Classification of carbohydrates

Think of a bead necklace. A bead can be on its own, two beads can be threaded together, or hundreds of beads can be threaded into one long necklace. Carbohydrates are the same: they are divided into three main groups according to how many units are joined together.

1. Monosaccharides

C₆H₁₂O₆

This is the single bead of the necklace — the basic unit from which every other carbohydrate is built. They are also called simple sugars. The three monosaccharides we meet most often are:

Glucose Fructose Galactose

2. Disaccharides

C₁₂H₂₂O₁₁

This is two beads threaded together — formed when two monosaccharide molecules join. A molecule of water is removed as they join. The three disaccharides are:

Maltose Sucrose Lactose

3. Polysaccharides

(C₆H₁₀O₅)_n

This is the long necklace — formed when a large number of monosaccharide molecules join together (polymerise). A molecule of water is removed at every link. The three polysaccharides are:

Starch Cellulose Glycogen

The n in the formula is the number of glucose units in the chain. Because it can be hundreds or even thousands, very large molecules can be built starting from one small glucose unit.