Abiogenesis - moving on from the Urey Miller Experiment

by cantleave 37 Replies latest watchtower beliefs

  • cantleave

    Abiogenesis is the field of study whereby the answers to how the chemistry of life was initiated are explored. Unlike evolution, which is described and understood via a number of falsifiable models which explain the observations made in the natural world, most models of abiogenesis will remain unfalsifiable and hence open to debate. The issue being of course that the conditions under which those first chemical reactions occurred no longer exist and trying to recreate an approximation of these in the lab requires a great deal patience, ingenuity and of course some intelligent guess work! Dr. Michael Russell of the Scottish Environmental Research Centre in Glasgow, on whose work this post is based, summed up this issue very well when he wrote...

    "Even if you were to make a reactor in the laboratory, and put hydrogen and carbon dioxide and nitrogen in one end, and out pops something like Escherichia coli at the other end, you still couldn't prove that we and our ancestors arose that way. You'd just have a narrative that made it more plausible."

    In this post I want to outline Dr. Russell's hypothesis. He suggests that the first life forms may have evolved within small compartments known as micro-caverns within iron sulphide (AKA Iron Pyrite or fool’s gold) deposits in alkaline thermal vents - deep sea hot springs. Please do not to be confuse these with the giant “black smokers” which billow out hydrothermal fluids at 350 – 400 deg C, these alkaline vents are much smaller and the water expelled through them is only c 100 deg C. When these micro-caverns first developed they would have been composed of a semi-permeable iron nickel sulphide (mackinawite) gel, across which a strong vertical chemistry gradient (a chemocline) could develop, allowing molecules to be concentrated. These were according to Russell's hypothesis the incubators for the first self-replicating molecules and the apparatus required to create life.

    The building blocks for these prebiotic molecules and the energy required for the reactions to create them, were provided by the constant flow of hydrothermal water through the vents. This water was rich in hydrogen, cyanide compounds, sulphides and carbon monoxide. The chemocline micro-caverns provided a microenvironment that allowed the migration of synthesized compounds from areas of high concentration to areas of low concentration which facilitated the accumulation, and subsequent catalysation (by the Iron and nickel) of these molecules to create simple monomers (including amino acids). These monomers formed short chain polymers (oligomers) such as peptides, which in turn gave rise to the proteins and the nucleotides required to synthesise RNA.
    What is interesting about this idea is there was no need for a lipid barrier or cell membrane until the majority of cellular functions had been developed. This means that according to this model LUCA, the "last universal common ancestor” was not a free living organic cell. The organic constituents making up “LUCA” were confined to the mineral based micro-caverns, which was functionally equivalent to a single cell. The lipid membrane required for free living cells was subsequently genetically encoded by the cellular apparatus.

    So what is about this hypothesis that gives it any kind of credibility? First of all it overcomes the question of how an accumulation of molecules could occur, without the chemocine these molecules would have been dispersed as soon as they were synthesised. It also explains the initial oligomerisation and subsequent polymerisation was catalysed. But in addition to these ideas this model also provides a fascinating explanation as to how the energy required to enable cellular chemical synthesis may have evolved.

    The ionic gradients that would have developed across the mackinawite gel are similar to the gradients that form across cell membranes. Inside the vent, the water would have been hot, alkaline and hydrogen rich, due to reactions between iron and water in a metamorphic process known as serpentinization. On the other side of the membrane outside the vent the oceanic water would have been cold and acidic. This creates a proton gradient, which could have been utilised to provide a source of energy to facilitate metabolic reactions within the micro-cavern. With a few notable exception modern living cells power much of their chemistry by creating similar gradients across their membranes, but rather than using an inorganic proton gradient they use a variety of proteins to do exactly the same thing. The inorganic proton gradient was initially used to power cell chemistry but life adapted, by changing the chemistry of proton gradient by using proteins, another step in life breaking free from the confines of its mineral incubator deep under the ocean, was established.

    Russell’s hypothesis was further developed by assimilating another model developed by Professor William Martin of the University of Dusseldorf, I will discuss this in another post.

  • cofty

    Thanks Cantleave. The first time I read about the work done by Russell and Martin I was amazed.

    As you say we may never know for sure exactly life began on earth, but I am certain we will know how it could have began.

  • prologos

    Very interesting that first life might have been a hermit hiding in a cave and using the energy gradients and working on improving the situaution. let us hear the sequel please.

  • cantleave

    I will work on part 2 next week when I am in Manchester.

  • 70wksfyrs

    Wow fantastic opening post. Your research on Russell’s hypothesis is extensive. I have not read his works, but maybe you could tell me when the formation of monomers was discovered was he able to identify the enantiomers that were formed or did the research not mention enantiomers.

    In my view I feel that the formation of the correct enantiomers within the DNA is an important clue how abiogenesis occurs at an amino acid stereoisomer stage. I believe this because mainly the L-enantiomers are found in living things. I think that’s where the forming of living things from non living amino acid stereoisomers could be explained. But maybe it can't be.

    These are my novice beliefs which are completely unsubstantiated and was just wondering what your opinion of my theory is.

  • Phizzy

    Thanks Cantleave, this is a subject I have been meaning to investigate some more, its been a while since I paid any attention to it. Your post is so helpful, and I look forward to your next one, watch out for the Mancs though, a dodgy lot ! ('specially United supporters).

    What I think is so great about this area of research is that it will cut out a lot of the silly arguments Creationists use, and will do what someone once said, (I forget who) "Every time Science discovers something, God gets pushed further back into the mists of time". (or substance thereof [TMS speak]).

  • rmt1


  • cantleave


    What a great question. For those that do not know the premise of this question some molecules, known as chiral molecules can form isomers (possessing the same molecular formula but different structures) which are mirror images of each other, each of these isomers is called an enantiomer. A mixture of equal parts of both enantiomers is called racemic mixture. Amino acids and sugars are usually chiral but life almost exclusively synthesizes only one enantiomer, a phenomenon known as homochirality. Homochirality is essential for the coding of amino acids and proteins by DNA and RNA.

    If you synthesise a chiral molecule in a lab the result is a racemic (equal) mix of both enantiomers, an imbalance is never observed. The homochirality of amino acids and sugars is often jumped on by creationists as an impossibility that could only have been overcome by divine intervention, and for decades it has has been something of a mystery to chemists and biologists.

    Russell and Martin have proposed a hypothesis for homochirality. It was elucidated from studies of the biosynthesis of 2 co-factors (non-proteins bound to a protein required for the protein's biological activity) pyridoxal phosphate (PLP) and Thiamine pyrophosphate (TPP). What is interesting from a stereochemistry perspective is that despite that fact chiral molecules are involved en route to their synthesis neither PLP or TPP do not show any chirality. The mechanisms involved in their synthesis indicates that there is no need to start from chiral materials since the proteins and RNA introduce the Chirality. This suggests that prebiotic synthesis of aromatic co-factors could have occurred prior to the origin of homochirality. The homochirality arose from the subsequent biosynthesis.

  • cofty

    Is this the same as the phrase "left-handed" amino acids and "right-handed" ones, and the fact that only 20 left-handed ones are found in organic proteins?

  • cantleave

    I am concerned that I may have over-simplified my explanations in this post. You may find the orginal paper of interest as the proposed chemistry is described in full...


Share this