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

Cell shapes are very diverse. In unicellular organisms, each cell is a separate organism. Its shape and structural features are associated with the environmental conditions in which this unicellular organism lives, with its lifestyle.

Differences in the structure of cells

The body of every multicellular animal and plant is composed of cells that differ in appearance, which is associated with their functions. So, in animals, one can immediately distinguish a nerve cell from a muscle or epithelial cell (epithelium-integumentary tissue). In plants, the structure of the cell of the leaf, stem, etc. is not the same.
The size of the cells is just as variable. The smallest of them (some) do not exceed 0.5 microns. The size of the cells of multicellular organisms ranges from several micrometers (the diameter of human leukocytes is 3-4 microns, the diameter of erythrocytes is 8 microns) to huge sizes (the processes of one human nerve cell have a length of more than 1 m ). In most plant and animal cells, their diameter ranges from 10 to 100 microns.
Despite the diversity of the structure of shapes and sizes, all living cells of any organism are similar in many ways of internal structure. Cell- a complex holistic physiological system in which all the basic processes of life are carried out: energy, irritability, growth and self-reproduction.

The main components in the structure of the cell

The main common components of a cell are the outer membrane, cytoplasm and nucleus. A cell can live and function normally only in the presence of all these components that closely interact with each other and with the environment.

Picture. 2. Cell structure: 1 - nucleus, 2 - nucleolus, 3 - nuclear membrane, 4 - cytoplasm, 5 - Golgi apparatus, 6 - mitochondria, 7 - lysosomes, 8 - endoplasmic reticulum, 9 - ribosomes, 10 - cell membrane

The structure of the outer membrane. It is a thin (about 7.5 nm2 thick) three-layer cell membrane, visible only in an electron microscope. The two extreme layers of the membrane are composed of proteins, and the middle one is formed by fat-like substances. The membrane has very small pores, due to which it easily passes some substances and retains others. The membrane takes part in phagocytosis (the capture of solid particles by the cell) and in pinocytosis (the capture by the cell of liquid droplets with substances dissolved in it). Thus, the membrane maintains the integrity of the cell and regulates the flow of substances from the environment into the cell and from the cell into its environment.
On its inner surface, the membrane forms invaginations and branches that penetrate deep into the cell. Through them, the outer membrane is connected to the shell of the nucleus. On the other hand, the membranes of neighboring cells, forming mutually adjoining invaginations and folds, very closely and reliably connect the cells into multicellular tissues.

Cytoplasm is a complex colloidal system. Its structure: a transparent semi-liquid solution and structural formations. The structural formations of the cytoplasm common to all cells are: mitochondria, endoplasmic reticulum, Golgi complex and ribosomes (Figure 2). All of them, together with the nucleus, are the centers of certain biochemical processes, which together make up the cell. These processes are extremely diverse and proceed simultaneously in a microscopically small volume of the cell. This is related to the general feature of the internal structure of all structural elements of the cell: despite their small size, they have a large surface on which biological catalysts (enzymes) are located and various biochemical reactions are carried out.

Mitochondria(Figure. 2, 6) - energy centers of the cell. These are very small bodies, but clearly visible in a light microscope (length 0.2-7.0 microns). They are located in the cytoplasm and vary greatly in shape and number in different cells. The liquid content of mitochondria is enclosed in two three-layer shells, each of which has the same structure as the outer membrane of the cell. The inner shell of the mitochondrion forms numerous protrusions and incomplete partitions inside the body of the mitochondrion (Fig. 3). These invaginations are called cristae. Thanks to them, with a small volume, a sharp increase in the surfaces on which biochemical reactions are carried out is achieved, and among them, first of all, the reactions of accumulation and release of energy through the enzymatic conversion of adenosine diphosphoric acid to adenosine triphosphoric acid and vice versa.

Endoplasmic reticulum(Figure 2, 8) is a multiply branched protrusion of the outer membrane of the cell. The membranes of the endoplasmic reticulum are usually arranged in pairs, and tubules are formed between them, which can expand into larger cavities filled with biosynthetic products. Around the nucleus, the membranes that make up the endoplasmic reticulum directly pass into the outer membrane of the nucleus. Thus, the endoplasmic reticulum links together all parts of the cell. In a light microscope, when examining the structure of the cell, the endoplasmic reticulum is not visible.

