What structural protein is found in the skin and connective tissue?

• A. Keratin
• B. Elastin
• C. Actin
• D. Collagen

Answer: (D)

Collagen is the main structural protein in skin and connective tissue. It forms strong, rope-like fibers in the extracellular matrix, giving skin its tensile strength and providing sturdy support for connective tissues such as ligaments and tendons. It’s the most abundant protein in the body and is produced by fibroblasts, with collagen fibers in the dermis helping to anchor layers of skin and maintain its structure. Keratin strengthens the epidermis, hair, and nails but is primarily inside epidermal cells rather than the connective tissue matrix. Elastin contributes elasticity but isn’t the primary load-bearing structural fiber in skin. Actin is a cytoskeletal protein inside cells, not a major extracellular component of the skin’s connective tissue.