Animal cell structure with symbols. The structure of the human cell, cell division and appearance, a description with pictures for children

The chemical composition of living organisms

The chemical composition of living organisms can be expressed in two forms: atomic and molecular. The atomic (elemental) composition shows the ratio of the atoms of the elements that make up living organisms. Molecular (material) composition reflects the ratio of molecules of substances.

Chemical elements are part of cells in the form of ions and molecules of inorganic and organic substances. The most important inorganic substances in the cell - water and mineral salts, the most important organic substances - carbohydrates, lipids, proteins and nucleic acids.

Water is the predominant component of all living organisms. The average water content in the cells of most living organisms is about 70%.

mineral salts In an aqueous solution, cells dissociate into cations and anions. The most important cations are K+, Ca2+, Mg2+, Na+, NHJ, anions - Cl-, SO2-, HPO2-, H2PO-, HCO-, NO-.

Carbohydrates - organic compounds consisting of one or more molecules of simple sugars. The content of carbohydrates in animal cells is 1-5%, and in some plant cells it reaches 70%.

Lipids - fats and fat-like organic compounds, practically insoluble in water. Their content in different cells varies greatly: from 2-3 to 50-90% in the cells of plant seeds and adipose tissue of animals.

Squirrels are biological heteropolymers whose monomers are amino acids. Only 20 amino acids are involved in the formation of proteins. They are called fundamental, or basic. Some of the amino acids are not synthesized in the organisms of animals and humans and must be supplied with plant foods (they are called essential).

Nucleic acids. There are two types of nucleic acids: DNA and RNA. Nucleic acids are polymers whose monomers are nucleotides.

Cell structure

The formation of cell theory

• Robert Hooke in 1665 discovered cells in a section of cork and was the first to use the term "cell".
• Anthony van Leeuwenhoek discovered unicellular organisms.
• Matthias Schleiden in 1838 and Thomas Schwann in 1839 formulated the main provisions of the cell theory. However, they erroneously believed that cells arise from the primary non-cellular substance.
• Rudolf Virchow proved in 1858 that all cells are formed from other cells by cell division.

Basic provisions of cell theory

1. The cell is the structural unit of all living things. All living organisms are made up of cells (viruses are an exception).
2. The cell is the functional unit of all living things. The cell shows the whole range of vital functions.
3. The cell is the unit of development of all living things. New cells are formed only as a result of the division of the original (mother) cell.
4. The cell is the genetic unit of all living things. The chromosomes of a cell contain information about the development of the whole organism.
5. The cells of all organisms are similar in chemical composition, structure and function.

Types of cell organization

Among living organisms, only viruses do not have a cellular structure. All other organisms are represented by cellular life forms. There are two types of cellular organization: prokaryotic and eukaryotic. Bacteria are prokaryotes, and plants, fungi, and animals are eukaryotes.

Prokaryotic cells are relatively simple. They do not have a nucleus, the location of DNA in the cytoplasm is called a nucleoid, the only DNA molecule is circular and not associated with proteins, cells are smaller than eukaryotic cells, the cell wall contains a glycopeptide - murein, there are no membrane organelles, their functions are performed by invaginations of the plasma membrane, ribosomes are small, microtubules are absent, so the cytoplasm is immobile, and the cilia and flagella have a special structure.

Eukaryotic cells have a nucleus in which chromosomes are located - linear DNA molecules associated with proteins; various membrane organelles are located in the cytoplasm.

Plant cells are distinguished by the presence of a thick cellulose cell wall, plastids, and a large central vacuole that shifts the nucleus to the periphery. The cell center of higher plants does not contain centrioles. The storage carbohydrate is starch.

Fungal cells have a cell membrane containing chitin, there is a central vacuole in the cytoplasm, and there are no plastids. Only some fungi have a centriole in the cell center. The main reserve carbohydrate is glycogen.

Animal cells have, as a rule, a thin cell wall, do not contain plastids and a central vacuole; a centriole is characteristic of the cell center. The storage carbohydrate is glycogen.

The structure of a eukaryotic cell

A typical eukaryotic cell consists of three components: a membrane, a cytoplasm, and a nucleus.

Cell wall

Outside, the cell is surrounded by a shell, the basis of which is the plasma membrane, or plasmalemma, which has a typical structure and a thickness of 7.5 nm.

The cell membrane performs important and very diverse functions: it determines and maintains the shape of the cell; protects the cell from the mechanical effects of the penetration of damaging biological agents; carries out the reception of many molecular signals (for example, hormones); limits the internal contents of the cell; regulates the metabolism between the cell and the environment, ensuring the constancy of the intracellular composition; participates in the formation of intercellular contacts and various kinds of specific protrusions of the cytoplasm (microvilli, cilia, flagella).

The carbon component in the membrane of animal cells is called the glycocalyx.

The exchange of substances between the cell and its environment occurs constantly. The mechanisms of transport of substances into and out of the cell depend on the size of the transported particles. Small molecules and ions are transported by the cell directly across the membrane in the form of active and passive transport.

Depending on the type and direction, endocytosis and exocytosis are distinguished.

The absorption and release of solid and large particles are called phagocytosis and reverse phagocytosis, respectively, liquid or dissolved particles - pinocytosis and reverse pinocytosis.

Cytoplasm

The cytoplasm is the internal contents of the cell and consists of hyaloplasm and various intracellular structures located in it.

Hyaloplasm (matrix) is an aqueous solution of inorganic and organic substances that can change its viscosity and are in constant motion. The ability to move or flow of the cytoplasm is called cyclosis.

The matrix is ​​an active medium in which many physical and chemical processes take place and which unites all elements of the cell into a single system.

The cytoplasmic structures of the cell are represented by inclusions and organelles. Inclusions are relatively non-permanent, occurring in certain types of cells at certain moments of life, for example, as a supply of nutrients (grains of starch, proteins, glycogen drops) or products to be excreted from the cell. Organelles are permanent and indispensable components of most cells that have a specific structure and perform a vital function.

The membrane organelles of a eukaryotic cell include the endoplasmic reticulum, the Golgi apparatus, mitochondria, lysosomes, and plastids.

Endoplasmic reticulum. The entire inner zone of the cytoplasm is filled with numerous small channels and cavities, the walls of which are membranes similar in structure to the plasma membrane. These channels branch, connect with each other and form a network called the endoplasmic reticulum.

The endoplasmic reticulum is heterogeneous in its structure. Two types of it are known - granular and smooth. On the membranes of the channels and cavities of the granular network there are many small round bodies - ribosomes, which give the membranes a rough appearance. The membranes of the smooth endoplasmic reticulum do not carry ribosomes on their surface.

The endoplasmic reticulum performs many different functions. The main function of the granular endoplasmic reticulum is participation in protein synthesis, which is carried out in ribosomes.

On the membranes of the smooth endoplasmic reticulum, lipids and carbohydrates are synthesized. All these synthesis products accumulate in channels and cavities, and then are transported to various cell organelles, where they are consumed or accumulated in the cytoplasm as cell inclusions. The endoplasmic reticulum connects the main organelles of the cell.

golgi apparatus

In many animal cells, such as nerve cells, it takes the form of a complex network located around the nucleus. In the cells of plants and protozoa, the Golgi apparatus is represented by individual sickle-shaped or rod-shaped bodies. The structure of this organoid is similar in the cells of plant and animal organisms, despite the variety of its shape.

