What is a cell nucleus in brief? What is a nucleus - in biology: properties and functions

The nucleus is the main component of a living cell, which carries hereditary information encoded by a set of genes. It occupies a central position in the cell. Sizes vary, the shape is usually spherical or oval. The diameter of the nucleus in different cells can be from 8 to 25 microns. There are exceptions, for example, fish eggs have nuclei with a diameter of 1 mm.

Features of the structure of the nucleus

The core is filled with liquid and several structural elements. It contains a shell, a set of chromosomes, nucleoplasm, and a nucleolus. The shell is double-membrane; between the membranes there is a perinuclear space.

Outer membrane similar in structure to the endoplasmic reticulum. It is connected to the ER, which seems to branch off from the nuclear envelope. Ribosomes are located outside the nucleus.

Inner membrane durable, as it contains lamina. It performs a supporting function and serves as an attachment point for chromatin.

The membrane has pores that ensure exchange processes with the cytoplasm. Nuclear pores consist of transport proteins that deliver substances into the karyoplasm by active transport. Only small molecules can pass through the pore openings passively. Also, each pore is covered with a porosoma, which regulates metabolic processes in the nucleus.

Number of Cores varies in cells with different specializations. In most cases, the cells are mononuclear, but there are tissues built from multinucleated cells (liver or brain tissue). There are cells without a nucleus - these are mature red blood cells.

In protozoa, there are two types of nuclei: some are responsible for storing information, others are responsible for protein synthesis.

The nucleus can be in a state of rest (interphase period) or division. Moving into interphase, it looks like a spherical formation with many white granules (chromatin). There are two types of chromatin: heterochromatin and euchromatin.

Euchromatin is an active chromatin that maintains a despiralized structure in the resting nucleus and is capable of intense RNA synthesis.

Heterochromatin is areas of chromatin that are in a condensed state. It can, if necessary, switch to a euchromatic state.

When using the cytological method of staining the nucleus (according to Romanovsky-Giemsa), it was revealed that heterochromatin changes color, but euchromatin does not. Chromatin is made up of nucleoprotein strands called chromosomes. Chromosomes carry the basic genetic information of each person. Chromatin is a form of existence of hereditary information in the interphase period of the cell cycle; during division it is transformed into chromosomes.

Chromosome structure

Each chromosome is made up of a pair of chromatids that are parallel to each other and connected only at one place - the centromere. The centromere divides the chromosome into two arms. Depending on the length of the arms, three types of chromosomes are distinguished:

Equal shoulders;
diversity,
one-shoulder

Some chromosomes have an additional section that is attached to the main one by thread-like connections - this is a satellite. Satellites help identify different pairs of chromosomes.

The metaphase nucleus is a plate where the chromosomes are located. It is during this phase of mitosis that the number and structure of chromosomes is studied. During metaphase, sister chromosomes move to the center and split into two chromatids.

Structure of the nucleolus

The nucleus also contains a non-membrane formation - the nucleolus. The nucleoli are compacted, round bodies capable of refracting light. This is the main site of synthesis of ribosomal RNA and essential proteins.

The number of nucleoli varies in different cells; they can unite into one large formation or exist separately from each other in the form of small particles. When synthetic processes are activated, the volume of the nucleolus increases. It lacks a shell and is surrounded by condensed chromatin. The nucleolus also contains metals, mostly zinc. Thus, the nucleolus is a dynamic, changing formation necessary for the synthesis of RNA and its transport into the cytoplasm.

Nucleoplasm fills the entire internal space of the nucleus. The nucleoplasm contains DNA, RNA, protein molecules, and enzymatic substances.

Functions of the nucleus in a cell

Takes part in the synthesis of protein and ribosomal RNA.
Regulates the functional activity of the cell.
Preservation of genetic information, its accurate replication and transmission to offspring.

Role and significance of the kernel

The nucleus is the main repository of hereditary information and determines the phenotype of the organism. In the nucleus, DNA exists unchanged thanks to nuclear repair enzymes that can eliminate damage and mutations. During cell division, nuclear mechanisms ensure that genetic information is distributed accurately and evenly to daughter cells.

