The structure of an animal cell. Cell structure of various organisms

The science that studies the structure and function of cells is called cytology.

Cell- an elementary structural and functional unit of living things.

Cells, despite their small size, are very complex. The internal semi-liquid contents of the cell are called cytoplasm.

Cell nucleus

The cell nucleus is the most important part cells.
The nucleus is separated from the cytoplasm by a shell consisting of two membranes. The core shell contains numerous pores in order to various substances could enter from the cytoplasm into the nucleus, and vice versa.
The internal contents of the kernel are called karyoplasma or nuclear juice. Located in the nuclear juice chromatin And nucleolus.
Chromatin is a strand of DNA. If the cell begins to divide, then the chromatin threads are tightly wound into a spiral around special proteins, like threads on a spool. Such dense formations are clearly visible under a microscope and are called chromosomes.

Core contains genetic information and controls the life of the cell.

Nucleolus is a dense round body inside the core. Typically, there are from one to seven nucleoli in the cell nucleus. They are clearly visible between cell divisions, and during division they are destroyed.

The function of the nucleoli is the synthesis of RNA and proteins, from which special organelles are formed - ribosomes.
Ribosomes participate in protein biosynthesis. In the cytoplasm, ribosomes are most often located on rough endoplasmic reticulum. Less commonly, they are freely suspended in the cytoplasm of the cell.

Endoplasmic reticulum (ER) participates in the synthesis of cell proteins and transport of substances within the cell.

A significant part of the substances synthesized by the cell (proteins, fats, carbohydrates) is not consumed immediately, but through the EPS channels enters for storage in special cavities laid in peculiar stacks, “cisterns”, and delimited from the cytoplasm by a membrane. These cavities are called Golgi apparatus (complex). Most often, the cisterns of the Golgi apparatus are located close to the cell nucleus.
Golgi apparatus takes part in the transformation of cell proteins and synthesizes lysosomes- digestive organelles of the cell.
Lysosomes represent digestive enzymes, “packed” into membrane vesicles, bud and spread throughout the cytoplasm.
The Golgi complex also accumulates substances that the cell synthesizes for the needs of the whole organism and which are removed from the cell to the outside.

Mitochondria- energy organelles of cells. They convert nutrients into energy (ATP) and participate in cell respiration.

Mitochondria are covered with two membranes: the outer membrane is smooth, and the inner one has numerous folds and projections - cristae.

Plasma membrane

For a cell to be a single system, it is necessary that all its parts (cytoplasm, nucleus, organelles) are held together. For this purpose, in the process of evolution, it developed plasma membrane, which, surrounding each cell, separates it from external environment. Outer membrane protects the internal contents of the cell - the cytoplasm and nucleus - from damage, maintains a constant shape of the cell, ensures communication between cells, selectively allows necessary substances into the cell and removes metabolic products from the cell.

The structure of the membrane is the same in all cells. The basis of the membrane is a double layer of lipid molecules, in which numerous protein molecules are located. Some proteins are located on the surface of the lipid layer, others penetrate both layers of lipids through and through.

Special proteins form the finest channels through which potassium, sodium, calcium ions and some other ions of small diameter can pass into or out of the cell. However, larger particles (molecules nutrients- proteins, carbohydrates, lipids) cannot pass through membrane channels and enter the cell using phagocytosis or pinocytosis:

• At the point where the food particle touches the outer membrane of the cell, an invagination is formed, and the particle enters the cell, surrounded by a membrane. This process is called phagocytosis (plant cells are covered with a dense layer of fiber (cell membrane) on top of the outer cell membrane and cannot capture substances by phagocytosis).
• Pinocytosis differs from phagocytosis only in that in this case the invagination of the outer membrane captures not solid particles, but droplets of liquid with substances dissolved in it. This is one of the main mechanisms for the penetration of substances into the cell.

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 differs from a plant cell. An animal cell does not have walls or chloroplasts (organelles that perform).

Drawing of an animal cell with captions

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

Most often, it contains the majority, sometimes all existing types organelles

Basic organelles and organelles of an animal cell

Organelles and organelles are the “organs” responsible for the functioning of a microorganism.

Core

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, strands of DNA wrap tightly around highly specialized proteins (histones) to form chromosomes.

The nucleus selects genes to control the activity and functioning 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 the other components.

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

Ribosomes

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

The mRNA strand 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 (cisternae) 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 of attached ribosomes and is involved in the creation of lipids and steroid hormones and the removal of toxic substances.