The structure of the cell is distinguished rough and smooth endoplasmic reticulum. The rough endoplasmic reticulum is densely surrounded by ribosomes, where protein synthesis occurs. The smooth endoplasmic reticulum is devoid of ribosomes and synthesis of fats and carbohydrates is carried out in it. Through the tubules of the endoplasmic reticulum, intracellular metabolism of substances synthesized in various parts of the cell, as well as exchange between cells, is carried out. At the same time, the endoplasmic reticulum, as a denser structural formation, performs the function of the skeleton of the cell, giving its shape a certain stability.

Ribosomes(Figure 2, 9) are located both in the cytoplasm of the cell and in its nucleus. These are the smallest grains with a diameter of about 15-20 nm, which makes them invisible in a light microscope. In the cytoplasm, the bulk of the ribosomes is concentrated on the surface of the tubules of the rough endoplasmic reticulum. The function of ribosomes lies in the most important process for the life of the cell and the organism in the whole process - in the synthesis of proteins.

Golgi complex(Figure 2, 5) was initially found only in animal cells. Recently, however, similar structures have been found in plant cells. The structure of the structure of the Golgi complex is close to the structural formations of the endoplasmic reticulum: these are tubules, cavities and vesicles of various shapes formed by three-layer membranes. In addition, the Golgi complex includes rather large vacuoles. They accumulate some products of synthesis, primarily enzymes and hormones. During certain periods of cell life, these reserved substances can be removed from this cell through the endoplasmic reticulum and are involved in the metabolic processes of the body as a whole.

Cell Center- formation, so far described only in the cells of animals and lower plants. It consists of two centrioles, the structure of each of which is a cylinder up to 1 micron in size. Centrioles play an important role in mitotic cell division. In addition to the described permanent structural formations, certain inclusions periodically appear in the cytoplasm of various cells. These are fat droplets, starch grains, protein crystals of a special form (aleurone grains), etc. Such inclusions are found in large numbers in the cells of storage tissues. However, in cells of other tissues, such inclusions can exist as a temporary reserve of nutrients.

Nucleus(Figure 2, 1), like the cytoplasm with an outer membrane, is an essential component of the vast majority of cells. Only in some bacteria, when considering the structure of their cells, it was not possible to identify a structurally formed nucleus, but in their cells all the chemicals inherent in the nuclei of other organisms were found. There are no nuclei in some specialized cells that have lost the ability to divide (mammalian erythrocytes, sieve tubes of plant phloem). On the other hand, there are multinucleated cells. The nucleus plays a very important role in the synthesis of enzyme proteins, in the transmission of hereditary information from generation to generation, in the processes of individual development of the organism.

The nucleus of a nondividing cell has a nuclear envelope. It consists of two three-layer membranes. The outer membrane is connected through the endoplasmic reticulum to the cell membrane. Through this entire system, there is a constant exchange of substances between the cytoplasm, the nucleus and the environment surrounding the cell. In addition, there are pores in the nuclear membrane through which the nucleus also communicates with the cytoplasm. Inside the nucleus is filled with nuclear juice, which contains clumps of chromatin, the nucleolus and ribosomes. Chromatin is made up of protein and DNA. This is the material substrate that, before cell division, is formed into chromosomes visible under a light microscope.

Chromosomes- constant in number and form of education, the same for all organisms of a given species. The functions of the nucleus listed above are primarily associated with chromosomes, or rather, with the DNA that is part of them.

nucleolus(Figure. 2.2) in the amount of one or more is present in the nucleus of a non-dividing cell and is clearly visible in the light micro-cleavage. At the time of cell division, it disappears. Recently, the enormous role of the nucleolus has been clarified: ribosomes are formed in it, which then enter the cytoplasm from the nucleus and carry out protein synthesis there.

All of the above applies equally to animal cells and plant cells. In connection with the specifics of metabolism, growth and development of plants and animals in the structure of the cells of both, there are additional structural features that distinguish plant cells from animal cells. More about this is written in the sections "Botany" and "Zoology"; here we note only the most general differences.