The cell nucleus is a structure surrounded by membranes that contains hereditary information and controls growth and reproduction. This is the command center of the eukaryotic cell and, as a rule, the most significant.

Structure and significance of the cell nucleus

Kernel structure diagram / Wikimedia

The cell nucleus is surrounded by a double membrane called the nuclear envelope. This membrane separates the contents of the nucleus from.

Like the cell membrane, the nuclear envelope is composed of phospholipids that form a lipid bilayer. It helps maintain the shape of the nucleus and regulates the flow of molecules into and out of the nucleus through nuclear pores.

Chromosomes are located inside the nucleus. They consist of DNA, which contains information about the heredity, growth, development and reproduction of cells. When a cell is in a state of “rest,” that is, not dividing, the chromosomes are organized into long, tangled structures called , rather than into individual chromosomes as we usually think of.

Nucleolus

Inside the nucleus is a dense structure made of RNA and proteins called the nucleolus, which contains nucleolar organizers, which are parts of chromosomes with genes for the synthesis of ribosomes. The nucleolus helps synthesize ribosomes by transcribing and assembling ribosomal RNA. The ribosome is made up of ribosomal RNA (rRNA) and proteins.

Protein synthesis

The nucleus regulates protein synthesis in the cytoplasm using messenger RNA (mRNA), which is a transcribed segment of DNA that serves as a template for protein production. It is produced in the nucleus and moves into the cytoplasm through nuclear pores in the membrane.

Once in the cytoplasm, ribosomes and other RNA molecules called messenger RNA work together to translate the mRNA to produce proteins.

Structure of eukaryotic cells

In addition to the cell nucleus, there are other types of cellular organelles. The following cell structures can also be found in a typical eukaryote:

- help organize the assembly of microtubules.
- storage of cellular DNA.
- provide cellular locomotion.
- protects the integrity of the interior of the cell.
- synthesizes carbohydrates and lipids.

The nucleus is the most important component of the cell. The cell nucleus contains DNA, i.e. genes, and, thanks to this, performs two main functions:

1) storage and reproduction of genetic information

2) regulation of metabolic processes occurring in the cell

A nuclear-free cell cannot exist for a long time, and the nucleus is also not capable of independent existence, therefore the cytoplasm and the nucleus form an interdependent system. Most cells have one nucleus. It is often possible to observe 2-3 nuclei in one, for example in liver cells. Multinucleate cells are also known, and the number of nuclei can reach several dozen. The shape of the nucleus depends largely on the shape of the cell; it can be completely irregular. There are spherical and multi-lobed kernels. Invaginations and outgrowths of the nuclear membrane significantly increase the surface of the nucleus and thereby strengthen the connection of nuclear and cytoplasmic structures and substances.

Core structure

The core is surrounded by a shell, which consists of two membranes with a typical structure. The outer nuclear membrane on the surface facing the cytoplasm is covered with ribosomes, the inner membrane is smooth.

The nuclear envelope is part of the membrane system of the cell. The outgrowths of the outer nuclear membrane connect with the channels of the endoplasmic reticulum, forming a single system of communicating channels. The exchange of substances between the nucleus and the cytoplasm occurs in two main ways. Firstly, the nuclear envelope is penetrated by numerous pores through which molecules are exchanged between the nucleus and the cytoplasm. Secondly, substances from the nucleus into the cytoplasm and back can enter due to the release of invaginations and outgrowths of the nuclear envelope. Despite the active exchange of substances between the nucleus and the cytoplasm, the nuclear envelope limits the nuclear contents from the cytoplasm, thereby ensuring differences in the chemical composition of nuclear juice and cytoplasm. This is necessary for the normal functioning of nuclear structures.

The contents of the nucleus are divided into nuclear juice, chromatin and nucleolus.

