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Thread: Origin of life status

  1. #31
    tWebber lee_merrill's Avatar
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    Quote Originally Posted by shunyadragon View Post
    Source: http://dirac.ruc.dk/~st/articles/article68print.pdf


    It is, however, not the establishment, but rather the preservation of homochirality, which is the problem.

    © Copyright Original Source

    Well, I disagree, establishing homochirality is at least as much of a problem as its preservation.

    Blessings,
    Lee
    "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

  2. #32
    tWebber shunyadragon's Avatar
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    Quote Originally Posted by lee_merrill View Post
    Well, I disagree, establishing homochirality is at least as much of a problem as its preservation.

    Blessings,
    Lee
    The problem is your still 'arguing from ignorance' concerning what you see as 'problems' that justify your agenda. Yes there are unresolved problems at present in all sciences, but that does not translate to being unresolvable. The following may shed some light on the problem from a scientific perspective without an agenda.

    Source: http://www.simsoup.info/Origin_Issues_Homochirality.html



    Origin Of Life: Issues

    Homochirality

    Chiral and Achiral Objects

    A left and right hand are mirror images of one another. Unlike a ball and its mirror image, a hand and its mirror image are not identical. In the unlikely event that you doubt this, try fitting a left handed glove onto your right hand!

    An object such as a hand that is not identical to its mirror image is chiral. An object such as a sphere which is identical to its mirror image is achiral. The word chiral derives from the Greek word for hand.

    Discovery of the Relationship between Optical Activity and Molecular Chirality
    In 1848, Louis Pasteur conducted an experiment in which he produced crystals of the sodium ammonium salt of what was (at the time) known as racemic acid. The crystals were of two kinds, known as "+" and "-" forms, which were mirror images of one another. Pasteur separated out the two kinds of crystals and then made two solutions, one from the "+" form crystals, and one from the "-" form crystals. He shone polarised light through each solution, and found that the two solutions had equal but opposite optical activity. That is, the angle of polarisation was rotated in each case by the same amount, but in opposite directions. If polarised light was shone through the original solution from which the crystals had been formed there was no rotation, the solution was optically inactive. Pasteur correctly concluded that racemic acid was a mixture of two different substances with opposite optical activity. Racemic acid was optically inactive because it was a mixture of two substances (actually different forms of tartaric acid) with equal and opposite optical activities which cancelled out.
    Pasteur saw that optical activity was a property of the molecules of tartaric acid. However, it was not until 25 years later that two scientists, J.H. van't Hoff and J. A. LeBel simultaneously but independently provided the explanation. They knew that there are two different ways in which four different objects can be arranged at the corners of a tetrahedron, and that the two arrangements are mirror images of one another. Van't Hoff and LeBel proposed that carbon has a tetrahedral structure, and that optically active substances have at least one carbon atom with four different groups attached. The "+" and "-" forms of tartaric acid therefore corresponded to molecules containing two mirror image tetrahedral structures, each centred on a carbon atom.

    It is worth noting that Van't Hoff and LeBel made their proposal at a time when very little was known about the structure of atoms or chemical bonds. It was initially controversial, but soon came to be generally accepted and is now regarded as fact.

    Contemporary Understanding of Chiral Molecules
    Today far more is known about atomic and molecular structure than was known in the time of Van't Hoff and LeBel. The figure below shows a schematic diagram of two tetrahedral mirror image molecules. The black sphere at the centre of each molecule represents a carbon atom. The four different coloured spheres linked to each black sphere represent four different atoms or groups of atoms bonded to the central carbon atom to form a complete molecule.
    Mirror Image Molecules>
    Schematic Diagram of Left and Right Handed Molecules (Enantiomers)
    The key point to note is that the two mirror image molecules are not identical. In particular, it is not possible to superimpose one molecule on the other. To see this, imagine moving the right hand molecule to the left so that the black, yellow and blue parts of each of the two molecules line up. The red and green parts will not line up, and there is no way to make them do so without physically breaking and re-making the bonds of one of the molecules. The molecules are therefore chiral.

    Now imagine replacing the red spheres with green spheres, so that each molecule now has two green parts. It is now possible to move the right hand molecule to the left so that all of its parts line up with the corresponding parts on the left hand molecule. In this case, we can see that the two mirror image molecules are identical, and therefore achiral.

    The Macro-Molecules of Life are Homochiral
    Most objects around us are chiral. Very few have the mirror image symmetry which is a property of achiral objects such as spheres and coffee mugs. Imagine picking up pebbles on a beach; if you came across one that was perfectly symmetrical, for example perfectly oval shaped, you would probably consider it to be remarkable.
    Given that most objects around us are chiral, it comes as no surprise that the same is also true of molecules, including those from which organic lifeforms are constructed. The simple fact is that there are vastly more ways of putting atoms together in a way that produces chiral molecules than there are ways of putting them together to make achiral molecules.

    It is however noteworthy that many of the key macro-molecules of life are constructed from chiral sub-units which are linked together in such a way that all the sub-units are of the same chirality.