Vesicles

Vesicles are small spheres of lipid bilayer that are part of the outer membrane. They are used to transport molecules throughout the cell from one organelle to another and participate in metabolism.

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

Golgi apparatus

The Golgi apparatus (Golgi complex, Golgi body) also consists of cisterns that are not interconnected (unlike the endoplasmic reticulum).

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

Mitochondria

The process of cellular respiration occurs in mitochondria. 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 called "generators".

Cell cytoplasm

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

Cytosol

Cytosol is called cellular fluid. The cytosol and all the organelles within it, excluding the nucleus, are collectively called the cytoplasm. The cytosol is primarily composed of 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 tissue;
• secures organelles in certain places;
• plays 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, and microtubules are the largest.

Cell membrane

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

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

The cell membrane is selectively permeable—it is capable of allowing certain molecules to pass through. Oxygen and carbon dioxide pass easily, while large or charged molecules must pass through a special channel in the membrane to maintain homeostasis.

Lysosomes

Lysosomes are organelles that degrade substances. The lysosome contains about 40 digestive enzymes. It is interesting that the cellular organism itself is protected from degradation in the event of a breakthrough of lysosomal enzymes into the cytoplasm; mitochondria that have completed their functions are subject to decomposition. After cleavage, 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. The 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 into a constantly changing organism that is in motion, it can be difficult to identify individual organelles.

The following parts are not in doubt:

• core;
• cytoplasm;
• cell membrane.

A higher resolution microscope, a carefully prepared specimen, and some practice will help you study the cell in more detail.

Centriole functions

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

The structure of a human cell - drawing with captions

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

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

Signs of a living cell

A living cell is similar in its characteristics to a living being as a whole. It breathes, eats, develops, divides, and various processes occur 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 complex acting organism, having distinctive features, functions, 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.

Studying the structure plant cell, a drawing with captions will be a useful visual summary for mastering this topic. But first, a little history.

The history of the discovery and study of cells is associated with the name of the English inventor Robert Hooke. In the 17th century, on a section of a plant plug examined under a microscope, R. Hooke discovered cells, which were later called cells.

Basic information about the cell was presented later by the German scientist T. Schwann in cell theory, formulated in 1838. The main provisions of this treatise read:

• all life on earth consists of structural units - cells;
• All cells have common features in structure and function. These elementary particles capable of reproduction, which is possible due to the division of the mother cell;
• in multicellular organisms, cells are able to unite based on general functions and structural and chemical organization in tissue.

plant cell

The plant cell, along with common features and similarity in structure with animals, has its own distinctive features unique to her:

• the presence of a cell wall (shell);
• presence of plastids;
• presence of a vacuole.

Structure of a plant cell

The figure schematically shows a model of a plant cell, what it consists of, and what its main parts are called.

Each of them will be discussed in detail below.

Cell organelles and their functions - descriptive table

The table contains important information about cell organelles. She will help the student create a story plan based on the drawing.

Cytoplasmic formations - cell organelles

Let's talk in more detail about the components of a plant cell.

Core

The core stores genetic information and implements inherited information. The storage location is DNA molecules. At the same time, repair enzymes are present in the nucleus, which are able to control and eliminate spontaneous damage to DNA molecules.

In addition, the DNA molecules themselves in the nucleus are subject to reduplication (doubling). In this case, the cells formed by dividing the original cell receive the same amount of genetic information in both qualitative and quantitative proportions.

Endoplasmic reticulum (ER)

There are two types: rough and smooth. The first type synthesizes proteins for export and cell membranes. The second type is able to detoxify harmful products exchange.

Golgi apparatus

Discovered by Italian researcher C. Golgi in 1898. In cells it is located near the nucleus. These organelles are membranous structures packed together. This accumulation zone is called a dictyosome.

They take part in the accumulation of products that are synthesized in the endoplasmic reticulum and are the source of cellular lysosomes.

Lysosomes

They are not independent structures. They are the result of the activity of the endoplasmic reticulum and the Golgi apparatus. Their main purpose is to participate in the breakdown processes inside the cell.

There are about four dozen enzymes in lysosomes that destroy most organic compounds. Moreover, the lysosome membrane itself is resistant to the action of such enzymes.

Mitochondria

Double membrane organelles. In each cell their number and size may vary. They are surrounded by two highly specialized membranes. Between them there is an intermembrane space.

The inner membrane is capable of forming folds - cristae. Due to the presence of cristae, the inner membrane is 5 times larger than the area of ​​the outer membrane.

