Oral Biochemistry

Question 1

Define ‘biomineralization’

Answer 1

process by which organisms form minerals

Question 2

Define ‘amorphous biomineralization’

Answer 2

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

Question 3

Define ‘crystalline biomineralization’

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

T/F - Nucleation is the easy step in mineralization (i.e. takes the shortest)

Answer 6

False, takes the longest, and is the difficult step

Question 7

Describe ‘dissolving’

Answer 7

Crystal components becoming integrate with water:

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

Question 8

Define solubility constant (Ksp)

Answer 8

Measure of how soluble a substance is

Question 9

Define Ksp

Answer 9

This is the product of the dissolved ion concentrations in solution at equilibrium.

Higher Ksp = Higher solubility

Question 10

Define saturated solution conditions

Answer 10

Ion product = Ksp

Question 11

Define supersaturated conditions

Answer 11

• Ion product > Ksp

- Precipitation/mineralization favoured

Question 12

Define undersaturated conditions

Answer 12

• Ion product < Ksp

- Dissolution/demineralization favoured

Question 13

When does enamel begin to dissolve?

Answer 13

• When hydroxyapatite Ksp = 0.7 mM^2 (very low)
• HA Ksp increases exponentially with lowering pH
• Saliva become unsaturated when pH < 5

Question 14

Define ‘Unit cells’

Answer 14

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 15

What is nucleation?

Answer 15

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

Question 16

Define matrix protein

Answer 16

Template protein to position the atoms to hydroxyapatite.

Question 17

Name functions of matrix vesicles

Answer 17

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

Question 18

List bone composition’s organic and inorganic material

Answer 18

Organic material:

• Cell
• Collagen
• Glycosaminoglycans
• Proteoglycans and proteins

Inorganic material:

• Hydroxyapatite
• Calcium carbonate

Question 19

Describe intramembranous ossification

Answer 19

Formed directly in loose mesenchyme from an osteoblast-secreting scaffold and matrix vesicles, then calcifying:

• bone that are constantly under tension
• Irregular bones (e.g. skull bones)

Question 20

Describe ‘endochondral ossification’

Answer 20

Formed from the replacement of a hyaline cartilage model. Primary and secondary ossification centres form:

• Bones that are needed to perform immediately and are constantly under pressure
• Long bones

Question 21

Describe osteoclast/osteoblast activity balance

Answer 21

Osteoblasts secrete RANKL and a decoy protein (OPG) that binds with the RANKL. If PTH is present, the decoy protein product is blocked. This allows the RANKL to bind with RANK receptors on pre-osteoclasts

• RANK receptors trigger production and maturation of osteoclasts
• PTH triggers osteoclast activity, by binding decoy protein (OPG)
• This ensures that osteoclastic activity only occurs in the presence of active osteoblasts
• This ensure that osteoblastic activity always matches osteoclastic activity.

Question 22

Clinically, how do you get netloss of bone during inflammation (e.g. alveolar bone loss in root inflammation)?

Answer 22

• Inflammation and bacteria intermediates bind directly to the RANK receptor and activate the RANK cascade, but not through the osteoblasts: Trigger osteoclast activity, disproportionally to osteoblast activity.
• Since osteoblast/osteoclast activity is so linked, replacement of loss bone is slow and often permanent.