Overview Synthesis and Structure Inside fibroblasts pre-pro-collagen α chain formation RER-bound ribosomes synthesize contains hydrophobic translocation sequence chain formed mainly of repeating tripeptide login to view 2 more bullets pro-collagen α chain formation hydrophobic sequence cleaved hydroxylated pro-collagen α chain formation X and Y position prolines and lysines are hydroxylated to form hydroxylysine and hydroxyproline. login to view 14 more bullets glycosylated pro-collagen α chain formation hydroxylysines are glycosylated pro-collagen α chain trimer formation three α chains associate moved from RER to Golgi secreted out of the fibroblast Outside fibroblasts collagen molecule (tropocollagen) formation propeptides cleaved from ends and becomes insoluble presence of propeptide does not allow assembly intracellularly collagen fibril formation catalyzed by lysyl oxidase login to view 15 more bullets collagen fiber formation fibrils aggregate to form final bundles of triple helix quaternary protein structure Collagen Types Type I thick, rope-like bundles of collagen strongest tensile form of collagen majority of collagen in the body (approx. 90%) found in locations where high tensile strength is needed bone, fascia, tendons, teeth (dentin), cornea, skin type III of early wound repair converted to type I in late wound repair defective in osteogenesis imperfecta (OI) type I aka brittle bone disease AD, in most cases presentation login to view 8 more bullets may be confused with child abuse defective in various forms of Ehlers-Danlos syndrome faulty collagen synthesis see above Type II spongy collagen to absorb shock found in tissues where there are compression forces cartilage (including hyaline), vitreous body of the eye, nucleus pulposus of vertebral disc Type III web-like fibers where forces pull from many directions aka reticulin found in tissues where strength is needed (but not compression or tensile) skin, blood vessels, uterus, fetal tissue granulation tissue login to view 1 more bullet defective in Ehlers-Danlos type IV faulty collagen synthesis associated with login to view 3 more bullets see above Type IV basement membrane especially kidney, ears, eyes, skin organizes/solidifies cellular structure defective in Alport's syndrome effects the tissues where type IV is most prominent login to view 3 more bullets majority of cases are X-linked dominant one of the causes of epidermolysis bullosa weak union of dermis and epidermis of the skin easily formed blisters Goodpasture's syndrome involves an auto-antibody against collagen type IV in pulmonary and glomerular capillaries presents with hemoptysis and glomerular disease