The composition of the Golgi apparatus includes: cavities limited by membranes and located in groups (5-10 each); large and small bubbles located at the ends of the cavities. All these elements form a single complex.

The Golgi apparatus performs many important functions. Through the channels of the endoplasmic reticulum, the products of the synthetic activity of the cell - proteins, carbohydrates and fats - are transported to it. All these substances first accumulate, and then enter the cytoplasm in the form of large and small bubbles and are either used in the cell itself during its life activity, or removed from it and used in the body. For example, in the cells of the pancreas of mammals, digestive enzymes are synthesized, which accumulate in the cavities of the organoid. Then vesicles filled with enzymes form. They are excreted from the cells into the pancreatic duct, from where they flow into the intestinal cavity. Another important function of this organoid is that fats and carbohydrates (polysaccharides) are synthesized on its membranes, which are used in the cell and which are part of the membranes. Thanks to the activity of the Golgi apparatus, the renewal and growth of the plasma membrane occurs.

Mitochondria

The cytoplasm of most animal and plant cells contains small bodies (0.2-7 microns) - mitochondria (Greek "mitos" - thread, "chondrion" - grain, granule).

Mitochondria are clearly visible in a light microscope, with which you can see their shape, location, count the number. Internal structure mitochondria studied using an electron microscope. The shell of the mitochondrion consists of two membranes - outer and inner. The outer membrane is smooth, it does not form any folds and outgrowths. The inner membrane, on the contrary, forms numerous folds that are directed into the cavity of the mitochondria. The folds of the inner membrane are called cristae (lat. "crista" - comb, outgrowth). The number of cristae is not the same in the mitochondria of different cells. There can be from several tens to several hundreds, and there are especially many cristae in the mitochondria of actively functioning cells, for example, muscle cells.

Mitochondria are called the "power stations" of cells" since their main function is the synthesis of adenosine triphosphate (ATP). This acid is synthesized in the mitochondria of the cells of all organisms and is a universal source of energy necessary for the implementation of the vital processes of the cell and the whole organism.

New mitochondria are formed by the division of already existing mitochondria in the cell.

Lysosomes

They are small round bodies. Each lysosome is separated from the cytoplasm by a membrane. Inside the lysosome are enzymes that break down proteins, fats, carbohydrates, nucleic acids.

Lysosomes approach the food particle that has entered the cytoplasm, merge with it, and one digestive vacuole is formed, inside of which there is a food particle surrounded by lysosome enzymes. Substances formed as a result of the digestion of a food particle enter the cytoplasm and are used by the cell.

Possessing the ability to actively digest nutrients, lysosomes are involved in the removal of parts of cells, whole cells and organs that die in the process of vital activity. The formation of new lysosomes occurs in the cell constantly. Enzymes contained in lysosomes, like any other proteins, are synthesized on the ribosomes of the cytoplasm. Then these enzymes enter through the channels of the endoplasmic reticulum to the Golgi apparatus, in the cavities of which lysosomes are formed. In this form, lysosomes enter the cytoplasm.

plastids

Plastids are found in the cytoplasm of all plant cells. There are no plastids in animal cells. There are three main types of plastids: green - chloroplasts; red, orange and yellow - chromoplasts; colorless - leukoplasts.

Mandatory for most cells are also organelles that do not have a membrane structure. These include ribosomes, microfilaments, microtubules, and the cell center.

Ribosomes. Ribosomes are found in the cells of all organisms. These are microscopic bodies of rounded shape with a diameter of 15-20 nm. Each ribosome consists of two particles of different sizes, small and large.

One cell contains many thousands of ribosomes, they are located either on the membranes of the granular endoplasmic reticulum, or lie freely in the cytoplasm. Ribosomes are made up of proteins and RNA. The function of ribosomes is protein synthesis. Protein synthesis is a complex process that is carried out not by one ribosome, but by a whole group, including up to several dozen combined ribosomes. This group of ribosomes is called a polysome. The synthesized proteins are first accumulated in the channels and cavities of the endoplasmic reticulum and then transported to the organelles and cell sites where they are consumed. The endoplasmic reticulum and the ribosomes located on its membranes are a single apparatus for the biosynthesis and transport of proteins.

Microtubules and microfilaments

Filamentous structures, consisting of various contractile proteins and causing the motor functions of the cell. Microtubules have the form of hollow cylinders, the walls of which are composed of proteins - tubulins. Microfilaments are very thin, long, filamentous structures composed of actin and myosin.

Microtubules and microfilaments penetrate the entire cytoplasm of the cell, forming its cytoskeleton, causing cyclosis, intracellular movements of organelles, segregation of chromosomes during the division of nuclear material, etc.

Cell center (centrosome). In animal cells, an organoid is located near the nucleus, which is called the cell center. The main part of the cell center is made up of two small bodies - centrioles located in a small area of ​​​​densified cytoplasm. Each centriole has the shape of a cylinder up to 1 µm long. Centrioles play an important role in cell division; they are involved in the formation of the fission spindle.

In the process of evolution, different cells adapted to living in different conditions and performing specific functions. This required the presence in them of special organoids, which are called specialized, in contrast to the general-purpose organelles discussed above. These include contractile vacuoles of protozoa, muscle fiber myofibrils, neurofibrils, and synaptic vesicles. nerve cells, microvilli epithelial cells, cilia and flagella of some protozoa.

Nucleus

The nucleus is the most important component of eukaryotic cells. Most cells have a single nucleus, but there are also multinucleated cells (in a number of protozoa, in the skeletal muscles of vertebrates). Some highly specialized cells lose nuclei (mammalian erythrocytes, for example).

The nucleus, as a rule, has a spherical or oval shape, less often it can be segmented or fusiform. The nucleus consists of the nuclear membrane and karyoplasm containing chromatin (chromosomes) and nucleoli.

The nuclear membrane is formed by two membranes (outer and inner) and contains numerous pores through which various substances are exchanged between the nucleus and the cytoplasm.

Karyoplasm (nucleoplasm) is a jelly-like solution that contains a variety of proteins, nucleotides, ions, as well as chromosomes and the nucleolus.

The nucleolus is a small rounded body, intensely stained and found in the nuclei of non-dividing cells. The function of the nucleolus is the synthesis of rRNA and their connection with proteins, i.e. assembly of ribosome subunits.

Chromatin - lumps, granules and filamentous structures that are specifically stained by some dyes, formed by DNA molecules in combination with proteins. Different parts of DNA molecules in the composition of chromatin have different degrees of helicity, and therefore differ in color intensity and the nature of genetic activity. Chromatin is a form of existence of genetic material in non-dividing cells and provides the possibility of doubling and realizing the information contained in it. In the process of cell division, DNA spiralization occurs and chromatin structures form chromosomes.

Chromosomes are dense, intensely staining structures that are units of the morphological organization of the genetic material and ensure its precise distribution during cell division.

