An Observable Quantum Biological Effect

Posted on 2012/02/04

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Feature Image - An Observable Quantum Biological Effect

With all my recent criticism of ‘quantum consciousness‘ I thought you might be interested in hearing about a quantum effect that ‘mainstream’ physicists think is exhibited in biological organisms.

I hope you will find it much more illuminating than the dense-vocabulary of quantum parapsychology.

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In 1848, Louis Pasteur discovered that some molecules can have the exact same chemical properties and arrangement, yet be mirror images of one another.[1]

One example of  such a molecule is the amino acid ‘alanine‘, pictured below.

These two molecules are not identical, although it might seem that way. It is not possible to superimpose one upon the other – the human left and right hands are not identical for the same reason.

Hands, and alanine molecules, are both examples of chiral structures – they are not identical to their mirror images.

Nevertheless, we might still suppose that the two molecules are chemically identical. They have the same elements, connected in the same arrangement, and electrically bound with the same energies. And so we could conclude that such molecules exist in equal ratios.

They don’t.

The puzzle Pasteur was trying to solve (concerning the polarization of light by biological molecules) led him to discover that there is in fact a distinct asymmetry in biological organisms. I say distinct assymetry, but I should probably say absolute assymetry! The ratio isn’t 3:1 or 10:1, or something like that, it’s 1:0!

For example, in each human you can find billions of L-alanine, but absolutely no D-alanine.

Further investigation becomes more puzzling. Not only are the distribution of these molecules asymmetric, but the asymmetry is uniform throughout the biological world. We only find L-alanine in the proteins of biological organisms and no D-alanine at all (except for a few non-protein uses).

The particle physicist, Richard Feynman, once remarked in his Caltec Lecture on ‘Symmetry in Physical Law’ that the asymmetry can be described very well by natural selection:

If life is entirely a physical and chemical phenomenon, then we can understand that the proteins are all made in the same corkscrew only from the idea that at the very beginning some living molecules, by accident, got started and a few won. Somewhere, once, one organic molecule was lopsided in a certain way, and from this particular thing, the “right” happened to evolve in our particular geography; a particular historical accident was one-sided, and ever since the lopsidedness has propagated itself. Once having arrived at the state that it is in now, of course, it will always continue – all the enzymes digest the right things, manufacture the right things: when the carbon dioxide in the water vapor, and so on, go in the plant leaves, the enzymes that make the sugars make the lopsided because the enzymes are lopsided. If any new kinds of virus or living thing were to originate at a later time, it would survive only if it could “eat” the kinds of living matter already present. Thus, it too must be of the same kind.

There is no conservation of the number of right handed molecules. Once started, we could keep increasing the number of right-handed molecules. So the presumption is, then, that the phenomena in the case of life do not show lack of symmetry in physical laws, but do show, on the contrary, the universal nature and the commonness of ultimate origin of all creatures on earth, in the sense described above.[2]

Here Feynman suggests that the presence of only one type of alanine in all biological organisms is compelling data for the common evolution of all species. In light of everything we know about evolution this seems to be correct.

But the asymmetry is even stranger than Feynman supposed.

As well as there being many molecules in biological organism that display the same asymmetry as alanine, there is a further pattern: ‘only left-handed amino acids and right-anded sugars are found.’[3] Might this be something more universal – other than an accident of evolutionary biology? Might it have something to do with physics?

Later in Feynman’s lecture he speaks of the phenomena of beta-decay. This curious phenomena (the central mechanics for a PET scanner) has been shown to be asymmetric under mirror reflection. Two experiment: one with an apparatus, the other with mirror-reflection of that apparatus – can produce asymmetric results!

Feynman likened it to building two clock in exactly the same way, except that you build one the mirror image of the other. You’d expect the clock to work exactly the same way. Set them up the same, and hey’d tick at exactly the same time.

Yet, two beta decay experiments, mirror images of one other, would produce results that did not ‘tick the same way’ – the results would not be mirror images of one another.

At the time of Feynman’s lectures (1961-1963) there was no good physical theory of beta decay.

In 1968, Abdus Salam, Steven Weinberg and Sheldon Glashow formulated their ‘electroweak theory‘, unifying electromagnetism with this new ‘weak interaction’ that beta decay exhibited.

The theory proposed the existence of 3 new particles responsible for the weak interaction: the W+, the W-, and the Z0. They were all discovered, with the predicted masses, at CERN in 1983.

The Z0 particle contributes the physics of chemical stability, although very weakly (which accounts for why it was unnoticed for so long). The Z0 interactions are also mirror-reflection asymmetric – some interactions are are ‘left-handed only’. Thus, we would expect an asymmetry in chemical stability.

Researchers at Kings College London found that:

‘with the Z0 force taken into account, the left-handed amino acids (and right-handed sugars) are more stable than the oppositely handed molecules. According to these calculations, there should be an excess of about 1 part in 100,000,000,000,000,000 of the more stable variety initially.’[4]

This, combined with natural selection over evolutionary gives a high probability to the more prominent, stable particles featuring exclusively in evolutionary biology (as Feynman earlier described). For more about the research at Kings College, see [5].

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So, what seemed to at first be a biological accident, in the light of new physics, now appears to be a quantum effects exhibiting macroscopically by natural selection over evolutionary time.

Abdus Salam even went to far as to say, ‘there is a growing confidence toay that the electroweak force is the true “force of life” and that the Lord created the Zo particle to provide handedness for the molecules of life.’[6] Although this phrase is confusing, emanating from a mind as great as Salam, it can offer solace to us all that we are not as stupid as we might suppose.

I think those of us who are not monotheists (such as the Muslim Salam) might digest the same curiosity in a slightly different manner.

What would the evolution of species on Earth be like if there were no reflection asymmetry in the weak-interaction? Would it take much longer?

Does asymmetry in chemical stability provide a ‘consensus’ for which chirality biological molecules evolve, and so  make their combination into multi-celluar organisms ‘easier’?

Perhaps in the future, if we find life on other worlds, we could investigate if the same amino acids and sugars predominate on other planets as they do here on Earth.

Until then, we are left with this interesting speculation.

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References

[1] Flack, H D (2009) “Louis Pasteur’s discovery of molecular chirality and spontaneous resolution in 1848, together with a complete review of his crystallographic and chemical work,” Acta Crystallographica, Section A, vol. 65, pages 371-389

[2] Feynman, Richard (1963) ‘Feynman Lecutres on Physics Vol. 1′ Chapter 52: Symmetry in Physical Law p 6

[3] Salam, Abdus (1990) ‘Unification of Fundamental Forces’ Cambridge University Press p 56

[4] Ibid. p 58

[5] Mason, Stephen F (1991) Origins of the Handedness of Biological Moleculesin ‘Biological Asymmetry and Handedness’ John Wiley & Sons

[6] Salam, Abdus (1990) ‘Unification of Fundamental Forces’ Cambridge University Press p 58

Posted in: Physics, Science