Carbohydrates are the most abundant of the biomolecules. If we were to identify the most important carbohydrate molecule on the planet, in terms of its ability to sustain life, we would undoubtedly select the monosaccharide glucose. Without glucose, nearly all animal life as we know it could not exist.

Carbohydrates can be classified into 4 major subtypes: monosaccharides, disaccharides, oligosaccharides and polysaccharides. These classifications are based on both the size and function of the molecule. The name "saccharide" is derived from Greek; it means “sugar.” Monosaccharides are the simplest form of carbohydrates and are composed of a single molecule or subunit. The disaccharides are composed of two monosaccharides linked together, while oligosaccharides are composed of between 3 and 20 monosaccharides and polysaccharides consist of hundreds or thousands of monosaccharides linked together. We will now examine each of these types of carbohydrates.