Keratin is a structural protein found in which tissues?

• A. Skin, Fur, Nails
• B. Blood
• C. Enzymes
• D. Nucleic acids

Answer: (A)

Keratin is a structural, fibrous protein that provides mechanical strength to tissues. In animals, it is a major component of tissues that form protective, tough coverings: the skin's outer layer and the appendages derived from it, such as hair (fur) and nails. The keratin in skin is softer and forms a resilient barrier, while the keratin in hair and nails is “hard keratin,” enriched with disulfide bonds that make these structures rigid and highly durable. This combination of properties explains why keratin is characteristic of skin, fur, and nails.

It isn’t a primary component of blood, enzymes are different proteins with catalytic roles, and nucleic acids are the genetic material, not proteins.