Functions of mitochondria in the cell. Mitochondria

Important role Special structures - mitochondria - play a role in the life activity of each cell. The structure of mitochondria allows the organelle to operate in a semi-autonomous mode.

general characteristics

Mitochondria were discovered in 1850. However, it became possible to understand the structure and functional purpose of mitochondria only in 1948.

Enough at the expense of our own large sizes organelles are clearly visible in a light microscope. The maximum length is 10 microns, the diameter does not exceed 1 micron.

Mitochondria are present in all eukaryotic cells. These are double-membrane organelles, usually bean-shaped. Mitochondria are also found in spherical, filamentous, and spiral shapes.

The number of mitochondria can vary significantly. For example, there are about a thousand of them in liver cells, and 300 thousand in oocytes. Plant cells contain fewer mitochondria than animals.

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Rice. 1. The location of mitochondria in the cell.

Mitochondria are plastic. They change shape and move to the active centers of the cell. Typically, there are more mitochondria in those cells and parts of the cytoplasm where the need for ATP is higher.

Structure

Each mitochondrion is separated from the cytoplasm by two membranes. The outer membrane is smooth. The structure of the inner membrane is more complex. It forms numerous folds - cristae, which increase the functional surface. Between the two membranes there is a space of 10-20 nm filled with enzymes. Inside the organelle there is a matrix - a gel-like substance.

Rice. 2. Internal structure mitochondria.

The table “Structure and functions of mitochondria” describes in detail the components of the organelle.

Compound	Description	Functions
Outer membrane	Consists of lipids. Contains a large amount of porin protein, which forms hydrophilic tubules. The entire outer membrane is permeated with pores through which molecules of substances enter the mitochondria. Also contains enzymes involved in lipid synthesis	Protects the organelle, promotes the transport of substances
	They are located perpendicular to the mitochondrial axis. They may look like plates or tubes. The number of cristae varies depending on the cell type. There are three times more of them in heart cells than in liver cells. Contains phospholipids and proteins of three types: Catalyzing - participate in oxidative processes; Enzymatic - participate in the formation of ATP; Transport - transport molecules from the matrix out and back	Carries out the second stage of breathing using the respiratory chain. Hydrogen oxidation occurs, producing 36 molecules of ATP and water
	Consists of a mixture of enzymes fatty acids, proteins, RNA, mitochondrial ribosomes. This is where mitochondria's own DNA is located.	Carries out the first stage of respiration - the Krebs cycle, as a result of which 2 ATP molecules are formed

The main function of mitochondria is the generation of cell energy in the form of ATP molecules due to the reaction of oxidative phosphorylation - cellular respiration.

In addition to mitochondria, plant cells contain additional semi-autonomous organelles - plastids.
Depending on the functional purpose, three types of plastids are distinguished:

• chromoplasts - accumulate and store pigments (carotenes) different shades, giving color to plant flowers;
• leucoplasts - store nutrients, such as starch, in the form of grains and granules;
• chloroplasts - the most important organelles that contain the green pigment (chlorophyll), which gives plants color, and carry out photosynthesis.

Rice. 3. Plastids.

What have we learned?

We examined the structural features of mitochondria - double-membrane organelles that carry out cellular respiration. The outer membrane consists of proteins and lipids and transports substances. The inner membrane forms folds - cristae, on which hydrogen oxidation occurs. The cristae are surrounded by a matrix - a gel-like substance in which some of the reactions of cellular respiration take place. The matrix contains mitochondrial DNA and RNA.

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Mitochondria are one of the most important components of any cell. They are also called chondriosomes. These are granular or thread-like organelles that are part of the cytoplasm of plants and animals. They are the producers of ATP molecules, which are so necessary for many processes in the cell.

What are mitochondria?

Mitochondria are the energy base of cells; their activity is based on the oxidation and use of energy released during the breakdown of ATP molecules. Biologists on in simple language it is called the energy production station for cells.

In 1850, mitochondria were identified as granules in muscles. Their number varied depending on growth conditions: they accumulate more in those cells where there is a high oxygen deficiency. This happens most often when physical activity. In such tissues, an acute lack of energy appears, which is replenished by mitochondria.

Appearance of the term and place in the theory of symbiogenesis

In 1897, Bend first introduced the concept of “mitochondrion” to designate a granular and filamentous structure in which they vary in shape and size: thickness is 0.6 µm, length - from 1 to 11 µm. In rare situations, mitochondria may be big size and a branched node.

