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These fibrils are twisted into a right handed coil (fibre) with a total weight of between 95000 and 102 000 Daltons (Waterlow et al.192; Woodhead-Galloway 1980:1-3, 23; Garlick 194; Smith et al. For the collagen fibre to fully mature a number of chemical bonds must form. Once these bonds form only a small fraction of collagen can be extracted by neutral salt solutions and organic acids or acid-citrate buffers.These include hydrogen bonds involving hydroxyproline, which stabilise the helix, and cross linkages involving hydroxylysine and lysine, which stabilise the fibrillar structure (Smith et al. These processes occur throughout the growth and maturity of an individual, consequently the density and stability of the bone tends to increase while the solubility decreases (Waterlow et al. The insoluble collagen which remains from such dissolutions, can however, be solubilised by heating above 58'C. Collagen in its unaltered state is also very resistant to proteolytic enzymes, however a group of enzymes exist which degrade native collagen fibrils under physiological conditions of temperature and p H; these are the collagenases (Waterlow 196; Smith et al. An enzyme secreted by the gas gangrene bacteria (Clostridium perfringens and Cl.
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The peptide's produced in such cleavage are then open to proteolytic attack from the more conventional enzymes (Waterlow 196).
Collagen molecules are composed of linear, unbranching sequences of approx 20 naturally occurring amino acids.
The structure of the molecule is stabilised by hydrogen bonds; the most common being between the amino group (-NH2) of one residue and the carboxyl group (-COOH) of a second residue, resulting in both acidic and basic properties.
Bone is a connective tissue largely composed of an organic protein; collagen and the inorganic mineral hydroxyapatite, which combine to provide a mechanical and supportive role in the body (Smith et al. Depending on the orientation of collagen fibres, two types of bone can be distinguished: lamellar bone (cortical bone) and non lamellar (trabecular or cancellous bone), which is found in vertebrae, at the ends of long bones, the mammalian foetus, at fracture joints, and in many lower vertebrates (Pritchard 1974:5; Smith et al. Three types of cavities exit in bone; Haversian canals, marrow cavities, and the lacuna, which contain the bone cells (osteocytes) from which canalicuae (small tunnels) extend (Pritchard 1974:3-4; Hare 198).
A number of different bone extracts have been used to obtain 14C determinations.
Initially analyses were carried out on whole bone, later the organic (collagen) or inorganic component of bone (hydroxyapatite) were separated and dated.A lack of success saw the dating of different fractions obtained during bone pretreatment, including the acid soluble (humics) as well as the "collagen" (acid insoluble component). 1989; Gurfinkel 1987); specific amino acids, for example hydroxyproline and proline (Wand 1981 in Taylor 1992; Stafford et al. 1984); a series of individual amino acids (Hare and Estep 1983 in Stafford et al. 1988); larger or smaller (peptide) parts of collagen (Brown et al.More recently 14C determinations have been carried out on mixtures of amino acids (Ho et al. 1988; van Klinken and Hedges 1992); and non-collagenous proteins such as osteocalcin (Ajie et al. Some extracted fractions of bone: Around 30% of bone is composed of organic compounds, of which 90 to 95% is collagen, the rest being non-collagenous proteins.Collagen is a fibrous protein which provides the bone with strength and flexibility, and is an important component of many other tissues, including skin and tendon.Individual collagen molecules contain three polypeptides of about 1000 amino acids per chain with a high glycine and hydroxyproline content.Bundles of these collagen molecules are arranged in fibrils with a molecular weight close to 97.1 Daltons.