Which fibrous protein is the principal component of hair and nails?

Keratin is the principal fibrous protein found in hair and nails. It plays a crucial role in providing strength and resilience to these structures. Keratin is a tough, protective protein that forms the primary structure of hair, nails, and the outer layer of skin, making them both durable and resilient to wear and tear.

Collagen, while also a fibrous protein, is primarily found in connective tissues such as skin, tendons, and ligaments, rather than in hair and nails. Elastin is another type of protein that allows tissues to resume their shape after stretching or contracting, primarily found in skin and arteries. Melanin is a pigment responsible for coloration in hair, skin, and eyes but does not contribute to the structural integrity of hair or nails. Thus, the unique properties of keratin make it the correct answer as the main component of both hair and nails, emphasizing its importance in the structure and function of these anatomical features.