by transmission em collagen can be seen as many

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Unformatted text preview: collagen fibers. Collagen protein is SLIGHTLY BASIC -- hence acidophilia of its staining. LONG CABLES w/ cross striation in TEM!!!! By transmission EM, collagen can be seen as many individual or bundled fibers, with each fiber having alternating light and dark bands in longitudinal view. long. transverse cut Fig. 5-8 There are 28 genes for collagen types, with type I collagen the most common. Type I collagen synthesis is best known. Major steps: These protein subunits combines in diff ways to make about 12 diff types of Collagen fibers! •  Translation of mRNA for preprocollagen occurs on RER; every 3rd amino acid is glycine •  Hydroxylation of prolines and lysines •  Glycosylation of hydroxylysines •  Assembly of triple helix of procollagen •  Secretion of procollagen by exocytosis •  Enzymatic trimming of ends to form collagen subunits •  Self-assembly of these into a large collagen fibril (with alternating light and dark periodicity) Fig. 5-10 Glycine = smallest AA. imp. for its helical structure….! The enzyme that does this requires VITAMIN C!!! So if VitC deficient, you can't maintain your CT..!! these are then secreted to outside of cell Procollagen gets ENDS TRIMMED to form collagen subunit rods -- these rods then self-assemble outside of cell and give rise to BUNDLES of COLLAGEN FIBRILS IMP .. LOOK @ THIS FIGURE!!!!! THIS IS A FIBROBLAST DOING ALL THE WORK. Self-assembly of collagen molecules outside the fibroblasts occurs in a precise manner that produces fibers with the alternating light and dark bands, and provides great strength and durability to the cable-like fiber. With type I collagen the fibers are then bundled into much larger structures shown here. With SEM, you can see ind. FIBRILS within a collagen BUNDLE. Fig. 5-11 Most important types of collagen and their major locations: Type I – most common; predominates in all forms of “CT proper”, bone, stromas & capsules of most organs Type II – in most cartilage Type III (aka reticulin) – stroma of ly...
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