Quantum criticality in biologic protein systems (Introduction)

by David Turell @, Wednesday, August 15, 2018, 21:17 (96 days ago)

The movement of electrons is poorly understood in the biochemistry of life:

https://phys.org/news/2015-04-quantum-criticality-life-proteins.html

"Stuart Kauffman, from the University of Calgary, and several of his colleagues have recently published a paper on the Arxiv server titled 'Quantum Criticality at the Origins of Life'. The idea of a quantum criticality, and more generally quantum critical states, comes perhaps not surprisingly, from solid state physics. It describes unusual electronic states that are are balanced somewhere between conduction and insulation. More specifically, under certain conditions, current flow at the critical point becomes unpredictable. When it does flow, it tends to do so in avalanches that vary by several orders of magnitude in size.

***

"The potential existence of quantum critical points in proteins is a new idea that will need some experimental evidence to back it up. Kauffman and his group eloquently describe the major differences between current flow in proteins as compared to metallic conductors.

"By contrast, this kind of a mechanism would appear to be uncommon in biological systems. The authors note that charges entering a critically conducting biomolecule will be under the joint influence of the quantum Hamiltonian and the excessive decoherence caused by the environment. Currently a huge focus in Quantum biology, this kind of conductance has been seen for example, for excitons in the light-harvesting systems. As might already be apparent here, the logical flow of the paper, at least to nonspecialists, quickly devolves into the more esoteric world of quantum Hamiltonians and niche concepts like 'Anderson localization.'

***

" Turin.. notes that the question of how electrons get across proteins is one of the great unsolved problems in biophysics, and that the Kauffman paper points in a novel direction to possibly explain conduction. Quantum tunnelling (which is an essential process, for example, in the joint special ops of proteins of the respiratory chain) works fine over small distances. However, rates fall precipitously with distance. Traditional hole and electron transport mechanisms butt against the high bandgap and absence of obvious acceptor impurities. Yet at rest our body's fuel cell generates 100 amps of electron current.

***

"In suggesting that biomolecules, or at least most of them, are quantum critical conductors, Kauffman and his group are claiming that their electronic properties are precisely tuned to the transition point between a metal and an insulator. An even stronger reading of this would have that there is a universal mechanism of charge transport in living matter which can exist only in highly evolved systems. To back all this up the group took a closer look at the electronic structure of a few of our standard issue proteins like myoglobin, profilin, and apolipoprotein E.

***

"However, in asking why life just uses the molecules that does, the authors don't explicitly address the question of just how many potential small biomolecules and or proteins would be expected to quantum critical in the first place. They do note that some biomolecules are actually fairly good conductors.
"We might call to mind at this point that others have looked for similar kinds of extreme behaviours in other examples of life's proteins. Stuart Hameroff has been a long time champion of networks of polymerized tubulins in the conduction of information in the cells through as yet fully defined mechanisms. In particular, we should mention recent work on driving the rapidly polymerization of microtubules through external electromagnetic fields raises the question of what new kinds of physics may be at play here. I discussed some of this in more detail elsewhere the other day, together with some of the researchers here for anyone interested to read a little more."

Comment: I am convinced that quantum mechanics underlies whatever is present in our universe and is actively present in the biochemistry of life. Foe example, in the past I have presented articles on photosynthesis, where quantum activity has been identified, as emphasized by my bold above. This is such a highly technical and theoretical field it is difficult to fully understand it, but then quantum theory is still at the outer edges of what it all means. Note this abstract:

http://iopscience.iop.org/article/10.1088/1742-6596/626/1/012023/pdf

"Abstract. Why life persists at the edge of chaos is a question at the very heart of evolution. Here we show that molecules taking part in biochemical processes from small molecules to proteins are critical quantum mechanically. Electronic Hamiltonians of biomolecules are tuned exactly to the critical point of the metal-insulator transition separating the Anderson localized insulator phase from the conducting disordered metal phase. Using tools from Random Matrix Theory we confirm that the energy level statistics of these biomolecules show the universal transitional distribution of the metal-insulator critical point and the wave functions are multifractals in accordance with the theory of Anderson transitions. The findings point to the existence of a universal mechanism of charge transport in living matter. The revealed bio-conductor material is neither a metal nor an insulator but a new quantum critical material which can exist only in highly evolved systems and has unique material properties."


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