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Glycosidic bonds

A glycosidic bond is a covalent bond formed between a carbohydrate molecule and another molecule. In this reaction, the hydroxyl group of the carbohydrate combines with the hydrogen of another organic molecule, releasing a molecule of water and forming a covalent bond. Glycosidic bonds can be of the alpha or the beta type.

An alpha-glycosidic bond is formed when both carbons have the same stereochemistry, whereas a beta-glycosidic bond occurs when the two carbons have different stereochemistry.

Both glucose and fructose have the chemical formula, C 6, H 12, O 6. The 6-membered ring form of glucose is made of carbons 1 to 5, with oxygen between carbon 1 and carbon 5. The OH groups at carbons 1, 2, and 4 point down. The O H group at carbon 3, and the C H 2 O H group at carbon 5, point up. The 5-membered ring form of fructose is made of carbons 2 to 5, with oxygen between carbon 2 and carbon 5. The O H groups at carbons 2 and 3, and the C H 2 O H group at carbon 5, point down. The O H group at carbon 4, and the C H 2 O H group at carbon 2, point up. The O H group at carbon 1 in glucose can react with the O H group at carbon 2 in fructose. This forms a glycosidic bond, which is a bond between carbon 1 in glucose, to oxygen, to carbon 2 in fructose. The product of this reaction is called sucrose.

Figure 1: Sucrose is formed when a monomer of glucose and a monomer of fructose are joined in a dehydration reaction to form a glycosidic bond between carbon 1 in glucose and carbon 2 in fructose. In the process, a water molecule is lost.

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Polysaccharides