Glucose, Fructose and Starch

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Starlight189
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Glucose, Fructose and Starch

Post by Starlight189 » Thu Apr 19, 2007 1:16 pm

Hi,

I believe that both glucose and fructose are monosaccharides and that both are stored as starch in a plant.

What I don't understand is how glucose promotes starch formation quicker than fructose if they are both monosaccharides. Surely it should take the same time? Or is there another structual difference I don't know of?

Any help would be very much appreciated, and thanks in advance.
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Post by blcr11 » Thu Apr 19, 2007 3:41 pm

They are both monosaccharides, as you've said, but only glucose is stored in starch or glycogen. Glucose is metabolically much more "plastic" than almost any other sugar. If fructose is to ever be incorporated into glycogen or starch, it will have to be first converted into one of the glucose-phosphates and from there it can get incorporated into glycogen/starch. Transport of glucose usually is linked directly to G1P formation, so as soon as it enters the cell, glucose is primed and ready to go for either glycolysis or glycogen sythesis depending on what is needed. The same is not true for fructose.

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Post by Odunitan » Thu Apr 19, 2007 7:02 pm

I believe that glucose $ frutose are monnosaccharides. But glucose is stored as starch in plants $ as glycogen in animals.

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Post by victor » Fri Apr 20, 2007 12:20 am

Yup, glucose is more 'plastic' than fructose. Even it's proved by hexokinase enzyme which has a lower Km value for glucose than fructose, which means that glucose is more preffered..... :lol:
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Post by Dr.Stein » Fri Apr 20, 2007 4:21 am

It is all about enzyme...
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