Biomineralization

Question 1

Describe biomineralization

Answer 1

Process by which organisms form minerals

Question 2

Amorphous biomineralization is?

Answer 2

Mineral structure doesn’t have regular size, shape or spatial organization.

Question 3

Crystalline biomineralization is?

Answer 3

Atoms in mineral are organized in repeated units.

Question 4

How can such complex shapes of minerals form within living organisms?

Answer 4

Scaffold - proteins (e.g. collagen) that give a rigid frame on which the mineral can form.

Hydroxyapatite - filling material that fills the scaffold frame

Question 5

Describe the two steps to crystallization

Answer 5

1. Nucleation: local region of solvent become saturated with solute, and solute molecule create a stable cluster. Requires molecules to line up just right for crystallization. Rare for complex crystals.
2. Growth: subsequent growth after nucleation has occurred.

Question 6

Nucleation is the difficult step in mineralization (i.e. takes the longest)

Answer 6

True

Question 7

Describe dissolving of the crystal components?

Answer 7

Dissolving so crystal components integrate with water.

• Gravity wants precipitates to form
• Water surrounds the ions to oppose gravity
• Increase temperature allows water to be “borrowed” by multiple ions; thus increasing solubility.

Question 8

Define solubility constant

Answer 8

Ksp = measure of how soluble a substance is.

Ksp is the product of the dissolved ion concentrations in solution at equilibrium: higher Ksp = higher solubility.

Question 9

Describe the different solution conditions

Answer 9

Saturated: ion product = Ksp

Supersaturated: ion product > Ksp. Precipitation/mineralization favoured.

Undersaturated: ion product < Ksp. Dissolution/demineralization favoured.

Question 10

Describe hydroxyapatite in relation to solubility constant

Answer 10

Ksp = 0.7 mM^2 (very low)

• HA Ksp increases exponentially with lowering pH
• Saliva becomes unsaturated when pH < 5. i.e. ENamel begins to dissolve

Question 11

Define unit cells

Answer 11

Regular repeated structure of crystals that fit together specifically. All atoms in a unit cell have a specific space and location (other atoms won’t fit there).

Question 12

Define nucleation

Answer 12

This is the formation of a critical amount of unit cells that act as template for new crystals to form

Question 13

Define matrix protein

Answer 13

Template protein to position the atoms of hydroxyapatite.

Question 14

Describe matrix protein properties and relations

Answer 14

• The first ions of the crystal are aligned in the matrix protein, so that the surface looks like the edge of a real unit cell.
• Matrix proteins allow crystal initiation (nucleation)
• Bypasses the hardest step of crystal formation (i.e. nucleation)
• HA is hard to form (naturally) because there are many crystals which all need to line up perfectly.
• Calculus is amorphous and doesn’t not need as strict alignment to crystallize.

Question 15

Describe the matrix vesicles

Answer 15

• Concentrate the intracellular phosphate and calcium
• Secrete the matrix vesicle to the cell surface
• Provide high concentration of “supplies” to the crystal growth site.