The theory of symbiogenesis gives a clear idea of ​​what mitochondria are and how they appeared in cells. It says that the chondriosome arose in the process of damage to bacterial cells, prokaryotes. Since they could not autonomously use oxygen to generate energy, this prevented them from fully developing, while progenotes could develop unhindered. During evolution, the connection between them made it possible for progenotes to transfer their genes to eukaryotes. Thanks to this progress, mitochondria are no longer independent organisms. Their gene pool cannot be fully realized, since it is partially blocked by enzymes that are present in any cell.

Where do they live?

Mitochondria are concentrated in those areas of the cytoplasm where the need for ATP appears. For example, in muscle tissue in the heart, they are located near the myofibrils, and in spermatozoa they form a protective camouflage around the axis of the tourniquet. There they generate a lot of energy to make the “tail” spin. This is how the sperm moves towards the egg.

In cells, new mitochondria are formed by simple division of previous organelles. During it, all hereditary information is preserved.

Mitochondria: what they look like

The shape of the mitochondria resembles a cylinder. They are often found in eukaryotes, occupying from 10 to 21% of the cell volume. Their sizes and shapes vary greatly and can change depending on conditions, but the width is constant: 0.5-1 microns. The movements of chondriosomes depend on the places in the cell where energy is rapidly wasted. They move through the cytoplasm using cytoskeletal structures for movement.

A replacement for mitochondria of different sizes, which work separately from each other and supply energy to certain zones of the cytoplasm, are long and branched mitochondria. They are able to provide energy to areas of cells located far from each other. Such joint work of chondriosomes is observed not only in unicellular organisms, but also in multicellular ones. The most complex structure of chondriosomes is found in the muscles of the mammalian skeleton, where the largest branched chondriosomes are joined to each other using intermitochondrial contacts (IMCs).

They are narrow gaps between adjacent mitochondrial membranes. This space has a high electron density. MMKs are more common in cells where they bind together with working chondriosomes.

To better understand the issue, you need to briefly describe the significance of mitochondria, the structure and functions of these amazing organelles.

How are they built?

To understand what mitochondria are, you need to know their structure. This unusual source of energy is spherical in shape, but often elongated. Two membranes are located close to each other:

• external (smooth);
• internal, which forms leaf-shaped (cristae) and tubular (tubules) outgrowths.

Apart from the size and shape of the mitochondria, their structure and functions are the same. The chondriosome is delimited by two membranes measuring 6 nm. The outer membrane of the mitochondria resembles a container that protects them from the hyaloplasm. The inner membrane is separated from the outer membrane by a region 11-19 nm wide. A distinctive feature of the inner membrane is its ability to protrude into the mitochondria, taking the form of flattened ridges.

The internal cavity of the mitochondrion is filled with a matrix, which has a fine-grained structure, where threads and granules (15-20 nm) are sometimes found. Matrix threads create organelles, and small granules create mitochondrial ribosomes.

At the first stage it takes place in the hyaloplasm. At this stage, the initial oxidation of substrates or glucose occurs to These procedures take place without oxygen - anaerobic oxidation. The next stage of energy production consists of aerobic oxidation and breakdown of ATP, this process occurs in the mitochondria of cells.

What do mitochondria do?

The main functions of this organelle are:

The presence of its own deoxyribonucleic acid in mitochondria once again confirms the symbiotic theory of the appearance of these organelles. Also, in addition to their main work, they are involved in the synthesis of hormones and amino acids.

Mitochondrial pathology

Mutations occurring in the mitochondrial genome lead to depressing consequences. The human carrier is DNA, which is passed on to offspring from parents, while the mitochondrial genome is passed on only from the mother. This fact is explained very simply: children receive the cytoplasm with chondriosomes enclosed in it along with the female egg; they are absent in sperm. Women with this disorder can pass on mitochondrial disease to their offspring, but a sick man cannot.

IN normal conditions Chondriosomes have the same copy of DNA - homoplasmy. Mutations can occur in the mitochondrial genome, and heteroplasmy occurs due to the coexistence of healthy and mutated cells.

Thanks to modern medicine To date, more than 200 diseases have been identified, the cause of which was a mutation in mitochondrial DNA. Not in all cases, but mitochondrial diseases respond well to therapeutic maintenance and treatment.

So we figured out the question of what mitochondria are. Like all other organelles, they are very important for the cell. They indirectly take part in all processes that require energy.

Mitochondria is a spiral, round, elongated or branched organelle.

