The nucleus of the cell

The nucleus of the cell is one of the basic constituents of all plant and animal cells, is inextricably linked with metabolism, reproduction, transmission of hereditary information and other
Form the nucleus of the cell varies depending on the type of cell. There are oval, spherical, and irregular shape - horseshoe or multi-core cells (leukocytes), beadlike the nucleus of the cell (some of infusoria)branched the nucleus of the cell (in glandular cells of insects) and other nuclear Magnitude cells of various, but usually related to the volume of the cytoplasm. Violation of this ratio in the growth of cells leads to cell division. The number of nuclei of cells are also different : most of the cells has one core, though there are dual-core and multi-core cells (for example, some liver cells and bone marrow). The position of the nucleus in the cell is a characteristic of cells of each type. Germ cells, the kernel is usually located in the centre of the cell, but may shift with the development of cells and education in the cytoplasm of specialized sections or deposits it back substances.
In the cell nucleus distinguish the basic structures: 1) nuclear shell (nuclear membrane), through the pores of which is exchanged between the cell nucleus and cytoplasm [there is evidence suggesting that the nuclear membrane (consisting of two layers) without a break goes into the membranes of endoplasmic reticulum (see Cytoplasm) and complex Golgi]; 2) nuclear juice, or the karyoplasm lying,- semi-liquid, poorly painted plasma mass, filling all the nucleus of the cell and contains other engine components; 3) the chromosomes (see), in which non-fissile core visible only with the help of special methods microscopy (painted cut non-dividing cells, the chromosomes are typically incorrect network of dark fibers and seeds, collectively called chromatin); 4) one or more spherical Taurus - nucleoli, which is a specialized part of the nucleus of the cell and connected with the synthesis of RNA and proteins.
The nucleus of the cell has a complex chemical organization, which is essential nucleoproteins - product compounds of nucleic acids and proteins. In the life of the cells there are two main periods: interphase, or metabolic, and mitotic, or the period of division. Both periods are characterized mainly by changes in the structure of the nucleus of the cell. In the interphase nucleus is in a dormant condition and is involved in protein synthesis, regulation of formation, process of secretion, and other survival items cells. In the period of division in the nucleus of the cell changes that lead to the redistribution of chromosomes and education of the daughter nuclei of cells; hereditary information is transmitted, thus, through nuclear structure to a new generation of cells.
The nucleus of the cell only multiply by division, and in most cases are divided, and the cells themselves. Usually distinguished: direct fission of the nucleus of the cell by peregorodki - amicos and the most common way of fission cell - typical indirect division, or mitosis (see).
The action of ionizing radiation and other factors can change the prisoner in the cell nucleus genetic information, leading to different changes nuclear device that can sometimes cause the death of cells or cause hereditary abnormalities in the offspring (see Heredity), So the study of the structure and functions of the nucleus of the cell, especially the links between chromosomal relations and inheritance, which is engaged in cytogenetics, has significant practical value for medicine (see Cytogenetic tests).
Cm. also the Cell.

The nucleus of the cell - the most important part of all plant and animal cells.
The cell, stripped kernel or damaged by the kernel is not able to properly perform its functions. The nucleus of the cell, rather, organized in the chromosomes (see) deoxyribonucleic acid (DNA),the carrier of genetic information that determines all the features of cells, tissues and whole organism, its ontogenesis and the body's own norms response to environmental impact. Enclosed in the core of hereditary information encoded in the components of chromosome DNA sequence of four nitrogenous bases: adenine, thymine, guanine and cytosine. This sequence is the matrix, which determines the structure of synthesized in the cell proteins.
Even minor violations of the structure of the nucleus of the cell lead to irreversible changes in cell behavior or death. The danger of ionizing radiation and many chemicals for inheritance (see) and for the normal development of the fetus is based on damage nuclei in germ cells of adult organism or in somatic cells of the developing embryo. In the basis of transformation of normal cells into malignant also are certain violations of the structure of the nucleus of the cell.
The size and shape of the nucleus of the cell and the ratio of its size and volume of the entire cell is specific to the various tissues. One of the main features that distinguish elements of white and red blood, are the shape and size of their nuclei. The nucleus of cells can be irregular: / Bently-kolbasino, his or beadlike; in the latter case, every part of the engine is connected to the neighbouring thin crosspiece. In Mature male sex cells (sperm) the nucleus of the cell is the bulk of the total volume of the cell.
Mature erythrocytes (see) of humans and mammals do not have a kernel, as they lose it in the process of differentiation. They have a limited life and is not able to reproduce. In bacteria and blue-green algae no sharply defined nucleus. However, they contain all characteristic of the nucleus of the cell chemicals, distributed by division for the child cells with the same accuracy as in the cells of higher multicellular organisms. Viruses and phages kernel represented by a single DNA molecule.
When considering stationary (non-dividing cells in a light microscope, the nucleus of the cell can be unstructured bubble with one or more nuclei. The nucleus of the cell is well painted special nuclear paints (hematoxylin, methylene blue, safranin and others)that are commonly used in laboratory practice. Using phase-contrast device the nucleus of the cell to explore and lifetime. In recent years, to study the processes taking place in the cell nucleus, is widely used microcinematography, tracers C14 and N3 (autoradiography) and microspectrophotometry. The last method is particularly successfully used to study the quantitative changes of DNA in the nucleus in the process of the life cycle of cells. Electron microscope allows you to reveal details of the fine structure of the kernel resting cells, undetectable in the optical microscope (Fig. 1).

