Which structural protein is most abundant in animals and found in skin and connective tissue?

Collagen is indeed the most abundant structural protein found in animals and plays a crucial role in maintaining the integrity and structure of various tissues, including skin and connective tissues. It provides strength and elasticity, forming a supportive network that helps tissues withstand stretching and deformation. Collagen fibers are primarily located in the extracellular matrix, giving structure to the skin, tendons, ligaments, and cartilage, thereby contributing significantly to the overall mechanical properties of these tissues.

When considering the role of other proteins in the choices provided, elastin is important for elasticity and flexibility in tissues, particularly in blood vessels and lungs, but it is not as abundant as collagen. Keratin, on the other hand, is primarily found in hair, nails, and the outer layer of skin, serving more of a protective function than providing structural support for connective tissues. Fibrin is a protein involved in blood clotting rather than in providing structural support to tissues. Therefore, collagen stands out as the key protein responsible for the structural framework in skin and connective tissue.