Professor Kate McGrath, of the MacDiarmid Institute, explains the process by which organisms that have hard structures such as bone and shell deposit mineral-rich hard tissues. The process is called biomineralisation. In the case of shellfish like pāua, it involves the laying down of a combination of the inorganic mineral calcium carbonate with biological components such as proteins and carbohydrates.
PROFESSOR KATE MCGRATH
Biomineralisation is the process by which organisms deposit their hard tissues. So basically, hard tissue, if we think about it from a human point of view, are things like our teeth, skeletons. If we consider things like oysters and pāua, it’s their shells. It’s always a combination of an inorganic mineral and biological components like proteins or carbohydrates, lipids, that kind of thing, so hence why it’s called biomineralisation – it’s mineral formation by a biological entity.
Humans biomineralise a lot of different things. Our full skeletal form is a biomineral, and it’s essentially hydroxylapatite and a proteincollagen. Our teeth are also a calcium phosphate system. We also in our inner ear produce calcium carbonate and so that’s in the form of otoliths, and the otoliths are our gravity receptors and so they allow us to effectively sit upright.
Nacre is a biomineral made from calcium carbonate and predominantly chitin, which is a carbohydrate. Most people would know it as ‘mother of pearl’ and recognise it in terms of that lustrous sort of gemstone that people utilise in a lot of jewellery. Oysters, pāua those kind of molluscs – that’s their biomineral. The thing that makes it a little bit different than other biominerals is that it has a structure that people correlate to say a brick wall. The calcium carbonate is the brick and then the protein and the carbohydrate is the mortar.
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