Cytoplasm

The cytoplasm (from the Greek kytos - cell and plasma - formed) is the content of plant or animal cells, except for the kernel (karyoplasm). The cytoplasm and the karyoplasm lying called protoplasm. In normal microscope it looks like a semi-liquid substance (base material, or hyaloplasm), where suspended variety droplets, vacuoles, granules, rod-shaped or filamentary structure. Under the electronic microscope cytoplasm has a more complicated form (a labyrinth of membranes with a prisoner between them the protoplasm). The cytoplasm is a complex mixture of proteins that are in a colloidal state, carbohydrates, lipids, nucleic acids and other organic compounds. From inorganic compounds in the cytoplasm water is present, and various minerals.
The outside of each cell is surrounded by the finest plasma membranes (i.e., shell), which plays an important role in the regulation of the composition of cell content and which is derived cytoplasm. The membrane is a three-layer structure (inner and outer layers are made of protein, between them is a layer of phospholipid molecules) with a total thickness of about 120 + (angstroms). Cell wall riddled with tiny holes - pores through which protoplasm one cell can share with protoplasm other, neighboring cells.
In the cytoplasm there are various organelles - specialized structures that perform certain functions in the life of the cells. Among them the most important role in metabolism play mitochondria; in ordinary microscope they are visible in the form of small sticks or seeds. Data electron microscopy indicate their complex structure. Each mitochondrion has a shell, consisting of three layers and inner cavity. From a shell in that cavity filled with liquid, resorted numerous partition, not reaching the opposite wall, called the Christ. With mitochondria are related respiratory processes. In the cytoplasm there is so called the endoplasmic network (reticulum) - large system of submicroscopic channel, pipes and tanks, limited membranes. Membranes of endoplasmic reticulum double. On the side facing the main substance of cytoplasm, on each membrane are numerous granules that contain ribonucleic acid, in accordance with what they were called ribosomes. With the participation of ribosomes in the endoplasmic reticulum is the synthesis of proteins.
One of the components of cytoplasm is net apparatus or Golgi complex", closely associated with the endoplasmic network and participating in the processes secretion. There are data showing that the membrane of nucleus of the cell (see) without interruption go into the membranes of endoplasmic reticulum and the Golgi complex. In the cytoplasm of some animal cells may be present fibrils - thin filiform education and tubes, which contractile elements. Often in the cytoplasm visible grain of glycogen (in plants - starch), fatty substances in the form of small droplets and other structures. Cm. also the Cell.

The cytoplasm (from the Greek. kytos - cell and plasma - anything fashioned formed) - the contents of the cells, with the exception of the kernel (the karyoplasm lying). The cytoplasm and the karyoplasm lying called protoplasm. Sometimes the term "protoplasm" is incorrectly used in the narrow sense of the word to refer to vpadiny part of the cell, but in this sense it is better to abandon the term "cytoplasm". In physico-chemical behaviour cytoplasm is multiphase colloidal system. Dispersive environment cytoplasm - water (up to 80%). The dispersed phase contains protein and fatty substances that form aggregates of molecules micelles. Cytoplasm - viscous liquid, almost colourless, with a specific gravity of approximately 1,04, often very refracting light, causing it to be seen under the microscope, even in unpainted cells.
A characteristic feature of cytoplasm, which determines its biological properties; - instability of colloids, the ability to quickly successive States of gelatinization and liquefaction. This explains the variety of patterns structure of the cytoplasm (grainy, filamentous, mesh, and so on), described by different researchers. Depending on the age of the cell, its physiological status, functions, and so on, may be a different structure of the cytoplasm. Of great importance is also the character of pre-processing (especially histological commit)applied in obtaining the drug. Morphology of cytoplasm depends on the state of its colloids.
In the cytoplasm find about 60 biogenic elements; its major chemical components - proteins, carbohydrates, lipids and some salt. The principal distinction of cytoplasm from the kernel - the presence of a significant number of ribonucleic acid (RNA).
Localized in the cytoplasm enzymes of carbohydrate and protein metabolism and other regulating cell energy. In an optical microscope cytoplasm often appears to be homogeneous or poorly structured colloidal mass in which, in addition to the kernel, there are organelles (organelle) and inclusion. The organelles - mandatory (or at least, constantly occurring in certain categories of cells) components of cytoplasm that performs a specific function and has a definite structure, the most corresponding to this function. The organelles are referred mitochondria, Golgi apparatus, cell centre, plastids of plant cells and other On - time education, associated with one or another stage of cell metabolism (secretion, deposition of waste substances, plastic and energy back substances, and so on). The most widespread inclusion of neutral fats and glycogen. The cytoplasm is painted acid dyes, and then it manifest two zones : Central, with a small viscosity and containing a large number of inclusions (endoplasm), and peripheral high density and inclusions (ectoplasm). The peripheral layer of ectoplasm (surface, or cortical) has a number of important properties, ensuring processes of chemical and physical interactions between the cell and the environment. In the cytoplasm of some cells (secretory, salivary and pancreas, blood) find sharply basophilic areas - elastoplast.
A significant change in views on the structure of the cytoplasm occurred in connection with the use of an electron microscope. It turned out that the cytoplasm consists of a base material (the matrix, hyaloplasm), which contains two other important component - the endoplasmic network and ribosomes, and in addition, the organelles and inclusions. Hyaloplasm - liquid or semi-continuous in the phase between denser components of cytoplasm. Hyaloplasm homogeneous or fine, but sometimes it find fibrillar components (so-called structural proteins), creating some stability to this part of the cytoplasm and explain these properties, as elasticity, airway, stability (rigidity) and other Viscosity of cytoplasm even the same type of cells of various: in the sea urchin eggs she is 3 SDRs, and in the ciliate the Paramecia - 8000 SDRs.


