Mirror, mirror, on the wall… Why are molecules asymmetric?


Left and right hands can demonstrate the principles of chirality

Physicists discover a property of electrons which can explain striking asymmetries in biology.

Ok, now I have lured you in with a picture of a cute kitten, let’s talk biochemistry!

Chirality (don’t be scared) is a term which means that two molecules can have the exact same chemical compositions but their shapes are mirror images of each other, like a left hand is the mirror image of a right hand (actually χειρ (kheir) is greek for “hand”). However, like our hands, the images of a chiral molecule cannot be superposed. Chirality can actually change the molecule’s characteristics drastically; for instance, limonene conveys the taste for both lemons and oranges, but it has opposite chirality in each fruit.

However, it’s been observed that surprisingly the main molecules composing life, the sugars and amino acids, have a strong propensity to be all be either “right-handed” or “left-handed”.

This tendency has often been attributed to random luck, but experimental data from Dreiling et al. suggest that the origin of this phenomenon seems to stem from newly discovered fundamental properties of some electrons which are generated “left” and “right-handed” (so called “spin-polarised electrons”).
These physicists investigated how polarised electrons interact with each other. It took a relatively long time to get the results for this experiment (13 years!).

“The scale of the asymmetry is as though we flip 20,000 coins again and again, and on average, 10,003 of them land on heads while 9,997 land on tails,” says Dreiling (source)

This bias was found to be tiny, but consistent. This asymmetry reverberating billions of years later could explain the drastic differences we see today.

For more information, see here. Follow me on twitter for the latest science news.

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Scientist studying the ins and outs of the interactions between the human host and the pathogens that infect it. I obtained my PhD in 2012 in the University of Bordeaux, France and I am currently working at Imperial College London, UK. I aim to share my passion for science by making it simple and approachable, so please feel free to post questions you'd like answered on twitter.com/Marianne_Guenot

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