Answer:
Collagen is synthesized by fibroblasts initially as procollagen alpha chains on membrane-bound ribosomes. The alpha chains then interact to form a triple-helical molecule after hydroxylation of proline and lysine amino acids. Stability is further enhanced by disulfide cross-linking. The procollagen is then packaged into secretory vesicles that move to the cell surface. At the cell membrane procollagen peptidases cleave the procollagen into collagen. There are 13 types of collagen and the five main types are described below:
Type I is found in all connective tissues except hyaline cartilage and basement membranes, forming striated supporting elements.
Type II is found in hyaline cartilage and cartilage-like tissues, such as vitreous humor. It forms striated supporting elements.
Type III is found in more distensible tissues like blood vessels, forming small fibrous elements similar to type II.
Type IV is found in basement membranes, forming a meshlike scaffold.
Type V is found in all tissues and functions similar to type II.