Increased functional activity of the cell is due to an increased number of mitochondria and a large number of cristae in them, while under conditions of physical inactivity the number of cristae in mitochondria and the number of mitochondria changes sharply and quickly.

Both mitochondrial membranes differ in their physiological properties. With increased or decreased osmotic pressure the inner membrane can shrink or stretch. The outer membrane is characterized only by irreversible stretching, which can lead to rupture. The entire complex of mitochondria that fills the cell is called a chondrion.

Plastids

In size, these organelles are second only to the nucleus. There are three types of plastids:

• responsible for the green color of plants - chloroplasts;
• responsible for autumn colors - orange, red, yellow, ocher - chromoplasts;
• colorless leucoplasts that do not affect coloring.

It is worth noting: It has been established that only one type of plastid can be present in cells at a time.

Structure and functions of chloroplasts

They carry out the processes of photosynthesis. Chlorophyll is present (gives it a green color). Shape: biconvex lens. The number in the cage is 40-50. Has a double membrane. The inner membrane forms flat vesicles - thylakoids, which are packed into stacks - grana.

Chromoplasts

Due to bright pigments they impart to plant organs bright colors: colorful flower petals, ripe fruits, autumn leaves and some root vegetables (carrots).

Chromoplasts do not have an internal membrane system. Pigments can accumulate in crystalline form, which gives plastids various shapes (plate, rhombus, triangle).

The functions of this type of plastid have not yet been fully studied. But according to available information, these are obsolete chloroplasts with destroyed chlorophyll.

Leukoplasts

Inherent in those parts of plants to which Sun rays don't hit. For example, tubers, seeds, bulbs, roots. Internal system membranes are less developed than those of chloroplasts.

They are responsible for nutrition, accumulate nutrients, and take part in synthesis. In the presence of light, leucoplasts can transform into chloroplasts.

Ribosomes

Small granules consisting of RNA and proteins. The only membraneless structures. They can be located singly or as part of a group (polysomes).

The ribosome is formed by a large and small subunit connected by magnesium ions. Function: protein synthesis.

Microtubules

These are long cylinders in the walls of which the protein tubulin is located. This organelle is a dynamic structure (its growth and decay can occur). They take an active part in the process of cell division.

Vacuole - structure and functions

The figure shows blue. Consists of a membrane (tonoplast) and internal environment(cell sap).

Occupies most of the cell, its central part.

Stores water and nutrients, as well as decay products.

Despite the uniform structural organization in the structure of the main organelles, enormous species diversity is observed in the plant world.

Any schoolchild, and especially an adult, needs to understand and know what essential parts a plant cell has and what its model looks like, what role they play, and what the names of the organelles responsible for the coloring of plant parts are called.

Objects of living nature have a cellular structure similar to all species. However, each kingdom has its own characteristics. This article will help you find out in more detail what the structure of an animal cell is, in which we will tell you not only about the features, but also introduce you to the functions of organelles.

A complex animal organism consists of a large number of tissues. The shape and purpose of the cell depends on the type of tissue it is part of. Despite their diversity, we can identify general properties in cellular structure:

• membrane consists of two layers that separate the contents from the external environment. Its structure is elastic, so cells can have a variety of shapes;
• cytoplasm located inside the cell membrane. It is a viscous liquid that is constantly moving;

Due to the movement of the cytoplasm, various chemical processes and metabolism occur inside the cell.

• core - It has big sizes, compared to plants. Located in the center, inside it there is nuclear juice, a nucleolus and chromosomes;
• mitochondria consist of many folds - cristae;
• endoplasmic reticulum has many channels through which nutrients enter the Golgi apparatus;
• a complex of tubules called Golgi apparatus , accumulates nutrients;
• lysosomes regulate the amount of carbon and other nutrients;
• ribosomes located around the endoplasmic reticulum. Their presence makes the network rough; the smooth surface of the ER indicates the absence of ribosomes;
• centrioles - special microtubules that are absent in plants.

Rice. 1. The structure of an animal cell.

Scientists have recently discovered the presence of centrioles. Because they can only be seen and studied using an electron microscope.

Functions of cell organelles

Each organelle performs certain functions, their joint work constitutes a single cohesive organism. For example:

• cell membrane ensures the transport of substances into and out of the cell;
• inside the core is genetic code, which is passed on from generation to generation. Exactly core regulates the functioning of other cell organelles;
• The energy stations of the body are mitochondria . It is here that the substance ATP is formed, the breakdown of which releases a large number of energy.

