The structure of the cell center. Features of the structure of the cell center
It was proved that cells of eukaryotic organismsare represented by a system of membranes forming organoids of the protein-phospholipid composition. However, there is an important exception to this rule. Two organelles (cell center and ribosome), as well as organelles of movement (flagella and cilia) have a non-membrane structure. What are they educated? In this paper we will try to find the answer to this question, and also we will study the structure of the cellular center of the cell, often called the centrosome.
Do all cells contain a cell center
The first fact that interested scientists isoptional presence of this organoid. Thus, in the lower fungi - chitridiomycetes - and in higher plants it is absent. As it turned out, in algae, in human cells and in most animals, the presence of a cell center is necessary for the realization of processes of mitosis and meiosis. The first way to divide somatic cells, and others - sex. A centrosome is an obligatory participant in both processes. The divergence of its centrioles to the poles of the dividing cell and the tension between the filament spindle threads also ensures a further divergence of the chromosomes attached to these filaments and to the poles of the mother cell.
Microscopic studies revealed featuresstructure of the cell center. It includes from one to several dense corpuscles - centrioles, from which the microtubules divergingly fan out. We will study in more detail the appearance, as well as the structure of the cell center.
Centrosome in an interphase cell
In the life cycle of cells, the cell center can beSee in a period called interphase. Near the core membrane there are usually two microcylinders. Each of them consists of protein tubes, collected in three pieces (triplets). Nine such structures form the surface of a centriole. If there are two of them (which happens most often), they are located at right angles to each other. In the period of life between two divisions, the structure of the cell center in the cell is almost the same for all eukaryotes.
Ultrastructure of the centrosome
To study the structure of the cell centerpossible as a result of using an electron microscope. Scientists have established that cylinders of centrosomes have the following dimensions: their length is 0.3-0.5 microns, diameter is 0.2 microns. The number of centrioles before division begins necessarily doubles. This is necessary so that the mother and daughter cells themselves, as a result of division, receive a cell center consisting of two centrioles. Features of the structure of the cell center are that the centrioles that make up it are not equivalent: one of them - mature (maternal) - contains additional elements: the pericentriolar satellite and its appendages. The immature centriole has a specific area called the wheel of a wheel.
The behavior of the centrosome in mitosis
It is well known that the growth of the body, as well as itsreproduction occurs at the level of an elementary unit of living nature, which is a cell. The structure of the cell, the localization and functions of the cell, as well as its organoids, are examined by cytology. Despite the fact that the scientists have conducted quite a lot of research, the cell center is still not fully understood, although its role in cell division has been fully clarified. In the prophase of mitosis and in the prophase of the reductive division of meiosis, the centrioles diverge to the poles of the maternal cell, and then the filament of the fission spindle is formed. They are attached to the centromeres of the primary constriction of chromosomes. Why is it necessary?
Spindle of anaphase cell division
Experiments G. Boveri, A. Neil and other scientists have made it possible to establish that the structure of the cell center and its functions are interrelated. The presence of two centrioles, bipolar with respect to the poles of the cell, and the spindle spindle between them, ensures a uniform distribution of chromosomes connected to microtubules to each of the poles of the mother cell.
Thus, the number of chromosomes will bethe same in the daughter cells as a result of mitosis or half as much (in meiosis) than in the original maternal cell. Particularly interesting is the fact that the structure of the cell center changes and is correlated with the stages of the cell's life cycle.
Chemical analysis of organelles
To better understand the functions and role of the centrosomewe will study what organic compounds are included in its composition. As you might expect, proteins are the leading ones. Suffice it to recall that the structure and functions of the cell membrane also depend on the presence of peptide molecules in it. Note that in the centrosome, proteins have a contractile ability. They are part of microtubules and are called tubulins. Studying the external and internal structure of the cell center, we mentioned auxiliary elements: pericentriolar satellites and appendages of centrioles. They include vesicin and mycithin.
There are also proteins that regulate metabolismorganoid. This kinase and phosphatase are special peptides responsible for the nucleation of microtubules, that is, for the formation of an active seed molecule, with which growth and synthesis of radial microfilaments begins.
Cellular center as an organizer of fibrillar proteins
In cytology was finally fixedrepresentation of the centrosome as the main organelle responsible for the formation of microtubules. Thanks to the generalization of research, Fulton can claim that the cell center provides this process in four ways. For example: polymerization of filament spindle fibers, the formation of percentoryles, the creation of a radial microtubule system of the interphase cell and, finally, the synthesis of elements in the primary cilium. This is a special education, characteristic of the maternal centriole. Studying the structure and functions of the cell membrane, scientists detect it under an electron microscope in the cell center after mitotic division of the cell or at the time of the onset of mitosis. In the G2 phase of the interphase, as well as in the early stages of prophase, the cilium disappears. According to the chemical composition, it consists of their tubulin molecules and is a label on which it is possible to identify a mature mother centriole. So how does the maturation of the centrosome occur? Consider all the nuances of this process.
Stages of centriole formation
Cytologists have established that the daughter and maternalcentrioles, forming a diplosome, are not identical in their structure. Thus, the mature structure is bordered by a layer of pericentriolar substance, the mitotic halo. Full maturation of the daughter centriole takes longer than one cell life cycle. At the end of stage G1 of the second cell cycle, the new centriole already acts as the organizer of microtubules and is capable of forming filament spindle threads, as well as the formation of special organelles of movement. They can be cilia and flagella found in unicellular protozoa (eg, euglenae of green, infusoria-shoe), as well as in many algae, for example chlamydomonades. The flagella formed by the microtubules of the cell center are equipped with many spores in algae, as well as sex cells of animals and humans.
The role of the centrosome in the life of the cell
So, we were convinced that one of the mostsmall cell organelles (occupying less than 1% of the cell volume) plays a leading role in the regulation of the metabolism of both plant and animal cells. Violation of the fission spindle formation entails the formation of genetically defective daughter cells. Their sets of chromosomes differ from the normal number, which leads to chromosomal aberrations. As a result - the development of abnormal individuals or their death. In medicine, the fact of the relationship between the number of centrioles and the risk of oncological diseases has been established. For example, if normal skin cells contain 2 centrioles, then tissue biopsy in case of skin cancer reveals an increase in their number to 4-6. These results serve as evidence of the centrosome's key role in controlling cell division. The latest experimental data indicate the important role of this organelle in the processes of intracellular transport. The unique structure of the cell center allows it to regulate both the shape of the cell and its alteration. In a normally developing unit, the centrosome is located next to the Golgi apparatus, close to the nucleus, and together with them provides integrative and signaling functions in the implementation of mitosis, meiosis, and programmed cell death, apoptosis. That is why modern cytologists consider centrosome an important uniting organoid of the cell, responsible both for its division and for the whole metabolism.