in the three cell types , the precursors of type i collagen are processed along the rough endoplasmic reticulum ( rer ) -golgi-secretory granule pathway in the same manner as secretory proteins , but the available evidence suggests a few special features : 1 ) from the rer site of synthesis , the initial collagen precursors , known as pro-alpha chains , are transported to the golgi apparatus within tubular structures , referred to as intermediate tubules , rather than within vesicles .
C0041455
type i collagen
C0009325
collagen