The number of chromosomes in the cells of each biological species is constant. Usually in the nuclei of body cells (somatic) chromosomes are presented in pairs, in germ cells they are not paired. A single set of chromosomes in germ cells is called haploid (n), a set of chromosomes in somatic cells is called diploid (2n). The chromosomes of different organisms differ in size and shape.

A diploid set of chromosomes in cells of a particular type of living organisms, characterized by the number, size and shape of chromosomes, is called a karyotype. In the chromosome set of somatic cells, paired chromosomes are called homologous, chromosomes from different pairs are called non-homologous. Homologous chromosomes are the same in size, shape, composition (one is inherited from the maternal, the other from the paternal organism). The chromosomes in the karyotype are also divided into autosomes, or non-sex chromosomes, which are the same in male and female individuals, and heterochromosomes, or sex chromosomes involved in sex determination and differing in males and females. The human karyotype is represented by 46 chromosomes (23 pairs): 44 autosomes and 2 sex chromosomes (the female has two identical X chromosomes, the male has X and Y chromosomes).

The nucleus stores and implements genetic information, controls the process of protein biosynthesis, and through proteins - all other life processes. The nucleus is involved in the replication and distribution of hereditary information between daughter cells, and, consequently, in the regulation of cell division and the development of the body.

Cell structure

Human body Like any other living organism, it is made up of cells. They play one of the main roles in our body. With the help of cells, growth, development and reproduction occur.

Now let's recall the definition of what is usually called a cell in biology.

A cell is such an elementary unit that is involved in the structure and functioning of all living organisms, with the exception of viruses. It has its own metabolism and is able not only to exist independently, but also to develop and reproduce itself. In short, we can conclude that the cell is the most important and necessary building material for any organism.

Of course, with the naked eye, you are unlikely to be able to see the cage. But with the help modern technologies a person has a great opportunity not only to examine the cell itself under a light or electron microscope, but also to study its structure, isolate and cultivate its individual tissues, and even decode the genetic cellular information.

And now, with the help of this figure, let's visually consider the structure of the cell:

Cell structure

But interestingly, it turns out that not all cells have the same structure. There is some difference between the cells of a living organism and the cells of plants. Indeed, in plant cells there are plastids, a membrane and vacuoles with cell sap. On the image you can see cellular structure animals and plants and see the difference between them:

For more information about the structure of plant and animal cells, you will learn by watching the video

As you can see, cells, although they have microscopic dimensions, but their structure is quite complex. Therefore, we will now move on to a more detailed study of the structure of the cell.

Plasma membrane of a cell

To give shape and to separate the cell from its kind, a membrane is located around the human cell.

Since the membrane has the ability to partially pass substances through itself, due to this, the necessary substances enter the cell, and waste products are removed from it.

Conventionally, we can say that the cell membrane is an ultramicroscopic film, which consists of two monomolecular layers of protein and a bimolecular layer of lipids, which is located between these layers.

From this we can conclude that the cell membrane plays an important role in its structure, as it performs a number of specific functions. It plays a protective, barrier and connecting function between other cells and for communication with the environment.

And now let's look at a more detailed structure of the membrane in the figure:

Cytoplasm

The next component of the internal environment of the cell is the cytoplasm. It is a semi-liquid substance in which other substances move and dissolve. The cytoplasm consists of proteins and water.

Inside the cell, there is a constant movement of the cytoplasm, which is called cyclosis. Cyclosis is circular or reticulate.

In addition, the cytoplasm connects different parts of the cell. In this environment, the organelles of the cell are located.

Organelles are permanent cellular structures with specific functions.

Such organelles include such structures as the cytoplasmic matrix, endoplasmic reticulum, ribosomes, mitochondria, etc.

Now we will try to take a closer look at these organelles and find out what functions they perform.

Cytoplasm

cytoplasmic matrix

One of the main parts of the cell is the cytoplasmic matrix. Thanks to it, biosynthesis processes take place in the cell, and its components contain enzymes that produce energy.

cytoplasmic matrix

Endoplasmic reticulum

Inside, the cytoplasmic zone consists of small channels and various cavities. These channels, connecting with each other, form the endoplasmic reticulum. Such a network is heterogeneous in its structure and can be granular or smooth.


Endoplasmic reticulum

cell nucleus

The most important part, which is present in almost all cells, is the cell nucleus. Cells that have a nucleus are called eukaryotes. Each cell nucleus contains DNA. It is the substance of heredity and all the properties of the cell are encrypted in it.

cell nucleus

Chromosomes

If we look at the structure of a chromosome under a microscope, we can see that it consists of two chromatids. As a rule, after nuclear division, the chromosome becomes single chromatid. But by the beginning of the next division, another chromatid appears on the chromosome.

Chromosomes

Cell Center

When considering the cell center, one can see that it consists of a maternal and daughter centrioles. Each such centriole is a cylindrical object, the walls are formed by nine triplets of tubules, and in the middle there is a homogeneous substance.

With the help of such a cell center, the division of animal and lower plant cells occurs.

Cell Center

Ribosomes

Ribosomes are universal organelles in both animal and plant cells. Their main function is protein synthesis in the functional center.

Ribosomes

Mitochondria

Mitochondria are also microscopic organelles, but unlike ribosomes, they have a two-membrane structure in which the outer membrane is smooth and the inner one has various shapes outgrowths called cristae. Mitochondria play the role of a respiratory and energy center

Mitochondria

golgi apparatus

But with the help of the Golgi apparatus, the accumulation and transportation of substances occurs. Also, thanks to this apparatus, the formation of lysosomes and the synthesis of lipids and carbohydrates occur.

In structure, the Golgi apparatus resembles individual bodies, which are crescent-shaped or rod-shaped.

golgi apparatus

plastids

But plastids for a plant cell play the role of an energy station. They tend to change from one species to another. Plastids are divided into such varieties as chloroplasts, chromoplasts, leukoplasts.

plastids

Lysosomes

The digestive vacuole, which is capable of dissolving enzymes, is called a lysosome. They are microscopic single-membrane organelles with a rounded shape. Their number directly depends on how viable the cell is and what its physical condition is.

In the event that the destruction of the lysosome membrane occurs, then in this case the cell is able to digest itself.

Lysosomes

Ways to feed the cell

Now let's look at how cells are fed:

How the cell is fed

It should be noted here that proteins and polysaccharides tend to penetrate the cell by phagocytosis, but liquid drops - by pinocytosis.

The method of nutrition of animal cells, in which nutrients enter it, is called phagocytosis. And such a universal way of feeding any cells, in which nutrients enter the cell already in a dissolved form, is called pinocytosis.

Cells are divided into prokaryotic and eukaryotic. The former are algae and bacteria, which contain genetic information in one single organelle, the chromosome, while eukaryotic cells, which make up more complex organisms such as the human body, have a clearly differentiated nucleus that contains several chromosomes with genetic material.

eukaryotic cell

prokaryotic cell

Structure

Cellular or cytoplasmic membrane

The cytoplasmic membrane (shell) is a thin structure that separates the contents of the cell from environment. It consists of a double layer of lipids with protein molecules approximately 75 angstroms thick.

The cell membrane is continuous, but it has numerous folds, convolutions, and pores, which allows you to control the passage of substances through it.

