Alpha keratin is an amino acid with a coiled-coil shape that is found in sheep's wool, hair, horns and tails. This amino acid's structure is maintained with hydrophobic bonds between apolar residues. Keratin is found in other forms throughout the body, especially on the skin's surface.
Rather than forming a ladder, the alpha helices in keratin wind around each other to produce a coil. It is made of a repeating heptameter of -a-b-c-d-e-f-g-, with a and d acting as non-polar elements. Alpha keratin is able to adopt its coiled shape as there are 700-degree turns between each helix.
During the production of alpha keratin, the cystine is reduced and cysteines are formed to break cross links. These cysteines then reoxidize, allowing new cross links to form. When hairdressers are carrying out perms, they reproduce this chemical reaction to generate curls, which eventually grow out.
While alpha keratin is found in hair, wool and similar substances, keratin is found throughout the body in other forms. In addition to being present in epithelial cells, filaments of it are in keratinocytes. The skin's top layer, the epidermis, is formed of the keratin filaments found in epithelial cells. These cells are eventually pushed to the top of the skin from deeper layers, and they undergo keratinization on the way. By the time they reach the top they are no longer live, and they eventually shed to make way for more keratinocytes.