It is composed of two monosaccharides, namely galactose and glucose molecules, linked by β(1 → 4) glycosidic linkage. The glycosidic linkage is between C-1 of β-galactose and C-4 of α-glucose (Figure 2.10). The anomeric carbon of glucose is free and hence lactose is considered to be a reducing disaccharide.

Occurrence Lactose is also known as milk sugar and is usually found in milk, occurring as β-lactose. This is produced in mammary glands.

It forms characteristic sunflower-shaped crystals with osazone reaction. The anomeric carbon of one glucose is free in maltose, and hence it possesses all the reducing properties of a reducing sugar. Isomaltose is also a reducing disaccharide. It consists of two molecules of glucose units. The type of linkage is α(1 → 4) glycosidic linkage. It…

It is composed of two molecules of glucose linked by α(1 → 4) linkage as shown in Figure 2.9. In the structure of maltose, the hydroxyl group on C-1 of the second sugar remains free, so it acts as a reducing disaccharide.

Occurrence It is an important component of malt. Maltose does not occur in the human body. It is produced when starch is hydrolysed by α-amylase.

Disaccharides are carbohydrates that consist of two molecules of the same or different monosaccharides. During hydrolysis, a disaccharide yields two moles of monosaccharides. The mode of linkage between these monosaccharides is the glycosidic linkage. The general molecular formula is CnH2nOn−1. Examples Maltose  Glucose glucose + (reducing sugar)Lactose  Galactose + glucose (reducing sugar)Sucrose  Glucose + fructose (non reducing sugar)

Esterification of carbohydrates with phosphoric acid usually happens in metabolism. For example, glucose-6-phosphate and glucose-1-phosphate are formed during metabolism. ATP donates the phosphate group for esterification.

Amino sugars are formed when the hydroxyl group is replaced by an —NH2 group. Examples are glucosamine and galactosamine. Amino sugars occur as N-acetyls in numerous biological important compounds. N-acetyl derivative of D-glucosamine is present in hyaluronic acid, heparin, and some blood group compounds. Galactosamine is present as N-acetylgalactosamine in chondroitin sulphate. Antibiotics such as erythromycin…

Deoxy sugars are the sugars in which the oxygen in the —OH group has been removed leaving the hydrogen. Thus, the —CHOH or —CH2OH becomes —CH2 or —CH3. Deoxy sugars are 2-deoxy-D-ribose found in nucleic acid (DNA) and 6-deoxy-L-galactose found as a constituent of bacterial polysaccharides.

D-glucuronic acid is present as the chief constituent of certain mucopolysaccharides. This is involved in the detoxication mechanism, where bilirubin is linked with D-glucuronic acid.