In a living cell, nuclear sap looks like a structureless mass that fills the gaps between the structures of the nucleus. Nuclear sap contains various proteins, including most nuclear enzymes, chromatin proteins and ribosomal proteins. Nuclear sap also contains free nucleotides necessary for the construction of DNA molecules and RNA, amino acids, all types of RNA, as well as products of the activity of the nucleolus and chromatin, which are then transported from the nucleus to the cytoplasm.

Chromatin (Greek chroma - color, color) is the name given to clumps, granules and network-like structures of the nucleus, which are intensely stained with some dyes and differ in shape from the nucleolus. Chromatin contains DNA and proteins and represents spiralized and compacted sections of chromosomes. Spiraled sections of chromosomes are genetically inactive.

Their specific role—transfer of genetic information—can only be performed by despiralized-untwisted sections of chromosomes, which, due to their small thickness, are not visible in a light microscope.

In dividing cells, all chromosomes are strongly spiralized, shortened and acquire compact sizes and shapes. A chromosome is an independent nuclear structure that has arms and a primary constriction. The shape of chromosomes depends on the position of the so-called primary constriction, or centormer, the region to which during cell division ( mitosis) spindle filaments are attached. The centromere divides the chromosome into two arms. The location of the centromere determines three main types of chromosomes:

1) equal shoulders - with shoulders of equal or almost equal length;

2) unequal shoulders - with shoulders of unequal length;

3) rod-shaped - with one long and second very short, sometimes difficult to detect, shoulder. There are also point chromosomes with very short arms.

The study of chromosomes made it possible to establish the following facts.

1. In all somatic cells of any plant or animal organism, the number of chromosomes is the same.

2. Sex cells always contain two fewer chromosomes than somatic cells of a given type of organism.

3. All organisms belonging to the same species have the same number of chromosomes in their cells.

The number of chromosomes does not depend on the level of organization and does not always indicate relationship: the same number can be found in systematic groups that are very distant from each other and can be very different in species that are close in origin.

Thus, the number of chromosomes in itself is not a species-specific feature. However, the characteristics of the chromosome set as a whole are species-specific, i.e. characteristic of only one type of organism, plants, plants or animals.

The set of quantitative (number and size) and qualitative (shape) characteristics of the chromosome set of a somatic cell is called a karyotype.

The number of chromosomes in the karyotype of most species of living organisms is even. This is explained by the fact that in somatic cells there are two chromosomes of the same shape and size - one from the paternal organism, the second from the maternal. Chromosomes that are the same in shape and size and carry the same genes are called homologous.

The chromosome set of a somatic cell, in which each chromosome has a pair, is called double or diploid and is designated 2N. The amount of DNA corresponding to a diploid set of chromosomes is designated 2C.

From each pair of homologous chromosomes, only one gets into the germ cells, and therefore the chromosome set of gametes is called single or haploid. The karyotype of such cells is designated 2n1c.

Diploid number of chromosomes in animals and plants.

Type of organisms	Number of chromosomes
Malarial plasmodium	2
Carp	104
Horse roundworm	2
Human	46
Drosophila fruit fly	8
Common ash	46
Head louse	12
Chimpanzee	48
Spinach	12
Cockroach	48
house fly	12
Pepper	48
Triton	24
Domestic sheep	54>
Fur tree, pine tree	24
Domestic dog	78
Perch	28
Pigeon	80

After cell division is completed, the chromosomes are disspiralized, and in the nuclei of the resulting daughter cells only a thin mesh and clumps of chromatin become visible again.

The third structure characteristic of a cell is the nucleolus. It is a dense round body immersed in nuclear juice. In the nuclei of different cells, as well as in the nucleus of the same cell, depending on its functional state, the number of nucleoli can vary from 1 to 5-7 or more. The number of nucleoli may exceed the number of chromosomes in the set; this occurs due to the selective reduplication of genes responsible for rRNA synthesis. Nucleoli are present only in non-dividing nuclei; during mitosis they disappear due to the spiralization of chromosomes and the release of all previously formed ribosomes into the cytoplasm, and after completion of division they appear again.

The nucleolus is not an independent structure of the nucleus. It is formed around the region of the chromosome in which the rRNA structure is encoded. This part of the chromosome - the gene - is called the nucleolar organizer (NO), and r-RNA synthesis occurs on it.

