The word protein is derived from the Greek word proteios. Protein means most important. Numerous amino acids linked together by peptide bonds form large molecules with high molecular weight called proteins. Protein is called the workhorse of life. Proteins have acidic and basic properties and are called amphiteric molecules. Dutch chemist G. Mulder (1839) was the first to use the term protein. One of the components of protoplasm is protein. Proteins are made up of 20 types of amino acids. 12% of the body is protein. 50% of the dry weight of cells is protein.