Biochemistry
We shifted gears today from glycolysis and looked at gluconeogenesis. Obviously, wasn't much different as gluconeogenesis is just the reverse of glycolysis with some slight differences. So the process begins with pyruvate in the mitochondrial matrix, and it looks to end with having glucose in the cytoplasm. The processes mainly differ at these irreversible steps:
(1) In glycolysis, you have a phosphate being added to Fructose-6-Phosphate to make Fructose-1,6-Bisphosphate. The reverse happens in gluconeogenesis: Fructose-1,6-Bisphosphate looses a P to Fructose-6-Phosphate through the actions of the enzyme Fructose-1,6-Bisphosphatase.
(2) In glycolysis, you have a phosphate being added to glucose when it enters the cell. The reverse happens in gluconeogenesis: a phosphate is removed from Glucose-6-Phosphate by Glucose-6-Phosphatase. This allows the glucose to be able to leave the cell; you will only find this specially functioning enzyme in liver and kidney cells.
(3) In glycolysis, you have pyruvate kinase removing a phosphate from phosphoenoylpyruvate to generate ATP and pyruvate. Since this cannot easily be reversed, gluconeogenesis uses a combination of reactions instead:
(a) carbon dioxide is added to pyruvate by pyruvate carboxylase, to form oxaloacetate
(b) oxaloacetate is transformed back to phosphoenol pyruvate by a long-named kinase.
At this point, oxaloacetate cannot move freely across the mitochondrial membrane in order to get to the cytoplasm, so it needs further conformation. It gets converted to malate, which can pass through, and then reconverted back to oxaloacetate. This process also generates NADH, which makes sense as glycolysis converts NAD+ to NADH; this allows for gluconeogenesis to take the NADH and convert it to NAD+ (remember, reverse of glycolysis!).
Principles of Dental Materials
Today we continued our look at gypsum (recall: dental plaster used to make models from alginate impressions). Some factors that change gypsum's properties include:
(1) the amount of water added; extra water makes models porous and weaker. If you find that the gypsum is setting too quickly, throw it out and start again.
(2) the temperature of the water: if water is too hot (about body temperature hot), it will affect the reaction and the gypsum will not set well. Cold water slows the setting down slightly, while warm water will speed up setting slightly.
(3) hardening solutions can be added to give gypsum a stronger microstructure (eg. colloidal silica, superplasticizers)
(4) environment it is stored in. Gypsum powder will pick up moisture from the environment.
(5) wetting agents
(6) accelerators and retarders. Potassium sulfate accelerates setting. Terra alba (water from grinding wheel) will accelerate setting. Colloidal organic particles (blood, saliva, unset alginate) will retard setting.You should clean off impressions with cold water before setting!
We also began to talk about different metals used in dentistry. There are two main types: nobel metals and base metals. Noble metals tend to be naturally resistant from oxidizing (eg. gold, platinum, iridium, osmium, palladium, rhodium, etc.), while base metals tend to oxidize, but can form a natural adherent oxide coating (eg. iron and cobalt with chromium [acts as a corrosion preventer], titanium, etc.).
An important theory in regards to dental materials is the Metal Deformation Theory. It states that metals develop slip systems, which are planes and directions within the crystal lattice along with atoms slip more easily. Results in materials to be more ductile (deformed). Face-centered cubic materials tend to have more slip systems than body and hexagon-close packed materials.
Can reduce dislocations through four techniques:
(1) create dislocation tangle
(2) add alloying elements for solid solution strengthening
(3) make dispersions of fine second phases
(4) increasing grain boundaries
Note: the fourth method is the best as it increases strength of the metal without decreasing its ducility.
Dental Anatomy
Today in DA we had an exam, so no new lectures. Next week will look at the anatomy of maxillary and mandibular premolars.
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