Các túi được cho là di chuyển từ các vùng trong bộ máy Golgi để nghỉ giải lao sâu tế bào chất, nơi mà họ hoàn thành nội dung của họ. Các nghiên cứu trên mô phôi cho thấy rằng N-propeptides vẫn còn gắn liền với sợi 20-30 nm | 24 Silver Freeman and Bradica molecules. Procollagen molecular assembly in vivo initiates within intracellular vesicles 41 . These vesicles are thought to move from regions within the Golgi apparatus to deep cytoplasmic recesses where they discharge their contents. Studies on embryonic tissue suggest that the N-propeptides remain attached to fibrils 20-30 nm in diameter after collagen is assembled however after the N-propeptide is cleaved fibril diameters appear to increase. This observation suggests that the N-propeptide is associated with the initiation of fibrillogenesis. The C-propeptide is removed before further lateral fibril growth occurs Fig. 4 ref. 42 . The C-propeptide of fibril-forming collagens appears to regulate later steps in the assembly of procollagen into fibrils it is removed from small-diameter fibrils during growth 43 possibly when fibril fusion occurs. The C-propeptide has been observed in fibrils with diameters between 30 and 100 nm 44 indicating that it is involved in the initiation and growth of fibrils Fig. 4 . Procollagen and the intermediates pN-collagen containing the N-propeptide and pC-collagen containing the C-propeptide are present in developing tendon up to 18-d embryonic 44 45 . Collagen oligomers isolated from developing chick tendons include 4-D staggered dimers the collagen molecule is D long where D is 67 nm of collagen molecules suggesting that this is a preferred molecular interaction for the initiation of collagen fibrillogenesis in vivo. About 50 of the fibrils formed in 18-d-old chick embryos are bipolar molecules run in both directions along the axis of the tendon whereas the other half is unipolar. Analysis of the staining pattern of fibrils reveals that the axial zone of molecular polarity isto be highly localized 46 . During chick tendon development the structure and mechanical properties of the tendon change rapidly 31 32 46-48 . The morphology of embryonic development of collagen fibrils in the chick tendon has
