The collagen triple helix structure is not found in -
Triple helix formation occurs in endoplasmic reticulum at procollagen level.
Triple helix of procollagen is packed into secretory intracellular vesicles in the Golgi-apparatus.
These vesicles then secrete the procollagen into extracellular space where it is converted to tropocollagen (collagen monomer).
Tropocollagens aggregate into collagen fibrils which intern become extensively cross-linked to form 'collagen fibers'.
Cytoplasm
Golgi apparatus
Lumen of endoplasmic reticulum
Intracellular vesicles