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Reason for one chiriality in biology

  1. May 28, 2016 #1
    We know that DNA and other biological molecules have only one chiriality of two possible. Is here any explanation of this or any speculations about this?
     
  2. jcsd
  3. May 28, 2016 #2

    mjs

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    I think this is debatable. Probabably it reflects their common origin.

    This is a fascinating topic because stereotactic conformations provide the 3D complexity needed to avoid equillibrium and thus, to allow life exist in the first place and sustain itself.
     
  4. May 28, 2016 #3

    Drakkith

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    There are certainly some ideas of how and why homochirality exists. See this article for example (abstract below): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857173/

    Abstract
    The single-handedness of biological molecules has fascinated scientists and laymen alike since Pasteur's first painstaking separation of the enantiomorphic crystals of a tartrate salt more than 150 yr ago. More recently, a number of theoretical and experimental investigations have helped to delineate models for how one enantiomer might have come to dominate over the other from what presumably was a racemic prebiotic world. This article highlights mechanisms for enantioenrichment that include either chemical or physical processes, or a combination of both. The scientific driving force for this work arises from an interest in understanding the origin of life, because the homochirality of biological molecules is a signature of life.
     
  5. May 28, 2016 #4
    I think it is much simpler than that. My pet theory is that homochirality stems from the intrinsic angular momentum of the earth spinning on its axis. This angular momentum favored one chirality over the other in the primordial soup.
     
  6. May 28, 2016 #5

    Drakkith

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    What possible connection could there be between the angular momentum of the Earth and the chirality of individual molecules?
     
  7. May 28, 2016 #6
    Perhaps the proto amino acids "felt" the angular momentum of rotation, and for that reason assumed the leverorotatory configuration as a result.
     
  8. May 28, 2016 #7

    Drakkith

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    Unless you have a reference that backs this up somehow then I'm afraid we can't discuss it. We don't allow personal theories here at PF.
     
  9. May 28, 2016 #8
    I looked for references, but apparently nobody knows exactly the angular velocity of the earth 3.8 billion years ago when coacervates were forming in the primordial seas. The only thing we can say for sure, it was greater then than today. For certain, the day was 22 hours long in the precambrian, about 500 million years ago. If we can't discuss it so be it.
     
  10. May 30, 2016 #9

    Fervent Freyja

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    D-sugars tend to be right-handed, while L-amino acids left-handed. I have read possible causes: 2nd law of thermodynamics affecting early molecular processes, asymmetrical physical laws (electroweak interaction), earths rotation, and it goes on and on.
     
  11. Jun 2, 2016 #10
    Disclaimer - I am not a chemist or biologist. I have a physics B.Sc and what I know about biology is only because I read a little bit about everything.

    I tried but failed to find a link to a page I read long ago about how chirality affects the way proteins fold, how DNA twists, etc. I think - but am not nearly sure - that I got led to that page from a page about thalidomide. However, the simple fact that chirality affects folding implies that chirality affects how molecules work ... and if they don't work properly that in turn implies that the process polices itself by discarding that which does not work.

    In case the above wasn't clear enough, suppose that during the assembly of a protein one of the molecules used as building bricks has left and right chirality. If the assembly process takes up a left chiral building block the protein will fold correctly. If it takes up a right chiral building block it will not fold correctly ... and that either halts the assembly process or results in a defective protein that is discarded.
     
  12. Jun 2, 2016 #11

    Ygggdrasil

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    Here's a nice news piece from the Royal Society of Chemistry on why homochirality is important: http://www.rsc.org/chemistryworld/2015/10/origin-homochirality-life-asymmetry
    That simple analogy refer to the concept of enantiomeric cross-inhibition (also the term for the idea expressed in the above post), and origin of life researchers have been thinking about how such obstacles might have been overcome duirng abiogenesis.
     
  13. Jun 3, 2016 #12

    Fervent Freyja

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    Another article I found after that one.

    The wording, "On the back of a comet...", just :)) :DD :H!

     
  14. Jun 3, 2016 #13

    Fervent Freyja

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    Yeah, difficult to find, but some not-entirely-credible sources say a 2.5 hour day at around 4 billion years, but others 6 hour days.

    We need a better understanding on how the earth and moon have interacted throughout history in order to also gain a better understanding of the formation of life on earth (and determine that angular velocity). Prior generations of biologists weren't taught enough mathematics to make those calculations. They are waiting on astronomers and physicists to help out.
     
  15. Jun 3, 2016 #14
    One way to check if angular momentum could cause homochirality is to reproduce Miller's experiment in a reaction vessel spinning at high rpm. Let the experiment play out long enough to see if it is time dependent as well. If there is an entantiomeric escess, then the theory could hold water.
     
  16. Jun 3, 2016 #15

    Drakkith

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    Again, unless someone can find a reference that suggests a method by which homochirality is due to a fast-spinning Earth, I ask that the idea not be brought up again. Further posts on it will be removed unless they contain a valid reference.
     
  17. Jun 4, 2016 #16
    I don't think we need theories to explain chiral exclusivity. I think someone should put forth a theory proving it was even reasonably possible to NOT have chiral exclusivity. Isn't it possible that there was no compelling reason for left vs right when we already are surrounded by compelling proof that having one "preference" or another is what allows life to exist as we know it? As the processes creating life evolved, eventually a process arose that was so complex, it would not continue without some inherent chirality. We know this is true because such conditions exist within our own biochemistry. Whichever chirality random luck gave at the time or the origin of a single form of actual life (or even before), that was the one to continue. We all like explanations, but we should remember what seems weird is sometimes what really should be expected. How could you NOT expect exclusive chirality from a single starting point of evolution when the complexity of life eventually demands chiral preference?
     
  18. Jun 4, 2016 #17

    Drakkith

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    If it is expected, then there needs to be a reason why. And that requires a theory.
     
  19. Jun 4, 2016 #18

    Vanadium 50

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    The idea is DOA. It would predict opposite chiralities in the nothern and southern hemispheres.

    While there is some evidence that there is an advantage to homochirality, as far as I know there is nothing but speculation on why or even if the handedness on Earth is more advantageous than the opposite one.
     
  20. Jun 7, 2016 #19

    Fervent Freyja

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  21. Jun 7, 2016 #20

    TeethWhitener

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    It would also predict that if you did a chemical reaction in the lab which produced a chiral center, you could get different enantiomeric enrichments depending on which way the stirbar in your flask was rotating.
     
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