group of fibrous proteins that occur in vertebrates as the chief constituent of connective tissue fibrils and in bones and yield gelatin and glue upon boiling with water

Collagen is a group of naturally occurring proteins. In nature, it is found exclusively in animals, especially in the flesh and connective tissues of mammals.[1]

Collagen with triple helix (left) and microscopic structure (right).

It is the main component of connective tissue, and is the most abundant protein in mammals. It makes up about 25% to 35% of the whole-body protein content.[2]

Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendon, ligament and skin, and is also abundant in cornea, cartilage, bone, blood vessels, the gut, and intervertebral discs.

Collagen makes up 1% to 2% of muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles.[3]

Gelatin, which is used in the food industry, is collagen that has been irreversibly hydrolyzed.


  1. Müller, Werner E.G. (2003). "The origin of metazoan complexity: Porifera as integrated animals". Integrated Computational Biology. 43 (1): 3–10. doi:10.1093/icb/43.1.3. PMID 21680404.
  2. Di Lullo, Gloria A.; Sweeney, Shawn M.; Körkkö, Jarmo; Ala-Kokko, Leena & San Antonio, James D. (2002). "Mapping the ligand-binding sites and disease-associated mutations on the most abundant protein in the human, Type I Collagen". Journal of Biological Chemistry. 277 (6): 4223–4231. doi:10.1074/jbc.M110709200. PMID 11704682.
  3. Sikorski, Zdzisław E. (2001). Chemical and functional properties of food proteins. Boca Raton: CRC Press. p. 242. ISBN 1566769604.