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Subject: �յ� 2

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Date Posted: 13:46:21 05/10/03 Sat
In reply to: hkcee 's message, "��bio" on 09:56:41 05/10/03 Sat

Although all three share the same molecular formula (C6H12O6), they get different arrangement of atoms. So they are called as structural isomers (identical molecular formulas but different structural formulas). As HKCEE level, I don't think it is necessary for you guys to know the 'ring' structures for those compounds. Fructose is intensely sweet and galactose is the least sweet.

Glucose is a reducing sugar and is also known as dextrose (dextrose should be out-of-syllabus and so I would not explain it. All I can say is that glucose has a -CHO group on right and fructose has it on left. Anyway, it is something about the structure and you guys should not bother about this).
It is also called blood sugar as it circulates in the blood (But I forget the concentration, someone please help). Glucose is initially synthesized by chlorophyll in plants using carbon dioxide from the air and sunlight as an energy source. It is further converted to starch for storage.

Fructose is commonly found together with glucose in honey and fruit juices and, like glucose, it is also a reducing sugar. It is also called levulose (because of the structure again). Bees gather nectar from flowers which contains sucrose and then to hydrolyze or break apart the sucrose into its component parts of glucose and fructose.

Galactose is more commonly found in the lactose or milk sugar.

Also, they can form different disaccharides with each other; for example,

Glucose + glucose = maltose (grains)
Glucose + fructose = sucrose (table sugar)
Glucose + galactose = lactose (milk products)

In digestion process, glucose and galactose are absorbed via active transport. On the other hands, fructose facilitates diffusion using carrier.

Hopefully I am not writing something wrong as I had not studied any biology in last 8 years. Please point out if I made any mistake. Thanks

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