In addition to the accumulation of r-RNA, ribosomal subunits are formed in the nucleolus, which then move into the cytoplasm and, combining with the participation of Ca2+ cations, form integral ribosomes capable of participating in protein biosynthesis.

Thus, the nucleolus is an accumulation of r-RNA and ribosomes at different stages of formation, which is based on a section of the chromosome that carries the gene - the nucleolar organizer, which contains hereditary information about the structure of r-RNA.

The cell nucleus is one of the main components of all plant and animal cells, inextricably linked with exchange, transmission of hereditary information, etc.

The shape of the cell nucleus varies depending on the type of cell. There are oval, spherical and irregularly shaped - horseshoe-shaped or multi-lobed cell nuclei (in leukocytes), bead-shaped cell nuclei (in some ciliates), branched cell nuclei (in glandular cells of insects), etc. The size of the cell nucleus is different, but is usually associated with the volume of the cytoplasm . Violation of this ratio during cell growth leads to cell division. The number of cell nuclei also varies - most cells have one nucleus, although binucleate and multinucleate cells are found (for example, some liver and bone marrow cells). The position of the nucleus in the cell is characteristic of each type of cell. In germ cells, the nucleus is usually located in the center of the cell, but can move as the cell develops and specialized areas are formed in the cytoplasm or reserve substances are deposited in it.

In the cell nucleus, the main structures are distinguished: 1) the nuclear membrane (nuclear membrane), through the pores of which exchange takes place between the cell nucleus and the cytoplasm [there is evidence indicating that the nuclear membrane (consisting of two layers) continuously passes into the membranes of the endoplasmic reticulum (see) and Golgi complex]; 2) nuclear juice, or karyoplasm, a semi-liquid, weakly stained plasmatic mass that fills all cell nuclei and contains the remaining components of the nucleus; 3) (see), which in a non-dividing nucleus are visible only with the help of special microscopy methods (on a stained section of a non-dividing cell, chromosomes usually look like an irregular network of dark strands and grains, collectively called); 4) one or more spherical bodies - nucleoli, which are a specialized part of the cell nucleus and are associated with the synthesis of ribonucleic acid and proteins.

The cell nucleus has a complex chemical organization, in which the most important role is played by nucleoproteins, the product of a combination with proteins. There are two main periods in the life of a cell: interphase, or metabolic, and mitotic, or division period. Both periods are characterized mainly by changes in the structure of the cell nucleus. In interphase, the cell nucleus is in a resting state and participates in protein synthesis, regulation of shape formation, secretion processes and other vital functions of the cell. During the period of division, changes occur in the cell nucleus, leading to the redistribution of chromosomes and the formation of daughter cell nuclei; hereditary information is thus transmitted through nuclear structures to a new generation of cells.

Cell nuclei reproduce only by division, and in most cases the cells themselves also divide. Usually a distinction is made between: direct division of the cell nucleus by ligation - amitosis and the most common way of dividing cell nuclei - typical indirect division, or mitosis (see).

The action of ionizing radiation and some other factors can change the genetic information contained in the cell nucleus, leading to various changes in the nuclear apparatus, which can sometimes lead to the death of the cells themselves or cause hereditary abnormalities in the offspring (see Heredity). Therefore, the study of the structure and functions of the nucleus cells, especially the connections between chromosomal relationships and the inheritance of traits, which are dealt with by cytogenetics, is of significant practical importance for medicine (see).

See also Cell.

The cell nucleus is the most important component of all plant and animal cells.

A cell lacking a nucleus or with a damaged nucleus is unable to perform its functions normally. The cell nucleus, or more precisely, deoxyribonucleic acid (DNA) organized in its chromosomes (see), is the carrier of hereditary information that determines all the characteristics of the cell, tissues and the whole organism, its ontogenesis and the body’s norms of response to environmental influences. The hereditary information contained in the nucleus is encoded in the DNA molecules that make up the chromosome by a sequence of four nitrogenous bases: adenine, thymine, guanine and cytosine. This sequence is the matrix that determines the structure of proteins synthesized in the cell.