The concept of mitochondria was first proposed by Benda in 1897. Mitochondria can be detected in living cells using phase contrast and interference microscopy in the form of grains, granules or filaments. These are quite mobile structures that can move, merge with each other, and divide. When painting special methods In dead cells, under light microscopy, mitochondria have the appearance of small grains (granules), diffusely distributed in the cytoplasm or concentrated in certain areas of it.

As a result of the destruction of glucose and fats in the presence of oxygen, energy is generated in the mitochondria, and organic substances are converted into water and carbon dioxide. This is how animal organisms obtain the basic energy necessary for life. Energy is stored in adenosine triphosphate (ATP), or more precisely, in its high-energy bonds. Mitochondrial function is closely related to oxidation organic compounds and using the energy released during their decay for the synthesis of ATP molecules. Therefore, mitochondria are often called the energy stations of the cell, or the organelles of cellular respiration. ATP acts as an energy supplier by transferring one of its energy-rich terminal phosphate groups to another molecule and converting it into ADP.

It is believed that in evolution, mitochondria were prokaryotic microorganisms that became symbiotes in the body of an ancient cell. Subsequently, they became vitally necessary, which was associated with an increase in the oxygen content in the Earth’s atmosphere. On the one hand, mitochondria removed excess oxygen, which is toxic to the cell, and on the other, they provided energy.

Without mitochondria, a cell is virtually unable to use oxygen as a substance to supply energy and can only meet its energy needs through anaerobic processes. Thus, oxygen is poison, but the poison is vital for the cell, and excess oxygen is just as harmful as its deficiency.

Mitochondria can change their shape and move to those areas of the cell where the need for them is highest. Thus, in cardiomyocytes, mitochondria are located near the myofibrils, in the cells of the renal tubules near the basal invaginations, etc. The cell contains up to a thousand mitochondria, and their number depends on the activity of the cell.

Mitochondria have an average transverse size of 0.5...3 µm. Depending on the size, small, medium, large and giant mitochondria are distinguished (they form a branched network - the mitochondrial reticulum). The size and number of mitochondria are closely related to cell activity and energy consumption. They are extremely variable and, depending on the activity of the cell, oxygen content, hormonal influences, can swell, change the number and structure of cristae, vary in number, shape and size, as well as enzymatic activity.

The volume density of mitochondria, the degree of development of their internal surface and other indicators depend on the energy needs of the cell. Lymphocytes have only a few mitochondria, while liver cells have 2–3 thousand.

Mitochondria consist of a matrix, an inner membrane, a perimitochondrial space, and an outer membrane. The outer mitochondrial membrane separates the organelle from the hyaloplasm. Usually she has smooth contours and is closed so that it represents a membrane bag.

The outer membrane is separated from the inner membrane by a perimitochondrial space about 10...20 nm wide. The inner mitochondrial membrane limits the actual internal contents of the mitochondrion - the matrix. The inner membrane forms numerous protrusions into the mitochondria, which look like flat ridges, or cristae.

The shape of the cristae can look like plates (trabecular) and tubes (multivesicular on a section), and they are directed longitudinally or transversely in relation to the mitochondria.

Each mitochondria is filled with a matrix that appears denser in electron micrographs than the surrounding cytoplasm. The mitochondrial matrix is ​​uniform (homogeneous), sometimes fine-grained, with varying electron densities. It reveals thin threads with a thickness of about 2...3 nm and granules with a size of about 15...20 nm. The matrix threads are DNA molecules, and the small granules are mitochondrial ribosomes. The matrix contains enzymes, one single-stranded, cyclic DNA, mitochondrial ribosomes, and many Ca 2+ ions.

Autonomous system protein synthesis of mitochondria is represented by DNA molecules free of histones. The DNA is short, ring-shaped (cyclic) and contains 37 genes. Unlike nuclear DNA, it contains virtually no non-coding nucleotide sequences. Features of structure and organization bring mitochondrial DNA closer to the DNA of bacterial cells. RNA molecules are synthesized on mitochondrial DNA different types: informational, transfer (transport) and ribosomal. The messenger RNA of mitochondria is not subject to splicing (cutting out areas that do not carry an information load). The small size of mitochondrial DNA molecules cannot determine the synthesis of all mitochondrial proteins. Most mitochondrial proteins are under genetic control cell nucleus and is synthesized in the cytoplasm, since mitochondrial DNA is weakly expressed and can provide the formation of only part of the enzymes of the oxidative phosphorylation chain. Mitochondrial DNA encodes no more than ten proteins that are localized in membranes and are structural proteins responsible for the correct integration of individual functional protein complexes of mitochondrial membranes. Proteins that perform transport functions are also synthesized. Such a system of protein synthesis does not provide all the functions of the mitochondrion, therefore the autonomy of the mitochondria is limited and relative.

