Fibrillar collagens fiber cross-linking

The synthesis of fibrillar collagen (e.g., types I, II, and III) begins Inside the cell with the chemical modification of newly made a chains and their assembly Into triple-helical procollagen within the endoplasmic reticulum. After secretion, procollagen molecules are cleaved, associate laterally, and are covalently cross-linked Into bundles called fibrils, which can form larger assemblies called fibers (see Figure 6-20). 

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