Phishfood

is there a REASON that glucose, mannose, and galactose are so damn popular in glycoproteins? they're everywhere!

-Pf

edited to add: my guess is just that they're structurally similar (being epimers and all...) and aldohexoses. so they're stable and there can be plenty of branching going on.

BioBeing

Errr - the Designer made it that way :Cheeky:

Why are (almost) all naturally occuring amino acids in the L configuration?

Phishfood

well i guess no one knows

theyeti

If I had to guess, I'd say it's because they're common sugars, and since they're all 6 membered rings, they can form ordered structures when polymerized. (Basically, you can use a bunch of hexagons to make whatever shape you want.) Since glycoproteins serve basically as recognition "keys", shape is important.

Of course, those three sugars are not the only ones found in glycoproteins.

theyeti

BioBeing

Lets ask our resident biologists over in E/C.

BioBeing,
S&S Mod

Coragyps

Glucose, at least, is probably common because of energetics: all of its bulky groups (hydroxyls and the hydroxymethyl) are in equatorial positions in its normal conformation. And too, there are only eight possible aldohexoses to pick from, so three is a decent number of them to be the "most common."

I may have to get out a pencil and go draw a bunch of cyclohexanes in the chair conformation now. And I apologize to all you non-chemists for our jargon - half an hour at a blackboard with some chalk, and I could explain that stuff to you, but this medium is a little more difficult to do interactive 3-D drawings on.

Coragyps

Well, I did go draw them.... do you think I should get a life?
Galactose and mannose only have one substituent axial and the rest equatorial, so they likely are the next most thermodynamically stable after glucose.