Features of the structure of the nucleus. Structure and functions of the cell nucleus

The nucleus of the cell is the most important organelle, the place of storage and reproduction of hereditary information. It is a membrane structure that occupies 10-40% of cells, the functions of which are very important for the life of eukaryotes. However, even without a kernel, the realization of hereditary information is possible. An example of this process is the vital activity of bacterial cells. Nevertheless, the features of the structure of the nucleus and its function are very important for a multicellular organism.

The location of the nucleus in the cell and its structure

The nucleus is located in the thickness of the cytoplasm and directly contacts the rough and smooth endoplasmic reticulum. It is surrounded by two membranes, between which is the perinuclear space. Inside the core there is a matrix, chromatin and a number of nucleoli.

Some mature human cells do not have a nucleus, while others function in conditions of severe oppression of its activity. In general, the structure of the nucleus (scheme) is represented as a nuclear cavity, bounded by a karyolemma from the cell, containing chromatin and nucleoli, fixed in the nucleoplasm by a nuclear matrix.

The structure of karyolemma

For the convenience of studying the nucleus cells, the latter should be perceived as bubbles confined to shells from other vesicles. The nucleus is a bubble with hereditary information, located in the thickness of the cell. From its cytoplasm, it is protected by a bilayer lipid coat. The structure of the shell of the nucleus is similar to the cell membrane. In reality, only the name and number of layers distinguish them. Without all this, they are the same in structure and function.

The structure of the karyolemma (nuclear membrane) is two-layered: it consists of two lipid layers. The outer bilipid layer of the karyolemma is directly in contact with the rough reticulum of the endoplasma of the cell. Inner karyolma - with the contents of the nucleus. Between the outer and inner karyomembryna there is a perinuclear space. Apparently, it was formed due to electrostatic phenomena - repulsion of the areas of glycerin residues.

The function of the nuclear membrane is to create a mechanical barrier separating the nucleus and the cytoplasm. The inner membrane of the nucleus serves as a fixation site for the nuclear matrix, a chain of protein molecules that support a three-dimensional structure. In two nuclear membranes, there are special pores: through them, information RNA leaves the cytoplasm to the ribosomes. In the very core of the nucleus there are several nucleoli and chromatin.

Internal structure of nucleoplasm

Features of the structure of the nucleus allow you to compare it with the cell itself. Inside the nucleus there is also a special medium (nucleoplasm), represented by a gel-sol, a colloidal solution of proteins. Inside it there is a nucleoskeleton (matrix), represented by fibrillar proteins. The main difference is that the nucleus contains mainly acidic proteins. Apparently, such a reaction of the medium is needed to preserve the chemical properties of nucleic acids and the course of biochemical reactions.

Nucleolus

The structure of the cell nucleus can not be completed without the nucleolus. He is a spiralized ribosomal RNA, which is in the ripening stage. Later, it will produce a ribosome - an organelle, necessary for protein synthesis. In the structure of the nucleolus two components are distinguished: fibrillar and globular. They differ only in electron microscopy and do not have their membranes.

The fibrillar component is located in the center of the nucleolus. It is a ribosomal type RNA, from which the ribosomal subunits will be assembled. If we consider the nucleus (structure and functions), then it is obvious that a granular component will subsequently be formed from them. These are the same maturing ribosomal subunits, which are at the later stages of their development. Of these, ribosomes are soon formed. They are removed from the nucleoplasm through the nuclear pores of the karyolemma and enter the membrane of the rough endoplasmic reticulum.

Chromatin and chromosomes

The structure and functions of the nucleus of the cell are organically linked: there are only those structures that are necessary for storing and reproducing hereditary information. There is also a carioskeleton (core matrix), whose function is to maintain the shape of the organelle. However, the most important constituent of the nucleus is chromatin. These are chromosomes, playing the role of card files of various groups of genes.

Chromatin is a complex protein that consists of a quaternary polypeptide linked to a nucleic acid (RNA or DNA). In plasmids of bacteria, chromatin is also present. Almost a quarter of the total chromatin weight is made up of histones - proteins responsible for the "packing" of hereditary information. This feature of the structure is studied by biochemistry and biology. The structure of the nucleus is complex precisely because of the chromatin and the presence of processes alternating its spiralization and despiralization.

