Why does fructose not form polymers like glucose?

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kluftern2
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Why does fructose not form polymers like glucose?

Post by kluftern2 » Sun Oct 15, 2006 5:16 am

First post at the forums,

My Biology teacher recently gave me a question he himself could not answer. Why does fructose not form polymers, while glucose does? Any help in clearing up this mystery would be greatly appreciated.

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MrMistery
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Post by MrMistery » Sun Oct 15, 2006 4:43 pm

Mystery? no..

Glucose is an aldose, a reducing sugar. it has an exposed glycosidic -OH group. thus it is able to form long polymers when the glycosidic -OH binds to a Hydrogen on another glucose. thus, bonds can be 1-4,1-2,1-5 etc

Fructose, on the other hand, is a ketose, a nonreudcing sugar. It has no exposed -OH group, so it has nothing to bind the next monomer in a hypothetic fructose polymer.

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Amrik
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Post by Amrik » Sun Oct 15, 2006 5:14 pm

well, maybe the teacher knows it but he is just wants you guys to find it out ;)
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kluftern2
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Post by kluftern2 » Mon Oct 16, 2006 1:18 am

lol no he really does not know
I do not understand how does fructose not have any exposed OH groups?
What do you mean by exposed?

Also i just looked up on Wikipedia that Fructose is a reducing sugar, as it does have an aldehyde group.

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Post by sdekivit » Mon Oct 16, 2006 7:44 am

forming of a polymer requires estereification due to 2 OH-groups, OH + COOH,OH + NH2 and COOH + NH2. Since fructose doesn't contain a OH-group on the anomeric C-atom because the open chain structure contains a ketogroup, fructose can't form polymers.

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Post by kluftern2 » Mon Oct 16, 2006 11:35 pm

so because it cannot bond in chain form it cannot bond in ring form?

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Post by victor » Tue Oct 17, 2006 11:13 am

fructose does form polymer. it's named inulin (mostly described as fructosan). Fructose does have OH group in its anomeric C atom.

Fructose is a reducing sugar, because it has a free carbonyl (ketone) group if we dee it as an acyclic form. this reduction involves a keto-enol tautomerism where, fructose/glucose will be converted into cis-1,2-enediol form (this is the reason why glucose and fructose can be interconverted).
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Post by kluftern2 » Tue Oct 17, 2006 11:12 pm

so what is the structural formula for inulin?

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