Animal cells, in addition to the listed components, in the structure of the cell, have special formations - lysosomes. These are ultramicroscopic vesicles in the cytoplasm filled with liquid digestive enzymes. Lysosomes carry out the function of splitting food substances into simpler chemicals. There are separate indications that lysosomes are also found in plant cells.
The most characteristic structural elements of plant cells (except for those common that are inherent in all cells) are plastids. They exist in three forms: green chloroplasts, red-orange-yellow
chromoplasts and colorless leucoplasts. Leukoplasts under certain conditions can turn into chloroplasts (greening of a potato tuber), and chloroplasts, in turn, can become chromoplasts (autumn yellowing of leaves).

Chloroplasts(Figure 4) represent a “factory” for the primary synthesis of organic substances from inorganic substances using solar energy. These are small bodies of a rather diverse shape, always green due to the presence of chlorophyll. The structure of chloroplasts in the cell: they have an internal structure that ensures the maximum development of free surfaces. These surfaces are created by numerous thin plates, the clusters of which are located inside the chloroplast.
From the surface, the chloroplast, like other structural elements of the cytoplasm, is covered with a double membrane. Each of them, in turn, is three-layered, like the outer membrane of the cell.

Cell structure

The human body, like any other living organism, 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 of 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. In the image you can see the cellular structure of 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 variously shaped 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.

Scientists position the animal cell as the main part of the body of a representative of the animal kingdom - both unicellular and multicellular.

They are eukaryotic, with a true nucleus and specialized structures - organelles that perform differentiated functions.

Plants, fungi, and protists have eukaryotic cells; bacteria and archaea have simpler prokaryotic cells.

The structure of an animal cell is different from a plant cell. An animal cell does not have walls or chloroplasts (organelles that perform).

Animal cell drawing with captions

The cell consists of many specialized organelles that perform various functions.

Most often, it contains most, sometimes all, existing types of organelles.

Major organelles and organelles of an animal cell

Organelles and organoids are the "organs" responsible for the functioning of a microorganism.

Nucleus

The nucleus is the source of deoxyribonucleic acid (DNA), the genetic material. DNA is the source of the creation of proteins that control the state of the body. In the nucleus, DNA strands wrap tightly around highly specialized proteins (histones) to form chromosomes.

The nucleus selects genes by controlling the activity and function of the tissue unit. Depending on the type of cell, it contains a different set of genes. DNA is found in the nucleoid region of the nucleus where ribosomes are formed. The nucleus is surrounded by a nuclear membrane (karyolemma), a double lipid bilayer that separates it from other components.

The nucleus regulates cell growth and division. When chromosomes are formed in the nucleus, which are duplicated in the process of reproduction, forming two daughter units. Organelles called centrosomes help organize DNA during division. The nucleus is usually represented in the singular.

Ribosomes

Ribosomes are the site of protein synthesis. They are found in all units of tissue, in plants and animals. In the nucleus, the DNA sequence that codes for a particular protein is copied into a free messenger RNA (mRNA) strand.

The mRNA chain travels to the ribosome via messenger RNA (tRNA) and its sequence is used to determine the arrangement of amino acids in the chain that makes up the protein. In animal tissue, ribosomes are located freely in the cytoplasm or attached to the membranes of the endoplasmic reticulum.

Endoplasmic reticulum

The endoplasmic reticulum (ER) is a network of membranous sacs (cistern) extending from the outer nuclear membrane. It modifies and transports proteins created by ribosomes.

There are two types of endoplasmic reticulum:

• granular;
• agranular.

The granular ER contains attached ribosomes. The agranular ER is free from attached ribosomes, participates in the creation of lipids and steroid hormones, and the removal of toxic substances.

Vesicles

Vesicles are small spheres of the lipid bilayer that make up the outer membrane. They are used to transport molecules through the cell from one organelle to another, and are involved in metabolism.

Specialized vesicles called lysosomes contain enzymes that digest large molecules (carbohydrates, lipids and proteins) into smaller ones for easier use by the tissue.

golgi apparatus

The Golgi apparatus (Golgi complex, Golgi body) also consists of unconnected cisterns (unlike the endoplasmic reticulum).

