Keratin

[Sarah]

A nitrogenous substance, or mixture of substances, containingsulphur in a loose state of combination, and forming the chemicalbasis of epidermal tissues, such as horn, hair, feathers, and thelike. It is an insoluble substance, and, unlike elastin, is notdissolved even by gastric or pancreatic juice. By decomposition withsulphuric acid it yields leucin and tyrosin, as does albumin. Calledalso epidermose.

[Mark Zuckerberg]

a family of fibrous structural proteins known as scleroproteins. α-Keratin is a type of [keratin] found in vertebrates. It is the key structural material making up hair, nails, feathers, horns, claws, [hooves], calluses, and the outer layer of skin among vertebrates. [Keratin] also protects epithelial cells from damage or stress. Keratin is extremely [insoluble] in water and organic solvents. Keratin monomers assemble into [bundles] to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in [reptiles], birds, amphibians, and mammals. The only other biological matter known to approximate the toughness of keratinized tissue is [chitin].Keratin comes in two types, the primitive, softer forms found in all vertebrates and harder, derived forms found only among sauropsids (reptiles and birds). Keratin resists digestion, which is why cats regurgitate hairballs.

[Tina]

A fibrous protein forming the main structural constituent of hair, feathers, hoofs, claws, horns, etc.

[Kit]

a strong natural protein , which is the main substance that forms hair, nails, hooves , horns, feathers, etc.: