Carbohydrate

Carbohydrates are a family of molecules commonly called "sugars".

Characteristics of carbohydrates

All carbohydrates have an aldehyde or ketone group and several OH groups. The crude formula of carbohydrates is usually therefore, Cn(H₂O)n, explaining why they are called carbohydrates. Some also have phosphorus or nitrogen atoms.

Diversity of carbohydrates

Carbohydrates can be classified into :

• monosaccharides: which are simple, unhydrolysable molecules (glucose, fructose, galactose etc);
• polysaccharides which contain more than one monosaccharide.
  • disaccharides, which are an association of two monosaccharides bound by a glucose bond: lactose, sucrose etc.
  • are distinguished from polysaccharides, which are chains (polymers) of monosaccharides, also connected by glucose bonds: starch, cellulose, glycogen etc.

Only monosaccharides and disaccharides can sweeten. The polysaccharides are tasteless.

Role of carbohydrates

Carbohydrates have a role providing energy. They are stored in polymers (starch in plants, glycogen in animals), and form an energy reserve that can be used in glycolysis (degradation of glucose) by forming molecules of ATP.

Carbohydrates also have a structural role. Long rigid cellulose gives a degree of solidity to plants. In animals chitin is the main component of the exoskeleton of insects and arthropods.