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The amazing role of quantum mechanics inside living cells

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The amazing role of quantum mechanics inside living cells

It's only in the last decade or so that careful experiments -- in biochemistry labs, using spectroscopy -- have shown very clear, firm evidence that there are certain specific mechanisms that require quantum mechanics to explain them. 1 Quantum biology brings together quantum physicists, biochemists, molecular biologists -- it's a very interdisciplinary field. A nanometer is a billionth of a meter. My area is the atomic nucleus, which is the tiny dot inside an atom. It's even smaller in scale. This is the domain of quantum mechanics, and physicists and chemists have had a long time to try and get used to it. Quantum mechanics was developed in the 1920s. It is a set of beautiful and powerful mathematical rules and ideas that explain the world of the very small. And it's a world that's very different from our everyday world, made up of trillions of atoms.Particles can multitask, they can be in two places at once. They can do more than one thing at the same time. Particles can behave like spread-out waves. It's almost like magic. In the last 10 years, there have been experiments emerging, showing where some of these certain phenomena in biology do seem to require quantum mechanics. Back in the 70s and 80s, it was discovered that quantum tunneling also takes place inside living cells. Enzymes, those workhorses of life, the catalysts of chemical reactions -- enzymes are biomolecules that speed up chemical reactions in living cells, by many, many orders of magnitude. And it's always been a mystery how they do this. It was discovered that one of the tricks that enzymes have evolved to make use of, is by transferring subatomic particles, like electrons and indeed protons, from one part of a molecule to another via quantum tunneling. It's efficient, it's fast, it can disappear -- a proton can disappear from one place, and reappear on the other. Enzymes help this take place.

Enzymes are involved in a well-orchestrated series of metabolic reactions that facilitate many processes essential to life. These biocatalysts greatly accelerate these chemical reactions, achieving rate enhancements as high as 10^25 relative to the corresponding uncatalyzed reactions 3  There is still a need for new ways of addressing pressing questions that current theories of enzyme catalysis and dynamics have not resolved. In particular, the participation of residues remote from the active site in the catalyzed bond activation is of great interest, as is the long-range communication of residues across the enzyme. Better understanding of global effects across the protein may reveal the purpose and function of the enzyme structure beyond the active site.

Quantum biology 4
Observations of long-range electron transfer through proteins often show exponential distance dependence as well as weak temperature dependence81, 83, providing a strong indication that a single-step tunnelling mechanism is responsible for these biological processes. It is remarkable that such long-distance electron transfer in biology occurs through quantum mechanical tunnelling, because electron tunnelling over such long distances would be impossible in vacuum.  

Enzyme-Catalysed Reactions through quantum Tunnelling

Enzymes use quantum tunneling to catalyze chemical reactions 2

Enzymes are great at taking time-consuming chemical reactions and speeding them up. They bend molecules into different shapes and are able to grab and hand off reactive groups between chemical constituents… or are they? Instead of the grab-and-pass model many biologists and chemists think of when imaging enzyme catalysis, it is  hypothesized that enzymes take advantage of quantum tunneling. When a particle undergoes quantum tunneling, it instantaneously “teleports” from its current position to a new position in space.
On a microscopic scale, nearly all the machinery that keeps our cells working involves chemical reactions of some sort and these reactions wouldn’t happen without enzymes – natural catalysts which make reactions happen very quickly, fast enough for life to be possible. How do they do this?  Understanding enzyme catalysis is a fundamental problem in biology.  Enzymes are superb catalysts, but the underlying physical principles are hotly debated.  If we could design catalysts like them, they could transform areas such as ‘green’ energy generation and would make it possible to make new molecules in environmentally friendly ways.  Engineered enzymes and designed protein catalysts are far less efficient than their natural counterparts, however.  Chemists have yet to achieve the dream of making catalysts as powerful as natural enzymes. This has led many researchers to propose that current theoretical models and concepts may not be adequate for understanding enzymes, and that new paradigms are required.  This is particularly true for enzyme reactions that involve a particular quantum mechanical phenomenon known as tunnelling. In quantum tunnelling, a particle passes through a barrier that, according to the laws of classical mechanics, it should not be able to get over.  Scientists have known for some time that a whole host of reactions across chemistry and biology involve quantum tunnelling (in particular, the many reactions that involve transfer of particles as small as hydrogen atoms) and they have developed accurate models to describe its effects for chemical reactions. However, some experimental observations for enzymes have led to recent suggestions that quantum tunnelling models for chemical reactions are inadequate when enzymes are involved.  These ideas propose that enzymes somehow force tunnelling to happen in some special way – and that we therefore require new models for understanding how enzymes work.  So: do we have the theoretical tools to understand enzymes, or are new models and concepts needed?

In a paper published in Nature Chemistry, Dr David Glowacki, Professor Jeremy Harvey and Professor Adrian Mulholland of Bristol’s School of Chemistry took Ockham’s razor to the enzyme tunnelling problem. They used some simple maths to show that standard models for describing quantum tunnelling can explain the experimental enzyme data, so long as one accounts for the fact that enzymes have many possible different structures.  Enzymes, like all proteins, are constantly fluctuating between many subtly different structures, which can have significantly different catalytic properties.
This dynamic nature of proteins has also been highlighted by scientists who study protein folding (the process by which a protein structure assumes its functional shape or conformation, the other ‘grand challenge’ of chemical biology).  The Bristol researchers' paper indicates that enzyme structural fluctuations are significant, and by including them in modelling, scientists have the theoretical tools needed to understand these amazing natural catalysts.  This should make it possible in future to design new catalysts using these principles.

3. file:///D:/Downloads/molecules-20-01192.pdf

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