The presence of histones makes it possible to compact and complete the strand of DNA in a small place - in the nucleus of the cell. This happens in the following way: histones form nucleosomes, which is a structure like beads. H2B, H3, H2A and H4 are the main histone proteins. The nucleosome is formed by four pairs of each of the presented histones. In this case, histone H1 is a linker: it is linked to DNA at the site of entry into the nucleosome. Packaging of DNA occurs as a result of the "winding" of a linear molecule into 8 proteins of the histone structure.

The structure of the nucleus, the scheme of which is presented above, assumes the presence of a solenoid-like structure of DNA, complete with histones. The thickness of this conglomerate is about 30 nm. In this case, the structure can be compacted further to occupy less space and less to undergo mechanical damage, inevitably occurring during the life of the cell.

Chromatin Fractions

The structure, structure and functions of the cell nucleus are looped on to support the dynamic processes of spiralization and despiralization of chromatin. Therefore, there are two main fractions: highly spiraling (heterochromatin) and sparse (euchromatin). They are divided both structurally and functionally. In heterochromatin, DNA is well protected against any effects and can not be transcribed. Euchromatin is less well protected, but genes can double for protein synthesis. Most often, heterochromatin and euchromatin regions alternate throughout the length of the entire chromosome.

Chromosomes

The cell nucleus, whose structure and functions are described in this publication, contains chromosomes. It is a complex and compactly packed chromatin, which can be seen with light microscopy. However, this is possible only if the cell is located on the slide in the stage of mitotic or meiotic division. One of the stages is chromatin chromatin co-chromatization. Their structure is extremely simple: the chromosome has a telomer and two arms. Each multicellular organism of the same species has the same core structure. The table of the chromosome set is also similar.

Implementing kernel functions

The main features of the structure of the kernel are associated with the performance of certain functions and the need for their control. The nucleus plays the role of a repository of hereditary information, that is, it is a sort of card file with recorded amino acid sequences of all proteins that can be synthesized in the cell. Hence, to perform a function, the cell must synthesize a protein whose structure is encoded in the gene.

In order for the nucleus to "understand" which specific protein should be synthesized at the right time, there is a system of external (membrane) and internal receptors. Information from them comes to the nucleus through molecular transmitters. This is most often realized by an adenylate cyclase mechanism. So the cell affects the hormones (adrenaline, norepinephrine) and some drugs with a hydrophilic structure.

The second mechanism for transferring information is internal. It is characteristic of lipophilic molecules - corticosteroids. This substance penetrates the bilipid membrane of the cell and is directed to the nucleus, where it interacts with its receptor. As a result of activation of receptor complexes located on the cell membrane (adenylate cyclase mechanism) or on the karyolemma, activation of a specific gene is triggered. It replicates, it is based on information RNA. Later, the structure of the latter synthesizes a protein that performs a certain function.

The nucleus of multicellular organisms

In a multicellular organism, the features of the structure of the nucleus are the same as in the unicellular organism. Although there are some nuances. First, multicellularity implies that a number of cells will have their own specific function (or several). This means that some genes will always be despiralized, while others are in an inactive state.

For example, in fatty tissue cells protein synthesis will go inactive, and therefore most of the chromatin is helical. And in cells, for example, the exocrine part of the pancreas, the processes of protein biosynthesis go on constantly. Because their chromatin is despiralized. On those sites, whose genes are replicated most often. At the same time, a key feature is important: the chromosome set of all cells of the same organism is the same. Only because of the differentiation of functions in the tissues, some of them are turned off from work, while others are despiralized more often than others.

Nuclear-free cells of the body

There are cells, the features of the structure of the nucleus which may not be considered, because they either depress its function as a result of its vital activity, or completely get rid of it. The simplest example is erythrocytes. These are blood cells, the nucleus of which is present only in the early stages of development, when hemoglobin is synthesized. As soon as its quantity is sufficient for the transfer of oxygen, the nucleus is removed from the cell in order to facilitate it not to interfere with the transport of oxygen.

In general, the erythrocyte is a cytoplasmic bag filled with hemoglobin. A similar structure is characteristic of fat cells. The structure of the cell nucleus of adipocytes is extremely simplified, it decreases and shifts to the membrane, and the processes of protein synthesis are maximally inhibited. These cells also resemble "bags" filled with fat, although, of course, the variety of biochemical reactions in them is slightly higher than in erythrocytes. Platelets also do not have a nucleus, but they should not be considered as full cells. These are the fragments of cells necessary for the realization of hemostasis processes.