Cells, tissues, organs, systems and apparatuses

Cells, The human body is a component of elements that work together to effectively perform all vital functions.

Textile- These are cells of the same shape and structure, specialized in performing the same function. Various tissues combine to form organs, each of which performs a specific function in a living organism. In addition, organs are also grouped into a system to perform a specific function.

Fabrics:

epithelial- Protects and coats the surface of the body and internal surfaces of organs.

Connective- fat, cartilage and bone. Performs various functions.

muscular- smooth muscle tissue, striated muscle tissue. Contracts and relaxes muscles.

nervous- neurons. Generates and transmits and receives impulses.

Cell size

The size of the cells is very different, although in general it ranges from 5 to 6 microns (1 micron = 0.001 mm). This explains the fact that many cells could not be seen before the invention of the electron microscope, the resolution of which is from 2 to 2000 angstroms (1 angstrom \u003d 0.000 000 1 mm). The size of some microorganisms is less than 5 microns, but there are also giant cells. Of the most famous - this is the yolk of bird eggs, an egg about 20 mm in size.

There are even more striking examples: the cell of acetabularia, a single-celled marine alga, reaches 100 mm, and ramie, a herbaceous plant, - 220 mm - more than a palm.

From parents to children thanks to chromosomes

The cell nucleus undergoes various changes when the cell begins to divide: the membrane and nucleoli disappear; at this time, chromatin becomes denser, eventually forming thick threads - chromosomes. The chromosome consists of two halves - chromatids connected at the site of constriction (centrometer).

Our cells, like all the cells of animals and plants, are subject to the so-called law of numerical constancy, according to which the number of chromosomes of a certain species is constant.

In addition, chromosomes are distributed in pairs that are identical to each other.

Each cell in our body has 23 pairs of chromosomes, which are several elongated DNA molecules. The DNA molecule takes the form of a double helix, consisting of two groups of sugar phosphate, from which the nitrogenous bases (purines and pyramidins) protrude in the form of steps of a spiral staircase.

Along each chromosome are genes responsible for heredity, the transfer of gene traits from parents to children. They determine the color of the eyes, skin, shape of the nose, etc.

Mitochondria

Mitochondria are round or elongated organelles distributed throughout the cytoplasm, containing an aqueous solution of enzymes, capable of carrying out numerous chemical reactions, such as cellular respiration.

This process releases the energy that the cell needs to perform its vital functions. Mitochondria are found mainly in the most active cells of living organisms: cells of the pancreas and liver.

cell nucleus

The nucleus, one in every human cell, is its main component, since it is the organism that controls the functions of the cell and the carrier of hereditary traits, which proves its importance in reproduction and the transmission of biological heredity.

In the core, the size of which ranges from 5 to 30 microns, the following elements can be distinguished:

• Nuclear shell. It is double and allows substances to pass between the nucleus and the cytoplasm due to its porous structure.
• nuclear plasma. Light, viscous liquid in which the rest of the nuclear structures are immersed.
• Nucleus. Spherical body, isolated or in groups, involved in the formation of ribosomes.
• Chromatin. A substance that can take on various colors, consisting of long strands of DNA (deoxyribonucleic acid). Threads are particles, genes, each of which contains information about a specific function of the cell.

The nucleus of a typical cell

Skin cells live an average of one week. Erythrocytes live 4 months, and bone cells - from 10 to 30 years.

centrosome

The centrosome is usually located near the nucleus and plays a critical role in mitosis, or cell division.

It consists of 3 elements:

• Diplosome. It consists of two centrioles - cylindrical structures located perpendicularly.
• Centrosphere. The translucent substance in which the diplosome is immersed.
• Aster. A radiant formation of filaments emerging from the centrosphere, having importance for mitosis.

Golgi complex, lysosomes

The Golgi complex consists of 5-10 flat disks (plates), in which the main element is distinguished - a cistern and several dictyosomes, or an accumulation of cistern. These dictyosomes separate and distribute evenly during mitosis, or cell division.

Lysosomes, the "stomach" of the cell, are formed from the vesicles of the Golgi complex: they contain digestive enzymes that allow them to digest food entering the cytoplasm. Their interior, or mycus, is lined with a thick layer of polysaccharides that prevent these enzymes from breaking down their own cellular material.

Ribosomes

Ribosomes are cell organelles with a diameter of about 150 angstroms that are attached to the membranes of the endoplasmic reticulum or are freely located in the cytoplasm.

They consist of two subunits:

• the large subunit consists of 45 protein molecules and 3 RNA (ribonucleic acid);
• the smaller subunit consists of 33 protein molecules and 1 RNA.

Ribosomes combine into polysomes with the help of an RNA molecule and synthesize proteins from amino acid molecules.

Cytoplasm

Cytoplasm is an organic mass located between the cytoplasmic membrane and the shell of the nucleus. It contains an internal environment - hyaloplasm - a viscous liquid consisting of a large amount of water and containing proteins, monosaccharides and fats in dissolved form.

It is a part of the cell endowed with vital activity, because various cell organelles move inside it and biochemical reactions occur. Organelles perform the same role in the cell as organs do in human body: produce vital substances, generate energy, perform the functions of digestion and excretion of organic substances, etc.

Approximately one third of the cytoplasm is water.

In addition, the cytoplasm contains 30% organic substances (carbohydrates, fats, proteins) and 2-3% inorganic substances.

Endoplasmic reticulum

The endoplasmic reticulum is a network-like structure formed by the wrapping of the cytoplasmic membrane into itself.

This process, known as invagination, is thought to have led to more complex creatures with greater protein requirements.

Depending on the presence or absence of ribosomes in the shells, two types of networks are distinguished:

1. The endoplasmic reticulum is folded. A collection of flat structures interconnected and communicating with the nuclear membrane. Attached to it a large number of ribosomes, so its function is to accumulate and release proteins synthesized in ribosomes.

2. Endoplasmic reticulum is smooth. A network of flat and tubular elements that communicates with the folded endoplasmic reticulum. Synthesizes, secretes and transports fats throughout the cell, together with the proteins of the folded reticulum.

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Cell- an elementary unit of the structure and vital activity of all living organisms (except for viruses, which are often referred to as non-cellular life forms), having its own metabolism, capable of independent existence, self-reproduction and development. All living organisms either, like multicellular animals, plants and fungi, consist of many cells, or, like many protozoa and bacteria, are unicellular organisms. The branch of biology that deals with the study of the structure and activity of cells is called cytology. Recently, it has also become customary to talk about cell biology, or cell biology.

cell structure All cellular life forms on earth can be divided into two kingdoms based on the structure of their constituent cells - prokaryotes (pre-nuclear) and eukaryotes (nuclear). Prokaryotic cells are simpler in structure, apparently, they arose earlier in the process of evolution. Eukaryotic cells - more complex, arose later. The cells that make up the human body are eukaryotic. Despite the variety of forms, the organization of the cells of all living organisms is subject to uniform structural principles. The living contents of the cell - the protoplast - is separated from the environment by the plasma membrane, or plasmalemma. Inside the cell is filled with cytoplasm, which contains various organelles and cellular inclusions, as well as genetic material in the form of a DNA molecule. Each of the organelles of the cell performs its own special function, and together they all determine the vital activity of the cell as a whole.

