Vital functions of the cell is made possible only because of the different enzymes and substances do not mix, and the cell is integrity.All this is only possible through a variety of membranes.A cell is generally separated from the other special structure called "cytoplasmic membrane."
whether it is seen in the light microscope?The answer is no, yes, we can see the border, but the membrane itself - too thin structure.Sometimes we do not see even the boundaries of cells, for example, when viewed in the light microscope the cells of the liver.But why then we see in other cases, the border cell membrane is not it?
Actually it nadmembrannye layers of carbohydrates, which are between the cells.They absorb the dye, so if all goes well the context of you might think that this is the plasma membrane.
In experiments it was found that cells which have been immersed in solutions with different osmotic pressure, swell or shrink, which means that they are surrounded by a membrane which is characterized by selective permeability.
It was also revealed that the cell membrane permeable well, if it try to penetrate substances that are soluble in lipids.In the classical conception gidrofilnye ends of the molecules of the membrane were considered facing outward and the hydrophobic - inside.Electron microscopy also proved that it is much more difficult.In particular, in electronic photo shows that the outer layers are dense and not internal, that is, lipid layers located at the edges.
plasma membrane through their device impermeable to macromolecules, so cytoplasm proteins are not able to get out of the cell through it.Proteins are in the cells, creating osmotic pressure, whereby the desired amount of water enters into the cell.However, this process is not infinite, because the interstitial fluid outside also have other materials which balance the osmotic pressure.To
potential difference remained stable plasma membrane should have dielectric properties.It also suggests scientists to think that a lot of lipids in the membrane, which have dielectric properties.Reluctantly disclose their plasma membrane properties.
structure and functions of its related, for example, the ability to maintain an unusual difference in the concentrations of potassium and sodium ions associated with a particular mechanism in the membrane - sodium-potassium pump.The transfer of ions at the same time provides a special enzyme, which runs on energy cells, this process is costly for her.Cage has to "pay" for the balance.Also require "investments" and the transfer of glucose, fatty acids, amino acids.
interesting feature of the cell membrane as it is asymmetric, that is, the inner and outer surface thereof are not the same, although initially the researchers on the basis of electron microscopy think so.All of the glycoprotein molecules uglevodosoderzhaschie in favor of the outer surface of the membrane and are involved in the formation of nadlipidnogo layer.The outer surface of the cell also contains special molecules called receptors, they act with a certain molecules of the environment.Since regulated activity of the cell, it can stimulate or suppress depending on the needs of the body.And in the inner part of the membrane contains a lot of cholesterol.
Biochemical studies have shown the cell membrane, proteins that the inner and outer membranes are not identical but different phospholipids in the composition of these two surfaces is also quite diverse.Some of these features can be seen even by using an electron microscope.
As you can see, elementary membrane is not so simple, but in order to understand all the processes, scientists had to build and reject many hypotheses.
