What is the protein that gives hair, nails, and skin its hardness and durability?

Keratin is the protein that is primarily responsible for providing hair, nails, and skin with their hardness and durability. This fibrous structural protein plays a crucial role in forming the protective outer layer of the skin and the structural core of hair and nails. Keratin's unique structure allows it to be strong and resistant to wear and tear, which is essential for protecting underlying tissues from damage and preventing water loss.

In hair, keratin contributes to its strength and elasticity, while in nails, it provides a hard surface that is resilient against everyday use. The presence of keratin in the skin helps maintain its integrity and prevents damage from environmental factors.

While melanosomes are involved in the production of melanin, the pigment that gives color to skin and hair, they do not contribute to the hardness or durability of these structures. Collagen, on the other hand, is essential for skin elasticity and firmness but is not the primary protein that imparts the hard characteristics found in hair and nails. Lastly, nerve cells are unrelated to the structural properties of hair, nails, or skin, as they serve the purpose of transmitting signals within the nervous system. Thus, keratin is the key protein responsible for the strength and resilience of these biological structures.