Chemistry Reference
In-Depth Information
Figure 4.
Schematic of biologically induced mineralization. Mineral precipitates form as a result of
metabolic activities that affect pH, pCO
2
, and secretion products. The cell is a causative agent only,
without control over mineral type or habit.
direct the nucleation, growth, morphology and final location of the mineral that is
deposited. While the degree of control varies across species, almost all controlled
mineralization processes occur in an isolated environment. The results can be remarkably
sophisticated, species-specific products that give the organism specialized biological
functions.
Biologically controlled mineralization processes can be described as occurring
extra-, inter- or intracellularly. These distinctions refer to the locations of the
mineralization site with reference to the cells responsible for mineralization. However,
not all mineralization processes can be classified in this simple manner. In some cases,
mineral formation begins within the cell and then proceeds outside the cell. Identifying
what are in essence, end members at least helps us understand the overall complexity. We
will therefore discuss extra-, inter- and intracellular biomineralization separately.
Biologically controlled extracellular mineralization
.
In extracellular mineralization,
the cell produces a macromolecular matrix outside the cell in an area that will become the
site of mineralization. The term matrix refers to a group of macromolecules comprised of
proteins, polysaccharides or glycoproteins that assemble to form a three-dimensional
framework. The matrix composition is unique in that many of its proteins contain a high
proportion of acidic amino acids (especially aspartate) and phosphorylated groups (Veis
and Perry 1967; Weiner 1979; Weiner et al. 1983a,b; Swift and Wheeler 1992). The
structures and compositions of these organic frameworks are genetically programmed to
perform essential regulating and/or organizing functions that will result in the formation
of composite biominerals.
