing how complex molecules can perform very precise functions. One of the behaviours of these molecules is called self-organisation, where different chemicals come together because of the many forces acting on them and become a molecular machine capable of even more complex tasks. Each living cell is full of these molecular machines.

Pasquale Stano at the University of Roma Tre and his colleagues were interested in using this knowledge to probe the origins of life. To make things simple, they chose an assembly that produces proteins. This assembly consists of 83 different molecules including DNA, which was programmed to produce a special green fluorescent protein (GFP) that could be observed under a confocal microscope.

The assembly can only produce proteins when its molecules are close enough together to react with each other. When the assembly is diluted with water, they can no longer react. This is one reason that the insides of living cells are very crowded, concentrated places: to allow the chemistry of life to work.

In order to recreate this molecular crowding, Stano added a chemical called POPC to the dilute solution. Fatty molecules such as POPC do not mix with water, and when placed into water they automatically form liposomes. These have a very similar structure to the membranes of living cells and are widely used to study the evolution of cells.

Stano reports in the journal Angewandte Chemie that many of these liposomes trapped some molecules of the assembly. But remarkably, five in every 1,000 such liposomes had all 83 of the molecules needed to produce a protein. These liposomes produced large amount of GFP and glowed green under a microscope.

Computer calculations reveal that even by chance, five liposomes in 1,000 could not have trapped all 83 molecules of the assembly. Their calculated probability for even one such liposome to form is essentially zero. The fact that any such liposomes formed and that GFP was produced means something quite unique is happening.

Stano and his colleagues do not yet understand why this happened. It may yet be a random process that a better statistical model will explain. It may be that these particular molecules are suited to this kind of self-organisation because they are already highly evolved. An important next step is to see if similar, but less complex, molecules are also capable of this feat.

Regardless of the limitations, Stano’s experiment has shown for the first time that self-assembly of molecular machines into simple cells may be an inevitable physical process. Finding out how exactly this self-assembly happens will mean taking a big step towards understanding how life was formed.

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10 Comments sorted by

  1. John Ahlstrom

    Contractor

    fluke
    flo͞ok
    noun
    1.
    unlikely chance occurrence, esp. a surprising piece of luck.
    "their triumph was no fluke"
    synonyms: chance, coincidence, accident, twist of fate;

    If it was not a fluke, what was it a dorsal fin?

    By what definition of fluke or by what set of circumstances and sequence of processes was this not a fluke?

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    1. Andrew Bissette

      PhD student at University of Oxford

      In reply to John Ahlstrom

      Hi John, thanks for your comment.

      As this article is written for a very general and non-scientific audience the language is deliberately a little imprecise.

      The word 'fluke' here is intended to contrast the two competing hypotheses considered by Stano et al: one, that the contents of each vesicle is random and the formation of super-concentrated vesicles is a statistical 'blip', or fluke; or two, that some (unidentified) process of specific recognition and self-organisation is in operation, giving rise to the super-concentrated vesicles.

      They modelled the uptake of the transcription-translation assembly with several statistical models and concluded that the formation of super-concentrated vesicles was inconsistent with random processes, and hence not a 'fluke' in the sense I described above.

      As a personal note, I am always very open to criticism of my writing and if you would like to elaborate on your criticism of my language I would be grateful for your feedback.

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    2. Jack McCadden

      Analyst

      In reply to John Ahlstrom

      John, that's a very cheap comment in reply to a fascinating piece of research. Lift.

      Great article Andrew, look forward to hearing how studies progress.

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    3. Paul Lucas

      logged in via LinkedIn

      In reply to John Ahlstrom

      John, chemistry is not chance (fluke). It is not chance that lipids form vesicles. It is not chance that the 83 proteins associate into a complex. What MIGHT be chance is that 5 vesicles out of 1,000 enclosed the entire 83 component complex. Then again, the complex may have binding sites for lipids.

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  2. Adhlu Hakk

    Administrator

    The glaringly obvious flaw right from the start is that they used biomolecules from EXISTING life forms. Furthermore, these biomolecules ONLY EXIST IN LIVING CELLS. I'm not a scientist, but I'm really fucking logical, and this fails right out of the gate. Anyone with half a brain should see the flaw in the first two paragraphs.

    Any attempt to explain how life must have started must begin from scratch, from basic elements, and then explain where information came from (DNA), because without DNA…

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    1. Andrew Bissette

      PhD student at University of Oxford

      In reply to Adhlu Hakk

      Thanks for your comment Adhlu.

      The molecules used in this study are common models used in biological and chemical research: the minimal set of proteins used by E coli for transcription and translation, the gene for GFP, and a lipid called POPC. As noted in the article, all of these are modern products shaped by evolution, and would not have existed on the early earth. Nobody is suggesting otherwise and if my article expressed this poorly then I sincerely apologise.

      This piece of research is…

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    2. Mike Hopkins

      logged in via email @hotmail.com

      In reply to Andrew Bissette

      When you say someone or something shows "life on Earth was not a fluke" then you are outright claiming that you do understand the origins of life and are not merely making progress on a small aspect of the problem. I suspect that the origin of life on Earth is not a fluke. But until a comprehensive account, supported by evidence, of how it happened accepted by the scientific community, then what I suspect is a guess as any notion of how likely life is requires that we know how it forms.

      If you oversell in your headlines, then don't be surprised if an ID creationist calls you on it as just happened. (Of course it can be pointed out that ID creationists often deny self-organization can happen at all and thus the study does have some relevance.)

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    3. Andrew Bissette

      PhD student at University of Oxford

      In reply to Mike Hopkins

      Hi Mike,

      As I'm sure you can imagine I did not intend to claim that I understand the origins or life or to oversell with the headline. Summarising a piece of work in 8 words is an art I'm still getting to grips with; I think this is a brilliant and important piece of work but I certainly don't want to overstate its importance. This article was reposted at Ars Technica with a different headline, "Chemists find biological complexes that beat chance", which I think is more appropriate.

      I hear your criticism and have taken it on board.

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    4. Paul Lucas

      logged in via LinkedIn

      In reply to Adhlu Hakk

      Adhlu: While your comments are true, the research wasn't trying to get abiogenesis from scratch. They were looking at one problem WITHIN abiogenesis: getting networks of proteins together so that they function. Having proteins scattered in solution does not allow protein A to hook up with proteins B, C, and D to form a continuous metabolic pathway. Even modern proteins. However, if you package them close together into cell-sized spheres, then the proteins do aggregate to form networks.

      Yes…

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  3. Paul Lucas

    logged in via LinkedIn

    This might be a time to remind people of the work of Sidney Fox. Thermal proteins will spontaneously form a cellular membrane and make cells approximately the size of bacteria. You don't need lipids for a cell membrane. Even in today's modern cells, 60% of the membrane is protein.

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