Which type of protein is primarily functional and not structural?

The classification of proteins into functional and structural categories is essential in understanding their roles in biological systems. Globular proteins are primarily functional due to their unique three-dimensional shapes and diverse roles in various biochemical processes.

Globular proteins are typically soluble in water and have a compact, folded structure. This conformation allows them to interact actively with other molecules, serving critical functions such as enzymes (catalyzing biochemical reactions), transport proteins (such as hemoglobin, which carries oxygen), antibodies (involved in the immune response), and hormones (messengers in signaling pathways). Their structure facilitates a range of interactions necessary for their biological activities, making them vital to cellular function and metabolism.

In contrast, fibrous proteins, represented by collagen and keratin, have elongated structures and primarily provide support, strength, and rigidity to cells and tissues rather than engaging in functional roles. The terms "spherical" and "linear" don't specifically denote categories recognized in classical protein biochemistry; rather, they describe shapes that may refer to structural characteristics of proteins but do not encapsulate the functional aspect that distinguishes globular proteins.

Therefore, the choice of globular proteins as primarily functional reflects their versatile roles and importance in various biochemical processes.