Keratin is a type of fibrous protein which is found is our skin that serves as outer layer. It also found as a structural component of our hair and nails. There are two classifications of keratins, the `alpha` -keratins and the `beta` -keratins. Although they differ slightly in structure, composition and properties, they have relatively similar function.
Since it is a protein, its subunits are amino acids. Keratin is mostly composed of alanine and glycine. They also contain cysteine which is used to add strength due to the formation of disulfide bridges.