Endoplasmic network (so named because it was first described in the inner parts of the cell) is a system of double membranes, between which there is space, forming tubules, bubbles and extended cavity of the tank. Endoplasmic network, forming the so-called using the cell system, connects the entire surface membrane of the cell cytoplasm, mitochondria and nuclear membrane. Due to the existence of such a connection possible continuous metabolic exchange between all parts of the cell.
On the outer surface membranes of endoplasmic basophilic territories (elastoplast) are the many ribosomes (granular type of endoplasmic reticulum); smooth type of organoid typical areas in which the synthesis of fats and carbohydrates. Endoplasmic network is found in all cells (except for the Mature erythrocytes mammals), but it is poorly developed in undifferentiated (for example, embryonic) cells and gets the most significant development in actively metabolish cells. Ribosomes - granules in diameter 150-350+. the necessary component of the cytoplasm. In the most primitive built cells they reside freely in hyaloplasm, in more highly organized, usually associated with the endoplasmic network. Ribosomes contain amino acids and RNA. The last thread connects them in active complexes, bearing the name of poliribonat. The main function of these organelles is the synthesis of a specific protein, a process in which the decisive role is played by the so-called messenger RNA.
The cell membrane surface area of cytoplasm - has a thickness of 70-120 + and consists of one lipoid and two protein layers; it is the existence of this shell determines the selective permeability of the cell for a number of substances. Surface area of cytoplasm carries out the initial stages of the process of phagocytosis (see), i.e., seizing solids, and pinocytosis (cm ), ingestion of liquids, which is crucial with the active penetration of these substances in the cell or protective capture it pathogens (bacteria, protozoa). In the cytoplasm occurs in some cases, the process of neutralizing them, while others (for example, viral infections), on the contrary,their reproduction.
The cytoplasm is the carrier of a hereditary units, determining the properties of the body that could be transmitted to the offspring (cytoplasmic inheritance). Correns (C. Correns) first showed that pestresistant and defects chloropropane in plants depends on the presence and distribution of colorless and colored organelles - plastids responsible for education in plant cell organic substances from water and carbon dioxide with the help of sunlight. Thus, through the cytoplasm passed to certain hereditary characteristics. Phenomena cytoplasmic inheritance, first described in plants, were then found in a variety of organisms. So, Efrussi (Century Ephrussi) showed that, influencing acridine connections, you can get a small hereditary race yeast. Its appearance is related to the changes of mitochondria. In Drosophila with cytoplasmic inheritance transmitted through the egg, connected to different sensitivity to the action of CO2. Finally, the antigenic properties of the cells of humans and animals that are transmitted from one generation to another are also, obviously, cytoplasmic inheritance. However, one should not assume that the properties of cytoplasm, including its participation in the inheritance of traits distinct from the properties of other components of cells, primarily kernel. Due to the existence using membrane system there is continuous communication for the exchange of materials between all components of the cell. It is especially increasing in some periods of life of the cells. So, in the fission process is mixed nuclear matter and cytoplasm and from the resulting mikoplazmy formed mitotic apparatus (see Mitosis).
The processes of synthesis of proteins in the cytoplasm begin with the output from the kernel the messenger RNA (see Nucleic acid).
Cm. also the Cell.