prokaryotic cell

prokaryotes(from Latin pro - before, to and Greek κάρῠον - core, nut) - organisms that, unlike eukaryotes, do not have a formed cell nucleus and other internal membrane organelles (with the exception of flat tanks in photosynthetic species, for example, in cyanobacteria ). The only large circular (in some species - linear) double-stranded DNA molecule, which contains the main part of the cell's genetic material (the so-called nucleoid) does not form a complex with histone proteins (the so-called chromatin). Prokaryotes include bacteria, including cyanobacteria (blue-green algae), and archaea. The descendants of prokaryotic cells are the organelles of eukaryotic cells - mitochondria and plastids.

eukaryotic cell

eukaryotes(eukaryotes) (from the Greek ευ - good, completely and κάρῠον - core, nut) - organisms that, unlike prokaryotes, have a well-shaped cell nucleus, delimited from the cytoplasm by the nuclear membrane. The genetic material is enclosed in several linear double-stranded DNA molecules (depending on the type of organisms, their number per nucleus can vary from two to several hundred), attached from the inside to the membrane of the cell nucleus and forming in the vast majority (except dinoflagellates) a complex with histone proteins, called chromatin. Eukaryotic cells have a system of internal membranes that form, in addition to the nucleus, a number of other organelles (endoplasmic reticulum, Golgi apparatus, etc.). In addition, the vast majority have permanent intracellular symbionts-prokaryotes - mitochondria, and algae and plants also have plastids.

cell membrane The cell membrane is a very important part of the cell. It holds together all cellular components and delimits the internal and external environment. In addition, modified cell membrane folds form many of the cell's organelles. The cell membrane is a double layer of molecules (bimolecular layer, or bilayer). Basically, these are molecules of phospholipids and other substances close to them. Lipid molecules have a dual nature, manifested in the way they behave in relation to water. The heads of the molecules are hydrophilic, i.e. have an affinity for water, and their hydrocarbon tails are hydrophobic. Therefore, when mixed with water, lipids form a film on its surface, similar to an oil film; at the same time, all their molecules are oriented in the same way: the heads of the molecules are in the water, and the hydrocarbon tails are above its surface. There are two such layers in the cell membrane, and in each of them the heads of the molecules are turned outward, and the tails are turned inside the membrane, one to the other, thus not coming into contact with water. The thickness of this membrane is approx. 7 nm. In addition to the main lipid components, it contains large protein molecules that are able to “float” in the lipid bilayer and are located so that one of their sides is turned inside the cell, and the other is in contact with the external environment. Some proteins are located only on the outer or only on the inner surface of the membrane, or are only partially immersed in the lipid bilayer.

Main cell membrane function It regulates the transport of substances into and out of the cell. Since the membrane is physically similar to oil to some extent, substances soluble in oil or organic solvents, such as ether, easily pass through it. The same applies to gases such as oxygen and carbon dioxide. At the same time, the membrane is practically impermeable to most water-soluble substances, in particular, to sugars and salts. Due to these properties, it is able to maintain a chemical environment inside the cell that differs from the outside. For example, in the blood, the concentration of sodium ions is high, and potassium ions are low, while in the intracellular fluid, these ions are present in the opposite ratio. A similar situation is typical for many other chemical compounds. Obviously, the cell, however, cannot be completely isolated from the environment, since it must receive the substances necessary for metabolism and get rid of its end products. In addition, the lipid bilayer is not completely impermeable even for water-soluble substances, but the so-called “layers” penetrating it. "Channel-forming" proteins create pores, or channels, which can open and close (depending on the change in protein conformation) and in the open state conduct certain ions (Na+, K+, Ca2+) along the concentration gradient. Consequently, the difference in concentrations inside the cell and outside cannot be maintained solely due to the low permeability of the membrane. In fact, it contains proteins that perform the function of a molecular "pump": they transport certain substances both into the cell and out of it, working against the concentration gradient. As a result, when the concentration of, for example, amino acids is high inside the cell and low outside, amino acids can still be transferred from the outside to the inside. Such transfer is called active transport, and energy supplied by metabolism is expended on it. Membrane pumps are highly specific: each of them is able to transport either only ions of a certain metal, or an amino acid, or sugar. Membrane ion channels are also specific. Such selective permeability is physiologically very important, and its absence is the first evidence of cell death. This can be easily illustrated with the example of beets. If a living beet root is immersed in cold water, then it retains its pigment; if the beets are boiled, then the cells die, become easily permeable and lose the pigment, which turns the water red. Large molecules such as protein cells can "swallow". Under the influence of some proteins, if they are present in the fluid surrounding the cell, an invagination occurs in the cell membrane, which then closes, forming a bubble - a small vacuole containing water and protein molecules; after that, the membrane around the vacuole breaks, and the contents enter the cell. This process is called pinocytosis (literally "cell drinking"), or endocytosis. Larger particles, such as food particles, can be absorbed in a similar way during the so-called. phagocytosis. As a rule, the vacuole formed during phagocytosis is larger, and the food is digested by the enzymes of the lysosomes inside the vacuole until the membrane surrounding it ruptures. This type of nutrition is typical for protozoa, for example, for amoebas that eat bacteria. However, the ability to phagocytosis is characteristic of both intestinal cells of lower animals, and phagocytes - one of the types of white blood cells(leukocytes) of vertebrates. In the latter case, the meaning of this process is not in the nutrition of the phagocytes themselves, but in the destruction of bacteria, viruses and other foreign material harmful to the body. The functions of vacuoles may be different. For example, protozoa living in fresh water, experience a constant osmotic influx of water, since the concentration of salts inside the cell is much higher than outside. They are able to secrete water into a special excreting (contractile) vacuole, which periodically pushes its contents out. In plant cells, there is often one large central vacuole that occupies almost the entire cell; the cytoplasm forms only a very thin layer between the cell wall and the vacuole. One of the functions of such a vacuole is the accumulation of water, which allows the cell to rapidly increase in size. This ability is especially needed at a time when plant tissues are growing and forming fibrous structures. In tissues, in places of tight junction of cells, their membranes contain numerous pores formed by proteins penetrating the membrane - the so-called. connectons. The pores of adjacent cells are located opposite each other, so that low molecular weight substances can move from cell to cell - this chemical communication system coordinates their vital activity. One example of such coordination is the more or less synchronous division of neighboring cells observed in many tissues.

Cytoplasm

In the cytoplasm there are inner membranes similar to the outer and forming organelles various types. These membranes can be thought of as folds of the outer membrane; sometimes the inner membranes form an integral whole with the outer one, but often the inner fold is laced up, and contact with the outer membrane is interrupted. However, even if contact is maintained, the inner and outer membranes are not always chemically identical. In particular, the composition of membrane proteins in different cell organelles differs.

The structure of the cytoplasm

The liquid component of the cytoplasm is also called the cytosol. Under a light microscope, it seemed that the cell was filled with something like liquid plasma or sol, in which the nucleus and other organelles “floated”. Actually it is not. The internal space of a eukaryotic cell is strictly ordered. The movement of organelles is coordinated with the help of specialized transport systems, the so-called microtubules, which serve as intracellular "roads" and special proteins dyneins and kinesins, which play the role of "engines". Separate protein molecules also do not freely diffuse throughout the entire intracellular space, but are directed to the necessary compartments using special signals on their surface, recognized by the cell's transport systems.

