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Thread: Molecular difference between Alpha and Beta Glucose?

  1. #1 Molecular difference between Alpha and Beta Glucose? 
    Forum Freshman
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    Damn, it's been a long, long time since I was last here. Maybe I should bake you guys a cake...

    Alpha and Beta glucose. C6H12O6. Beautiful. But there is a difference, as I can tell. Starch and Cellulose are made up of Alpha and Beta Glucose respectively. Take a look a this diagram:



    Pretty nifty diagram, right? Didn't make it myself, but I wish I had. As you can see from the picture, the 1st Carbon's hydroxyl group is flipped. Why does this matter so much? When we get macromolecular level this matters a buttass load it seems.

    Here's some starch



    Here's some cellulose



    Here is Oscar Wilde.



    The difference is I wouldn't have sex with starch or cellulose, right? Wrong. Apparently, when they bond it makes H2O. Huh...I guess my question is more chemically related, but..

    Since when has it mattered where an atom is located in a bond? The hydroxyl group will remain above the 1st Carbon no matter what? Atoms don't move?


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  3. #2  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    It has to do with the structures of the anomers, it's stereochemistry. Have you taken any courses in organic chem?

    Edit: A chemist could probably explain this better than I can.

    In cellulose the hydroxy groups are able to form hydrogen bonds with the adjacent glucose molecule, this is what accounts for the high stability of cellulose.


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  4. #3  
    Forum Freshman electricant's Avatar
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    alpha and beta glucose are anomers, if the C1 hydroxyl is not involved in a glycosidic bond then the two forms exist in equilibrium via a linear intermediate.

    It may look like a trivial difference but it has big implications structurally, which isn't very well represented in the figures you posted. The third figure shows ugly looking z-shaped bonds between each glucose monomer. In reality the middle glucose is upside down in relation to the two residues to which it is bound. This has big implications on the hydrogen bonding which occurs in the chain and therefore starch (a1-4 polymer) and cellulose (b1-4 polymer) have very different secondary structures.

    These structures look very different to enzymes. We can degrade the a1-4 links in starch and therefore we can eats things like potatoes, but we can't break down the b1-4 links in cellulose and live off grass!
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  5. #4 Not constructive, just reminiscing... 
    Forum Bachelors Degree
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    "The hydroxyl group is on the bottom in Alpha glucose, because Australia is at the bottom of the world"

    Ahh Dan...

    xx.

    Tridimity :wink:
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