Collagen is a strong, ropelike molecule that forms stretch-resistant fibers. The most abundant protein in our bodies, collagen accounts for roughly one-quarter of our total protein mass. Among its many functions is giving strength to our tendons, ligaments and bones, and providing scaffolding for skin wounds to heal. There are about 20 different types of collagen, each adapted to the needs of specific tissues.
Image courtesy of Tom Deerinck, NCMIR, UCSD.