Some types of carbohydrate molecules include monosaccharides, disaccharides and polysaccharides. These molecules are often called sugars. Other carbohydrate molecules are oligosaccharides and nucleotides. Carbohydrates are regarded as the most plentiful compounds available on earth.
Commonly referred to as saccharides, carbohydrates are molecular compounds consisting mostly of three elements: hydrogen, carbon and oxygen. Monosaccharides, often called simple sugars, are the simplest form of carbohydrate and are the basic building blocks of complex carbohydrates. They are represented with a general formula, (C•H2O) n, where n can take such values as 3, 5 or 6.
Monosaccharides can be categorized based on the number of carbon atoms in a molecule. Trioses, such as glyceraldehyde, have three carbon atoms. Pentose, including ribose and deoxyribose, have five carbon atoms. Hexoses, such as fructose, glucose and galactose, consist of six carbon atoms. Monosaccharides are the principal source of energy for organisms.
Disaccharides are made up of two monosaccharides linked by a covalent bond known as glycosidic linkage. These are the simplest polysaccharides, and include sucrose and lactose. The unmodified disaccharide has the formula, C12H22O11. Polysaccharides are formed from a series of reactions of monosaccharides. The process involves addition of one unit at a time resulting into a large molecule via condensation polymerization. The most common types of polysaccharides include starch and glycogen. Starch is made strictly by plants, while glycogen is made strictly by animals.