    The "+" and "-" forms of chiral molecules are known as dextrorotatory ("+" form) and levorotatory ("-" form). Dextrorotatory molecules rotate polarised light in a clockwise direction. In the case of levorotatory molecules, the direction of rotation is anti-clockwise.

    All protein molecules in all contemporary species, from bacteria to humans, are constructed from the same set of 20 amino acids. With the exception of glycine, which has a symmetric structure and is therefore achiral, all amino acid molecules are chiral; they can exist in two mirror image forms. However, in proteins they exist only in their levorotatory form. A similar point applies to other important biological macro-molecules including DNA; they are constructed from sub-units of uniform chirality. Such macro-molecules are described as homochiral.

    The homochirality of biological macro-molecules such as DNA and proteins can be understood as a necessity for contemporary life-forms. Structure is crucial to the correct functioning of both DNA and proteins. Were a molecule of 'DNA' to be constructed from sub-units of different chirality, it would not correctly form the familiar double helix structure. A similar point can be made about proteins. These macro-molecules perform an enormous range of functions in living organisms, and in most (if not all) cases the physical shape of the protein plays a key role in determining its function. If a particular protein molecule is always constructed from amino acids of uniform chirality, then the polypeptide string formed by the amino acids will always fold in the same way so that the protein molecule formed will always have the same shape. If amino acids of randomly mixed chirality were used, then the resulting polypeptide string would hardly ever fold into the same shape, with the result that most of the 'protein' molecules formed would not be able to function effectively.

    The Origin of Chiral Discrimination and Homochirality
    Homochirality is essential to the correct functioning of many of the mechanisms of contemporary life-forms. But how did it arise in the first place? In order for homochiral macro-molecules to have evolved there must have been a mechanism which could discriminate between the molecular sub-units from their mirror images, and construct the macro-molecules from the sub-units of correct chirality. In contemporary life-forms this is done using complex mechanisms in which highly evolved (homochiral) molecules perform key functions. Clearly such highly evolved molecules would not have been available from the outset. We must therefore ask: What was the origin of chiral discrimination? This, as Graham Cairns-Smith pointed out in his book "Genetic Takeover" (Cairns-Smith, 1982) is the nub question. To date, there is no generally accepted answer to this question. Noam Lahav (in Lahav, 1999, page 257) indicates that the organic chemist William Bonner argued at a meeting in the mid 1990's that there was a big gap between the origin of homochirality and the origin of life, and that homochirality must have preceeded life. Bonner said "I happen to think that you have to understand the origin of homochirality before you can bridge that gap. Stepwise, one has to deal with the origin of homochirality first, and then how do you get to living organisms". He went on to say "I spent 25 years looking for terrestrial mechanisms for homochirality and trying to experimentally investigate them and didn't find any supporting evidence". Bonner has suggested an extraterrestrial source for homochiral molecules. Others, including Stanley Miller and Jeffrey Bada have argued that homochirality is an "artefact of life" rather than a precondition.

    © Copyright Original Source

    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

  3. #33
    tWebber lee_merrill's Avatar
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    "What was the origin of chiral discrimination? This, as Graham Cairns-Smith pointed out in his book 'Genetic Takeover' (Cairns-Smith, 1982) is the nub question. To date, there is no generally accepted answer to this question."

    It sounds like we have a problem...

    Blessings,
    Lee
    "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

  4. #34
    tWebber shunyadragon's Avatar
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    Quote Originally Posted by lee_merrill View Post
    "What was the origin of chiral discrimination? This, as Graham Cairns-Smith pointed out in his book 'Genetic Takeover' (Cairns-Smith, 1982) is the nub question. To date, there is no generally accepted answer to this question."

    It sounds like we have a problem...

    Blessings,
    Lee
    Of course, there are always problems, which is normal in science, but they are not justification of a religious agenda of ID.

    Source: https://www.ncbi.nlm.nih.gov/sites/myncbi/recentactivity



    Origin of Homochirality in Biosystems
    Søren Toxvaerd
    Author information Article notes Copyright and License information Disclaimer
    This article has been cited by other articles in PMC.
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    Abstract
    Experimental data for a series of central and simple molecules in biosystems show that some amino acids and a simple sugar molecule have a chiral discrimination in favor of homochirality. Models for segregation of racemic mixtures of chiral amphiphiles and lipophiles in aqueous solutions show that the amphiphiles with an active isomerization kinetics can perform a spontaneous break of symmetry during the segregation and self-assembly to homochiral matter. Based on this observation it is argued that biomolecules with a sufficiently strong chiral discrimination could be the origin of homochirality in biological systems.

