- Discussion:
    - type I is the major collagen of tendon and bone, but it is also the predominant in lung, skin, dentin, heart valves, fascia, scar tissue, cornea,
            and liver;
          - type I collagen is essential for the tensile strength of bone; it is final amount and distribution of these collagen fibers that will determine 
                 the size, shape, and ultimate density of the bone;
    - collagen fibers are characterized by an axial periodicity of 640 Ang to approximately 700  depending upon source of collagen;
    - presence of high and low protein densities gives it distinctive light and dark bands;
    - collagen is unique in that it contains about 1/3 glycine residues;
    - it is also rich in hydroxyproline and hydroxylysine residues, contains many alanine residues and very few aromatic amino acids;
    - single collagen fibril is made of 3 polypeptides called alpha chains;

- Molecular Defects:
    - see collagen disorders
    - molecular defects involving type I procollagen have been identified in several patients & families w/ osteogenesis imperfecta;
    - Marfan's syndrome:
           - Marfan syndrome produces long, thin extremities, redundant ligaments & joint capsules, ectopia lentis, & dilatation & rupture of aorta;
           - this syndrome may be caused by mutations in genes for type I procollagen or for enzymes that process protein