Proteins are essential compounds for living cells. The name protein (Greek : Proteios = pre-eminent or first) was suggested by Berzelius. According to him, proteins are complex organic nitrogeneous substances found in the cells of the living beings and essential to cell structure and cell function. Thus, proteins are vital chemical substances essential for the growth and maintenance of life. Proteins are present in almost all living cells of plants and animals.

Enzymes are defined as the complex nitrogenous organic compounds produced by living plants and animals. They are polypeptides i.c. proteins of high molecular mass responsible for catalyzing natural processes prevailing in the bodies of animals and plants.

During hemiacetal formation C 1 — aldehydic group combines with C 5 — OH group resulting with a chiral centre at C 1 and thus it has two possible arrangements of H and OH groups around it. Hence, D-glucose exists in two stereoisomeric forms i.e. α - D —glucose and β - D —glucose. Such pair of stereoisomers which differ in configuration only around C 1 are called anomers and C 1 carbon is called anomeric carbon.