Even the most minor disturbances in the structure of the cell nucleus lead to irreversible changes in the properties of the cell or to its death. The danger of ionizing radiation and many chemicals for heredity (see) and for the normal development of the fetus is based on damage to the nuclei in the germ cells of an adult organism or in the somatic cells of a developing embryo. The transformation of a normal cell into a malignant one is also based on certain disturbances in the structure of the cell nucleus.

The size and shape of the cell nucleus and the ratio of its volume to the volume of the entire cell are characteristic of various tissues. One of the main characteristics that distinguishes the elements of white and red blood is the shape and size of their nuclei. The nuclei of leukocytes can be irregular in shape: curved-sausage-shaped, claw-shaped or bead-shaped; in the latter case, each section of the core is connected to the neighboring one by a thin jumper. In mature male germ cells (sperm), the cell nucleus makes up the vast majority of the total cell volume.

Mature erythrocytes (see) of humans and mammals do not have a nucleus, since they lose it during the process of differentiation. They have a limited lifespan and are unable to reproduce. The cells of bacteria and blue-green algae lack a sharply defined nucleus. However, they contain all the chemical substances characteristic of the cell nucleus, which are distributed during division into daughter cells with the same regularity as in the cells of higher multicellular organisms. In viruses and phages, the nucleus is represented by a single DNA molecule.

When examining a resting (non-dividing) cell under a light microscope, the cell nucleus may have the appearance of a structureless vesicle with one or several nucleoli. The cell nucleus is well stained with special nuclear dyes (hematoxylin, methylene blue, safranin, etc.), which are usually used in laboratory practice. Using a phase-contrast device, the cell nucleus can be examined intravitally. In recent years, microcinematography, labeled C14 and H3 atoms (autoradiography) and microspectrophotometry have been widely used to study the processes occurring in the cell nucleus. The latter method is especially successfully used to study quantitative changes in DNA in the nucleus during the cell life cycle. An electron microscope allows one to reveal details of the fine structure of the nucleus of a resting cell that are undetectable in an optical microscope (Fig. 1).

Rice. 1. Modern diagram of the cell structure, based on observations in an electron microscope: 1 - cytoplasm; 2 - Golgi apparatus; 3 - centrosomes; 4 - endoplasmic reticulum; 5 - mitochondria; 6 - cell membrane; 7 - core shell; 8 - nucleolus; 9 - core.

During cell division - karyokinesis or mitosis (see) - the cell nucleus undergoes a series of complex transformations (Fig. 2), during which its chromosomes become clearly visible. Before cell division, each chromosome of the nucleus synthesizes a similar one from substances present in the nuclear sap, after which the mother and daughter chromosomes diverge to opposite poles of the dividing cell. As a result, each daughter cell receives the same chromosome set as the mother cell had, and with it the hereditary information contained in it. Mitosis ensures the ideally correct division of all chromosomes of the nucleus into two equal parts.

Mitosis and meiosis (see) are the most important mechanisms that ensure the patterns of heredity phenomena. In some simple organisms, as well as in pathological cases in mammalian and human cells, cell nuclei divide by simple constriction, or amitosis. In recent years, it has been shown that even during amitosis, processes occur that ensure the division of the cell nucleus into two equal parts.

The set of chromosomes in the nucleus of an individual’s cell is called a karyotype (see). The karyotype in all cells of a given individual is usually the same. Many congenital anomalies and deformities (Down syndrome, Klinefelter syndrome, Turner-Shereshevsky syndrome, etc.) are caused by various karyotype abnormalities that arose either in the early stages of embryogenesis or during the maturation of the germ cell from which the abnormal individual arose. Developmental anomalies associated with visible disturbances in the chromosomal structures of the cell nucleus are called chromosomal diseases (see Hereditary diseases). Various chromosome damage can be caused by the action of physical or chemical mutagens (Fig. 3). Currently, methods that make it possible to quickly and accurately establish a person’s karyotype are used for early diagnosis of chromosomal diseases and to clarify the etiology of certain diseases.

