Peptides containing more than $10 \mathrm{u}$ amino acids are called polypeptides. Polypeptides are formed by the linear sequence of amino acids. Some proteins are composed of two or more poly peptide chains. Relatively shorter peptides are known as oligo peptides whereas longer polymers are called polypeptides. Polypeptides containing more than $100 \mathrm{u}$ amino acids having molecular mass higher than $10,000 \mathrm{u}$ are generally called as proteins. However, the distinctive between a polypeptide and a protein is not sharp.