Endoplasmic reticulum

In a eukaryotic cell, there is a system of membrane compartments passing into each other (tubes and tanks), which is called the endoplasmic reticulum (or endoplasmic reticulum, EPR or EPS). That part of the EPR, to the membranes of which ribosomes are attached, is referred to as the granular (or rough) endoplasmic reticulum, and protein synthesis occurs on its membranes. Those compartments, on the walls of which there are no ribosomes, are referred to as smooth (or agranular) ER, which takes part in lipid synthesis. The internal spaces of the smooth and granular ER are not isolated, but pass into each other and communicate with the lumen of the nuclear membrane.

golgi apparatus

The Golgi apparatus is a stack of flat membrane cisterns, somewhat expanded closer to the edges. In the tanks of the Golgi apparatus, some proteins synthesized on the membranes of the granular ER and intended for secretion or the formation of lysosomes mature. The Golgi apparatus is asymmetric - the tanks located closer to the cell nucleus (cis-Golgi) contain the least mature proteins, membrane vesicles - vesicles, budding from the endoplasmic reticulum, are continuously attached to these tanks. Apparently, with the help of the same vesicles, the further movement of maturing proteins from one tank to another takes place. Eventually, vesicles containing fully mature proteins bud off from the opposite end of the organelle (trans-Golgi).

Nucleus

The nucleus is surrounded by a double membrane. A very narrow (about 40 nm) space between two membranes is called perinuclear. The membranes of the nucleus pass into the membranes of the endoplasmic reticulum, and the perinuclear space opens into the reticular. Typically, the nuclear membrane has very narrow pores. Apparently, large molecules are transferred through them, such as messenger RNA, which is synthesized on DNA and then enters the cytoplasm. The main part of the genetic material is located in the chromosomes of the cell nucleus. Chromosomes consist of long chains of double-stranded DNA, to which basic (i.e., alkaline) proteins are attached. Sometimes chromosomes have several identical strands of DNA lying next to each other - such chromosomes are called polytene (multifilamentous). The number of chromosomes in different types unequally. Diploid cells of the human body contain 46 chromosomes, or 23 pairs. In a nondividing cell, the chromosomes are attached at one or more points to the nuclear membrane. In the normal non-spiralized state, the chromosomes are so thin that they are not visible under a light microscope. At certain loci (areas) of one or more chromosomes, a dense body present in the nuclei of most cells is formed - the so-called. nucleolus. In the nucleolus, RNA is synthesized and accumulated, which is used to build ribosomes, as well as some other types of RNA.

Lysosomes

Lysosomes are small vesicles surrounded by a single membrane. They bud from the Golgi apparatus and possibly from the endoplasmic reticulum. Lysosomes contain a variety of enzymes that break down large molecules, in particular proteins. Due to their destructive action, these enzymes are, as it were, "locked" in lysosomes and are released only as needed. So, during intracellular digestion, enzymes are released from lysosomes into digestive vacuoles. Lysosomes are also necessary for cell destruction; for example, during the transformation of a tadpole into an adult frog, the release of lysosomal enzymes ensures the destruction of tail cells. In this case, this is normal and beneficial for the body, but sometimes such cell destruction is pathological. For example, when asbestos dust is inhaled, it can enter the cells of the lungs, and then lysosomes rupture, cells are destroyed, and lung disease develops.

cytoskeleton

The elements of the cytoskeleton include protein fibrillar structures located in the cytoplasm of the cell: microtubules, actin and intermediate filaments. Microtubules take part in the transport of organelles, are part of the flagella, and the mitotic spindle is built from microtubules. Actin filaments are essential for maintaining cell shape, pseudopodial reactions. The role of intermediate filaments also seems to be to maintain the structure of the cell. Proteins of the cytoskeleton make up several tens of percent of the mass of the cellular protein.

Centrioles

Centrioles are cylindrical protein structures located near the nucleus of animal cells (plants do not have centrioles). The centriole is a cylinder, the lateral surface of which is formed by nine sets of microtubules. The number of microtubules in a set can vary for different organisms from 1 to 3. Around the centrioles is the so-called center of organization of the cytoskeleton, the area in which the minus ends of the microtubules of the cell are grouped. Before dividing, the cell contains two centrioles located at right angles to each other. During mitosis, they diverge to different ends of the cell, forming the poles of the spindle of division. After cytokinesis, each daughter cell receives one centriole, which doubles for the next division. Doubling of centrioles occurs not by division, but by the synthesis of a new structure perpendicular to the existing one. The centrioles appear to be homologous to the basal bodies of the flagella and cilia.

Mitochondria

Mitochondria are special cell organelles whose main function is the synthesis of ATP, a universal energy carrier. Respiration (oxygen absorption and carbon dioxide release) also occurs due to the enzymatic systems of mitochondria. The inner lumen of mitochondria, called the matrix, is separated from the cytoplasm by two membranes, outer and inner, between which there is an intermembrane space. The inner membrane of the mitochondria forms folds, the so-called cristae. The matrix contains various enzymes involved in respiration and ATP synthesis. The hydrogen potential of the inner mitochondrial membrane is of central importance for ATP synthesis. Mitochondria have their own DNA genome and prokaryotic ribosomes, which certainly indicates the symbiotic origin of these organelles. Not all mitochondrial proteins are encoded in mitochondrial DNA, most of the mitochondrial protein genes are located in the nuclear genome, and their corresponding products are synthesized in the cytoplasm and then transported to mitochondria. Mitochondrial genomes vary in size: for example, the human mitochondrial genome contains only 13 genes. The largest number of mitochondrial genes (97) of the studied organisms is found in the protozoan Reclinomonas americana.

The chemical composition of the cell

Usually 70-80% of the cell mass is water, in which various salts and low molecular weight organic compounds are dissolved. The most characteristic components of a cell are proteins and nucleic acids. Some proteins are structural components of the cell, others are enzymes, i.e. catalysts that determine the speed and direction of chemical reactions occurring in cells. Nucleic acids serve as carriers of hereditary information, which is realized in the process of intracellular protein synthesis. Cells often contain a certain amount of reserve substances that serve as a food reserve. Plant cells primarily store starch, the polymeric form of carbohydrates. In the cells of the liver and muscles, another carbohydrate polymer, glycogen, is stored. Fat is also among the commonly stocked foods, although some fats perform a different function, namely, they serve as the most important structural components. Proteins in cells (with the exception of seed cells) are usually not stored. It is not possible to describe the typical composition of a cell, primarily because there are large differences in the amount of stored food and water. The liver cells contain, for example, 70% water, 17% proteins, 5% fats, 2% carbohydrates and 0.1% nucleic acids; the remaining 6% are salts and low molecular weight organic compounds, in particular amino acids. Plant cells usually contain less protein, significantly more carbohydrates, and somewhat more water; the exception is cells that are in a state of rest. A resting cell of a wheat grain, which is a source of nutrients for the embryo, contains approx. 12% protein (mainly stored protein), 2% fat and 72% carbohydrates. The amount of water reaches normal level(70-80%) only at the beginning of grain germination.