In mammals, mitochondria are transferred during fertilization only through the egg, and the sperm introduces nuclear DNA into the new organism.

Ribosomes are formed in the mitochondrial matrix, which differ from the ribosomes of the cytoplasm. They are involved in the synthesis of a number of mitochondrial proteins that are not encoded by the nucleus. Mitochondrial ribosomes have a sedimentation number of 60 (in contrast to cytoplasmic ribosomes with a sedimentation number of 80). The sedimentation number is the rate of sedimentation during centrifugation and ultracentrifugation. In structure, mitochondrial ribosomes are close to the ribosomes of prokaryotic organisms, but are smaller in size and are sensitive to certain antibiotics (chloramphenicol, tetracycline, etc.).

The inner membrane of the mitochondrion has a high degree of selectivity in the transport of substances. Closely adjacent enzymes of the oxidative phosphorylation chain, electron carrier proteins, transport systems ATP, ADP, pyruvate, etc. are attached to its inner surface. As a result of the close arrangement of enzymes on the inner membrane, high conjugacy (interconnectedness) of biochemical processes is ensured, increasing the speed and efficiency of catalytic processes.

At electron microscopy mushroom-shaped particles protruding into the lumen of the matrix are identified. They have ATP-synthetic (forms ATP from ADP) activity. Electron transport occurs along the respiratory chain, localized in the inner membrane, which contains four large enzyme complexes (cytochromes). As electrons pass through the respiratory chain, hydrogen ions are pumped out of the matrix into the perimitochondrial space, which ensures the formation of a proton gradient (pump). The energy of this gradient (differences in the concentration of substances and the formation of membrane potential) is used for the synthesis of ATP and the transport of metabolites and inorganic ions. Carrier proteins contained on the inner membrane transport organic phosphates, ATP, ADP, amino acids, fatty acids, tri- and dicarboxylic acids through it.

The outer membrane of the mitochondria is more permeable to low molecular weight substances, since it contains many hydrophilic protein channels. On the outer membrane there are specific receptor complexes through which proteins from the matrix are transported into the perimitochondria space.

In my own way chemical composition and properties, the outer membrane is close to other intracellular membranes and the plasmalemma. It contains enzymes that metabolize fats, activate (catalyze) the transformation of amines, amine oxidase. If the enzymes of the outer membrane remain active, then this is an indicator of the functional safety of mitochondria.

Mitochondria have two autonomous subcompartments. While the permitochondrial space, or outer chamber of the mitochondrion (external subcompartment), is formed due to the penetration of protein complexes of the hyaloplasm, the internal subcompartment (mitochondrial matrix) is partially formed due to the synthetic activity of mitochondrial DNA. The internal subcompartment (matrix) contains DNA, RNA and ribosomes. He's different high level Ca 2+ ions in comparison with hyaloplasm. Hydrogen ions accumulate in the outer subcompartment. The enzymatic activity of the external and internal subcompartments and the composition of proteins differ greatly. The inner subcompartment has a higher electron density than the outer one.

Specific markers of mitochondria are the enzymes cytochrome oxidase and succinate dehydrogenase, the identification of which makes it possible to quantitatively characterize energy processes in mitochondria.

Main function of mitochondria- ATP synthesis. First, sugars (glucose) are broken down in the hyaloplasm to lactic and pyruvic acids (pyruvate), with the simultaneous synthesis of a small amount of ATP. As a result of glycolysis of one glucose molecule, two ATP molecules are used and four are produced. Thus, the positive balance is made up of only two ATP molecules. These processes occur without oxygen (anaerobic glycolysis).

All subsequent stages of energy production occur through the process of aerobic oxidation, which ensures the synthesis of large amounts of ATP. In this case, organic substances are destroyed to CO 2 and water. Oxidation is accompanied by the transfer of protons to their acceptors. These reactions are carried out using a number of enzymes of the tricarboxylic acid cycle, which are located in the mitochondrial matrix.

Systems for electron transfer and associated ADP phosphorylation (oxidative phosphorylation) are built into the cristae membranes. In this case, electrons are transferred from one electron acceptor protein to another and, finally, they bind with oxygen, resulting in the formation of water. At the same time, part of the energy released during such oxidation in the electron transport chain is stored in the form of a high-energy bond during the phosphorylation of ADP, which leads to the formation of a large number of ATP molecules - the main intracellular energy equivalent. On the membranes of the mitochondrial cristae, the process of oxidative phosphorylation occurs with the help of the oxidation chain proteins and the phosphorylation enzyme ADP ATP synthetase located here. As a result of oxidative phosphorylation, 36 ATP molecules are formed from one glucose molecule.

