• Quantum mechanics could explain why DNA

    From ScienceDaily@1:317/3 to All on Thu May 5 22:30:40 2022
    Quantum mechanics could explain why DNA can spontaneously mutate

    Date:
    May 5, 2022
    Source:
    University of Surrey
    Summary:
    The molecules of life, DNA, replicate with astounding precision,
    yet this process is not immune to mistakes and can lead to
    mutations. Using sophisticated computer modelling, a team of
    physicists and chemist have shown that such errors in copying can
    arise due to the strange rules of the quantum world.



    FULL STORY ==========================================================================
    The molecules of life, DNA, replicate with astounding precision, yet
    this process is not immune to mistakes and can lead to mutations. Using sophisticated computer modelling, a team of physicists and chemists
    at the University of Surrey have shown that such errors in copying can
    arise due to the strange rules of the quantum world.


    ==========================================================================
    The two strands of the famous DNA double helix are linked together by
    subatomic particles called protons -?the nuclei of atoms of hydrogen --
    which provide the glue that bonds molecules called bases together. These so-called hydrogen bonds are like the rungs of a twisted ladder that
    makes up the double helix structure discovered in 1952 by James Watson and Francis Crick based on the work of Rosalind Franklin and Maurice Wilkins.

    Normally, these DNA bases (called A, C, T and G) follow strict rules
    on how they bond together: A always bonds to T and C always to G. This
    strict pairing is determined by the molecules' shape, fitting them
    together like pieces in a jigsaw, but if the nature of the hydrogen bonds changes slightly, this can cause the pairing rule to break down, leading
    to the wrong bases being linked and hence a mutation. Although predicted
    by Crick and Watson, it is only now that sophisticated computational
    modelling has been able to quantify the process accurately.

    The team, part of Surrey's research programme in the exciting new field
    of quantum biology, have shown that this modification in the bonds
    between the DNA strands is far more prevalent than has hitherto been
    thought. The protons can easily jump from their usual site on one side of
    an energy barrier to land on the other side. If this happens just before
    the two strands are unzipped in the first step of the copying process,
    then the error can pass through the replication machinery in the cell,
    leading to what is called a DNA mismatch and, potentially, a mutation.

    In a paper published this week in the journal Nature Communications
    Physics, the Surrey team based in the Leverhulme Quantum Biology Doctoral Training Centre used an approach called open quantum systems to determine
    the physical mechanisms that might cause the protons to jump across
    between the DNA strands.

    But, most intriguingly, it is thanks to a well-known yet almost magical
    quantum mechanism called tunnelling -- akin to a phantom passing through
    a solid wall - - that they manage to get across.

    It had previously been thought that such quantum behaviour could not
    occur inside a living cell's warm, wet and complex environment. However,
    the Austrian physicist Erwin Schro"dinger had suggested in his 1944 book
    What is Life? that quantum mechanics can play a role in living systems
    since they behave rather differently from inanimate matter. This latest
    work seems to confirm Schro"dinger's theory.



    ==========================================================================
    In their study, the authors determine that the local cellular environment causes the protons, which behave like spread out waves, to be thermally activated and encouraged through the energy barrier. In fact, the
    protons are found to be continuously and very rapidly tunnelling back
    and forth between the two strands. Then, when the DNA is cleaved into
    its separate strands, some of the protons are caught on the wrong side,
    leading to an error.

    Dr Louie Slocombe, who performed these calculations during his
    PhD, explains that: " The protons in the DNA can tunnel along the
    hydrogen bonds in DNA and modify the bases which encode the genetic information. The modified bases are called "tautomers" and can survive the
    DNA cleavage and replication processes, causing "transcription errors"
    or mutations." Dr Slocombe's work at the Surrey's Leverhulme Quantum
    Biology Doctoral Training Centre was supervised by Prof Jim Al-Khalili (Physics, Surrey) and Dr Marco Sacchi (Chemistry, Surrey) and published
    in Communications Physics.

    Prof Al-Khalili comments: "Watson and Crick speculated about the
    existence and importance of quantum mechanical effects in DNA well
    over 50 years ago, however, the mechanism has been largely overlooked."
    Dr Sacchi continues: "Biologists would typically expect tunnelling to
    play a significant role only at low temperatures and in relatively simple systems. Therefore, they tended to discount quantum effects in DNA. With
    our study, we believe we have proved that these assumptions do not hold."

    ========================================================================== Story Source: Materials provided by University_of_Surrey. Note: Content
    may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Louie Slocombe, Marco Sacchi, Jim Al-Khalili. An open quantum
    systems
    approach to proton tunnelling in DNA. Communications Physics,
    2022; 5 (1) DOI: 10.1038/s42005-022-00881-8 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/05/220505085605.htm

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