The Golgi apparatus receives proteins, sorts them, and packages them into vesicles.

Mitochondria

In mitochondria, the process of cellular respiration takes place. Sugars and fats are broken down and energy is released in the form of adenosine triphosphate (ATP). ATP controls all cellular processes, mitochondria produce ATP cells. Mitochondria are sometimes referred to as "generators".

Cell cytoplasm

The cytoplasm is the fluid environment of the cell. It can function even without a core, however, for a short time.

Cytosol

The cytosol is called the cell fluid. The cytosol and all the organelles within it, with the exception of the nucleus, are collectively referred to as the cytoplasm. The cytosol is mostly water and also contains ions (potassium, proteins, and small molecules).

cytoskeleton

The cytoskeleton is a network of filaments and tubes distributed throughout the cytoplasm.

It performs the following functions:

• gives shape;
• provides strength;
• stabilizes tissues;
• fixes organelles in certain places;
• plays an important role in signal transmission.

There are three types of cytoskeletal filaments: microfilaments, microtubules, and intermediate filaments. Microfilaments are the smallest elements of the cytoskeleton, while microtubules are the largest.

cell membrane

The cell membrane completely surrounds the animal cell, which does not have a cell wall, unlike plants. The cell membrane is a double layer of phospholipids.

Phospholipids are molecules containing phosphates attached to glycerol and fatty acid radicals. They spontaneously form double membranes in water due to their both hydrophilic and hydrophobic properties.

The cell membrane is selectively permeable - it is able to let certain molecules through. Oxygen and carbon dioxide pass easily, while large or charged molecules must pass through a special channel in the membrane that maintains homeostasis.

Lysosomes

Lysosomes are organelles that carry out the degradation of substances. The lysosome contains about 40 enzymes. Interestingly, the cellular organism itself is protected from degradation in the event of a breakthrough of lysosomal enzymes into the cytoplasm; mitochondria that have finished their functions are subjected to decomposition. After splitting, residual bodies are formed, primary lysosomes turn into secondary ones.

Centriole

Centrioles are dense bodies located near the nucleus. The number of centrioles varies, most often there are two. Centrioles are connected by an endoplasmic bridge.

What does an animal cell look like under a microscope?

Under a standard optical microscope, the main components are visible. Due to the fact that they are connected in a continuously changing organism that is in motion, it can be difficult to identify individual organelles.

The following parts are not in doubt:

• nucleus;
• cytoplasm;
• cell membrane.

The large resolution of the microscope, a carefully prepared preparation and some practice will help to study the cell in more detail.

Centriole Functions

The exact functions of the centriole remain unknown. There is a widespread hypothesis that centrioles are involved in the division process, forming the spindle of division and determining its direction, but there is no certainty in the scientific world.

The structure of the human cell - drawing with captions

A unit of human cell tissue has a complex structure. The figure shows the main structures.

Each component has its own purpose, only in a conglomerate they ensure the functioning of an important part of a living organism.

Signs of a living cell

A living cell in its characteristics is similar to a living being as a whole. It breathes, feeds, develops, divides, various processes take place in its structure. It is clear that the fading of natural processes for the body means death.

Distinctive features of plant and animal cells in the table

Plant and animal cells have both similarities and differences, which are briefly described in the table:

The main components are similar for both plant and animal particles.

Conclusion

An animal cell is a complex acting organism with distinctive features, functions, and the purpose of existence. All organelles and organoids contribute to the life process of this microorganism.

Some components have been studied by scientists, while the functions and features of others have yet to be discovered.

The elementary and functional unit of all life on our planet is the cell. In this article, you will learn in detail about its structure, the functions of organelles, and also find the answer to the question: “What is the difference between the structure of plant and animal cells?”.

Cell structure

The science that studies the structure of the cell and its functions is called cytology. Despite their small size, these parts of the body have a complex structure. Inside is a semi-liquid substance called the cytoplasm. All vital processes take place here and the constituent parts are located - organelles. Learn more about their features below.

Nucleus

The most important part is the core. It is separated from the cytoplasm by a membrane, which consists of two membranes. They have pores so that substances can get from the nucleus to the cytoplasm and vice versa. Inside is the nuclear juice (karyoplasm), which contains the nucleolus and chromatin.