For some hormones and substances, mitochondria have specialized (affinity) receptors. Triiodothyronine normally accelerates the synthetic activity of mitochondria. Interleukin-1 and high concentrations of triiodothyronine uncouple the chains of oxidative phosphorylation and cause mitochondrial swelling, which is accompanied by an increase in the production of thermal energy.

New mitochondria are formed by fission, constriction or budding. In the latter case, a protomitochondrion is formed, gradually increasing in size.

Protomitochondrion is a small organelle with outer and inner membranes. The inner membrane does not have or contains poorly developed cristae. The organelle is characterized low level aerobic phosphorylation. When a constriction is formed, the contents of the mitochondrion are distributed between two new rather large organelles. With any method of reproduction, each of the newly formed mitochondria has its own genome.

Old mitochondria are destroyed by autolysis (self-digestion by the cell using lysosomes) to form autolysosomes. A residual body is formed from the autolysosome. Upon complete digestion, the contents of the residual body, consisting of low molecular weight organic matter, is eliminated by exocytosis. If digestion is incomplete, mitochondrial remnants can accumulate in the cell in the form of layered bodies or granules with nipofuscin. In some mitochondria, insoluble calcium salts accumulate with the formation of crystals - calcifications. The accumulation of mitochondrial degeneration products can lead to cell degeneration.

Mitochondria (from Greek μίτος (mitos) - thread and χονδρίον (chondrion) - granule) is a cellular two-membrane organelle that contains its own genetic material, mitochondrial. They are found as spherical or tubular cell structures in almost all eukaryotes, but not in prokaryotes.

Mitochondria are organelles that regenerate the high-energy molecule adenosine triphosphate through the respiratory chain. In addition to this oxidative phosphorylation, they perform other important tasks, For example, participate in the formation of iron and sulfur clusters. The structure and functions of such organelles are discussed in detail below.

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General information

There are especially many mitochondria in areas with high energy consumption. These include muscle, nerve, sensory cells and oocytes. In the cellular structures of the heart muscle, the volume fraction of these organelles reaches 36%. They have a diameter of about 0.5-1.5 microns and a variety of shapes, from spheres to complex threads. Their number is adjusted taking into account the energy needs of the cell.

Eukaryotic cells that lose their mitochondria can't restore them. There are also eukaryotes without them, for example, some protozoa. The number of these organelles per cell unit is usually from 1000 to 2000 with a volume fraction of 25%. But these values ​​can vary greatly depending on the type cell structure and the body. IN mature cell There are about four to five sperm, in a mature egg there are several hundred thousand.

Mitochondria are transmitted through the plasma of the egg only from the mother, which was the reason for the study of maternal lines. It has now been established that also through sperm, some male organelles are imported into the plasma of the fertilized egg (zygote). They will probably be resolved fairly quickly. However, there are several cases where doctors were able to prove that the child's mitochondria were from the paternal line. Diseases caused by mutations in mitochondrial genes are inherited only from the mother.

Interesting! The popular scientific term "powerhouse of the cell" was coined in 1957 by Philip Sikiewitz.

Mitochondria structure diagram

Let us consider the structural features of these important structures. They are formed as a result of a combination of several elements. The shell of these organelles consists of an outer and inner membrane; they, in turn, consist of phospholipid bilayers and proteins. Both shells differ in their properties. Between them there are five different compartments: the outer membrane, the intermembrane space (the space between the two membranes), the inner membrane, the crista and the matrix (the space inside the inner membrane), in general - internal structures organoid.

In illustrations in textbooks, the mitochondrion primarily looks like a separate bean-shaped organelle. Is it really? No, they form tubular mitochondrial network, which can pass through and change the entire cellular unit. Mitochondria in a cell are capable of combining (by fusion) and re-dividing (by fission).

Note! In yeast, about two mitochondrial fusions occur in one minute. Therefore it is impossible precise definition the current number of mitochondria in cells.

Outer membrane

The outer shell surrounds the entire organelle and includes channels of protein complexes that allow the exchange of molecules and ions between the mitochondrion and the cytosol. Large molecules cannot pass through the membrane.

