Mitochondria form substances in the cell. Why do mitochondria need their own genes? Excerpt characterizing Mitochondria

Mitochondria (MT) is one of the most interesting areas of research for me. The union of mitochondria with another cell during endosymbiosis about 1.6 billion years ago became the basis of all multicellular eukaryotes with a complex structure. Mitochondria are thought to have originated from cells resembling α-proteobacteria.

The best recent review of mitochondria is Werner Kuhlbrandt's “Structure and Function of Mitochondrial Membrane Protein Complexes.” If you know English and are interested in the structure of these organelles, I highly recommend reading it. This article is so good that it could easily be a chapter in a good molecular biology textbook. At first I wanted to translate the entire article, but it would have taken an unforgivably long time and would have taken me away from other things. Therefore, I will limit myself to theses and pictures. Periodically diluting everything with your thoughts.

The mitochondrion itself encodes only 13 proteins, despite the presence of DNA (mtDNA) separate from the cell and the entire “production” cycle for protein transcription. An isolated mitochondria can maintain its composition and function for some time.

Figure 1. Components of the mitochondrial membrane. The outer membrane separates the mitochondrion from the cytoplasm. It surrounds the inner membrane, which separates the intermembrane space from the protein-rich central matrix. The inner membrane is divided into the internal limiting membrane and cristae. These two parts are continuous at the places where the cristae are attached (cristae junction). The cristae extend more or less deep into the matrix and are the main site of mitochondrial energy conversion. A small proton gradient in the intermembrane space (pH7.2-7.4) and matrix (pH7.9-8.0) lead to the formation of ATP by ATP synthase in the membranes of the cristae.

The outer membrane is porous and allows substances from the cytoplasm to pass through it. The inner membrane is dense, transport proteins are needed to cross it [Gilbert Ling reasonably disagrees], the continuity of the barrier allows the inner membrane to have an electrochemical potential of -180 mV. The matrix has a fairly high pH (7.9-8). Let me delve deeper into Ling once again. Alkaline (above 7) pH promotes a more unfolded conformation of proteins. High pH disrupts hydrogen and salt bonds, making polarized CO and NH available to water molecules, thereby enhancing the dipole moment of all intracellular water and binding it. In this vein, the presence of a membrane is necessary not to “retain” protoplasm inside the cell (this is done by the proteins themselves at high pH), but for the presence of potential.

mtDNA is found in nucleotides, of which there are approximately 1000 per cell. The protein density of the matrix is ​​quite high (up to 500 mg/ml), which is close to crystallized proteins.

The inner membrane forms invaginations called cristae, which penetrate deeply into the matrix. Cristae define the third “compartment” of mitochondria - the lumen of the cristae (cristae lumen). The crista membranes contain most, if not all, fully assembled electron transport chain and ATP synthase complexes. The lumen of the crista contains large amounts of a small, soluble electron transport protein (cytochrome c). Mitochondrial cristae are thus the main site of biological energy conversion in all non-photosynthetic eukaryotes.

There are also a lot of interesting things with Christs. The optical properties of the crista influence the propagation and generation of light in tissues. I have even seen ideas that the surface of the cristae is similar (assumption) to the surfaces of topological insulators (implying superconductivity without charge dissipation).

Figure 2. Membrane protein complexes of the respiratory chain. ComplexI (NADH/ ubiquinone oxidoreductase, blue), ComplexII(succinate dehydrogenase, rose), ComplexIII(cytochrome C reductase, orange), ComplexIV(cytochrome C oxidase, green) and mitochondrial ATP synthase (known as complexV, beige) work together during oxidative phosphorylation so cells can use energy. ComplexesI, III, IVpump protons along the crista membrane, creating a proton gradient that stimulates ATP synthesis.

Now a little attention to complex II. You will remember that fat (keto) metabolism emphasizes FADH2 and complex II. They reduce the CoQ pair, at some point there is not enough oxidized CoQ to transport electrons to complex III and forms a reverse flow of electrons to complex I to form superoxide. With long-term HFLC nutrition, complex I will be reversibly destroyed, while this is a normal physiological optimization.

I also ask you to note that complex II does not pump out protons. What dissipates the proton gradient in us, disrupts phosphorylation and stimulates fat burning for heat? That's right, cold stress. Thermogenesis is coupled to metabolism through a complex that does not pump out protons, thereby providing no additional protons for ATP synthase. One can only be amazed at how wonderfully our body is thought out.

Mounting crystals andMICOS

The cristae junctions are small round holes approximately 25 nm in diameter. The mitochondria of all organisms contain the MICOS system (mitochondria contact site and cristae to outer membrane), an assembly of five membrane and one soluble proteins that attach the cristae to the outer membrane.