Rice. 2. The structure of mitochondria

• on the walls Golgi apparatus fats and carbohydrates are synthesized, which are necessary for building the membranes of other organelles;
• lysosomes break down unnecessary fats and carbohydrates, as well as harmful substances;
• ribosomes synthesize protein;
• cell center (centrioles) play an important role in the formation of the spindle during cell mitosis.

Rice. 3. Centrioles.

Unlike a plant cell, an animal cell does not have vacuoles. However, temporary small vacuoles may form that contain substances to be removed from the body.

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What have we learned?

The structure of an animal cell, which is studied in biology lessons in grades 7-9, is no different from the structure of other living cells. A feature of an animal cell is the presence of a cell center, the so-called centrioles, which participate in the formation of the spindle during mitosis. Unlike plant organism there are no vacuoles, plastids or cellulose cell wall. The cell membrane is quite elastic, which makes it possible for cells to acquire various shapes and sizes.

Chemical composition of living organisms

The chemical composition of living organisms can be expressed in two forms: atomic and molecular. Atomic (elemental) composition shows the ratio of atoms of elements included in 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 are water and mineral salts, the most important organic substances are 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 are Cl-, SO2-, HPO2-, H2PO-, HCO-, NO-.

Carbohydrates - organic compounds consisting of one or many molecules simple sugars. The carbohydrate content 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 animals and humans and must be obtained from plant foods(they are called irreplaceable).

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

Cell structure

The emergence of cell theory

• Robert Hooke discovered cells in a section of cork in 1665 and first used the term “cell.”
• Anthony van Leeuwenhoek discovered single-celled organisms.
• Matthias Schleiden in 1838 and Thomas Schwann in 1839 formulated the basic principles of cell theory. However, they mistakenly believed that cells arise from a primary noncellular substance.
• Rudolf Virchow proved in 1858 that all cells are formed from other cells by cell division.

Basic principles of cell theory

1. The cell is the structural unit of all living things. All living organisms are made up of cells (with the exception of viruses).
2. The cell is the functional unit of all living things. The cell exhibits the entire complex of vital functions.
3. The cell is the unit of development of all living things. New cells are formed only as a result of 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 entire organism.
5. The cells of all organisms are similar in chemical composition, structure and functions.

Types of Cellular 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. Prokaryotes include bacteria, eukaryotes include plants, fungi and animals.

Prokaryotic cells are relatively simple. They do not have a nucleus, the area where DNA is located in the cytoplasm is called a nucleoid, the only DNA molecule is circular and not associated with proteins, the cells are smaller than eukaryotic cells, the cell wall includes a glycopeptide - murein, there are no membrane organelles, their functions are performed by invaginations of the plasma membrane, ribosomes are small, There are no microtubules, so the cytoplasm is motionless, and 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 displaces 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 wall containing chitin, a central vacuole in the cytoplasm, and no plastids. Only some fungi have a centriole in the cell center. The main reserve carbohydrate is glycogen.

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

Structure of a eukaryotic cell

A typical eukaryotic cell has three components: the membrane, the cytoplasm, and the nucleus.

Cell membrane

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

The cell membrane performs important and very diverse functions: determines and maintains the shape of the cell; protects the cell from mechanical influences penetration of damaging biological agents; carries out the reception of many molecular signals (for example, hormones); limits the internal contents of the cell; regulates metabolism between cells and 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 are called pinocytosis and reverse pinocytosis.

Cytoplasm

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

Hyaloplasm (matrix) is water solution inorganic and organic substances that are capable of changing their viscosity and are in constant motion. The ability to move or flow the cytoplasm is called cyclosis.

Matrix is active medium, in which many physical and chemical processes take place and which unites all the elements of the cell into a single system.

The cytoplasmic structures of the cell are represented by inclusions and organelles. Inclusions are relatively unstable, found in certain types of cells at certain moments of life, for example, as a supply of nutrients (starch grains, proteins, glycogen drops) or products to be released from the cell. Organelles are permanent and essential components of most cells, having a specific structure and performing a vital function.

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

Endoplasmic reticulum. All inner zone 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. There are two known types of it: 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 diverse functions. The main function of the granular endoplasmic reticulum is participation in protein synthesis, which occurs in ribosomes.