Rice. 2. Stages of mitosis in human tissue culture cells (transplantable strain HEp-2): 1 - early prophase; 2 - late prophase (disappearance of the nuclear membrane); 3 - metaphase (mother star stage), top view; 4 - metaphase, side view; 5 - anaphase, the beginning of chromosome divergence; 6 - anaphase, chromosomes have separated; 7 - telophase, stage of daughter coils; 8 - telophase and division of the cell body.

Rice. 3. Damage to chromosomes caused by ionizing radiation and chemical mutagens: 1 - normal telophase; 2-4 - telophases with bridges and fragments in human embryonic fibroblasts irradiated with X-rays at a dose of 10 r; 5 and 6 - the same in the hematopoietic cells of the guinea pig; 7 - chromosome bridge in the corneal epithelium of a mouse irradiated with a dose of 25 r; 8 - fragmentation of chromosomes in human embryonic fibroblasts as a result of exposure to nitrosoethylurea.

An important organelle of the cell nucleus - the nucleolus - is a product of the vital activity of chromosomes. It produces ribonucleic acid (RNA), which is an essential intermediate in the synthesis of proteins produced by every cell.

The cell nucleus is separated from the surrounding cytoplasm (see) by a membrane, the thickness of which is 60-70 Å.

Through pores in the membrane, substances synthesized in the nucleus enter the cytoplasm. The space between the nuclear shell and all its organelles is filled with karyoplasm, consisting of basic and acidic proteins, enzymes, nucleotides, inorganic salts and other low-molecular compounds necessary for the synthesis of daughter chromosomes during division of the cell nucleus.

Many biochemical reactions and processes take place in every living cell. To control them, as well as regulate many vital factors, a special structure is needed. What is a nucleus in biology? What makes it effective at accomplishing its task?

What is a nucleus in biology. Definition

The nucleus is an essential structure of any cell in the body. What is the core? In biology, it is the most important component of every organism. The nucleus can be found in both unicellular protozoa and highly organized representatives of the eukaryotic world. The main function of this structure is the storage and transmission of genetic information, which is also contained here.

After fertilization of the egg by the sperm, the fusion of two haploid nuclei occurs. After the fusion of germ cells, a zygote is formed, the nucleus of which already carries a diploid set of chromosomes. This means that the karyotype (genetic information of the nucleus) already contains copies of genes from both the mother and father.

Kernel composition

What is the characteristic of the kernel? Biology carefully studies the composition of the nuclear apparatus, since this can give impetus to the development of genetics, selection and molecular biology.

The nucleus is a double membrane structure. Membranes are an extension of what is necessary for the transport of formed substances from the cell. The contents of the nucleus are called nucleoplasm.

Chromatin is the main substance of the nucleoplasm. The composition of chromatin is diverse: it contains primarily nucleic acids (DNA and RNA), as well as proteins and many metal ions. DNA in the nucleoplasm is arranged in an orderly manner in the form of chromosomes. It is the chromosomes that double during division, after which each set of them passes into daughter cells.

RNA in the nucleoplasm is most often found in two types: mRNA and rRNA. is formed during the process of transcription - reading information from DNA. The molecule of such ribonucleic acid later leaves the nucleus and subsequently serves as a template for the formation of new proteins.

Ribosomal RNA is produced in special structures called nucleoli. The nucleolus is built from the terminal sections of chromosomes formed by secondary constrictions. This structure can be seen under a light microscope as a compacted speck on the nucleus. Ribosomal RNAs, which are synthesized here, also enter the cytoplasm and then, together with proteins, form ribosomes.

The composition of the core has a direct influence on the functions. Biology as a science studies the properties of chromatin to better understand the processes of transcription and cell division.

Kernel functions. Biology of processes in the nucleus

The first and most important function of the nucleus is the storage and transmission of hereditary information. The nucleus is a unique structure of the cell because it contains most of the human genes. The karyotype can be haploid, diploid, triploid, and so on. The ploidy of the venom depends on the function of the cell itself: gametes are haploid, and somatic cells are diploid. The endosperm cells of angiosperms are triploid, and, finally, many varieties of crops have a polyploid set of chromosomes.

