Structure, functions and methods of research of biological membranes The general structure of cell
Cells at animals and plants very much are various. Uniform principles of construction of all cells exist. All cells consist of the cytoplasm surrounded plasmatic (cellular) membrane. A kernel, organoid of cells and various inclusions are in cytoplasm (fig. 1). Mitochondrion, lysosome, device Goldzhi, endoplasmic reticulum, ribosomes concern to organoid of cells.
The cellular membrane is covered by thicker blanket in some cells. These layers can be considered in a microscope. For example, the thick cellulose shell is available for the majority of the vegetative cells, surrounding and protecting a true cellular membrane. Animal cells also can have the external shells consisting from polysacharides or glycoprotein. These shells carry out functions of mechanical protection of a cell, as possess immunologic and filtrational properties (passing to a surface of cells only molecules of the certain size). They have ion-exchange properties (participating in preservation of a constancy of the microhabetat surrounding a cell).
Various substances: proteins, lipoid, carbohydrates, organic acids, vitamins, electrolytes and water are a part of cytoplasm. 75-85 % of water, 10-20 % of proteins, 2-3 % of lipids, 1 % of carbohydrates and nearby 1 % of salts and other substances contain in cytoplasm.
The water which is being a cell, carries out the following the basic functions: 1) serves as solvent of organic and inorganic substances; 2) serves as dispersive environment of colloidal of systems; 3) participates in a metabolism of a cell (receipt of substances, chemical processes, deducing of products of an exchange); 4) participates in heat regulation; 5) creates turgor of cells.
The valent corner (a corner between communications of atoms of hydrogen with atoms of oxygen) is equal approximately 109o in the molecule of water. Therefore the molecule of water gets character of a dipole with greater dipole the moment which defines high value of dielectric permeability of water.
Molecules of water cooperate with each other and form dynamic structure owing to dipole to properties. Modern methods have established, that intracellular water is in an original condition of continuously going transitions between phase: a crystal - a liquid, a liquid - a crystal.
Greater dielectric permeability of water explains its ability to dissolve polar substances. As all chemical communications are electrostatic forces, in water these forces decrease in 80 times (dielectric permeability of water is equal 80 at 20oC). Thus molecules of electrolytes break up to ions, around of which are formed hydrate shells. Dissolution of polar substances is caused by interaction of polar groups of molecules with dipoles of water. Because molecules of water it is dipoles, water serves not only solvent, but also defines structure of a solution.
W
ater
in a cell shares on free water and connected. Free water makes 95 %
of all water of a cell. Free water is used as solvent and as
dispersive shell
environment
of colloidal system of cytoplasm. The connected water makes 4-5 % of
all water. Molecules of the connected water form weak communications
with polar groups of various molecules (basically protein).
Movement of molecules of the water connected by protein is limited. The connected water cannot serve as solvent for other substances.
Quantity of
the w
ater
connected by protein, it is possible to define by measurement of
quantity of the water adsorbed on dried up fiber. Besides the
quantity of the connected water is defined by thermodynamic methods,
for example a method of Hill - measurement of elasticity pair above a
fabric. Water of a cell is filled due to receipt from an
intercellular liquid and partially due to its formation at oxidizing
processes in a cell. The h
omogeneous,
amorphous, transparent substance remains after removal from a cell of
all organelles and all inclusions. It is possible by means of
centrifugation cellular homogenate. This remained substance is called
hyaloplasm. It is the internal environment of a cell.
In the physical and chemical attitude hyaloplasm it is multiphase colloidal system. Colloids of cytoplasm are mainly hydrophilic colloids. The colloidal system of cytoplasm is formed by complex high-polymer connections. Proteins, polysacharides, nucleinic acids are such connections. All these connections differ from the big degree of polymerization. Lipids take part in formation of structure of hyaloplasm. They create coacervate system.
Colloids of cytoplasm can be in a condition sol or gel. Transitive conditions are available between them. Transitions from one condition in another occur in cytoplasm all time. These transitions are nonsynchronous in different sites of cells.