Describe the organelles mitochondria and the cell center. II

Structure. The surface apparatus of mitochondria consists of two membranes - outer and inner. Outer membrane smooth, it separates the mitochondria from the hyaloplasm. Beneath it is a folded inner membrane, which forms Christie(ridges). On both sides of the cristae, small mushroom-shaped bodies called oxysomes, or ATP-somami. They contain enzymes involved in oxidative phosphorylation (the addition of phosphate residues to ADP to form ATP). The number of cristae in mitochondria is related to the energy needs of the cell; in particular, in muscle cells, mitochondria contain very large number christ. With increased cell function, mitochondria become more oval or elongated, and the number of cristae increases.

Mitochondria have their own genome; their 70S type ribosomes differ from the ribosomes of the cytoplasm. Mitochondrial DNA predominantly has a cyclic form (plasmids), encodes all three types of its own RNA and supplies information for the synthesis of some mitochondrial proteins (about 9%). So, mitochondria can be considered semi-autonomous organelles. Mitochondria are self-replicating (capable of reproduction) organelles. Mitochondrial renewal occurs throughout the cell cycle. For example, in liver cells they are replaced by new ones after almost 10 days. The most likely way of reproducing mitochondria is considered to be their division: a constriction appears in the middle of the mitochondria or a septum appears, after which the organelles split into two new mitochondria. Mitochondria are formed with promitochondria - round bodies with a diameter of up to 50 nm with a double membrane.

Functions . Mitochondria are involved in the energy processes of the cell; they contain enzymes associated with energy production and cellular respiration. In other words, the mitochondrion is a kind of biochemical mini-factory that converts energy organic compounds on applied energy of ATP. In mitochondria, the energy process begins in the matrix, where the breakdown of pyruvic acid occurs in the Krebs cycle. During this process, hydrogen atoms are released and transported by the respiratory chain. The energy that is released in this case is used in several parts of the respiratory chain to carry out the phosphorylation reaction - the synthesis of ATP, that is, the addition of a phosphate group to ADP. This occurs on the inner membrane of mitochondria. So, energy function mitochondria integrates with: a) the oxidation of organic compounds that occurs in the matrix, due to which mitochondria are called respiratory center of cells b) ATP synthesis is carried out on cristae, due to which mitochondria are called energy stations cells. In addition, mitochondria take part in the regulation of water metabolism, the deposition of calcium ions, the production of steroid hormone precursors, metabolism (for example, mitochondria in liver cells contain enzymes that allow them to neutralize ammonia) and others.

BIOLOGY + Mitochondrial diseases are a group of hereditary diseases associated with mitochondrial defects that lead to impaired cellular respiration. They are transmitted through the female line to children of both sexes, since the egg has a larger volume of cytoplasm and, accordingly, passes it on to descendants and more mitochondria. Mitochondrial DNA, unlike nuclear DNA, is not protected by histone proteins, and the repair mechanisms inherited from ancestral bacteria are imperfect. Therefore, mutations accumulate in mitochondrial DNA 10-20 times faster than in nuclear DNA, which leads to mitochondrial diseases. In modern medicine, about 50 of them are now known. For example, chronic fatigue syndrome, migraine, Barth syndrome, Pearson syndrome and many others.

(from the Greek mitos - thread, chondrion - grain, soma - body) are granular or filamentous organelles (Fig. 1, a). Mitochondria can be observed in living cells because they have a fairly high density. In such cells, mitochondria can move, move, and merge with each other. Mitochondria are especially well identified in preparations stained in various ways. The size of mitochondria is variable different types, their shape is also changeable. Still, in most cells the thickness of these structures is relatively constant (about 0.5 µm), but the length varies, reaching 7-60 µm in filamentous forms.

Mitochondria, regardless of their size and shape, have a universal structure, their ultrastructure is uniform. Mitochondria are bounded by two membranes (Fig. 1b), they have four subcompartments: mitochondrial matrix, inner membrane, membrane space and outer membrane facing the cytosol. An outer membrane separates it from the rest of the cytoplasm. The thickness of the outer membrane is about 7 nm, it is not connected to any other membranes of the cytoplasm and is closed on itself, so that it is a membrane sac. The outer membrane is separated from the inner membrane by an intermembrane space about 10-20 nm wide. The inner membrane (about 7 nm thick) limits the actual internal contents of the mitochondrion, its matrix, or mitoplasm. Characteristic feature The inner membranes of mitochondria are their ability to form numerous protrusions (folds) inside the mitochondria. Such protrusions (cristae, Fig. 27) most often have the appearance of flat ridges. Mitochondria carry out the synthesis of ATP, which occurs as a result of the oxidation of organic substrates and phosphorylation of ADP.

