L4

Question 1

Gar fish

Answer 1

scales made of dentin with some enamel. Also have enamel teeth.

Question 2

Most fundamental aspect of enamel formation

Answer 2

innovation occured betwen 520 and 400 mil years ago, ameloblasts on dentin surface start to deposit ribbons to make enamel layer.

Question 3

Enamel crystals are organized into

Answer 3

cylindrical rods (prisms) embedded in interrod enamel (interprismatic substance).

Question 4

Each rod contains

Answer 4

~10,000 crystals, all oriented in the direction of the rod.

Question 5

Sparc-L1

Answer 5

encodes for basement membrane protein on surface of dentin

Question 6

Enamel was made in the

Answer 6

scales and teeth of the common ancestor of coelacanth & the gar (>450 Mya).

Question 7

More than 520 Ma fish were

Answer 7

soft-bodied and lacked skeletons, jaws, teeth, & scales.

Question 8

Earliest Fish (Chordates =

Answer 8

Notochord)

Question 9

Vertebrate features

Answer 9

: a notochord, a pair of prominent camera-type eyes, paired nasal sacs, possible cranium and arcualia, W-shaped myomeres, and a post-anal tail.

Question 10

The Gar

Answer 10

Long slender bodies covered in rock-hard ganoid scales.

Many large pointed teeth.

Can breathe air.
swim bladder they fill by gulping air to supplement their gill breathing in low-oxygen environments.

Can remain out of water for nearly 1 h without dying.

A thick coat of scales make the alligator gar the best protected fish species.

Question 11

The Coelacanth: More Living than Fossil

Answer 11

Lobe-finned fish with lungs: close relative to amphibians

Coelacanths (seel-a-canths) were once known only from fossils and were thought to have gone extinct approximately 65 million years ago (mya), during the great extinction in which the dinosaurs disappeared. The most recent fossil record dates from about 80 mya but the earliest records date back as far as approximately 360 mya. At one time coelacanths were a large group comprising about 90 valid species that were distributed worldwide in both marine and freshwaters. Today, there are two known living species.

Question 12

1. Enamel Formation is a Unique

Answer 12

Epithelial Mineralization Process That Evolved in Response to Evolutionary Pressures for Harder Teeth & Scales.

Question 13

2 The Fundamental Innovations Were to Form & Support a

Answer 13

Mineralization Front Apparatus Along the Secretory Surface of the Ameloblast Apical Membrane to Initiate, Extend & Orient Enamel Mineral Ribbons, and Then Harden this Mineral Layer by Thickening the Ribbons.

Question 14

The secretory calcium-binding phosphoprotein (SCPP) gene family evolved by

Answer 14

gene duplication from a single ancestral gene (SPARC-L1).

Question 15

SCPP: Two groups:

Answer 15

Acidic/Proline & Glutamine rich proteins

Question 16

SCPP proteins: Non-collagenous proteins of

Answer 16

bone, dentin, and enamel; milk, salivary proteins, homeostasis, mineral inhibitor.

Question 17

Human SCPP genes are clustered on

Answer 17

Chromosome 4.

Question 18

17. A patient with the following oral and radiographic presentation is likely to develop what other phenotype?

Answer 18

kidney calcifications

Question 19

These enamel malformations were observed in a patient with no skin fragility, but she had a sibliing with enamel malformations and skin fragility. She is likley a carrier for which of these conditions?

Answer 19

Junctional epidermolysis bullosa

Question 20

Secretory Stage:

Answer 20

Crystals grow in length

Question 21

Maturation Stage:

Answer 21

Crystals thicken

Question 22

Forming mineralization front;

Answer 22

Basement membrane of the Inner Enamel Epithelium fenestrates.
Finger-like ameloblast processes (*) penetrate into the pre-dentin (pd) matrix.
Onset of mineral foci in dentin, which coalesce into a continuous mineral layer.

Question 23

If you have a problem with ribbon extension, you have

Answer 23

thin enamel.

Question 24

Lama3-/- Mice: Defects Start at

Answer 24

Secretory Stage

Question 25

Presecretory ameloblasts of wild-type (F) and mutant animals (J) are indistinguishable. Secretory ameloblasts are

Answer 25

pathological (K).

Question 26

Enamel mineral ribbons initiate directly on

Answer 26

dentin mineral and most obviously onto the sides and tips of mineralized collagen fibers, and extend from there to the ameloblast membrane.