In cells with increased energy demands, such as skeletal and cardiac muscles, cristae densely fill most of the mitochondrial volume. In tissues with lower energy requirements, such as the liver and kidneys, the cristae are not as densely packed together. There is more space in the matrix for biosynthetic enzymes.

Figure 3. Tomographic volume of mouse heart mitochondria. A) Three-dimensional volume of mouse heart mitochondria captured by cryo-ET. The outer membrane (gray) envelops the inner membrane (light blue). The inner membrane is densely filled with cristae b) Tomographic section of the volume. The densely packed matrix containing most of the mitochondrial proteins appears dark under an electron microscope. While the intermembrane space and the lumens of the cristae appear light due to the low concentration of proteins.

ATP synthase dimers

Mitochondrial F1-F0 ATP synthase is the most prominent protein complex of the crista. ATP synthase is an ancient nanomachine that uses the electrochemical Protnov gradient around the inner membrane to create ATP through rotational catalysis. Protons moving through the F0 complex of the membrane rotate a rotor of 8 (in mammals) or 10 (in yeast) c-sites. The central stalk transmits c-rotor torque to the F1 catalytic head, where ATP is formed from ADP and phosphate through a sequence of conformational changes. The peripheral stalk prevents the unproductive rotation of the F1 Head against the F0 complex.

For many years, it was believed that ATP synthase was located randomly on the inner membrane. But it turned out that ATP synthase is arranged in double rows. Moreover, the linear series of ATP synthase are a fundamental attribute of all living mitochondria.

Figure 4. Double rows of ATP synthase in seven different species.

The rows of ATP synthase are located mainly along the ridges of the cristae. Dimers bend the lipid bilayer and, as a result, self-organize into rows. When nodes e and g of APT synthase were knocked out of yeast mitochondria, the strain grew 60% slower than its wild counterparts, and the membrane potential of their mitochondria was reduced by half. Prokaryotic APT synthase lacks several dimer-related nodes; a number of dimers have not been found in bacteria and archaea. The cristae and rows of AFT synthase dimers are thus an adaptation to the greater energy demands of the body.

Figure 5. Structure of the ATP synthase dimer from the mitochondria of polymella sp. Side view of a V-shaped ATP synthase dimer.

Complexes and supercomplexes of the respiratory chain

The proton gradient around the inner membrane is created by three large membrane complexes known as complex I, complex III and complex IV (see Figure 2). Complex I feeds electrons from NADH, the energy released by electron transfer pumping out four protons. Complex III receives an electron from the reduced quinol and transfers it to the electron carrier (cytochrome c), pumping out one proton in the process. Complex IV receives an electron from cytochrome c and transfers it to molecular oxygen, pumping out 4 protons for every oxygen molecule converted to water. Complex II does not pump out protons, directly donating electrons to the quinol. How electron transfer from NADH to quinol is related to proton translocation is not yet clear. Complex I is larger than III and IV combined.

Figure 6. Complex I of bovine heart mitochondria. The matrix portion contains a series of eight iron-sulfur (Fe-S) clusters that funnel electrons from NADH to the quinol at the matrix-membrane intersection. The membrane part consists of 78 blades, including the proton-pumping molecule.

ComplexesI,III andIV are combined into supercomplexes or respirasomes. Baker's yeast ( saccharomycescerevisiae) there is no complex I, their supercomplexes consist of III and IV. The role of supercomplexes is not yet clear. It is believed that this makes electron transport more efficient, but there is no direct evidence for this yet.

Figure 7. Cow heart mitochondria supercomplex. Pay attention to the distance between complexes I and III, which must be done with quinol. Arrows – electron movements in the supercomplex.

The main protein of the crista lumen is cytochrome c, which transfers electrons from complex III to complex IV. If cytochrome c is released into the cytoplasm of the cell, it causes apoptosis.

Figure 8. Rows of ATP synthase dimers give the shape of the cristae. At the crista ridge, APT synthase (yellow) forms a sink for protons (red), electron chain proton pumps (green) are located on either side of the rows of dimers. By directing protons from the source to ATP synthase, cristae act as proton guides allowing efficient production of ATP. Red arrows show the direction of proton flow.

Membrane reorganization during aging

Aging is a fundamental and poorly understood process in all eukaryotes. Mitochondrial aging was studied in mushrooms Podospora anserina, which live only 18 days. In normal mitochondria, cristae penetrate deep into the matrix. This requires rows of ATP synthase dimers and the MICOS complex at the cristae attachment sites. With age, the cristae begin to move closer to the surface of the membrane, ATP synthase dimers turn into monomers, and everything ends with the release of cytochrome c and cell death.