Methods for studying the cell

light microscope.

In the study of cell shape and structure, the first instrument was the light microscope. Its resolution is limited to dimensions comparable to the wavelength of light (0.4-0.7 microns for visible light). However, many elements of the cellular structure are much smaller in size. Another difficulty is that most cellular components are transparent and their refractive index is almost the same as that of water. To improve visibility, dyes are often used that have different affinities for different cellular components. Staining is also used to study the chemistry of the cell. For example, some dyes bind predominantly to nucleic acids and thereby reveal their localization in the cell. A small part of the dyes - they are called intravital - can be used to stain living cells, but usually the cells must be pre-fixed (using substances that coagulate the protein) and only then can they be stained. Before testing, cells or pieces of tissue are usually embedded in paraffin or plastic and then cut into very thin sections using a microtome. This method is widely used in clinical laboratories to detect tumor cells. In addition to conventional light microscopy, other optical methods for studying cells have also been developed: fluorescence microscopy, phase-contrast microscopy, spectroscopy, and X-ray diffraction analysis.

Electron microscope.

The electron microscope has a resolution of approx. 1-2 nm. This is sufficient for the study of large protein molecules. It is usually necessary to stain and contrast the object with metal salts or metals. For this reason, and also because objects are examined in a vacuum, only dead cells can be studied with an electron microscope.

If a radioactive isotope absorbed by cells during metabolism is added to the medium, then its intracellular localization can then be detected using autoradiography. In this method, thin sections of cells are placed on film. The film darkens under those places where there are radioactive isotopes.

centrifugation.

For the biochemical study of cellular components, cells must be destroyed - mechanically, chemically or by ultrasound. The released components are suspended in the liquid and can be isolated and purified by centrifugation (most often in a density gradient). Typically, such purified components retain high biochemical activity.

cell cultures.

Some tissues can be divided into individual cells in such a way that the cells remain alive and are often able to reproduce. This fact finally confirms the idea of ​​a cell as a unit of life. A sponge, a primitive multicellular organism, can be divided into cells by rubbing through a sieve. After a while, these cells recombine and form a sponge. Animal embryonic tissues can be made to dissociate using enzymes or other means that weaken the bonds between cells. The American embryologist R. Harrison (1879-1959) was the first to show that embryonic and even some mature cells can grow and multiply outside the body in a suitable environment. This technique, called cell culture, was perfected by the French biologist A. Carrel (1873-1959). Plant cells can also be grown in culture, but compared to animal cells, they form larger clusters and are more strongly attached to each other, so tissue is formed during culture growth, rather than individual cells. In cell culture, a whole adult plant, such as a carrot, can be grown from a single cell.

Microsurgery.

With the help of a micromanipulator, individual parts of the cell can be removed, added, or modified in some way. A large amoeba cell can be divided into three main components - the cell membrane, cytoplasm and nucleus, and then these components can be reassembled and a living cell is obtained. In this way, artificial cells can be obtained, consisting of components of different types of amoebas. Considering that it is possible to synthesize some cellular components artificially, experiments on the assembly of artificial cells may be the first step towards the creation of new life forms in the laboratory. Since each organism develops from a single cell, the method of obtaining artificial cells in principle allows the construction of organisms of a given type, if at the same time using components that are slightly different from those found in currently existing cells. In reality, however, complete synthesis of all cellular components is not required. The structure of most, if not all, components of a cell is determined by nucleic acids. Thus, the problem of creating new organisms is reduced to the synthesis of new types of nucleic acids and their replacement of natural nucleic acids in certain cells.

cell fusion.

Another type of artificial cells can be obtained by fusion of cells of the same or different types. To achieve fusion, the cells are exposed to viral enzymes; in this case, the outer surfaces of two cells stick together, and the membrane between them collapses, and a cell is formed in which two sets of chromosomes are enclosed in one nucleus. Cells can be drained different types or at different stages division. Using this method, it was possible to obtain hybrid cells of a mouse and a chicken, a human and a mouse, a human and a toad. Such cells are hybrid only initially, and after numerous cell divisions they lose most of the chromosomes of either one or another type. The end product becomes, for example, essentially a mouse cell, where human genes are absent or present only in small quantities. Of particular interest is the fusion of normal and malignant cells. In some cases, the hybrids become malignant, in others they do not; both properties can appear both as dominant and as recessive. This result is not unexpected, since malignancy can be caused by various factors and has a complex mechanism.

Animal and plant cells, both multicellular and unicellular, are in principle similar in structure. Differences in the details of the structure of cells are associated with their functional specialization.

The main elements of all cells are the nucleus and cytoplasm. The nucleus has a complex structure that changes at different phases of cell division, or cycle. The nucleus of a nondividing cell occupies approximately 10–20% of its total volume. It consists of a karyoplasm (nucleoplasm), one or more nucleoli (nucleolus) and a nuclear envelope. Karyoplasm is a nuclear juice, or karyolymph, in which there are chromatin threads that form chromosomes.

The main properties of the cell:

• metabolism
• sensitivity
• ability to reproduce

The cell lives in the internal environment of the body - blood, lymph and tissue fluid. The main processes in the cell are oxidation, glycolysis - the breakdown of carbohydrates without oxygen. Cell permeability is selective. It is determined by the reaction to high or low salt concentration, phago- and pinocytosis. Secretion - the formation and secretion by cells of mucus-like substances (mucin and mucoids), which protect against damage and participate in the formation of intercellular substance.

Types of cell movements:

1. amoeboid (false legs) - leukocytes and macrophages.
2. sliding - fibroblasts
3. flagellate type - spermatozoa (cilia and flagella)

Cell division:

1. indirect (mitosis, karyokinesis, meiosis)
2. direct (amitosis)

During mitosis, the nuclear substance is distributed evenly between the daughter cells, because The chromatin of the nucleus is concentrated in chromosomes, which split into two chromatids, diverging into daughter cells.

Structures of a living cell

Chromosomes

Mandatory elements of the nucleus are chromosomes that have a specific chemical and morphological structure. They take an active part in the metabolism in the cell and are directly related to the hereditary transmission of properties from one generation to another. However, it should be borne in mind that, although heredity is ensured by the whole cell as a single system, nuclear structures, namely chromosomes, occupy a special place in this. Chromosomes, unlike cell organelles, are unique structures characterized by a constant qualitative and quantitative composition. They cannot interchange each other. An imbalance in the chromosome set of a cell ultimately leads to its death.

Cytoplasm

The cytoplasm of a cell exhibits a very complex structure. The introduction of the technique of thin sections and electron microscopy made it possible to see fine structure basic cytoplasm. It has been established that the latter consists of parallel arranged complex structures in the form of plates and tubules, on the surface of which there are the smallest granules with a diameter of 100–120 Å. These formations are called the endoplasmic complex. This complex includes various differentiated organelles: mitochondria, ribosomes, the Golgi apparatus, in the cells of lower animals and plants - the centrosome, in animals - lysosomes, in plants - plastids. In addition, a number of inclusions are found in the cytoplasm that take part in the metabolism of the cell: starch, fat droplets, urea crystals, etc.