The outer one, which spans the entire organelle and is not folded, has a phospholipid to protein weight ratio of 1:1 and is thus similar to the eukaryotic plasma membrane. It contains many integral proteins, porins. Porins form channels that allow free diffusion of molecules with a mass of up to 5000 daltons through the membrane. Larger proteins can invade when a signal sequence at the N-terminus binds to the large subunit of the transloxase protein, from which they then actively move along the membrane envelope.

If cracks occur in the outer membrane, proteins from the intermembrane space can escape into the cytosol, which can lead to cell death. The outer membrane can fuse with the endoplasmic reticulum membrane and then form a structure called MAM (mitochondrion-associated ER). It is important for signaling between the ER and the mitochondrion, which is also necessary for transport.

Intermembrane space

The area is a gap between the outer and inner membranes. Since the external one allows the free penetration of small molecules, their concentration, such as ions and sugars, in the intermembrane space is identical to the concentrations in the cytosol. However, large proteins require the transmission of a specific signal sequence, so that protein composition differs between the intermembrane space and the cytosol. Thus, the protein that is retained in the intermembrane space is cytochrome.

Inner membrane

The inner mitochondrial membrane contains proteins with four types of functions:

• Proteins - carry out oxidation reactions of the respiratory chain.
• Adenosine triphosphate synthase, which produces ATP in the matrix.
• Specific transport proteins that regulate the passage of metabolites between the matrix and the cytoplasm.
• Protein import systems.

The internal one has, in particular, a double phospholipid, cardiolipin, replaced by four fatty acids. Cardiolipin is usually found in mitochondrial membranes and bacterial plasma membranes. It is mainly present in the human body in areas of high metabolic activity or high energy activity, such as contractile cardiomyocytes, in the myocardium.

Attention! The inner membrane contains more than 150 different polypeptides, about 1/8 of all mitochondrial proteins. As a result, the lipid concentration is lower than that of the outer bilayer and its permeability is lower.

Divided into numerous cristae, they expand the outer region of the inner mitochondrial membrane, increasing its ability to produce ATP.

In a typical liver mitochondria, for example, the outer region, particularly the cristae, is approximately five times the area of ​​the outer membrane. Energy stations of cells that have higher ATP requirements, e.g. muscle cells contain more cristae, than a typical liver mitochondria.

The inner shell encloses the matrix, internal fluid mitochondria. It corresponds to the cytosol of bacteria and contains mitochondrial DNA, citrate cycle enzymes and their own mitochondrial ribosomes, which are different from the ribosomes in the cytosol (but also from bacteria). The intermembrane space contains enzymes that can phosphorylate nucleotides by consuming ATP.

Functions

• Important degradation pathways: the citrate cycle, for which pyruvate is introduced from the cytosol into the matrix. Pyruvate is then decarboxylated by pyruvate dehydrogenase to acetyl coenzyme A. Another source of acetyl coenzyme A is the degradation of fatty acids (β-oxidation), which occurs in animal cells in mitochondria, but in plant cells only in glyoxysomes and peroxisomes. For this purpose, acyl-coenzyme A is transferred from the cytosol by binding to carnitine across the inner mitochondrial membrane and converted into acetyl-coenzyme A. From this, most of the reducing equivalents in the Krebs cycle (also known as the Krebs cycle or tricarboxylic acid cycle), which are then converted to ATP in the oxidative chain .
• Oxidative chain. An electrochemical gradient has been established between the intermembrane space and the mitochondrial matrix, which serves to produce ATP using ATP synthase, through the processes of electron transfer and proton accumulation. The electrons and protons needed to create the gradient are obtained by oxidative degradation from nutrients (such as glucose) absorbed by the body. Glycolysis initially occurs in the cytoplasm.
• Apoptosis (programmed cell death)
• Calcium storage: Through the ability to absorb calcium ions and then release them, mitochondria interfere with cell homeostasis.
• Synthesis of iron-sulfur clusters required, among other things, by many enzymes of the respiratory chain. This function is now considered an essential function of mitochondria, i.e. as this is the reason why almost all cells rely on energy stations for survival.

Matrix

This is a space included in the inner mitochondrial membrane. Contains about two thirds total protein. Plays a crucial role in the production of ATP through ATP synthase, included in the inner membrane. Contains a highly concentrated mixture of hundreds of different enzymes (mainly involved in the degradation of fatty acids and pyruvate), mitochondria-specific ribosomes, messenger RNA and several copies of the DNA of the mitochondrial genome.

These organelles have their own genome, as well as the enzymatic equipment necessary for carrying out its own protein biosynthesis.

