2.3.9—Collagen structure and function

Collagen is suited to support because its triple-helix molecules assemble into parallel fibrils and then larger collagen fibres. The organised fibres have high tensile strength: they resist being pulled apart along their length.

• Molecular links: Covalent cross-links between neighbouring, parallel triple-helix molecules hold them together in fibrils.
• Fibre organisation: Many fibrils combine to form collagen fibres, with molecules arranged in a staggered pattern that adds strength.
• Force alignment: Collagen fibres can be lined up with the forces they must withstand, so the load is shared along the fibre direction.
• Functional result: The triple-helix stability, cross-links and parallel alignment together produce a strong supporting material suitable for tissues such as tendons and ligaments.

Triple helices provide stable collagen molecules; cross-links join neighbouring molecules; fibrils bundle into fibres; and aligned fibres transmit pulling forces. This structure-to-function chain explains why collagen is a fibrous support protein rather than a compact, soluble transport protein.

Do not reduce collagen strength to a single bond or to the triple helix alone: cross-linking, staggered molecular arrangement and fibre alignment also matter. This card explains the structural basis for support; it does not add unsupported tissue physiology.