Transfer to the cytoplasm from the nucleus occurs during the formation of mRNA. During the process of transcription, the necessary genes of the karyotype are read, and ultimately messenger or messenger RNA molecules are synthesized.

Heredity also manifests itself during cell division by mitosis, meiosis or amitosis. In each case, the kernel performs its specific function. For example, in the prophase of mitosis, the nuclear membrane is destroyed and highly compacted chromosomes enter the cytoplasm. However, in meiosis, chromosome crossing over occurs before the membrane is destroyed in the nucleus. And in amitosis, the nucleus is completely destroyed and makes a small contribution to the division process.

In addition, the nucleus is indirectly involved in the transport of substances from the cell due to the direct connection of the membrane with the EPS. This is what a nucleus is in biology.

Shape of kernels

The nucleus, its structure and functions may depend on the shape of the membrane. The nuclear apparatus can be round, elongated, in the form of blades, etc. Often the shape of the nucleus is specific to individual tissues and cells. Single-celled organisms differ in the type of nutrition and life cycle, and at the same time, the shapes of the nuclear membranes also differ.

Diversity in the shape and size of the nucleus can be seen in the example of leukocytes.

The neutrophil nucleus can be segmented or non-segmented. In the first case, they speak of a horseshoe-shaped nucleus, and this shape is characteristic of young cells. The segmented nucleus is the result of the formation of several partitions in the membrane, resulting in the formation of several parts connected to each other.
In eosinophils, the nucleus has a characteristic dumbbell shape. In this case, the nuclear apparatus consists of two segments connected by a partition.
Almost the entire volume of lymphocytes is occupied by a huge nucleus. Only a small part of the cytoplasm remains at the periphery of the cell.
In glandular cells of insects, the nucleus may have a branched structure.

The number of nuclei in one cell may vary

There is not always only one nucleus present in an organism cell. Sometimes it is necessary to have two or more nuclear devices to perform several functions simultaneously. Conversely, some cells can do without a nucleus altogether. Here are some examples of unusual cells that have more than one nucleus or no nucleus at all.

1. Red blood cells and platelets. These blood cells transport hemoglobin and fibrinogen, respectively. In order for one cell to contain the maximum amount of substance, it has lost its nucleus. This feature is not typical for all representatives of the animal world: frogs have huge red blood cells in their blood with a pronounced nucleus. This shows the primitiveness of this class in comparison with more developed taxa.

2. Liver hepatocytes. These cells contain two nuclei. One of them regulates the purification of blood from toxins, and the other is responsible for the formation of heme, which will subsequently become part of the hemoglobin in the blood.

3. Myocytes of striated skeletal tissue. Muscle cells are multinucleated. This is due to the fact that they actively undergo the synthesis and breakdown of ATP, as well as the assembly of proteins.

Features of the nuclear apparatus in protozoa

For example, consider two types of protozoa: ciliates and amoebas.

1. Slipper ciliates. This representative of unicellular organisms has two nuclei: vegetative and generative. Since they differ both in function and size, this feature is called nuclear dualism.

The vegetative nucleus is responsible for the daily functioning of the cell. It regulates its metabolic processes. The generative nucleus is involved in cell division and in conjugation - a sexual process in which genetic information is exchanged with individuals of the same species.

Diseases

Many genetic diseases are associated with abnormalities in the number of chromosomes. Here is a list of the most well-known deviations in the genetic apparatus of the nucleus:

Down syndrome;
Patau cider;
Klinefelter's syndrome;
Shereshevsky-Turner syndrome.

The list goes on, and each of the diseases differs in the serial number of a pair of chromosomes. Also, such diseases often affect the sex X and Y chromosomes.

Conclusion

The nucleus plays an important role in It regulates biochemical processes and is a repository of hereditary information. The transport of substances from the cell and the synthesis of proteins are also associated with the functioning of this central structure of the cell. This is what a nucleus is in biology.