The term “protein” is derived from the Greek word “Proteios,” meaning “first.” Proteins are nitrogenous macromolecules that are present in all cells of living organisms. They hold a central role in the structure and functioning of living matter. Proteins consist mainly of carbon, hydrogen, nitrogen, and oxygen, with occasional presence of Sulphur and phosphorus. A protein is defined as a polymer, composed of simple units known as amino acids, linked together to form a larger molecule.
Amino acids are building blocks of proteins. They are bi-functional compounds and contain basic amino (-NH₂) and acidic carboxyl group (-COOH) groups. Upto twenty amino acids have been found in nature, ten are essential and remaining ten non- essential. Body can only synthesize non-essential ten amino acids. The general formula for amino acids is:
Where ‘R’ is the chain of carbon atoms. During the condensation of amino acids, -OH (from the carboxyl group) of one amino acid and H (from the amino group) of another amino acid are combined and eliminated as water (H₂O) molecules. Thus a new linkage is formed between two amino acid units known as peptide linkage/ bond. Due to this linkage protein is formed.
Proteins may contain 60 to 6000 amino acid molecules. A protein molecule formed with two amino acids is termed a dipeptide, with three tripeptides, and so on. Generally, the molecular weight of proteins ranges from 43000 50,000,000 daltons (1 dalton = 1a.m.u).
The important sources of proteins are eggs, meat, pulses, beans, peas, cheese etc.