The collagen triple helix structure is not found in

Like most secreted proteins, collagen is synthesized on ribosomes in a precursor form, preprocollagen, which contains a leader or signal sequence that directs the polypeptide chain into the lumen of the endoplasmic reticulum. As it enters the endoplasmic reticulum, this leader sequence is enzymatically removed.Following secretion from the cell by way of the Golgi apparatus, extracellular enzymes called procollagen aminoproteinase and procollagen carboxyproteinase remove the extension peptides at the amino and carboxyl terminal ends, respectively forming the monomeric units of collagen, termed tropocollagen. Newly synthesized proteins are soed first according to the soing signals available in the proteins. Then they are packaged into transpo vesicles having different types of coat proteins. Finally they are transpoed into various destinations; this is an energy dependent process Ref: Harper's Illustrated Biochemistry, 26th edition, page no: 535 Ref: Textbook of Biochemistry for Medical Students, 7E (DM Vasudevan)(2013)Pg no 12.