If these groups are close to each other, either on the same chain or on different chains, they will tend to associate, forming hydrogen bonds, but these bonds are easily broken and reformed. Hydrogen bonding makes it possible for glue molecules to interact strongly with appropriate substrates such as wood and to act as powerful adhesives. It is fibrous in nature and is a major component of the connective tissue that sheaths muscles and attaches them to bone through tendons or that attaches skeletal elements together through cartilage. It also forms the bulk of the proteins found in hides and skin. When extracted from hide, tendon, cartilage, and bones, collagen becomes the primary component of glues.
Fibrous proteins are well suited to their task of support and connection.
They are formed from very long, thin fibers of amino acids covalently bonded in specific sequence. This sequence gives collagen a specific shape and strength that is a consequence of intramolecular hydrogen bonding. In the 1950s, Linus Pauling, Robert B. Corey, and H. R. Branson determined that collagen exists as a molecule that is tightly coiled about itself forming a secondary structure termed an -helix. Hydroxyproline's rigid structure causes a twist in the coil wherever it occurs. The molecules bunch together in groups of three, forming a larger coil that gives collagen fibers their strength in living tissue.