Rice. 1. The structure of the nucleus.

It is the nucleus that controls the life of the cell and stores genetic information.

The functions of the internal contents of the nucleus are the synthesis of protein and RNA. They form special organelles - ribosomes.

Ribosomes

They are located around the endoplasmic reticulum, while making its surface rough. Sometimes ribosomes are freely located in the cytoplasm. Their functions include protein synthesis.

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Endoplasmic reticulum

EPS can have a rough or smooth surface. The rough surface is formed due to the presence of ribosomes on it.

The functions of EPS include protein synthesis and internal transport of substances. Part of the formed proteins, carbohydrates and fats through the channels of the endoplasmic reticulum enters special storage containers. These cavities are called the Golgi apparatus, they are presented in the form of stacks of "tanks", which are separated from the cytoplasm by a membrane.

golgi apparatus

Most often located near the nucleus. Its functions include protein conversion and the formation of lysosomes. This complex stores substances that were synthesized by the cell itself for the needs of the whole organism, and will later be removed from it.

Lysosomes are presented in the form of digestive enzymes, which are enclosed by a membrane in vesicles and carried through the cytoplasm.

Mitochondria

These organelles are covered with a double membrane:

• smooth - outer shell;
• cristae - the inner layer having folds and protrusions.

Rice. 2. The structure of mitochondria.

The functions of mitochondria are respiration and the conversion of nutrients into energy. The cristae contain an enzyme that synthesizes ATP molecules from nutrients. This substance is a universal source of energy for various processes.

The cell wall separates and protects the internal contents from the external environment. It maintains its shape, provides interconnection with other cells, and ensures the process of metabolism. The membrane consists of a double layer of lipids, between which are proteins.

Comparative characteristics

Plant and animal cells differ from each other in their structure, size and shape. Namely:

• the cell wall of a plant organism has a dense structure due to the presence of cellulose;
• a plant cell has plastids and vacuoles;
• the animal cell has centrioles, which are important in the process of division;
• The outer membrane of an animal organism is flexible and can take on various forms.

Rice. 3. Scheme of the structure of plant and animal cells.

The following table will help to summarize the knowledge about the main parts of the cellular organism:

Table "Cell Structure"

What have we learned?

A living organism consists of cells that have a rather complex structure. Outside, it is covered with a dense shell that protects the internal contents from the effects of the external environment. Inside there is a nucleus that regulates all ongoing processes and stores the genetic code. Around the nucleus is the cytoplasm with organelles, each of which has its own characteristics and characteristics.

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cell membrane . A cell (Fig. 1.1), as a living system, needs to maintain certain internal conditions: the concentration of various substances, the temperature inside the cell, etc. Some of these parameters are maintained at a constant level, since their change will lead to cell death, others are of lesser importance for maintaining her life activity.

Rice. 1.1.

cell membrane should ensure the delimitation of the contents of the cell from the environment to maintain the required concentration of substances inside the cell, at the same time it must be permeable for constant exchange of substances between the cell and the environment (Fig. 1.2). The membranes also limit the internal structures of the cell - organelles(organelles) - from the cytoplasm. However, the ego is not just dividing barriers. Cell membranes themselves are the most important organ of the cell, providing not only its structure, but also many functions. In addition to separating cells from each other and separating them from the external environment, membranes unite cells into tissues, regulate the exchange between the cell and the environment, they themselves are the site of many biochemical reactions, and serve as transmitters of information between cells.

According to modern data, plasma membranes are lipoprotein structures (lipoproteins are compounds of protein and fat molecules). Lipids (fats) spontaneously form a double layer, and membrane proteins "swim" in it, like islands in the ocean. There are several thousand different proteins in membranes: structural proteins, carriers, enzymes, etc. In addition, there are pores between protein molecules through which certain substances can pass. Special glycosyl groups are connected to the surface of the membrane, which are involved in the process of cell recognition during tissue formation.

Rice. 1.2.