Question 27

Parallel enamel ribbons run in

Answer 27

clusters from a common origin on dentin to a common section of ameloblast membrane.

Question 28

Each cluster of enamel ribbons is initiated by a single

Answer 28

ameloblast process and is extended by it as the process retracts into the ameloblast distal membrane.

Question 29

The orientations of the initial enamel ribbons on dentin are determined by the

Answer 29

path of the retrograde movement of the ameloblast membrane.

Question 30

The more highly mineralized dentin contrasts with the overlying

Answer 30

enamel mineral ribbons, so that while this interface was highly irregular, the boundary between the two mineralized tissues was always distinct, even though the enamel ribbons were directly continuous with the dentin mineral.

Question 31

Initial Enamel Mineralization

Answer 31

no rods initially, extends up to flattened surface from dentin.

Question 32

No enamel ribbons form in

Answer 32

Ambn & Enam null mice. The process initiates but quickly turns pathological in Amelx and Mmp20 null mice.

Question 33

SCPP all have

Answer 33

phosphorylation site.

Question 34

FAM20C, or Golgi Casein Kinase, is a

Answer 34

secretory pathway protein kinase that phosphorylates the majority of the secreted phosphoproteins in plasma, serum, milk and csf, as well as many of the extracellular matrix proteins in enamel and other mineralized tissues.

Question 35

FAM20A is closely related to FAM20C but does not have

Answer 35

kinase activity. Instead it forms a functional complex with FAM20C, which allosterically enhances FAM20C activity.

Question 36

The problem with FAM20C kinase is that

Answer 36

all of these effected proteins are not phosphorylated - results in enamel-renal syndrome, others.

Question 37

CLDN16 is an integral membrane protein component of

Answer 37

tight junctions. Its absence can affect the paracellular transportation of Mg2+ & Ca2+.

Question 38

Ameloblasts undergo

Answer 38

repetitive alternations between ruffle-ended and smooth-ended morphologies throughout the maturation stage.

Question 39

In rat incisors each modulation cycle lasts about

Answer 39

8 h (3 per day). Ameloblasts spend ~4 h as ruffle-ended, ~2 h as smooth-ended, and ~2 h re-creating the ruffled border after having been smooth-ended.
The predominant maturation ameloblast morphology is ruffle-ended. Ameloblasts initially form the ruffled border when they complete post-secretory transition at the beginning of the maturation stage and re-create the ruffled border multiple times throughout the maturation stage, following each successive smooth-ended transition.
Ameloblasts are “smooth-ended” when the apical invaginations are missing and apical junctional complexes are disassociated and leaky.
About 25% of the total ameloblast population entering post-secretory transition die in a matter of hours, leaving ~75% of the original population that formed enamel rods to initiate rhythmic modulations at the surface of the maturing enamel. An additional 25% of the ameloblast population dies as ameloblasts modulate, so that only 50% of the original population that formed enamel rods eventually finishes the maturation stage.

Question 40

Because of enamel formation chemistry, you produce

Answer 40

acid (11 protons for every 10 calciums). This acidifies the matrix.

Question 41

Smooth ameloblast

Answer 41

spends 3/4 time as rough, at the end the matrix is neutralized. There are cycles of acidity.

Question 42

Mineralization front apparatus is replaced with a

Answer 42

specialized basement membrane that tightly adheres the cells to the enamel layer. Amelotin (AMTN) and ODAM contribute to this attachment.

Question 43

Stromal Interaction Molecule 1 (STIM1)

STIM1 is a

Answer 43

transmembrane protein with Ca2+ binding domains in ER that is activated by depletion of ER Ca2+ stores. After store emptying, STIM1 forms multimers that passively migrate to ER-plasma membrane junctions where they activate the Ca2+ channel ORAI1.

Question 44

2. Calcium release-activated calcium channel protein 1 (ORAI1)

Answer 44

Together, STIM1 & ORAI1 mediate store-operated calcium entry (SOCE), which is a Ca2+ influx pathway critical for the normal functioning of many cell types, including T cells, muscle cells, and ameloblasts. Homozygous loss of function mutations in ORAI1 and STIM1 cause Immunodeficiency 9 and 10, respectively, which feature severe immunodeficiency, congenital myopathy, ectodermal dysplasia, and AI.

Question 45

3. Potassium-dependent sodium-calcium exchanger (SLC24A4)

Answer 45

Uses a Na+ gradient to transport Ca2+ out of the cell (efflux).