Mitochondria specialize in ATP synthesis through electron transport and oxidative phosphorylation. (Figure 21-1). Although they have their own DNA and protein synthesis machinery, most of their proteins are encoded by cellular DNA and come from the cytosol. Moreover, each protein entering the organelle must reach a specific subcompartment in which it functions.

Mitochondria are the “energy stations” of eukaryotic cells. The cristae contain enzymes that are involved in converting the energy of nutrients entering the cell from the outside into the energy of ATP molecules. ATP is the “universal currency” with which cells pay for all their energy costs. The folding of the inner membrane increases the surface area on which enzymes that synthesize ATP are located. The number of cristae in a mitochondria and the number of mitochondria themselves in a cell are greater, the more energy expenditure a given cell makes. In insect flight muscles, each cell contains several thousand mitochondria. Their number also changes during the process of individual development (ontogenesis): in young embryonic cells they are more numerous than in aging cells. Typically, mitochondria accumulate near those areas of the cytoplasm where the need for ATP, which is formed in mitochondria, arises.

The distance between the membranes in the crista is about 10-20 nm. In the simplest, unicellular algae, in some plant and animal cells, outgrowths of the inner membrane have the form of tubes with a diameter of about 50 nm. These are the so-called tubular cristae.

The mitochondrial matrix is ​​homogeneous and has a denser consistency than the hyaloplasm surrounding the mitochondrion. The matrix contains thin strands of DNA and RNA, as well as mitochondrial ribosomes, on which some mitochondrial proteins are synthesized. Using an electron microscope, mushroom-shaped formations - ATP-somes - can be seen on the inner membrane and cristae on the matrix side. These are enzymes that form ATP molecules. There can be up to 400 per 1 micron.

The few proteins that are encoded by the mitochondria's own genome are located primarily in the inner membrane. They usually form subunits of protein complexes, the other components of which are encoded by nuclear genes and come from the cytosol. The formation of such hybrid aggregates requires balancing the synthesis of these two types of subunits; How is protein synthesis coordinated on ribosomes? different types, separated by two membranes, remains a mystery.

Typically, mitochondria are located in places where energy is needed for any life processes. The question arose of how energy is transported in the cell - is it by diffusion of ATP and are there structures in the cells that play the role of electrical conductors, which could energetically unite areas of the cell that are distant from each other. The hypothesis is that the potential difference in a certain area of ​​the mitochondrial membrane is transmitted along it and converted into work in another area of ​​the same membrane [Skulachev V.P., 1989].

It seemed that the membranes of mitochondria themselves could be suitable candidates for the same role. In addition, researchers were interested in the interaction of multiple mitochondria in a cell with each other, the work of the entire ensemble of mitochondria, the entire chondriome - the totality of all mitochondria.

Mitochondria are characteristic, with few exceptions, of all eukaryotic cells of both autotrophic (photosynthetic plants) and heterotrophic (animals, fungi) organisms. Their main function is associated with the oxidation of organic compounds and the use of energy released during the breakdown of these compounds in the synthesis of ATP molecules. Therefore, mitochondria are often called the energy stations of the cell.

Mitochondria are the “powerhouses” of eukaryotes, producing energy for cellular activity. These generate energy by converting it into forms that can be used by the cell. Located in, mitochondria serve as the “base” for cellular respiration. - a process that generates energy for cell activity. Mitochondria are also involved in other cellular processes such as growth and.

Distinctive characteristics

Mitochondria have a characteristic oblong or oval shape and are covered with a double membrane. They are found both in and in. The number of mitochondria within a cell varies depending on the type and function of the cell. Some cells, such as mature red blood cells, do not contain mitochondria at all. The absence of mitochondria and other organelles leaves room for the millions of hemoglobin molecules needed to transport oxygen throughout the body. On the other hand, muscle cells can contain thousands of mitochondria, which generate the energy needed for muscle activity. Mitochondria are also abundant in fat cells and liver cells.

Mitochondrial DNA

Mitochondria have their own DNA (mtDNA) and can synthesize their own proteins. mtDNA encodes proteins involved in electron transfer and oxidative phosphorylation that occur during cellular respiration. Oxidative phosphorylation generates energy in the form of ATP in the mitochondrial matrix. Proteins synthesized from mtDNA are also encoded to produce RNA molecules that transmit RNA and ribosomal RNA.

Mitochondrial DNA differs from the DNA found in , in that it does not possess the DNA repair mechanisms that help prevent mutations in nuclear DNA. As a result, mtDNA has much more high speed mutations than nuclear DNA. Exposure to reactive oxygen produced by oxidative phosphorylation also damages mtDNA.