    Keywords: Origin of chirality, Origin of Life, Prebiotic self-assembly
    Go to:
    1. Introduction
    The homochirality of amino acids and sugar molecules in biosystems is a necessity for life, and the preservation of homochirality over long periods of time in a prebiotic fluid environment is the problem. It is the problem because it is not sufficient to obtain homochirality. Due to the active isomerization kinetics in fluid systems [1, 2], which in general drives a chiral system toward a racemic composition, it is of utmost importance to determine the condition and mechanism for preservation of homochirality in prebiotic systems. From a thermodynamical and physico-chemical point of view biosystems consist of big molecules of homochiral units and in a soft condensed state in an aqueous solution. If the origin of life is not based on an extremely rare event we therefore need an explanation of how to maintain homochirality in such a prebiotic state for millions of years. If the creation of ”simple” biosystems is obtained by a steady state synthesis, the prebiotic fluid state must necessarily have been rather constant over very long times in order to build up the very unique and complicated templates for life, where RNA is probable the original template. Even in a deterministically driven self-organisation such template-molecule is not established “overnight”. This is why a mechanism ensuring the preservation of homochirality for a very long time is needed. A period of time which is much longer than the time in which an (diluted) aqueous solution of an amino acid will racemize [1], i.e. in the order of thousands of years. Sugar molecules are much less stable than amino acids and racemize within hours or days depending on the physico-chemical conditions [2]; however, both key-molecules are central in all biosystems. Almost all theories dealing with homochirality have concentrated on explaining its origin, but, irrespective of whether L-amino acids float to us from Space or are obtained by a kind of autocatalysis, it is irrelevant, as we need to ensure its stability during long periods of time within the fluid state when biosystems were synthesized probably around 4 billion years ago. Finally it shall be emphasized that it is not sufficient to explain the origin and preservation of one of the homociral species in biosystems, e.g. D-sugars. One needs to explain the preservation of D-sugars as well as L-amino acids in a prebiotic fluid state.

    The strong chiral discrimination of some of the central biomolecules offers such an explanation not only for a spontaneously break of symmetry and the origin of chirality [4], but also for the preservation of the homochiral states of D-sugar and L-amino acids.

    © Copyright Original Source

    Last edited by shunyadragon; 01-05-2020 at 04:30 PM.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

  5. #35
    tWebber lee_merrill's Avatar
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    Quote Originally Posted by shunyadragon View Post
    Source: Toxvaerd

    The strong chiral discrimination of some of the central biomolecules offers such an explanation not only for a spontaneously break of symmetry and the origin of chirality [4], but also for the preservation of the homochiral states of D-sugar and L-amino acids.

    Source

    © Copyright Original Source

    I corrected the link. Now this seems to be an overstatement above, since we also read:

    Source: Toxvaerd

    Only for an infinite strong chiral dominance of EDD = ELL = ∞ (d in the figure) does this system end in a pure homochiral fluid.

    © Copyright Original Source


    The problem with an impure fluid is that (as I have heard) any wronghanded sugar or amino acid messes up the chain in the biomolecule.

    Blessings,
    Lee
    "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

  6. #36
    tWebber shunyadragon's Avatar
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    Quote Originally Posted by lee_merrill View Post
    I corrected the link. Now this seems to be an overstatement above, since we also read:

    Source: Toxvaerd

    Only for an infinite strong chiral dominance of EDD = ELL = ∞ (d in the figure) does this system end in a pure homochiral fluid.

    © Copyright Original Source


    The problem with an impure fluid is that (as I have heard) any wronghanded sugar or amino acid messes up the chain in the biomolecule.

    Blessings,
    Lee
    Selective biased citations with a religious agenda that do not reflect the conclusions of the reference are not ethical.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

  7. #37
    Technology Staff Leonhard's Avatar
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    Quote Originally Posted by lee_merrill View Post
    "What was the origin of chiral discrimination? This, as Graham Cairns-Smith pointed out in his book 'Genetic Takeover' (Cairns-Smith, 1982) is the nub question. To date, there is no generally accepted answer to this question."

    It sounds like we have a problem...

    Blessings,
    Lee
    Why is it a problem? Other than a mystery to be explored?

  8. #38
    tWebber lee_merrill's Avatar
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    Quote Originally Posted by Leonhard View Post
    Why is it a problem? Other than a mystery to be explored?
    Exploring mysteries is fine, I think we know enough about life to be able to estimate a bound on the probability of it forming naturally, and that probability bound is very low.

    Blessings,
    Lee
    "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

  9. #39
    Technology Staff Leonhard's Avatar
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    Quote Originally Posted by lee_merrill View Post
    Exploring mysteries is fine, I think we know enough about life to be able to estimate a bound on the probability of it forming naturally, and that probability bound is very low.

    Blessings,
    Lee
    I agree this is your opinion, but you failed to answer the question. Why is it a problem that we don’t understand the origin of chirality?

    You seem to imply an argument from ignorance here.

  10. #40
    tWebber lee_merrill's Avatar
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    Quote Originally Posted by Leonhard View Post
    I agree this is your opinion, but you failed to answer the question. Why is it a problem that we don’t understand the origin of chirality?

    You seem to imply an argument from ignorance here.
    No, I'm saying based on what we know, we can see whether an event is likely or not. Now any estimate we make involves some uncertainty, but that does not mean we are arguing from ignorance.

    Blessings,
    Lee
    "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

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