Five facts about smell

Five facts about smell squeezed in to 10 minutes.

I had so much fun giving this talk. There is a mistake on slide 15 which I have left in for the lols.

Transcript

1. FIVE FACTS ABOUT SMELL BY @ALICEBARTLETT
2. 1. Humans have three chemical senses.
3. 1. Taste
   2. Smell
   3. Trigeminal
4. 2. 1.2% of people do not have a sense of smell*. [Gilbert and Wysocki 1987]
5. *I am one of those people. Hello.
6. 3. Some smells are easily detectable to humans even at very low concentrations. Nobody knows why.
7. **SUB-LIST TIME**
8. FIVE SMELLY SMELLS:
   ! 1. GRAPEFRUIT JUICE
   2. CORK ODOUR
   3. BUTTER
   4. PEPPERONI
   5. STRAWBERRY [Ohloff 1990]
9. FIVE SMELLY SMELLS:
   ! Nobody knows why the human nose is better at detecting these compounds but it really is.
10. Comparison of detection thresholds in water:
    ! Limonene: 10ppb
    ! Menthene-8-thiol: 0.00001ppb (grapefruit) Demole E., P Enggist and G. Ohloff, Helv. Chem. Acta, 65, 1785-1794 (1982) (limonene)Fazzalari, F A., editor, Compilation of Odor and Taste Threshold Data, ASTM Data Series DS 48A (1978)
11. TODAY YOU LEARNT:
    ! Grapefruits are 1 million times smellier than lemons*. *kinda
12. 4. There are seven primary smells
13. These classifications are more psychological than chemical but are very handy for talking about smells.
    
14. **SUB-LIST TIME**
15. SEVEN PRIMARY ODOURS:
    ! 1. Musky (moth balls)
    2. Floral (roses)
    3. Pepperminty
    4. Ethereal (detergent)
    5. Pungent (vinegar)
    6. Putrid (bad eggs) [Amoore et al. 1964]
16. 5. We don’t really know how humans detect smell.
17. The facts:
18. You have between five and six million smell receptors
    
19. You have 347 different types of olfactory receptor.
20. One olfactory receptor will detect several (similar) molecules and react with different intensities to them.
21. Your olfactory receptors seem to react in a combinatorial way. [Buck et al. 1999]
22. The problem
23. We don’t know how this reaction works. There are two theories and neither have been disproven
24. “Shape Theory” states that molecules fit into receptors like a lock and key.
25. This makes sense intuitively and is the historically preferred theory
26. BUT
27. Whilst shape theory works for most compounds, there are some exceptions:
28. Some compounds with vastly different shapes smell the same
29. And some compounds with very similar shapes smell totally different
30. This model has also not been able to predict any smells from looking at the shape, which you would expect it to be able to.
31. “Vibration Theory” states that it is not the shape but the vibration pattern of the molecule that determines it’s odour
32. This would explain why two compounds with different shapes can smell the same.
33. But there are still challenges.
34. Whilst some compounds with the same vibration energy smell the same, some smell different!