MSGID: 1:317/3 6274a4ca   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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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