Mitochondria What is Mitochondria and its functions

Structure and functioning of mitochondria

Conclusion

Thus, mitochondria are called cellular power plants that produce energy and occupy a leading place in the life and survival of an individual cell in particular and a living organism in general. Mitochondria are an integral part of a living cell, including plant cells, which have not yet been fully studied. There are especially many mitochondria in those cells that require more energy.

MITOCHONDRIA (mitochondria; grech, mitos thread + chondrion grain) - organelles present in the cytoplasm of cells of animal and plant organisms. M. take part in the processes of respiration and oxidative phosphorylation, producing the energy necessary for the functioning of the cell, thus representing its “power stations”.

The term "mitochondria" was proposed in 1894 by S. Benda. In the mid-30s. 20th century It was possible for the first time to isolate M. from liver cells, which made it possible to study these structures using biochemical methods. In 1948, G. Hogeboom obtained definitive evidence that M. are indeed centers of cellular respiration. Significant advances in the study of these organelles were made in the 60-70s. in connection with the use of electron microscopy and molecular biology methods.

M.'s shape varies from almost round to highly elongated, thread-like (Fig. 1). Their size ranges from 0.1 to 7 microns. The number of M. in a cell depends on the type of tissue and functional state body. Thus, in spermatozoa the number of M. is small - approx. 20 (per cell), in the epithelial cells of the renal tubules of mammals there are up to 300 of them each, and in the giant amoeba ( Chaos chaos) 500,000 mitochondria were found. In one rat liver cell, approx. 3000 M., however, during the starvation of an animal, the number of M. can be reduced to 700. Usually M. are distributed in the cytoplasm quite evenly, but in the cells of certain tissues M. can be constantly localized in areas that especially need energy. For example, in skeletal muscle, M. are often in contact with the contractile areas of myofibrils, forming regular three-dimensional structures. In spermatozoa, the spermatozoa form a spiral sheath around the axial filament of the tail, which is probably due to the ability to use the ATP energy synthesized in the spermatozoa for tail movements. In axons, M. are concentrated near synaptic endings, where the process of transmission of nerve impulses occurs, accompanied by energy consumption. In epithelial cells of the renal tubules, M. are associated with protrusions of the basal cell membrane. This is caused by the need for a constant and intensive energy supply to the process of active transfer of water and substances dissolved in it, which occurs in the kidneys.

Electron microscopy has established that M. contains two membranes - outer and inner. The thickness of each membrane is approx. 6 nm, the distance between them is 6-8 nm. The outer membrane is smooth, the inner one forms complex projections (cristae) protruding into the cavity of the mitochondria (Fig. 2). The internal space of M. is called the matrix. Membranes are a film of compactly packed molecules of proteins and lipids, while the matrix is ​​similar to a gel and contains soluble proteins, phosphates and other chemicals. connections. Usually the matrix looks homogeneous, only in certain cases can thin threads, tubes and granules containing calcium and magnesium ions be found in it.

Of the structural features of the inner membrane, it is necessary to note the presence of spherical particles in it of approx. 8-10 nm in diameter, sitting on short leg and sometimes protruding into the matrix. These particles were discovered in 1962 by H. Fernandez-Moran. They consist of a protein with ATPase activity, designated F1. The protein attaches to the inner membrane only on the side facing the matrix. F1 particles are located at a distance of 10 nm from each other, and each M contains 10 4 -10 5 such particles.

The cristae and internal membranes of the M. contain the majority of respiratory enzymes (see); respiratory enzymes are organized into compact ensembles distributed at regular intervals in the M. cristae at a distance of 20 nm from each other.

M. of almost all types of animal and plant cells are built according to a single principle, but deviations in details are possible. Thus, cristae can be located not only across the long axis of the organelle, but also longitudinally, for example, in the M. of the synaptic zone of the axon. In some cases, the cristae may branch. In the microorganisms of protozoa, some insects, and in the cells of the zona glomerulosa of the adrenal glands, the cristae have the shape of tubes. The number of cristae varies; Thus, in M. there are very few liver cells and germ cells of cristae and they are short, while the matrix is ​​abundant; in M. muscle cells The cristae are numerous, but the matrix is ​​small. There is an opinion that the number of cristae correlates with the oxidative activity of M.

In the inner membrane of M., three processes are carried out in parallel: oxidation of the substrate of the Krebs cycle (see Tricarboxylic acid cycle), transfer of electrons released during this process, and accumulation of energy through the formation of high-energy bonds of adenosine triphosphate (see Adenosine phosphoric acids). The main function of M. is the coupling of ATP synthesis (from ADP and inorganic phosphorus) and the aerobic oxidation process (see Biological oxidation). The energy accumulated in ATP molecules can be transformed into mechanical (in muscles), electrical ( nervous system), osmotic (kidneys), etc. Processes aerobic respiration(see Biological oxidation) and associated oxidative phosphorylation (see) are the main functions of M. In addition, oxidation can occur in the outer membrane of M. fatty ones, phospholipids and certain other compounds.

