* Collagen is one of the 3 types of connective tissue fibers produced by fibroblasts.
* It is the most abundant protein found in mammals and is found in the extracellular matrix of various tissues and organ systems in the body including: loose connective tissue, bone, tendons, skin, blood vessels, and the cornea.
* Collagen synthesis and assembly into fibrils occurs via a series of intracellular and extracellular events:
* Under the direction of mRNA, various alpha chains of preprocollagen are encoded for synthesis at the rough endoplasmic reticulum (RER). Preprocollagen as the name suggests is a precursor of collagen.
* Certain proline and lysine residues of the growing polypeptide chain are hydroxylated within the RER. Specific enzymes called hydroxylases catalyze this reaction with the help of Vitamin C as a cofactor.
* The third step involves the addition of sugar molecules (glycosylation) to specific hydroxylysine residues within the RER.
* Propeptides regulate the formation of procollagen formation in the RER. The three alpha chains on procollagen align and coil into a triple helix.
* Procollagen is then transported to the Golgi complex where carbohydrates are added. This completes the molecule’s oligosaccharide side chains.
* Secretory vesicles from the Golgi complex guide procollagen to the cell surface along microtubules. Secretion of procollagen then occurs via exocytosis.
* Procollagen peptidases catalyze the cleavage of procollagen, which yields tropocollagen, also known as collagen.
* Self-assembly of tropocollagen occurs as insoluble tropocollagen molecules aggregate near the cell surface.
* Types I, II, III, V, and VII collagen fibrils are produced. Fibrils, which are highly organized polymers, are the result of collagen biogenesis.
* Cross-linking between adjacent tropocollagen molecules... [continues]
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