Question

Keratin, a structural protein is present in:
A. Hair
B. Skin
C. Wool
D. All

Answer 1

Keratin is a type of fibrous structural proteins which are found in various vertebrates in various parts of their body. It has two types $\alpha - keratin$ and $\beta - keratin$ .

Complete step by step answer:
Here, we need to know everything about keratin.
Keratin is one of a family of fibrous structural proteins which are known as scleroproteins. $\alpha - keratin$ is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, calluses and the outer layer of skin among vertebrates. It also protects epithelial cells from damage or stress. It is highly insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments which are tough and form strong un-mineralized epidermal appendages found in reptiles, birds, amphibians and mammals. $\beta - keratin$ which are harder are found in the nails, scales and claws of reptiles in some reptile shells and in the feathers, beaks and claws of birds.
Keratin has two types which are primitive, softer forms found in all vertebrates and harder, derived forms found only among sauropsids. It also resists digestion which is why cats regurgitate hairballs. Also, spider silk is classified as keratin, although production of the protein may have evolved independently of the process in vertebrates.
The first sequences of keratins were determined by Israel Haukoglu and Elaie fuchs. These sequences revealed that there are two distinct but homologous keratin families which were named type I and type II keratins.
The silk fibroins produced by insects and spiders are often classified as keratins even though it is unclear whether they are phylogenetically related to vertebrate keratins. Silk found in insect pupae and in spider webs and egg casings has twisted b-pleated sheets incorporated into fibres into larger super molecular aggregates.

**Therefore, as it is present in all hair, skin and wool, the correct answer is option D.

Note:**
Keratin is a type of fibrous structural proteins which are found in various vertebrates in various parts of their body like hair, nails, skin, horns, claws etc. It has two types $\alpha - keratin$ and $\beta - keratin$ .