The Asymmetry of Existence

Daniel Curry

Human beings carry a fixation with symmetry. Western art in particular often includes completely symmetrical patterns and features. Sculpted gardens and extravagant buildings are an excellent example of engineered symmetry.

A famous piece of artwork by Leonardo da Vinci is “The Vitruvian Man”. This shows the human figure and highlights it’s symmetry. However, this is created by the artist. Humans are symmetrical only on the surface with two arms and legs either side of a body, and a head on top. By adding details the symmetry disappears instantly. Under the skin, humans are even further asymmetrical. The internal organs are placed equally along a centre line. The left lung is smaller than the right to make room for the heart to sit behind it. The stomach also sits on the left side.

Life itself is asymmetrical, the galaxy we are in is asymmetrical and the universe is certainly not symmetrical. This lack of balance allowed the universe to form the way it has, and ultimately, has allowed life to come into existence.

In the very beginning, the theory is that the universe was balanced equally in amounts of matter and of antimatter. However, if this was still the case, then matter and antimatter would annihilate each other and only photons would remain. (Belle Dume 2006) Our universe is matter dominated therefore something must have caused an imbalance.

Chirality

Chirality is “The characteristic of a structure that makes it impossible to superimpose on it’s mirror image”. (American Heritage Science Dictionary definition as of 19/11/2009). Jean Baptist Biot first observed chirality in 1815, though at the time, he was studying tartaric acid. He noticed that the acid rotated polarised light. Louis Pasteur went on in 1847 to study the crystals of tartaric acid. He found that the crystals were the mirror image of each other. He separated the two types of crystals manually, and found that tartaric acid made with one type of crystal rotated polarised light clockwise, and the other rotated it anticlockwise. When there was a mixture of the two, there was no optical activity. This was the beginning of studies on structures that affect the rotation of polarised light. Further science has shown that any molecule with a tetrahedral structure can act like the tartaric acid crystals. This is chirality. The molecules are said to be chiral. This is also called stereoisomerism and is very important in the synthesis of chemicals and the production of drugs. In order to differentiate between the two versions of a molecule (called enantiomers) the Cahn-Ingold Prelog can be applied. The molecule is drawn out in a Fischer projection and each group on the molecule is given a priority based upon it’s molecular mass. If the lowest is not at the bottom of the drawing, then it is swapped into that position, and the remaining two groups are also swapped to retain balance. The orders of priority are then observed and if they run in a clockwise direction (1>2>3>4), designation ‘R’ is given. If anticlockwise is shown (4>3>2>1) then ‘S’ is given. See example below:

Chirality is important in the formation of life as amino acids, which are the building blocks of life, are chiral. They can exist in both the left and right handed forms. Studies have shown that all amino acids used in known lifeforms are of the left handed variant. (R. Graham Cooks 2001). As these amino acids are left handed, right handed sugars such as Deoxyribonucleic Acid (DNA) have formed. Again, these sugars and other chemicals which interact with amino acids have become the right handed version. Natural selection is thought to have taken place due to left handed amino acids forming first.

Image via Wikipedia

The question remains as to why left handed amino acids were formed, when laboratory experiments to synthesise amino acids have shown a 50/50 racemic mix of left and right handed molecules. One theory, based upon the notion that radiation can also display chirality, is that a star forming cloud in the constellation of Orion (M42) produces a stream of radiation. This radiation is polarised and follows a corkscrew pattern (Malcolm W. Browne 2001). Studies on amino acids show that amino acids are prone to decomposition when absorbing ultraviolet radiation (L. F. Stakhov, V. G. Ladygin, and L. N. Stakhova 2001). If this radiation is circularly polarised (follows a corkscrew pattern) it preferentially decomposes either the left or right hand variant of amino acids (Malcolm W. Browne 2001). This would mean, combined with the theory that amino acids fell to the earth on meteorites based on studies on the meteorite that was discovered in Murchison, Australia 1969, that amino acids travelled across space and were exposed to this radiation stream from M42 and the right hand amino acids were decomposed. This would leave the left handed amino acids to reach Earth and replicate going on to form life. Evidence to support this was provided by an American scientist, Breslow. He found that the Australian meteorite contained a variety of carbon based molecules, including amino acids. Again, all amino acids present were the left hand versions. Critics claimed that this was due to terrestrial contamination and that the amino acids had not come from space. Further study discovered new amino acids not present naturally on Earth and this helped to again bolster the argument that amino acids did come from space.

Image via Wikipedia

This asymmetrical imbalance has created life that is effected by chirality. Tastes and smells are dependant on chiralilty. A good example of this is the molecule Carvone.

The two molecules are chiral and have very different smells and tastes. R-carvone is the flavouring of spearmint, and S-carvone is the flavouring of caraway. Laws are in place to ensure that all synthesised drugs are created as enamtiomerically pure. This was following the thalidomide cases. R-thalidomide is a sedative and an anti-sickness drug, whereas S-thalidomide causes birth defects.

Conclusion

If the universe was symmetrical then we would not be here. There would be no universe as we know it, possibly just a sea of photons. An early imbalance between matter and antimatter allowed for the galaxies and planets to form. Ultimately this led to the formation of the building blocks of life. For these to actually become life, another imbalance was needed to create our asymmetrical existence.

References

Books

Close, F. E. Lucifers Legacy, the Meaning of Asymmetry

Engel, M. H. and S. A. Macko. 1997. Isotopic evidence for extraterrestrial non-racemic amino acids in the Murchison meteorite. Nature 389: 265-268. See also: Chyba, C. R., 1997. A left-handed Solar System? Nature 389: 234-235

Housecroft, C.E. Constable, E.C. Chemistry 3rd edition. 809-820

Online

American Heritage Science Dictionary. Houghton Mifflin company. “Chirality” (http://dictionary.reference.com/browse/chirality accessed 19/01/2009

Browne, M.W. NY Times publication (http://query.nytimes.com/gst/fullpage.html?res=9E06E6D91338F932A05754C0A96E958260&sec=&spon=&pagewanted=all accessed 19/01/2009

Close, F. ‘Its done with mirrors’ (http://www.gresham.ac.uk/printtranscript.asp?eventid=7) accessed 21/01/2009

Witold K. R. ‘Asymmetric autocatalysis: crystallization-induced highly enantioselective synthesis of a conglomerating oxo-rhenium(V) complex’ (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THT-4TPF763-2&_user=1583747&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000053884&_version=1&_urlVersion=0&_userid=1583747&md5=1dc34595216bda4399e0ea16c2d93935) accessed 13/02/2009

(unknown author) Molecule of the Day (http://www.moleculeoftheday.com/2006/05/12/carvone-you-can-smell-chirality/) accessed 15/02/2009