connective tissue

Collagen is the most abundant protein in the body.! • Over 90% of the collagen in the body is Type I.! • Collagen fiber is the most abundant type of connective tissue fibers.!

Biological Significance of Collagen and Collagen Fibers

• Scars originate mainly from fibroblasts and their extracellular products. ! • Scurvy: defects in collagen synthesis due to Vitamin C deficiency! • Marfans syndrome: defects in the synthesis of the fibrillin component of elastic fibers

Clinical relevances of connective tissue

(as seen in a whole-mount spread of mesentery stained with resorcin-fuchsin) • Produced by fibroblasts and smooth muscle cells! • Contain the proteins elastin & fibrillin (arrayed as microfibrils)!

Elastic Fibers

N- and C-terminal propeptides are! cleaved -> molecular collagen filaments! • Collagen filaments associate laterally and are cross-linked to produce fibrils! • Local production of many fibrils -> fibers!

Extracellular events!

Nucleus:transcription! • Ribosomes:translation! - Protein synthesis of preprocollagen (apha-1 and alpha-2 chains) ! • LumenofrER:! - Signal peptides are cleaved -> Pro-alpha chains! - Hydroxylation of lysine and proline occurs (Vitamin C dependent)! - Glycosylation of specific hydroxy-lysine residues occurs! - Triple-Helical structure is formed -> Procollagen! ! • Golgi:Procollagenispackedandsecretedby exocytosis!

Intracellular events (collegen synthesis)

1. Cells ! !-Sparsely distributed ! !-But functions are extremely important! 2. Extracellular matrix (ECM)! - Extracellular Fibers! • Collagenous fibers! • Reticular fibers! • Elastic fibers! - Ground Substance (only briefly mentioned here and on the next slide)! • Glycosaminoglycans (GAGs)! • Proteoglycans = GAGs bound to the core protein! • Multiadhesive Glycoproteins!

The Components of Loose Connective Tissue