why Sugar got sweet taste?

[Sherif]

Can anyone tell me why the sugar tastes sweet knowing that it consists of carbon, hydrosion, and Oxygen? And the fact that nothing of these got sweet taste?![/b]

[MrMistery]

Sugar is only sweet because you can sense it to be sweet. It is sweet because the sugar molecules bind to specific receptors on the membranes of cells on your tongue and trigger a signal transduction pathway that creates the sweet taste in your brain. O, H, C can not bind to that receptor, so they do not taste sweet

[victor]

It's also related to the sugar molecule's geometry. Something must be soluted into liquid so it can give 'taste'.
Just take an example of glucose. When it's soluted into water, the molecule's geometry is changed from aliphatic chain form (see Fischer projection for glucose) into cyclic form (see Haworth projection).
Glucose can give sweet taste if it's in cyclic form..that's why glucose is oftenly said as beta-dextro-glukopiranose. Pirane word there is shown to implied that the glucose is in cyclic form...

That's from chemie side....

[MrMistery]

From what i remember from the first chapter in Campbell, the glucose molecule is in a constant equilibrium of an isomerisation reaction. And this equilibrium greatly favours the cyclic form.
Also vic, oxygen can disolve into water, or else there wouldn't be many fish around

[victor]

Um, I think I can't catch your last sentence...could you please elaborate it???

[MrMistery]

Something must be soluted into liquid so it can give 'taste'

This is not the only reason why glucose has sweet taste, as oxygen can also dissolve into water and it doesn't have any taste..

[victor]

That's because our papilla lingualis (filiformis/fungiformis) have a kinda stereospecific receptor for certain molecule....since Oxygen is not a stereogenic molecule, then it's not sweet...
sorry...I forgot to add this thing...

[MrMistery]

What is a stereogenic molecule?

[victor]

stereogenic molecule = a molecule that has a stereogenic center...

stereogenic center = is a center where there're 4 different kinds of atom/molecule binding...
ex: 2-buthanol (try to make the structure). You can see that C-2 (C which binds -OH molecule) is also binds another 3 different molecules which are methyl, ethyl and H atom......that C atom is called stereogenic center.
Try to face that molecule with a mirror, and you'll see that between the real molecule with it's mirror image cannot be superimposed. Or in a simple word, it's specific...

[swatkat]

are u referring to the chiral condition as in optical activity ,victor?(atleast thats what i understood )
ok i wanted to ask
which is the sweetest sugar to taste????

[MrMistery]

dulcine, or something like that is 500 times sweeter than glucose. For that reason, it was used as a sweetner ~50 years ago. But it cause cancer or a similar..

[victor]

@swatkat
yup, chiral molecules and optical activity..

@Andrew
I think that swatkat asked is about sugar, not a synthesized sweeteners...so, I would go to fructose.. At least, that's what I catch from your previous post..