A Nobel trilogy of flavours

By AlphaZeta (Own work) [Public domain],
via Wikimedia Commons

This year's Nobel prize was awarded "for studies of G-protein-coupled receptors". This concludes a marvellous trilogy of Nobel prizes which in sum give us a rather complete picture of how it comes that we are able to sense flavours, that is how we can taste and smell.

Let's for now disregard other senses such as hearing, texture and so forth and consider the flavour of something we eat as being mainly a combination of tasting (tongue) and smelling (nose). This is of course simplistic, but still taste and scent are two of the most important senses involved in our perception of food. If we concentrate on these two senses, which are both so-called chemical senses, we can actually invoke three Nobel prizes to illustrate important parts of this sensing process. They are all very elegantly described in both popular and scientific terms, depending on your background or taste, at the web site of the Nobel prize:

Step 1 - What happens when food aromas reach our nose? "The big picture"

Richard Axel and Linda B. Buck - The Nobel Prize in Physiology or Medicine of 2004

Popular information: An elegantly illustrated information "cartoon" at the Nobel prize site.

Photo by Bill Branson, NIH Medical Arts and Photography
Branch [Public domain], via Wikimedia Commons

Axel and Buck received the prize "for their discoveries of odorant receptors and the organization of the olfactory system". Basically this means: what actually happens when "smelly molecules" from the food reach your nose? The molecules obviously have to be in the gas phase, they have to evaporate. That's the reason why salt and sugar don't smell, and also that's why hot food smells stronger than cold food. When the odorant molecules reach your nose they "dock" onto so-called receptors, but this only happens if the molecule fits snugly into the "docking station", the receptor. In our nose we have around 1000 different receptors with different shape that can accept different sorts of molecules.

Axel and Buck revealed through their work answers to questions such as

• how come that we can smell more than 10 000 different odours when we only have around 1000 different receptors?
• What happens when the molecules "dock" onto the receptors and the signals are forwarded to the brain?
• How come that humans, mice and dogs have so different thresholds to smelling things?

The answers can be found nicely illustrated in the above mentioned popular information. These results also have bearing on the sense of taste since both taste and odour molecules are sensed through so-called G-protein coupled receptors.

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Step 2 - What happens when tasting or odorant molecules reach our taste or smell receptors?

Robert J. Lefkowitz and Brian K. Kobilka - The Nobel Prize in Chemistry 2012 "for studies of G-protein-coupled receptors"

Popular information: An illustrated popular article at the Nobel prize site.

Cross section of a cell membrane with G-protein coupled
receptor (coloured) which is responsible for receiving chemical
substances and forwarding the signal to the inside of the cell.
By Bensaccount [Public domain], via Wikimedia Commons

Lefkowitz and Kobilka received their joint prize "for studies of G-protein-coupled receptors". They discovered that these G-protein coupled receptors are a very general type of receptors that are responsible for a lot of processes which are controlled by chemical substances. Examples are how various organs react when hormones are released, such as why our heart races, our breathing rate increases and digestion is given less priority when adrenalin is released if we get scared. However, this type of receptor is also responsible for receiving chemical substances when we smell and taste. You might say that Lefkowitz and Kobilka revealed detailed information about one step in the process described by Axel and Buck, namely what exactly happens when molecules dock onto our taste buds on the tongue or odour receptors in the nose.

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Step 3 - What happens when the signal has been received by the receptor?

Alfred G. Gilman and Martin Rodbell - The Nobel Prize in Physiology or Medicine 1994 "for their discovery of G-proteins and the role of these proteins in signal transduction in cells"

Popular information: An illustrated information "cartoon" at the Nobel prize site.

Gilman and Rodbell received their prize ten years earlier than Axel and Buck. Their discoveries must have been vital for both later prizes. Particularly Lefkowitz and Kobilka's work (step 2 above) builds directly on this work. Whereas Lefkowitz and Kobilka got their prize in 2012 for work on the receptors (see picture above), Gilman and Rodbell got their prize 18 years earlier for what happens when the signal is being transmitted further by the receptor. Inside the cell, close to the inside-part of the receptor, there are so-called G-proteins. When the receptor is activated (e.g. by an odorant molecule) it puts the G-protein into work which in turn does its job in transmitting the signal further. This "job" can be G-proteins in the brain registering light (responsible for you being able to see), forwarding signals from your tongue or nose to the brain and so forth. This research describes thus one part of the previous step, so you may say that this work is in a way at an even more detailed level than the two above.

Cross section of  cell membrane, outside up and inside down. Chemical substance (e.g. odour or taste molecule) docks to the receptor (blue rods). The receptor affects the G-protein inside the cell (pink dot cluster), carrying out its function.
Illustration by S. Jähnichen, via Wikimedia Commons

Conclusion

In my eyes, these three prizes reveal how wonderfully complex biological systems are (this is just a very few processes of our biology). At the same time they demonstrate the immense achievements of ingenious researchers, as result of loads of hard work, persistence and elegant solutions in solving these puzzles. Finally they demonstrate how science is built brick by brick; the results we get today or tomorrow all build upon the work of others.

References

The Nobel Prize in Physiology or Medicine of 2004: http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004

The Nobel Prize in Chemistry 2012: http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2012

The Nobel Prize in Physiology or Medicine of 1994: http://www.nobelprize.org/nobel_prizes/medicine/laureates/1994