Collagen's tensile strength from molecular and fibrillar structure

Steps:

• Recall collagen's triple helix (feature 1) provides rigidity against stretching.
• Note staggered arrangement of helices in fibrils (feature 2) distributes load evenly.
• Identify covalent cross-links between chains and fibrils (feature 3) enhance resistance to shear.
• Exclude feature 4 (e.g., simple linear chains) as it lacks hierarchical reinforcement.

Why A is correct:

• Features 1, 2, and 3 align with collagen's quaternary structure, where triple helices form staggered fibrils stabilized by cross-links, per biochemical models of extracellular matrix strength.

Why the others are wrong:

• B omits staggered arrangement (2), weakening load distribution.
• C excludes cross-links (3), reducing overall cohesion.
• D misses triple helix (1), the core rigid scaffold.

Final answer: A