Electron transport creates superoxide in complexes I and III. It is a metabolic byproduct. Simultaneously necessary and deadly. During aging, fission begins to prevail over fusion. This prevents damaged mitochondria from being “saved” by fusion and speeds up the inevitable.

A double-membrane organelle, the mitochondrion, is characteristic of eukaryotic cells. The functioning of the body as a whole depends on the functions of mitochondria.

Structure

Mitochondria consist of three interconnected components:

• outer membrane;
• inner membrane;
• matrix.

The outer smooth membrane consists of lipids, between which there are hydrophilic proteins that form tubules. Molecules pass through these tubules during the transport of substances.

The outer and inner membranes are located at a distance of 10-20 nm. The intermembrane space is filled with enzymes. Unlike lysosome enzymes involved in the breakdown of substances, enzymes in the intermembrane space transfer phosphoric acid residues to the substrate with the consumption of ATP (phosphorylation process).

The inner membrane is packed under the outer membrane in the form of numerous folds - cristae.
They are educated:

• lipids, permeable only to oxygen, carbon dioxide, water;
• enzymatic, transport proteins involved in oxidative processes and transport of substances.

Here, due to the respiratory chain, the second stage of cellular respiration occurs and the formation of 36 ATP molecules.

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Between the folds there is a semi-liquid substance - the matrix.
The matrix includes:

• enzymes (hundreds of different types);
• fatty acids;
• proteins (67% mitochondrial proteins);
• mitochondrial circular DNA;
• mitochondrial ribosomes.

The presence of ribosomes and DNA indicates some autonomy of the organelle.

Rice. 1. The structure of mitochondria.

Enzymatic matrix proteins are involved in the oxidation of pyruvate - pyruvic acid during cellular respiration.

Meaning

The main function of mitochondria in a cell is the synthesis of ATP, i.e. energy generation. As a result of cellular respiration (oxidation), 38 ATP molecules are formed. ATP synthesis occurs based on the oxidation of organic compounds (substrate) and phosphorylation of ADP. The substrate for mitochondria is fatty acids and pyruvate.

Rice. 2. Formation of pyruvate as a result of glycolysis.

A general description of the breathing process is presented in the table.

Rice. 3. The process of cellular respiration.

Mitochondria are organelles on which the functioning of the whole organism depends. Signs of mitochondrial dysfunction are a decrease in the rate of oxygen consumption, an increase in the permeability of the inner membrane, and swelling of the mitochondria. These changes occur due to toxic poisoning, infectious disease, hypoxia. 4.5. Total ratings received: 89.

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 amount of M in a cell depends on the type of tissue and the functional state of the 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, however, 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 some cases thin threads, tubes and granules containing calcium and magnesium ions can 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 a short stalk 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. The processes of aerobic respiration (see Biological oxidation) and associated oxidative phosphorylation (see) are the main ones functions of M. In addition, oxidation of fatty acids, phospholipids and certain other compounds can occur in the outer membrane of M.

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 their division 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; presence of ribosomes in M.; DNA-dependent RNA synthesis; sensitivity of mitochondrial proteins to the antibacterial drug chloramphenicol; similarity with bacteria in the implementation of the respiratory chain; morphol., biochemical, and physiol, differences between the inner and outer membrane. According to the symbiotic theory, the host cell is considered 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 that cause changes in water metabolism. 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 thyroid function) underwent a puncture of the skeletal muscle and found an increased M number, 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.

Structure and functions of the plant cell nucleus.

Core- an essential part of a eukaryotic cell. This is the place of storage and reproduction of hereditary information. The nucleus also serves as the control center for metabolism and almost all processes occurring in the cell. Most often, cells have only one nucleus, rarely two or more. Its shape is most often spherical or ellipsoidal. In young, especially meristematic, cells it occupies a central position, but later it usually moves to the membrane, pushed aside by the growing vacuole. On the outside, the nucleus is covered with a double membrane - a nuclear membrane, permeated with pores (nuclear pores are dynamic formations, they can open and close; in this way the exchange between the nucleus and the cytoplasm can be regulated) at the edges of which the outer membrane passes into the inner one. The outer nuclear membrane connects to the membrane channels of the ER. Ribosomes are located on it. The inner membrane may develop invaginations.

The internal contents of the nucleus are karyoplasm with chromatin, nucleoli, and ribosomes embedded in it. Karyoplasm (nucleoplasm) is a jelly-like solution that fills the space between the nuclear structures (chromatin and nucleoli). It contains ions, nucleotides, enzymes.

Chromatin is a despiralized form of chromosome existence. In a despiralized state, chromatin is found in the nucleus of a nondividing cell. Chromatin and chromosomes interchange into each other. In terms of chemical organization, both chromatin and chromosomes do not differ. The chemical basis is deoxyribonucleoprotein - a complex of DNA with proteins. With the help of proteins, multi-level packaging of DNA molecules occurs, while chromatin takes on a compact shape.

