Editing Collagen (section)

=== Collagen I formation ===
Most collagen forms in a similar manner, but the following process is typical for type I:

# Inside the cell
## Two types of alpha chains – alpha-1 and alpha 2, are formed during [[translation (genetics)|translation]] on ribosomes along the [[rough endoplasmic reticulum]] (RER). These peptide chains known as preprocollagen, have registration peptides on each end and a [[signal peptide]].<ref name="Dict">{{cite web |title=preprocollagen |url=https://medical-dictionary.thefreedictionary.com/preprocollagen |website=The Free Dictionary}}</ref>
## Polypeptide chains are released into the lumen of the RER.
## Signal peptides are cleaved inside the RER and the chains are now known as pro-alpha chains.
## [[Hydroxylation]] of lysine and proline amino acids occurs inside the lumen. This process is dependent on and consumes [[ascorbic acid]] (vitamin C) as a [[cofactor (biochemistry)|cofactor]].
## [[Glycosylation]] of specific hydroxylysine residues occurs.
## Triple alpha helical structure is formed inside the endoplasmic reticulum from two alpha-1 chains and one alpha-2 chain.
## [[Procollagen]] is shipped to the [[Golgi apparatus]], where it is packaged and secreted into the extracellular space by [[exocytosis]].
# Outside the cell
## Registration peptides are cleaved, and tropocollagen is formed by [[procollagen peptidase]].
## Multiple tropocollagen molecules form collagen fibrils, via covalent cross-linking ([[aldol reaction]]) by [[lysyl oxidase]] which links hydroxylysine and lysine residues. Multiple collagen fibrils form into collagen fibers.
## Collagen may be attached to cell membranes via several types of protein, including [[fibronectin]], [[laminin]], [[fibulin]], and [[integrin]].