is smell related to molecular weight ?

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brötchen
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is smell related to molecular weight ?

Postby brötchen » Tue Aug 24, 2010 7:59 pm UTC

for a long time now i was thinking that smell was basically a sens of molecular weight in much the same way color perception is a sense of wavelength (what i mean by that is that while our eye isn't really capable of distinguishing more than 3 wavelength it still gives a rough idea of wavelength) . but recently i was told that molecular weight has, in fact ,nothing to do with smell... now I'm kinda confused ... molecular weight was such an elegant answer to the question what smell really is . so what is smell if its not molecular weight ?


brötchen
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Re: is smell related to molecular weight ?

Postby brötchen » Tue Aug 24, 2010 8:14 pm UTC

i don't see how this answers my question... all the article says is that there are receptors for different kinds of molecules and that we apparently don't jet fully understand what property of a molecule determines which receptor it will triger with what intensity :
"An alternative theory, the vibration theory proposed by Luca Turin[6][7], posits that odor receptors detect the frequencies of vibrations of odor molecules in the infrared range by electron tunnelling. However, the behavioral predictions of this theory have been called into question.[8] As of yet, there is no theory that explains olfactory perception completely." the thing about the vibration sound like it could be related to molecular weight but apparently its not really the most common explanation.

lucius_vorenus
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Re: is smell related to molecular weight ?

Postby lucius_vorenus » Tue Aug 24, 2010 8:57 pm UTC

Perhaps there's a way to find out. Find two chemicals with the same molecular weight and find out if they smell the same. (If that's possible)

I always just assumed it was similar to an enzyme/substrate relationship, certain chemical shapes/structures trigger different receptors (possibly in different ways even?) and the collection of the resulting signals is interpreted by the brain.

But this is a pure laymen's guess.

tuseroni
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Re: is smell related to molecular weight ?

Postby tuseroni » Tue Aug 24, 2010 10:15 pm UTC

from what i understand smell and taste evolved to tell you which foods were good for you (in the context of an animal hunting/scavenging for food) and which ones are likely to kill you. often the things that taste the worst are in fact poisonous, things which smell bad are in fact diseased. a cooked steak to a rotting corpse for instance.
but there is no inherent quality of the molecule that makes it smell good or bad. a rotting corpse must smell delicious to a vulture. as must a pile of dung to a dung beetle.
equally such, no object has an inherent TASTE. good and bad taste are evolved to encourage or discourage the consumption of certain matter which may be harmful.
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lucius_vorenus
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Re: is smell related to molecular weight ?

Postby lucius_vorenus » Wed Aug 25, 2010 12:00 am UTC

tuseroni wrote:from what i understand smell and taste evolved to tell you which foods were good for you (in the context of an animal hunting/scavenging for food) and which ones are likely to kill you. often the things that taste the worst are in fact poisonous, things which smell bad are in fact diseased. a cooked steak to a rotting corpse for instance.
but there is no inherent quality of the molecule that makes it smell good or bad. a rotting corpse must smell delicious to a vulture. as must a pile of dung to a dung beetle.
equally such, no object has an inherent TASTE. good and bad taste are evolved to encourage or discourage the consumption of certain matter which may be harmful.


Correct, but there is a specific way in which the human body physically detects an odor, initially, to transmit the above information to the brain for processing. More or less, if the pattern of signals received match a certain neuro-computational algorithm (I'm generalizing here), or serve as an input to some other psychological process that eventually creates such an information state, then phenomenal qualia, such as 'taste' or 'smell' will arise. The quality of this smell/taste is ultimately determined, as you said, by the neural hardwiring of the individual, molded by evolution.

Nevertheless, if two different molecules, no matter how different in size, shape, property, or effect on human health, affect a set of sense receptors in exactly the same way, the brain in question will be unable to distinguish one from the other, thereby producing the same phenomenal experience in the individual. Again, yes it is true that the qualia experienced is ultimately determined by the individuals brain structure, but that's not what's at question here.

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Re: is smell related to molecular weight ?

Postby Izawwlgood » Wed Aug 25, 2010 12:36 am UTC

I actually just got out of a talk about smell/taste receptors being similar to temperature sensors, called Transient Receptor Potential channels. Certain foods, namely capsesin and mint families, will signal hot or cold sensations. I'm not sure why you'd feel that molecular weight is somehow the relavent factor here, beyond the likelihood that a heavier aromatic molecule would perhaps have a more difficult time arriving at a receptor than a lighter one would.
In short, eyes recieve stimuli in the form of photons of specific wavelengths. Your olfactory sense does not recieve information from molecules due to their weight, but due to their conformation. It's like saying a radio and a door lock work on the same principal, because radio waves and keys both operate on the same principal, you know, one using wavelength and the other using number of notches.
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tuseroni
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Re: is smell related to molecular weight ?

Postby tuseroni » Wed Aug 25, 2010 4:00 am UTC

why single out taste and smell, the body is made of billions of receptors all of which respond in a certain way to a certain molecule.
one need only look at the effect of dopamine on neural receptors in the brain for an analogue of what to expect of sensory organs (i just picked dopamine because its an excitatory molecule...and one i know off the top of my head, no pun intended) the molecule hits a receptor causing a chemical reaction, this sends electrical signals through electron pathways to the brain. in the end the reaction is just like any chemical reaction which has a release of energy. then that energy is sent to the brain for processing.

but im also kinda tired right now so i may be talking out my arse ^_^
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Re: is smell related to molecular weight ?

Postby gmalivuk » Wed Aug 25, 2010 7:04 pm UTC

brötchen wrote:all the article says is that there are receptors for different kinds of molecules and that we apparently don't jet fully understand what property of a molecule determines which receptor it will triger with what intensity
Not fully, no. But we have some pretty damn good ideas, and none of them has anything (directly) to do with molecular weight. Smell and taste detect some of the *chemical* properties of the molecule in question. They bind to different receptors based on how they react to those receptors *chemically*. There's nothing in there that can directly detect how big or heavy a molecule is, because there's no evolutionary benefit to be able to distinguish based on molecular size rather than on chemical properties. (After all, it's the chemical properties that will determine whether something will nourish you or kill you, not the molecular weight.)
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Simius
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Re: is smell related to molecular weight ?

Postby Simius » Thu Aug 26, 2010 9:16 am UTC

Brötchen, quoting Wikipedia wrote:"An alternative theory, the vibration theory proposed by Luca Turin[6][7], posits that odor receptors detect the frequencies of vibrations of odor molecules in the infrared range by electron tunnelling. However, the behavioral predictions of this theory have been called into question.[8] As of yet, there is no theory that explains olfactory perception completely."

There's an interesting TED talk from that guy about his theory and the science of smell.


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