Classification of Carbohydrates

Classification

Carbohydrates are often referred to as saccharides. They are classified into three main groups

i) Monosaccharides        ii) Oligosaccharides        iii) Polysaccharides.

1. Monosaccharides:

Monosaccharides are the simplest group of carbohydrates which cannot be hydrolysed further. They are often referred to as “simple sugars”. They have the general formula C_n(H₂O)_n. They can be further subdivided on the basis of number of carbon atoms (triose, tetrose, pentose etc.) and on the basis of the functional group (aldose, ketose) as given in Table – 5.1.

2. Oligosaccharides :

Oligosaccharides are the carbohydrates which yield two to ten monosaccharide units on hydrolysis. They are further classified into di, tri, tetra (or) penta saccharides respectively containing 2, 3, 4 (or) 5 monosaccharide units.

Example:

a.  Maltose (disaccharide) (Glucose + Glucose)

b.  Sucrose (disaccharide) (Glucose + Fructose)

c.   Lactose (disaccharide) (Glucose + Galactose)

d.  Isomaltose (disaccharide) (Glucose + Glucose)

e.   Raffinose (Trisaccharide) (Fructose + Glucose + Galactose)

f.    Stachyose (tetrasaccharide) (Galactose + Galactose + Glucose + Fructose)

g.  Verbascose (pentasaccharide) (Galactose + Galactose + Galactose + Glucose + Fructose)

3. Polysaccharides

Polysaccharides are the carbohydrates which yield more than ten molecules of monosaccharides on hydrolysis. They are usually tasteless (non-sugars). They have the general formula (C₆H₁₀O₅)_n.

a. The polysaccharides composed of a single type of monosaccharide are called homoglycans (or) homopolysaccharides. They have the general formula (C₆H₁₀O₅)_n.

Example : Starch, cellulose, glycogen, insulin.

b. Polysaccharides composed of two (or) more different types of monosaccharides are called heteroglycans (or) heteropolysaccharides.

Example : Agar, heparin, pectins, gum arabic, hyaluronic acid etc.