lecture 17: biomineralization Flashcards
Biomineralization
- Refers to processes by which organisms form solids from inorganic precursors (anions & cations)
- Organisms cannot violate physical laws of thermodynamics
- Organisms can control location, growth rate, shape, and type of biomineral deposited
where are biominerals found
EVERYWHERE
Mineral Component
- Solid consisting of inorganic anion + cation
- Minerals are defined by their chemical
composition AND morphology - Amorphous or crystalline
e.g. calcium carbonate (CaCO3) can occur as: Different crystal morphologies
* Vaterite,
* Calcite
* Aragonite
* Amorphous
***components are same - CaCO3, but arranged in different way
Types of Biominerals
- ~ 60 different types of biominerals
- Common cations:
– Calcium, Silica, Iron, Manganese, Zinc, Copper - Common anions:
– Carbonate, Phosphate, Sulfate
Why so much calcium?
over 50% is calcium
bc of Phosphate
also calcium phosphate
- our bones
- brachiopod shells are this too
– calcium is abundant in marine systems
— calcium ions can precipitate phosphate
- almost everything requires phosphate ions to function
— cellular respiration - know how to pump calcium already
Functions of Biominerals
- Stiffen skeletal levers
- Protection – armour
- Harden jaws
- Anchorage - like tubeworms and corals - not just armour, but anchors them to substrate
- Storage system for metabolically important ions
- Sensory reception
- Gravity
- Earth’s magnetic field
*** examples: statocysts in cnidarians, magnetite crystals in bacteria
Mechanism of Biomineralization
1) Space delineation
2) Subdivision of space by organic matrix
3) Generating saturated solution
4) Nucleation
5) Growth and shape modulation
6) Cessation
Space Delineation
for Mineral Nucleation & Growth
control where biomineralization happens -
**has to happen in controlled space or volume
Generating saturated solution of ions
need calcium and carbonate
- pump w CO2
- spend energy to pump ions into here
- the CO2 in water will form carbonate ions (CO3) and calcium —> calcium carbonate
Mollusc shells often have multiple shell layers
- Layers may consist of calcite or aragonite
- Different layers may have different crystal orientations
Arresting crack propagation
requires more energy to break bc diff material
need more energy to keep
cracking thru diff materials
take more energy to make a big fracture from a microfracture if different material
ex//
- Mollusc shell: plywood construction
– Strengthens by resisting crack propagation
how to resist crack propagation?
1) Strengthens by resisting crack propagation - having different materials
2) gap adds a need for energy - having gaps and voids make cracks stop at this spot
crack cant go around has to go through
an EXAMPLE is porous echinoderm ossicles
why is Shell Dissolution important
1) Enlarge shell apertures for water flow e.g. scaphopods, keyhole limpets
2) Enlarge living space
- cone snails get around the thin cracking
from predators by having a non-existent spire - but this means they have to dissolve their own
shell over and over
reasons for shell dissolution w examples (5)
- Enlarge shell apertures for water flow
e.g. scaphopods, keyhole limpets - Enlarge living space
e.g. cone snails - Buffering of physiological acids
e.g. during anaerobic metabolism - Remodeling during morphogenesis
e.g. nudibranch larval shell - Mineral recycling
e.g. crustacean molting cycle