Different types of membranes differ in their thickness (usually it is from 5 to 10 nm). The consistency of the membrane resembles olive oil. The most important property of the cell membrane is semipermeability”, i.e. the ability to pass only certain substances. The passage of various substances through the plasma membrane is necessary to deliver nutrients and oxygen to the cell, remove toxic waste, create a difference in the concentration of individual trace elements to maintain nervous and muscle activity. Mechanisms of transport of substances through the membrane:

• diffusion - gases, fat-soluble molecules penetrate directly through the plasma membrane, including facilitated diffusion, when a water-soluble substance passes through the membrane through a special channel;
• osmosis - diffusion of water through semi-impermeable membranes towards a lower concentration of ions;
• active transport - the transfer of molecules from an area with a lower concentration to an area with a higher concentration with the help of special transport proteins;
• endocytosis - the transfer of molecules with the help of vesicles (vacuoles) formed by the retraction of the membrane; distinguish between phagocytosis (absorption of solid particles) and ninocytosis (absorption of liquids) (Fig. 1.3);
• exocytosis - a process reverse to endocytosis; through it, solid particles and liquid secretions can be removed from the cells (Fig. 1.4).

Diffusion and osmosis do not require additional energy; active transport, endocytosis and exocytosis need to provide the energy that the cell receives from the breakdown of the nutrients it has absorbed.

Rice. 1.3.

Rice. 1.4.

Regulation of the passage of various substances through the plasma membrane is one of its most important functions. Depending on external conditions, the structure of the membrane can change: it can become more liquid, active and permeable. Membrane permeability is regulated by the fat-like substance cholesterol.

The outer structure of the cell is supported by a denser structure - cell membrane. The cell membrane can have a very different structure (be elastic, have a rigid frame, bristles, antennae, etc.) and perform quite complex functions.

Nucleus found in all cells of the human body, with the exception of erythrocytes. As a rule, a cell contains only one nucleus, but there are exceptions - for example, striated muscle cells contain many nuclei. The nucleus has a spherical shape, its dimensions vary from 10 to 20 microns (Fig. 1.5).

The nucleus is separated from the cytoplasm nuclear envelope, consisting of two membranes - outer and inner, similar to the cell membrane, and a narrow gap between them, containing a semi-liquid medium; through the pores of the nuclear membrane, an intensive exchange of substances between the nucleus and the cytoplasm takes place. On the outer membrane of the shell there are many ribosomes - protein-synthesizing organelles.

Under the nuclear envelope is karyoplasm(nuclear juice), which receives substances from the cytoplasm. Karyoplasm contains chromogo soma(elongated structures containing DNA, in which information about the structure of proteins specific to a given cell is “recorded” - hereditary, or genetic information) and nucleoli(rounded structures within the nucleus in which ribosome formation occurs).

Rice. 1.5.

The set of chromosomes contained in the nucleus is called chromosome set. The number of chromosomes in somatic cells is even - diploid (in humans, these are 44 autosomes and 2 sex chromosomes that determine sex), the sex cells involved in fertilization carry a half set (in humans, 22 autosomes and 1 sex chromosome) (Fig. 1.6).

Rice. 1.6.

The most important function of the nucleus is the transfer of genetic information to daughter cells: when a cell divides, the nucleus divides in two, and the DNC located in it is copied (DNA replication) - this allows each daughter cell to have complete information received from the original (mother) cell (see Fig. cell reproduction).

Cytoplasm(cytosol) - a gelatinous substance containing about 90% water, in which all organelles are located, contains true and colloidal solutions of nutrients and insoluble waste products of metabolic processes, biochemical processes occur: glycolysis, synthesis of fatty acids, nucleic acids and other substances. Organelles in the cytoplasm move, the cytoplasm itself also performs a periodic active movement - cyclosis.

Cell structures(organelles, or organelles) are the "internal organs" of the cell (Table 1.1). They provide the vital processes of the cell, the production of certain substances by the cell (secretion, hormones, enzymes), the overall activity of body tissues, the ability to perform functions specific to a given tissue depend on their vital activity. The structures of the cell, like the cell itself, go through their life cycles: they are born (created by reproduction), actively function, grow old and collapse. Most body cells are able to recover at the subcellular level due to the reproduction and renewal of the organelles included in its structure.

Table 1.1

Cellular organelles, their structure and functions

The end of the table. 1.1