Final answer:
Keratins are not found in bones; they are structural proteins present in hair, feathers, nails, and the skin's outer layer. They provide toughness and protection to these structures while enabling functional benefits such as tactile sensitivity and heat insulation.
Step-by-step explanation:
Keratins are fibrous structural proteins that are key components in the structure of various tissues such as hair, feathers, nails, and the outer layer of skin. They are not found in bones. These tough proteins form keratinized cells in structures like the epidermis, the lining of the mouth and nose, and the hair and nails. Keratin's role is to provide protection and add strength, making these structures tough and resistant to wear and tear.
Two functions of nails include protecting the fingertip tissues and enhancing our sense of touch. Likewise, some functions of hair are preventing heat loss, particularly from the head, and trapping dust particles in the nose to prevent them from entering the lungs. While hair is typically associated with mammals, other animals that possess hair or hair-like structures include certain amphibians that have a less tough form of keratin in their skin.