col·la·gen 
(kŏlə-jən)
(kŏlə-jən)n.
1. Any of a class of extracellular proteins that are composed of three coiled polypeptide chains, form strong fibers, and are the main constituents of cartilage, bone, and other connective tissues in animals.
2. Material composed principally of collagen proteins. Collagen is converted into gelatin when boiled in water.
[Greek kolla, glue + -GEN.]
col′la·genic (-jĕnĭk), col·lage·nous (kə-lăjə-nəs) adj.