The synthesis of lipids and carbohydrates occurs on the membranes of the smooth endoplasmic reticulum. All these synthesis products accumulate in channels and cavities, and are then transported to various organelles of the cell, where they are consumed or accumulated in the cytoplasm as cellular 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- or rod-shaped bodies. The structure of this organelle is similar in the cells of plant and animal organisms, despite the diversity of its shape.

The Golgi apparatus includes: cavities bounded by membranes and located in groups (5-10); 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. The products of the cell's synthetic activity - proteins, carbohydrates and fats - are transported to it through the channels of the endoplasmic reticulum. All these substances first accumulate, and then, in the form of large and small bubbles, enter the cytoplasm and are either used in the cell itself during its life, or removed from it and used in the body. For example, in the cells of the mammalian pancreas, digestive enzymes are synthesized, which accumulate in the cavities of the organelle. Bubbles filled with enzymes then form. They are excreted from the cells into the pancreatic duct, from where they flow into the intestinal cavity. Another one important function of this organelle is that on its membranes the synthesis of fats and carbohydrates (polysaccharides) occurs, which are used in the cell and which are part of the membranes. Thanks to the activity of the Golgi apparatus, 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 examine their shape, location, and count their number. Internal structure mitochondria were studied using an electron microscope. The mitochondrial shell consists of two membranes - outer and inner. The outer membrane is smooth, it does not form any folds or outgrowths. The inner membrane, on the contrary, forms numerous folds that are directed into the mitochondrial cavity. Folds inner membrane called cristae (Latin “crista” - ridge, outgrowth) The number of cristae is not the same in the mitochondria of different cells. There can be from several tens to several hundred of them, with especially many cristae in the mitochondria of actively functioning cells, such as muscle cells.

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

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

Lysosomes

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

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

Possessing the ability to actively digest nutrients, lysosomes participate in the removal of cell parts, whole cells and organs that die during vital activity. The formation of new lysosomes occurs constantly in the cell. Enzymes contained in lysosomes, like any other proteins, are synthesized on ribosomes in the cytoplasm. These enzymes then travel through 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 - leucoplasts.

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

Ribosomes. Ribosomes are found in the cells of all organisms. These are microscopic round bodies with a diameter of 15-20 nm. Each ribosome consists of two particles of unequal size, 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 contain proteins and RNA. The function of ribosomes is protein synthesis. Protein synthesis - difficult process, which is carried out not by one ribosome, but by a whole group, including up to several dozen united ribosomes. This group of ribosomes is called a polysome. Synthesized proteins first accumulate in the channels and cavities of the endoplasmic reticulum and are then transported to organelles and cell sites where they are consumed. The endoplasmic reticulum and ribosomes located on its membranes represent a single apparatus for the biosynthesis and transport of proteins.

Microtubules and microfilaments

Thread-like structures consisting of various contractile proteins and causing motor functions cells. Microtubules look like hollow cylinders, the walls of which consist of proteins - tubulins. Microfilaments are very thin, long, thread-like structures composed of actin and myosin.

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

Cellular center (centrosome). In animal cells, near the nucleus there is an organelle called the cell center. The main part of the cell center consists 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 participate in the formation of the division spindle.

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

Core

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

The nucleus is usually spherical or oval shape, less often it can be segmented or fusiform. The nucleus consists of a nuclear envelope and karyoplasm containing chromatin (chromosomes) and nucleoli.

The nuclear envelope 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 containing various proteins, nucleotides, ions, as well as chromosomes and the nucleolus.

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

Chromatin is clumps, granules and filamentous structures formed by DNA molecules in complex with proteins that are specifically stained with certain dyes. Various sections of DNA molecules within chromatin have to varying degrees spiralization, and therefore differ in the intensity of color 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 implementing the information contained in it. During cell division, DNA spirals and chromatin structures form chromosomes.

Chromosomes are dense, intensely stained structures that are units of morphological organization of 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 in pairs. A single set of chromosomes in germ cells is called haploid (n), while a set of chromosomes in somatic cells is called diploid (2n). Chromosomes of different organisms vary in size and shape.

A diploid set of chromosomes of cells of a particular type of living organism, 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 identical in size, shape, and composition (one is inherited from the maternal organism, the other from the paternal organism). Chromosomes as part of a karyotype are also divided into autosomes, or non-sex chromosomes, which are the same in male and female individuals, and heterochromosomes, or sex chromosomes, which are involved in sex determination and differ in males and females. The human karyotype is represented by 46 chromosomes (23 pairs): 44 autosomes and 2 sex chromosomes (females have two identical X chromosomes, males have 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 development processes of the body.