Disaccharides

Pages 1110-1111

Disaccharides are formed from two monosaccharide units that are connected by a glycosidic bond. Some of the important disaccharides are shown below.

	Maltose Maltose is a disaccharide formed from two molecules of glucose that are linked by a glycosidic bond from the hydroxy group (O is blue) on carbon 4 (gold) of one glucose to carbon 1 (the acetal carbon, green) of the other with alpha stereochemistry. (The bond from the blue O to the green C is alpha.) The other oxygens are red in this model.
	Cellobiose Cellobiose is a stereoisomer of maltose with beta-stereochemistry at the glycosidic linkage. It is formed from two molecules of glucose that are linked by a glycosidic bond from the hydroxy group (O is blue) on carbon 4 (gold) of one glucose to carbon 1 (the acetal carbon, green) of the other with beta stereochemistry. (The bond from the blue O to the green C is beta.) The other oxygens are red in this model.
	Lactose Lactose is formed from a molecule of galactose and a molecule of glucose that are linked by a glycosidic bond from the hydroxy group (O is blue) on carbon 4 (gold) of the glucose to carbon 1 (the acetal carbon, green) of the galactose with beta stereochemistry. It differs from cellobiose only in the configuration of the hydroxy group (O is black) on one carbon (carbon 4 of the galactose ring). The other oxygens are red in this model.
	Sucrose Sucrose is formed from a molecule of fructose and a molecule of glucose. It differs from the other disaccharides in that its glycosidic bond is formed between carbon 1 (the acetal carbon, green in the model) of glucose and carbon 2 (the acetal carbon, blue in the model) of fructose. Because of this connection, it has no hemiacetal group but has two acetal groups instead. The glucose is in a pyranose ring (six-membered) with an alpha-glycosidic bond, while the fructose is in a furanose ring (five-membered) with a beta-glycosidic bond. In the model, the oxygen connecting the rings is gold and the other oxygens are red.