Figure 1.
Electron microscopy of a single procollagen molecule and a collagen fibril formed in vitro by self-assembly of collagen molecules. A procollagen molecule, 300 nm in length, consists of the triple-helical domain flanked with the N propeptide and the C propeptide. Upon cleavage of the propeptides by specific enzymes, collagen molecules self-assemble to form collagen fibrils.