Some small molecules such as penicillin cannot trigger an allergic response themselves (haptens). But why is it that the IgE can't be triggered by small molecules ( penicillin monomer, ethanol, water, carbon dioxide) ? I thought it was the shape that was required, not size, to trigger a reaction.
But brain receptors can bind to things such as melatonin, i.e very small molecules. 1. What is the minimum size? 2. Why is size of a molecule so important to an IgE when brain receptors have no issue with size?
You need to look at a bigger picture that includes water. If we mix water and oil, these two materials will phase separate into two layers. This is due to surface tension and the need to lower the energy. Absorption of molecules by protein, occur within water, and is partly of a phase separation process. Many small molecules are more soluble in water with water creating more of an extraction than a phase separation onto specific protein.
Both the water and the oil are in the same phase - they are both liquid. Actually I think the reason is that water is polar and oil is nonpolar, so they cannot mix. Additionally, oil is less dense than water so the oil floats on the water. I always thought it was kind of cool that soap can be made by boiling lard with NaOH. The long chain polymers of the fat will react with the NaOH so that there is an Na+ on the end of the nonpolar polymer. The nonpolar end can mix with oily materials and the polar end of the polymer allows it to mix with water to so the oil can be rinsed away with water one molecule at a time.
Gas, liquid and solid is one definition that illustrates three phases. But in a more general terms, such as within phase diagrams, phases can be subsets within gas, liquid and solid, connected to specific combinations and orientations of atoms and molecules than can separate from each other. In a loose sense, a cell has its own phase diagram with the various organelles phases within the water matrix of the cell. Like any phase diagram, these are repeatable as long as the parameters (position) on the phase diagram are the same. Picture this system. We have oil and water with the oil floating on the water; two liquid phase system. We have a second beaker with methylene chloride and water, with the water floating on the methylene chloride. We carefully stack these three phases (oil, water and methylene chloride) with oil on top, then the water and finally methylene chloride on the bottom. Since the oil and the methylene chloride are mutually soluble (non polar), if we shake this the three phase system will end up with two layers. But if we are careful, we can form a metastable three phase system, that will slowly attempt to form two layers since this is at lowest energy. The shaking create the activation energy for a quick change. The cellular phase diagram is designed in this way. The innards of many protein are more hydrophobic and the surface more hydrophilic. This means the innards could mutually dissolve into each other, but the water in the middle keeps then apart in a slightly potentiated state. There is built in energy created within these metastable phases that is being partitioned by the water so it remains as a separate phase. If we go back to water and small chemicals, say we start with our three layer system of oil, water, methylene chloride, with the water in the middle. I will inject a fourth material, which in this case is an alcohol, into the middle water phase. This will define a new water-alcohol phase on the diagram. This new phase will have an impact of the surface energy that separates the layers. The three layer system is not quite as stable. If we go back to small molecules and protein, when we add these to water phase, there is an altering of phase separation energy. This may cause the protein to be stuck open or closed.
Uh phase diagrams do talk about the phases of liquid solid and gas. When you make a mistake or are wrong it is ok to admit it. Loose sense, like goofy made up stuff?
The most common phases are gas, liquid and solid but things can get more complicated. Below is PVT 3-D plot that shows stable phases that are a combination of gas-liquid, liquid-solid, etc. The phase diagram of carbon steel, next to that, has various phases within the solid phases, with each having different properties in terms of material fabrication and performance. Please Register or Log in to view the hidden image!,Please Register or Log in to view the hidden image! Looking at a cell as a complex phase diagram based on water and organic materials creates predictability in terms of thermodynamic properties. For example, the hierarchy within cellular synthesis stays consistent based on phase considerations. These line up along a phase boundary. An interesting phase diagram for water/steam is a plot of entropy versus temperature. Although entropy is often considered a random nebulous thing, when quantified as energy and plotted, it represents very distant states that are quite predictable when conditions are exact. The cell takes advantage of this to target what appears to be randomness to get predictable output out of the DNA phase. Please Register or Log in to view the hidden image! If we get back to the original topic, and if we had the right phase diagram, allergic has a position.
Yep, but they are still composed of only 3 phases. Liguid-solid is not a phase it is a combination of 2 phases. Those are not phases. The different areas are crystal types that result from different amounts of carbon in the iron at different temperatures. It is more about the solubility of carbon in iron. I think the horse is dead....
Melatonin's pretty small, true, and some proteins are water-soluble. But there has to be a problem with increasingly small molecules triggering a surface protein itself. Otherwise, there'd be constant physiological reactions to everyday solutes and ions.