In 1963, Nass and Nass (M. Nass, S. Nass) established that M. contains DNA (one or more molecules). All mitochondrial DNA from animal cells studied so far consist of covalently closed rings of diameter. OK. 5 nm. In plants, mitochondrial DNA is much longer and does not always have a ring shape. Mitochondrial DNA differs from nuclear DNA in many ways. DNA replication occurs using the usual mechanism, but does not coincide in time with nuclear DNA replication. The amount of genetic information contained in the mitochondrial DNA molecule is apparently insufficient to encode all the proteins and enzymes contained in M. Mitochondrial genes encode mainly structural membrane proteins and proteins involved in the morphogenesis of mitochondria. M. have their own transport RNAs and synthetases and contain all the components necessary for protein synthesis; their ribosomes are smaller than cytoplasmic ones and more similar to bacterial ribosomes.

M.'s life expectancy is relatively short. Thus, the time for renewal of half the amount of M is 9.6-10.2 days for the liver, and 12.4 days for the kidney. Replenishment of the M. population occurs, as a rule, from pre-existing (maternal) M. by dividing or budding.

It has long been suggested that in the process of evolution, bacteria probably arose through endosymbiosis of primitive nucleated cells with bacteria-like organisms. There is a large amount of evidence for this: the presence of its own DNA, which is more similar to the DNA of bacteria than to the DNA of the cell nucleus; the presence of ribosomes in M.; DNA-dependent RNA synthesis; sensitivity of mitochondrial proteins to antibacterial drug- chloramphenicol; similarity with bacteria in the implementation of the respiratory chain; morphol., biochemical, and physiol, differences between internal and outer membrane. According to the symbiotic theory, the host cell is considered as an anaerobic organism, the source of energy for which is glycolysis (occurring in the cytoplasm). In the “symbiont” the Krebs cycle and the respiratory chain are realized; it is capable of respiration and oxidative phosphorylation (see).

M. are very labile intracellular organelles that react earlier than others to the occurrence of any pathol, conditions. Changes in the number of microbes in a cell (or rather, in their populations) or changes in their structure are possible. For example, during fasting or exposure to ionizing radiation, the number of M decreases. Structural changes usually consist of swelling of the entire organelle, clearing of the matrix, destruction of cristae, and disruption of the integrity of the outer membrane.

Swelling is accompanied by a significant change in the volume of the muscle. In particular, with myocardial ischemia, the volume of the muscle increases 10 times or more. There are two types of swelling: in one case it is associated with changes in osmotic pressure inside the cell, in other cases - with changes in cellular respiration associated with enzymatic reactions and primary functional disorders, causing change water exchange. In addition to swelling, vacuolization of M. may occur.

Regardless of the reasons causing patol, the condition (hypoxia, hyperfunction, intoxication), M.’s changes are quite stereotypical and nonspecific.

Such changes in the structure and function of M. are observed, which, apparently, became the cause of the disease. In 1962, R. Luft described a case of “mitochondrial disease.” A patient with a sharply increased metabolic rate (with normal function thyroid gland) a puncture was made skeletal muscle and an increased number of M. was found, as well as a violation of the structure of the cristae. Defective mitochondria in liver cells were also observed in cases of severe thyrotoxicosis. J. Vinograd et al. (1937 to 1969) found that in patients with certain forms of leukemia, mitochondrial DNA from white blood cells was markedly different from normal. They were open rings or groups of interlocking rings. The frequency of these abnormal forms decreased as a result of chemotherapy.

Bibliography: Gause G. G. Mitochondrial DNA, M., 1977, bibliogr.; D e P o-bertis E., Novinsky V. and S a e s F. Cell biology, trans. from English, M., 1973; Ozernyuk N.D. Growth and reproduction of mitochondria, M., 1978, bibliogr.; Polikar A. and Bessi M. Elements of cell pathology, trans. from French, M., 1970; RudinD. and Wilkie D. Biogenesis of mitochondria, trans. from English, M., 1970, bibliogr.; Serov V.V. and Paukov V.S. Ultrastructural pathology, M., 1975; S e d e r R. Cytoplasmic genes and organelles, trans. from English, M., 1975.

T. A. Zaletayeva.