The organic component of bone that provides elasticity is primarily which substance?

• A. 86% type I collagen
• B. 60% elastin
• C. 70% proteoglycans
• D. Osteocalcin

Answer: (B)

Elasticity in bone mainly comes from the organic collagen matrix. The organic component, especially type I collagen, forms a fibrous network that can stretch slightly under load and then recover, giving bone its toughness and some elastic behavior. Elastin is not a major constituent of bone; it’s more abundant in tissues that require substantial elasticity, like skin and blood vessels. Proteoglycans and other non-collagenous proteins play roles in hydration, load distribution, and mineralization, but they do not provide the primary elastic recoil. Osteocalcin is involved in mineral deposition and bone remodeling, not elasticity. So the substance that best accounts for bone’s elasticity is the collagen network.