the scheme of the structure of cells
Fig. 1. Modern scheme of the structure of cells, based on observations in the electronic microscope: 1 - the cytoplasm; 2 - the Golgi apparatus; 3 - the centrosome; 4 - endoplasmic reticulum; 5 - mitochondria; 6 - sheath cells; 7 - shell nuclei; 8 - centered; 9 - kernel.

When cells divide - mitosis or mitosis (see) - the nucleus of the cell undergoes a series of complex transformation (Fig. 2), during which become clearly visible its chromosomes. Before cell division each chromosome engine synthesizes substance that is present in nuclear juice, similar, then parent chromosomes apart to opposite poles dividing cells. As a result, each daughter cell receives the same chromosome set, what was the maternal cells, and with it contained in it hereditary information. Mitosis provides the perfect separation of all the chromosomes of the nucleus into two equal parts.
Mitosis and meiosis (see) are the most important mechanisms of the phenomena of heredity. Some of the simplest organisms, and also in pathological cases in mammals and humans kernel cells divide by simple banners, or amitiza. In recent years shows that when amitone processes that ensure the separation of the nucleus of the cell into two equal parts.
Chromosomes in the cell nucleus individuals called the karyotype (see). Karyotype in all the cells of the individual, generally the same. Many congenital anomalies and deformities (syndromes down, Kleinfelter, Turner-Shereshevsky and others) due to various violations of the karyotype arising out of or in the early stages of embryogenesis or during maturation of the reproductive cells, from which arose the anomalous specimen. Anomalies of development that are associated with visible disabilities chromosomal structures the nucleus of the cell, called a chromosome diseases (see Hereditary diseases). A variety of chromosome damage can be caused by physical or chemical mutagens (Fig. 3). Nowadays methods, allowing to quickly and precisely identify the human karyotype is used for early diagnosis of chromosomal diseases and to clarify the etiology of certain diseases.

stage mitoza in cells
Fig. 2. Stage mitoza in tissue culture cells person (transplantable strain ner-2): 1 - early profesa; 2 - late profesa (disappearance of the nuclear envelope); 3 - metaphase (stage parent star), top view; 4 - metaphase, side view; 5 - anaphase the beginning of a divergence of chromosomes; 6 - anaphase chromosome parted; 7 - telophase, stage of child balls; 8 - telophase and separation of cell in the body.
damage of chromosomes
Fig. 3. Of chromosome damage caused by ionizing radiation and chemical mutagens: 1 - normal telophase; 2-4 - telepathy with bridges and fragments in embryonic fibroblasts exposed to x-rays in a dose of 10 R; 5 and 6 - the same in hematopoietic cells Guinea pigs; 7 - chromosomal bridge in the epithelium of the cornea mouse, irradiated at doses of 25 R; 8 - fragmentation of chromosomes in embryonic fibroblasts caused by nitrozometilmocevina.

Important organoid the nucleus of the cell is the nucleus, is the product of vital activity of chromosomes. It produces ribonucleic acid (RNA), which is mandatory intermediate in the synthesis of protein produced by every cell.
The nucleus of the cell is separated from the surrounding cytoplasm (see) shell, the thickness of which 60-70+.
Through pores in the shell substance synthesized in the kernel, enter the cytoplasm. The space between the shell to the kernel and all its organelles filled karyoplasm lying, consisting of basic and acid proteins, enzymes, nucleotides, inorganic salts and other low-molecular compounds necessary for the synthesis of child chromosomes in the fission of the nucleus of the cell.
Cm. also the Cell.