composition of bone Bone is made up of organic component 40% of dry weight inorganic component 60% of dry weight Organic component Components include collagen 90% of organic component primarily type I collagen provides tensile strength it is a triple helix composed of one alpha-2 and two alpha-1 chains proteoglycans responsible for compressive strength inhibit mineralization composed of glycosaminoglycan-protein complexes matrix proteins includes noncollagenous proteins function to promote mineralization and bone formation three main types of proteins involved in bone matrix osteocalcin most abundant non-collagenous protein in the matrix (10%-20% of total) produced by mature osteoblasts function promotes mineralization and formation of bone directly involved in regulation of bone density attracts osteoclasts signaling stimulated by 1,25 dihydroxyvitamin D3 inhibited by PTH clinical application marker of bone turnover can be measured in urine or serum osteonectin secreted by platelets and osteoblasts function believed to have a role in regulating calcium or organizing mineral in matrix osteopontin function cell-binding protein cytokine and growth factors small amounts present in matrix aid in bone cell differentiation, activation, growth, and turnover include IL-1, IL-6, IGF, TGF-beta, BMPs Inorganic component Components include calcium hydroxyapatite (Ca10(PO4)6(OH)2 provides compressive strength osteocalcium phosphate (brushite)