The nucleolus, usually spherical in shape (one or more), is not surrounded by a membrane, contains fibrillar protein threads and RNA. Nucleoli are not permanent formations; they disappear at the beginning of cell division and are restored after its completion. Nucleoli are present only in non-dividing cells. In the nucleoli, ribosomes are formed and nuclear proteins are synthesized. The nucleoli themselves are formed in areas of secondary chromosome constrictions (nucleolar organizers).

The nucleus is an essential part of a eukaryotic cell. The core diameter ranges from 5 to 20 microns. The main function of the nucleus is to store genetic material in the form of DNA and transfer it to daughter cells during cell division. In addition, the nucleus controls protein synthesis and controls all vital processes of the cell. (in a plant cell the nucleus was described by R. Brown in 1831, in an animal cell by T. Schwann in 1838).

The chemical composition of the nucleus is represented mainly by nucleic acids and proteins.

Structure and functions of mitochondria.

Mitochondria or chondriosomes are the “power” stations of the cell; most of the respiration reactions are localized in them (aerobic phase). In mitochondria, respiration energy is accumulated in adenosine triphosphate (ATP). The energy stored in ATP serves as the main source for the physiological activities of the cell. Mitochondria usually have an elongated rod-shaped shape with a length of 4-7 µm and a diameter of 0.5-2 µm. The number of mitochondria in a cell can vary from 500 to 1000 and depends on the role of this organ in energy metabolism processes.

The chemical composition of mitochondria varies somewhat. These are mainly protein-lipid organelles. The protein content in them is 60-65%, with structural and enzymatic proteins contained in approximately equal proportions, as well as about 30% lipids. It is very important that mitochondria contain nucleic acids: RNA - 1% and DNA -0.5%. Mitochondria contain not only DNA, but also the entire protein synthesis system, including ribosomes.

Mitochondria are surrounded by a double membrane. The thickness of the membranes is 6-10 nm. Mitochondria membranes are 70% protein. Membrane phospholipids are represented by phosphatidtylcholine, phosphatidylethanolamine, as well as specific phospholipids, for example, cardiolipin. Mitochondrial membranes do not allow H+ to pass through and serve as a barrier to their transport.

Between the membranes there is a fluid-filled perimitochondrial space. The internal space of mitochondria is filled with a matrix in the form of a gelatinous semi-liquid mass. The enzymes of the Krebs cycle are concentrated in the matrix. The inner membrane gives rise to outgrowths - cristae in the form of plates and tubes; they divide the internal space of mitochondria into separate compartments. The respiratory chain (electron transport chain) is localized in the inner membrane.

Main functions of mitochondria:
1) play the role of energy stations of cells. They undergo processes of oxidative phosphorylation (enzymatic oxidation of various substances with subsequent accumulation of energy in the form of molecules of adenosine triphosphate -ATP);
2) store hereditary material in the form of mitochondrial DNA. Mitochondria for their work require proteins encoded in nuclear DNA genes, since mitochondria's own mitochondrial DNA can provide
only a few proteins.
Side functions - participation in the synthesis of steroid hormones, some amino acids (for example, glutamine).

The structure of mitochondria
Mitochondria have two membranes: outer (smooth) and inner (forming outgrowths - leaf-shaped (cristae) and tubular (tubules)). Membranes differ in chemical composition, set of enzymes and functions.
In mitochondria, the internal content is matrix - a colloidal substance in which grains with a diameter of 20-30 nm were discovered using an electron microscope (they accumulate calcium and magnesium ions, reserves of nutrients, for example, glycogen).
The matrix houses the organelle protein biosynthesis apparatus:
2-6 copies of circular DNA devoid of histone proteins (as
in prokaryotes), ribosomes, a set of t-RNAs, reduplication enzymes,
transcription, translation of hereditary information. This device
in general, very similar to that of prokaryotes (in number,
the structure and size of ribosomes, the organization of its own hereditary apparatus, etc.), which confirms the symbiotic concept of the origin of the eukaryotic cell.
Both the matrix and the surface of the inner membrane, on which the electron transport chain (cytochromes) and ATP synthase are located, catalyzing the oxidative phosphorylation of ADP, which converts it into ATP, are actively involved in the implementation of the energy function of mitochondria.
Mitochondria reproduce by interlacing, so when cells divide they are distributed more or less evenly between daughter cells. Thus, continuity occurs between the mitochondria of cells of successive generations.
Thus, mitochondria are characterized by relative autonomy within the cell (unlike other organelles). They arise during the division of maternal mitochondria and have their own DNA, which differs from the nuclear system of protein synthesis and energy storage.