Concept:Globular proteins are compact, roughly spherical molecules, while fibrous proteins are long and thread-like.
Explanation:Keratin is a structural protein present in hair, nails, wool, and the outer layer of skin.
It is a fibrous protein because its polypeptide chains are arranged in long parallel sheets or coils, which provides mechanical strength and water insolubility.
On the other hand, serum albumin, insulin, and egg albumin are globular proteins.
They fold into a compact, spherical tertiary structure with hydrophobic groups buried inside and hydrophilic groups on the surface, making them water-soluble.
Therefore, among the given options, keratin does not belong to the globular protein category.
Answer:Option D: Keratin