Which type of protein structure is characterized as long and narrow?

The characteristic of being long and narrow describes fibrous proteins effectively. These proteins typically form structural components in various biological systems and are known for their elongated, filamentous shapes. Examples include collagen, which provides strength to connective tissues, and keratin, found in hair, nails, and the outer layer of skin.

Fibrous proteins are generally insoluble in water due to their tightly packed structural formations, which provide significant tensile strength and resistance to stretching. This physical configuration contrasts with globular proteins, which are more spherical and often play roles as enzymes, hormones, and transport molecules within the body. Transmembrane proteins span biological membranes and are usually more complex in structure, while enzymatic proteins are typically globular and specialized for catalyzing biochemical reactions. Thus, the nature of fibrous proteins as long and narrow fits the description perfectly.