The extracellular organic matrix (osteoid), which contains calcium in the form of hexagonal hydroxyapatite crystals;
A cellular component of bone-forming osteoblasts and bone-resorbing osteo-clasts. The cells are embedded in the matrix.
The extracellular matrix
Collagen, mainly type I. This has a triple helical structure, with two identical alpha 1 chains and one unique alpha 2 chain cross-linked by hydrogen bonding between hydroxyproline and other charged residues.
Other proteins and proteoglycans: Proteoglycans I and II Matrix GIa protein Osteonectin
Osteocalcin (bone G1a protein)
RGD (arg-gly-asp)-containing glycoproteins: Thrombospondin
Fibronectin, laminin: adhesive proteins
Bone sialoproteins I and II
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