Membrane

The cell is surrounded by a plasma membrane (from Latin "membrane" - skin, film). Its functions are very diverse, but the main one is protective: it protects the internal contents of the cell from the effects of the external environment. Due to various outgrowths, folds on the surface of the membrane, the cells are firmly interconnected. The membrane is permeated with special proteins through which certain substances necessary for the cell or to be removed from it can move. Thus, the exchange of substances is carried out through the membrane. Moreover, what is very important, substances are passed through the membrane selectively, due to which the required set of substances is maintained in the cell.

In plants, the plasma membrane is covered on the outside with a dense membrane consisting of cellulose (fiber). The shell performs protective and supporting functions. It serves as the outer frame of the cell, giving it a certain shape and size, preventing excessive swelling.

Nucleus

Located in the center of the cell and separated by a two-layer membrane. It has a spherical or elongated shape. The shell - the karyolemma - has pores necessary for the exchange of substances between the nucleus and the cytoplasm. The contents of the nucleus are liquid - karyoplasm, which contains dense bodies - nucleoli. They are granular - ribosomes. The bulk of the nucleus - nuclear proteins - nucleoproteins, in the nucleoli - ribonucleoproteins, and in the karyoplasm - deoxyribonucleoproteins. The cell is covered with a cell membrane, which consists of protein and lipid molecules having a mosaic structure. The membrane ensures the exchange of substances between the cell and the intercellular fluid.

EPS

This is a system of tubules and cavities, on the walls of which there are ribosomes that provide protein synthesis. Ribosomes can also be freely located in the cytoplasm. There are two types of ER - rough and smooth: on the rough ER (or granular) there are many ribosomes that carry out protein synthesis. Ribosomes give membranes a rough appearance. Smooth ER membranes do not carry ribosomes on their surface; they contain enzymes for the synthesis and breakdown of carbohydrates and lipids. Smooth EPS looks like a system of thin tubes and tanks.

Ribosomes

Small bodies with a diameter of 15–20 mm. Carry out the synthesis of protein molecules, their assembly from amino acids.

Mitochondria

These are two-membrane organelles, the inner membrane of which has outgrowths - cristae. The contents of the cavities is the matrix. Mitochondria contain a large number of lipoproteins and enzymes. These are the energy stations of the cell.

Plastids (peculiar to plant cells only!)

Their content in the cell is the main feature of the plant organism. There are three main types of plastids: leucoplasts, chromoplasts, and chloroplasts. They have different colors. Colorless leukoplasts are found in the cytoplasm of the cells of the unstained parts of plants: stems, roots, tubers. For example, there are many of them in potato tubers, in which starch grains accumulate. Chromoplasts are found in the cytoplasm of flowers, fruits, stems, and leaves. Chromoplasts provide the yellow, red, orange color of plants. Green chloroplasts are found in the cells of leaves, stems, and other plant parts, as well as in a variety of algae. Chloroplasts are 4-6 µm in size and often have an oval shape. In higher plants, one cell contains several dozen chloroplasts.

Green chloroplasts are able to transform into chromoplasts, which is why leaves turn yellow in autumn, and green tomatoes turn red when ripe. Leukoplasts can turn into chloroplasts (greening of potato tubers in the light). Thus, chloroplasts, chromoplasts and leukoplasts are capable of mutual transition.

The main function of chloroplasts is photosynthesis, i.e. in chloroplasts in the light, organic substances are synthesized from inorganic substances due to the transformation solar energy into the energy of ATP molecules. Chloroplasts of higher plants are 5-10 microns in size and resemble a biconvex lens in shape. Each chloroplast is surrounded by a double membrane with selective permeability. Outside, there is a smooth membrane, and the inside has a folded structure. The main structural unit of the chloroplast is the thylakoid, a flat two-membrane sac that plays a leading role in the process of photosynthesis. The thylakoid membrane contains proteins similar to mitochondrial proteins that are involved in the electron transfer chain. The thylakoids are arranged in stacks resembling stacks of coins (from 10 to 150) and called grana. Grana has a complex structure: in the center is chlorophyll, surrounded by a layer of protein; then there is a layer of lipoids, again protein and chlorophyll.

Golgi complex

This is a system of cavities delimited from the cytoplasm by a membrane, which may have different shape. The accumulation of proteins, fats and carbohydrates in them. Implementation of the synthesis of fats and carbohydrates on membranes. Forms lysosomes.

The main structural element of the Golgi apparatus is a membrane that forms packages of flattened cisterns, large and small vesicles. The cisterns of the Golgi apparatus are connected to the channels of the endoplasmic reticulum. Proteins, polysaccharides, fats produced on the membranes of the endoplasmic reticulum are transferred to the Golgi apparatus, accumulated inside its structures and “packed” in the form of a substance ready either for release or for use in the cell itself during its life. Lysosomes are formed in the Golgi apparatus. In addition, it is involved in the growth of the cytoplasmic membrane, for example, during cell division.

Lysosomes

Bodies separated from the cytoplasm by a single membrane. The enzymes contained in them accelerate the reaction of splitting complex molecules to simple ones: proteins to amino acids, complex carbohydrates to simple ones, lipids to glycerol and fatty acids, and also destroy dead parts of the cell, whole cells. Lysosomes contain more than 30 types of enzymes (substances of a protein nature that increase the rate of a chemical reaction by tens and hundreds of thousands of times) that can break down proteins, nucleic acids, polysaccharides, fats and other substances. The breakdown of substances with the help of enzymes is called lysis, hence the name of the organoid. Lysosomes are formed either from the structures of the Golgi complex, or from the endoplasmic reticulum. One of the main functions of lysosomes is participation in the intracellular digestion of nutrients. In addition, lysosomes can destroy the structures of the cell itself when it dies, during embryonic development, and in a number of other cases.

Vacuoles

They are cavities in the cytoplasm filled with cell sap, a place of accumulation of reserve nutrients, harmful substances; they regulate the water content in the cell.

Cell Center

It consists of two small bodies - centrioles and centrosphere - a compacted area of ​​​​the cytoplasm. Plays an important role in cell division

Organelles of cell movement

1. Flagella and cilia, which are cell outgrowths and have the same structure in animals and plants
2. Myofibrils - thin threads more than 1 cm long with a diameter of 1 micron, arranged in bundles along the muscle fiber
3. Pseudopodia (perform the function of movement; due to them, muscle contraction occurs)

Similarities between plant and animal cells

The features that plant and animal cells are similar to include the following:

1. A similar structure of the structure system, i.e. the presence of a nucleus and cytoplasm.
2. The exchange process of substances and energy is similar in principle of implementation.
3. Both animal and plant cells have a membrane structure.
4. The chemical composition of cells is very similar.
5. In plant and animal cells, there is a similar process of cell division.
6. The plant cell and the animal have the same principle of transmitting the code of heredity.

Significant differences between plant and animal cells

In addition to the general features of the structure and vital activity of plant and animal cells, there are special distinctive features of each of them.

Thus, we can say that plant and animal cells are similar to each other in the content of some important elements and some life processes, and also have significant differences in structure and metabolic processes.