Question 46

Mg2+ is actively pumped out by

Answer 46

CNNM4 in the basolateral (proximal) membrane toward the blood supply. Green = positive immunostaining for CNNM4. Red immunostains intercellular junctions.

Question 47

Mg2+ passively exits the enamel layer and into ameloblasts through

Answer 47

channels in the distal membrane.

Question 48

H+ are Released

Answer 48

During HAP Formation

~11 H+ for each unit cell at pH 7.2

Question 49

Ameloblasts undergo repetitive alternations between

Answer 49

ruffle-ended and smooth-ended morphologies throughout the maturation stage.
In rat incisors each modulation cycle lasts about 8 h (3 per day). Ameloblasts spend ~4 h as ruffle-ended, ~2 h as smooth-ended, and ~2 h re-creating the ruffled border after having been smooth-ended.
The predominant maturation ameloblast morphology is ruffle-ended. Ameloblasts initially form the ruffled border when they complete post-secretory transition at the beginning of the maturation stage and re-create the ruffled border multiple times throughout the maturation stage, following each successive smooth-ended transition.

Question 50

Ameloblasts are “smooth-ended” when the

Answer 50

apical invaginations are missing and apical junctional complexes are disassociated and leaky.
About 25% of the total ameloblast population entering post-secretory transition die in a matter of hours, leaving ~75% of the original population that formed enamel rods to initiate rhythmic modulations at the surface of the maturing enamel. An additional 25% of the ameloblast population dies as ameloblasts modulate, so that only 50% of the original population that formed enamel rods eventually finishes the maturation stage.

Question 51

Structure of Calcium Hydroxyapatite

Substitution of

Answer 51

oH- by Fluoride

Question 52

Closest structural analogue to the mineral in bones & teeth is

Answer 52

calcium hydroxyapatite (HAP)

The same mineral is in mineralized cartilage, bone, cementum, dentin, and enamel.

Dental Enamel is ~ 96% mineral (by Weight)

Dentin is ~ 70% mineral

Bone is ~ 65-70% mineral

Question 53

Coulomb’s Law

Answer 53

Hydroxyapatite holds together by electrostatic interactions. The force of attraction is described by Coulomb’s law. Note that the force holding together the crystal is greatly reduced by increasing the distance between ions in the lattice

Question 54

Substitution of OH- with F-

Answer 54

A hexagonal close packed (HCP) arrangement represents the densest possible packing of the phosphate “spheres”, which are the largest ion in HAP.

The dense packing decreases the distance between opposite charges.

There are twice as many interstices as there are PO43- ions, which provide the exact number of spaces needed for the calcium and hydroxyl ions.

Ca2+ and OH- ions occupy the interstices between phosphates, but force the phosphate ions apart slightly, so they not as closely packed as they could be.

Hydroxyl ions are larger than the calcium ions and expand the crystal structure to a greater degree. Fluoride ions are smaller than hydroxyl ions, so substituting F- for OH- allows the phosphates to achieve closer packing, increasing the stability of the crystal.

Question 55

The solubility product constant (Ksp) is the ion product of a solution that is at

Answer 55

equilibrium with a crystal.

Question 56

The ion product (Qsp) is equal to the product of the

Answer 56

concen-trations of the ions involved in the equilibrium, each raised to the power of its coefficient in the equilibrium equation.

Question 57

The ionic product (Qsp) can depend on the

Answer 57

pH of the solution.

A crystal is at equilibrium with the surrounding solution when Qsp = Ksp, and the solution is said to be “saturated”.

Question 58

The smaller the Ksp (higher negative exponent), the less

Answer 58

soluble is the crystal.

Question 59

Dissolving An Ionic Solid (Salt)

Answer 59

The salt starts to dissociate into its component ions (dissolve).

Ions in the water begin to collide with the crystal and add back to the lattice (precipitate).

Eventually the dissociation rate equals the precipitation rate.

The solution is now saturated. It has reached equilibrium.

Question 60

In solution, phosphate exists in

Answer 60

4 forms. The relative abundance of these 4 forms depends upon the [H+], or pH. In strongly-basic conditions, the phosphate ion (PO43−) predominates, whereas in weakly-basic conditions, the hydrogen phosphate ion (HPO42−) is prevalent. In weakly-acid conditions, the dihydrogen phosphate ion (H2PO4−) is most common. In strongly-acid conditions, aqueous phosphoric acid (H3PO4) is the main form.