Proteins are the complex organic substances which are the basis of protoplasm and are found in all living organisms. The name protein (Greek, proteios means first) was introduced by Mudlar (1839) because of prime importance of such substances to animal life. In human beings, proteins constitute about 18% by mass of the body.
In general, proteins are polymers of a-amino acids. The amino acid units in proteins are held by peptide (-CONH-) linkage. Polymeric products of α-amino acids with molecular mass up to 10,000 are called polypeptides while those having molecular mass more that 10,000 are considered as proteins. However, there is no sharp demarcation between polypeptides and proteins.
SOURCES OF PROTEINS
Proteins are found in the animal as well as plant foods. Animal foods such as meat, poultry fish, eggs” milk and cheese contain <proteins with many essential amino acids. Plant products such as beans, groundnuts, cashew nut, cereals (maize and wheat) and pulses are also good protein food, though they contain fewer essential amino acids.