Introduction
Carbohydrates, the most abundant biological molecules, are important
constituents of all living cells. They are classified as polyhydroxy aldehydes
or ketones and their derivatives. Generally, their chemical structure is simple,
containing just three elements—carbon, hydrogen, and oxygen—combined
according to the formula (CH2O)n where n = 3 or more. The basic
carbohydrate units, a single unit of polyhydroxy aldehydes or ketones that
cannot be hydrolysed into simpler compounds, are named monosaccharides
(sometimes called simple sugars). These include arabinose, ribose, glucose,
galactose, fructose and so on. Oligosaccharides contain 2 – 10 units of
monosaccharides (monomers) linked to each other via glycosidic bond. The
important compounds of this group are disaccharides such as sucrose,
maltose and lactose. Carbohydrates that are composed of more than 10
monosaccharide units are referred to polysaccharides including starch,
glycogen and cellulose. In nature, more than 90% of the carbohydrate is
polysaccharides. Starch and glycogen polymers are the examples of
polysaccharides that humans can digest and use as energy source.
Furthermore, complex compounds between carbohydrates and proteins—
known as glycoproteins—have been reported to play important roles in cell-
surface recognition.