Therefore, a liberal supply of protein is necessary to the organisms and without it no life is possible. It must be constantly supplied to organisms for growth and repair. Mulder was the first man who introduced the word protein in 1840. Actually the term ‘protein’ comes from the Greek word ‘protos’ meaning first.
Proteins are polymeric molecules in which the subunits are monomers or amino acids which are co-valently bonded by peptide linkages or peptide bonds formed between the carboxyl group of one amino acid and the amino group of the next. Proteins may be composed of a single polypeptide chain (a polypeptide may be defined as a chain of three or more amino acids joined together by peptide linkages) or of several polypeptide chains. The composition of the protein in terms of these amino acids as well as their actual arrangement in the molecule is of great importance not only to the structure of the polymer but also to fts biologic activity. In other words, biologic activity is to be understood in terms of protein structure. The actual sequence of amino acids, called the primary structure, is determined genetically and resides in the language of the DNA molecules.
Proteins are responsible for most fundamental features of structure and function which underlie all living systems and are also the cause of the tremendous diversity of living systems.
Enzymes are proteins which catalyze the different chemical reactions taking place in the living systems.
Thus, proteins play the unique role of determining the pattern of chemical transformations in biological systems. As important components of muscle, tendon, bone, membrane, and skin, proteins are involved in structure and motility.
Similarly there are specific proteins which transport and storage the small molecules and ions and give high tensile strength to skin and bones and capable for generation and transmission of nerve impulses.
Thus, their diverse physical, chemical, and biologic properties are dependent on the nature and arrangement of their constituent’s subunits, the amino acids.