The Quantum Mechanics of Smell

Quantum mechanics seems to play a crucial role in the atomic world.

Big deal, right?  Quantum mechanics is for theorists that want to dig into the atomic world.

Not true. If it wasn’t for quantum mechanics, life wouldn’t even exist. Quantum mechanics is a model of how things behave in the atomic scale, but these quantum mechanisms affect the macro scale from the bottom up.

Scientists are starting to realize that nature has used quantum weird behavior and exploited it to create effective systems that are embedded in live creatures.

One great example is a quantum mechanical model of our sense of smell. Prior theories have proposed a lock and key mechanism (very common to theories in biology and medicine). This model suggests that if an odor molecule finds the correct receptor that has complementary shape, it then ignites the smell. Look at the image below.





There are some important features of smell that this model failed to explain. For example, how could molecules with the same shape smell very different?

In 1997, Luca Turin proposed a different model for smell. He proposed that electrons from the odor receptor tunnel through the molecule with the correct vibration that is analogous to the receptor. This tunneling causes the nerve attached to the receptor to ingite and produce the signal that the brain interprets as smell.

The tunnelling effect is a quantum phenomenon where an electron — due to its wave matter properties — can surpass an energy barrier that it wouldn’t ordinarily have the energy to pass over. The probability is low, but the tunnelling is possible. It is sort of as if you could sometimes pass through a wall.

This provides a much more robust model to explains the phenomenon of extremely similar molecules producing very different odor. We know that even an atom could cause a shift in the vibrational modes of a molecule and thus produce a different energy barrier. If a molecule differs in a single atom from another, then the tunneling will not happen in the receptor, causing the receptor not to fire signals to the brain. This explains the selectivity of the receptors for almost the same molecules. The tunneling of the electrons depends on the interaction and the energy barrier created by the molecule and the receptor combined.

We see now how important quantum mechanics is to our everyday life. QM will play a crucial role in the future as we explain more and more biological phenomena that involves quantum weirdnessIf you want more technical details about the QM model of smell you may download the original article here

See Also

A New Route for Quantum Computing

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