The structure of mitochondria

Mitochondria are surrounded by double . Each of these membranes is a phospholipid bilayer with embedded proteins. The outer membrane is smooth, but the inner membrane has many folds. These folds are called cristae. They increase the “productivity” of cellular respiration by increasing the available surface area.

Double membranes divide the mitochondrion into two distinct parts: the intermembrane space and the mitochondrial matrix. The intermembrane space is the narrow part between two membranes, while the mitochondrial matrix is ​​the part enclosed within the membranes.

The mitochondrial matrix contains mtDNA, ribosomes and enzymes. Some of the stages of cellular respiration, including the cycle citric acid and oxidative phosphorylation occur in the matrix due to the high concentration of enzymes.

Mitochondria are semi-autonomous, as they are only partially dependent on the cell to replicate and grow. They have their own DNA, ribosomes, proteins and control over their synthesis. Like bacteria, mitochondria have circular DNA and replicate by a reproductive process called binary fission. Before replication, mitochondria fuse together in a process called fusion. This is necessary to maintain stability, since without it the mitochondria will shrink as they divide. Reduced mitochondria are not able to produce enough energy necessary for normal cell functioning.

Outer membrane
Inner membrane
Matrix m-na, matrix, cristas. it has smooth contours and does not form indentations or folds. It accounts for about 7% of the total area cell membranes. Its thickness is about 7 nm, it is not connected to any other membranes of the cytoplasm and is closed on itself, so that it is a membrane sac. Separates the outer membrane from the inner intermembrane space about 10-20 nm wide. The inner membrane (about 7 nm thick) limits the actual internal contents of the mitochondrion,
its matrix or mitoplasm. A characteristic feature of the inner membrane of mitochondria is their ability to form numerous invaginations into the mitochondria. Such invaginations most often take the form of flat ridges, or cristae. The distance between the membranes in the crista is about 10-20 nm. Often the cristae may branch or form finger-like processes, bend and have no clear orientation. In protozoa, single-celled algae, in some cells higher plants and animals, the outgrowths of the inner membrane have the form of tubes (tubular cristae).
The mitochondrial matrix has a fine-grained homogeneous structure; thin filaments collected in a ball (about 2-3 nm) and granules about 15-20 nm are sometimes detected in it. It has now become known that the filaments of the mitochondrial matrix are DNA molecules within the mitochondrial nucleoid, and the small granules are mitochondrial ribosomes.

Functions of mitochondria

1. ATP synthesis occurs in mitochondria (see Oxidative phosphorylation)

PH of the intermembrane space ~4, pH of the matrix ~8 | protein content in m: 67% - matrix, 21% - outer m-on, 6% - inner m-on and 6% - in interstitial mass
Handrioma – unified system mitochondria
external m-na: porins-pores allow passage of up to 5 kD | internal m-na: cardiolipin - makes the m-n impermeable to ions |
intermittent production: groups of enzymes phosphorylate nucleotides and sugars of nucleotides
internal m-na:
matrix: metabolic enzymes - lipid oxidation, carbohydrate oxidation, tricarboxylic acid cycle, Krebs cycle
Origin from bacteria: the amoeba Pelomyxa palustris does not contain any eukaryotes, lives in symbiosis with aerobic bacteria | own DNA | processes similar to bacteria

Mitochondrial DNA

Myochondrial division

replicated
in interphase | replication is not associated with S-phase | during the CL cycle, the mitochs divide once in two, forming a constriction, the constriction first on the inner side | ~16.5 kb | circular, encodes 2 rRNA, 22 tRNA and 13 proteins |
protein transport: signal peptide | amphiphilic curl | mitochondrial recognition receptor |
Oxidative phosphorylation
Electron transport chain
ATP synthase
in the liver cell, m live ~20 days, division of mitochondria through the formation of a constriction

16569 bp = 13 proteins, 22 tRNA, 2 pRNA | smooth outer membrane (porins - protein permeability up to 10 kDa) folded internal membrane (cristae) matrix (75% proteins: transport carrier proteins, proteins, components of the respiratory chain and ATP synthase, cardiolipin) matrix ( enriched with substances of the citrate cycle) intermittent production

Divides all cells (or living organisms) into two types: prokaryotes And eukaryotes. Prokaryotes are nuclear-free cells or organisms, which include viruses, prokaryotic bacteria and blue-green algae, in which the cell consists directly of the cytoplasm, in which one chromosome is located - DNA molecule(sometimes RNA).

Eukaryotic cells have a core containing nucleoproteins (histone protein + DNA complex), as well as others organoids. Most modern animals are eukaryotes known to science unicellular and multicellular living organisms (including plants).

The structure of eukaryotic granoids.

Cell nucleus is the main and most complex organelle of the cell, so we will consider it