The number of cristae in the mitochondria of various cells. Mitochondria. Structure and functions of mitochondria

What are mitochondria? If the answer to this question is difficult for you, then our article is just for you. We will consider the structural features of these organelles in relation to the functions they perform.

What are organelles

But first, let's remember what organelles are. This is what permanent cellular structures are called. Mitochondria, ribosomes, plastids, lysosomes... All these are organelles. Like the cell itself, each such structure has a general structural plan. Organelles consist of a surface apparatus and internal contents - the matrix. Each of them can be compared to the organs of living beings. Organelles also have their own characteristic features that determine their biological role.

Classification of Cell Structures

Organelles are grouped based on the structure of their surface apparatus. There are single-, double- and non-membrane permanent cellular structures. The first group includes lysosomes, the Golgi complex, the endoplasmic reticulum, peroxisomes and various types of vacuoles. The nucleus, mitochondria and plastids are double-membrane. And ribosomes, the cell center and organelles of movement are completely devoid of surface apparatus.

Symbiogenesis theory

What are mitochondria? For evolutionary teaching, these are not just cell structures. According to the symbiotic theory, mitochondria and chloroplasts are the result of metamorphoses of prokaryotes. It is possible that mitochondria originated from aerobic bacteria, and plastids from photosynthetic bacteria. Proof of this theory is the fact that these structures have their own genetic apparatus, represented by a circular DNA molecule, a double membrane and ribosomes. There is also an assumption that animal eukaryotic cells subsequently evolved from mitochondria, and plant cells from chloroplasts.

Location in cells

Mitochondria are an integral part of the cells of the majority of plants, animals and fungi. They are absent only in anaerobic unicellular eukaryotes living in an oxygen-free environment.

The structure and biological role of mitochondria have long remained a mystery. They were first seen using a microscope by Rudolf Kölliker in 1850. In the muscle cells, the scientist discovered numerous granules that looked like fluff in the light. Understanding the role of these amazing structures was made possible thanks to the invention of University of Pennsylvania professor Britton Chance. He designed a device that allowed him to see through organelles. This is how the structure was determined and the role of mitochondria in providing energy to cells and the body as a whole was proven.

Shape and size of mitochondria

General plan of the building

Let's consider what mitochondria are from the point of view of their structural features. These are double-membrane organelles. Moreover, the outer one is smooth, and the inner one has outgrowths. The mitochondrial matrix is ​​represented by various enzymes, ribosomes, monomers of organic substances, ions and clusters of circular DNA molecules. This composition makes it possible for the most important chemical reactions to occur: the tricarboxylic acid cycle, urea, and oxidative phosphorylation.

The meaning of kinetoplast

Mitochondria membrane

Mitochondria membranes are not identical in structure. The closed outer one is smooth. It is formed by a bilayer of lipids with fragments of protein molecules. Its total thickness is 7 nm. This structure performs the functions of delimitation from the cytoplasm, as well as the relationship of the organelle with the environment. The latter is possible due to the presence of the porin protein, which forms the channels. Molecules move along them through active and passive transport.

The chemical basis of the inner membrane is proteins. It forms numerous folds inside the organoid - cristae. These structures significantly increase the active surface of the organelle. The main feature of the structure of the inner membrane is complete impermeability to protons. It does not form channels for the penetration of ions from the outside. In some places the outer and inner contact. A special receptor protein is located here. This is a kind of conductor. With its help, mitochondrial proteins, which are encoded in the nucleus, penetrate into the organelle. Between the membranes there is a space up to 20 nm thick. It contains various types of proteins, which are essential components of the respiratory chain.

Functions of mitochondria

The structure of the mitochondrion is directly related to the functions it performs. The main one is the synthesis of adenosine triphosphate (ATP). This is a macromolecule that is the main carrier of energy in the cell. It consists of the nitrogenous base adenine, the monosaccharide ribose and three phosphoric acid residues. It is between the last elements that the main amount of energy is contained. When one of them ruptures, a maximum of 60 kJ can be released. In total, a prokaryotic cell contains 1 billion ATP molecules. These structures are constantly in operation: the existence of each of them in an unchanged form does not last more than one minute. ATP molecules are constantly synthesized and broken down, providing the body with energy at the moment when it is needed.

For this reason, mitochondria are called "energy stations." It is in them that the oxidation of organic substances occurs under the action of enzymes. The energy that is generated in this case is stored and stored in the form of ATP. For example, when 1 g of carbohydrates is oxidized, 36 macromolecules of this substance are formed.

The structure of mitochondria allows them to perform another function. Due to their semi-autonomy, they are an additional carrier of hereditary information. Scientists have found that the DNA of the organelles themselves cannot function independently. The fact is that they do not contain all the proteins necessary for their work, so they borrow them from the hereditary material of the nuclear apparatus.

So, in our article we looked at what mitochondria are. These are double-membrane cellular structures, in the matrix of which a number of complex chemical processes take place. The result of the work of mitochondria is the synthesis of ATP - a compound that provides the body with the necessary amount of energy.

Mitochondria.

Mitochondria- an organelle consisting of two membranes with a thickness of about 0.5 microns.

Energy station of the cell; the main function is the oxidation of organic compounds and the use of energy released during their breakdown in the synthesis of ATP molecules (a universal source of energy for all biochemical processes).

In their structure, they are cylindrical organelles, found in a eukaryotic cell in quantities from several hundred to 1-2 thousand and occupying 10-20% of its internal volume. The size (from 1 to 70 microns) and shape of mitochondria also vary greatly. Moreover, the width of these parts of the cell is relatively constant (0.5-1 µm). Capable of changing shape. Depending on which areas of the cell at any given moment there is increased energy consumption, mitochondria are able to move through the cytoplasm to areas of greatest energy consumption, using the structures of the cellular framework of the eukaryotic cell for movement.

Beautiful mitochondria in 3D representation)

An alternative to many scattered small mitochondria functioning independently of each other and supplying ATP to small areas of the cytoplasm is the existence of long and branched mitochondria, each of which can provide energy to distant areas of the cell. A variant of such an extended system can also be an ordered spatial association of many mitochondria (chondriomes or mitochondria), ensuring their cooperative work.

This type of chondrioma is especially complex in muscles, where groups of giant branched mitochondria are connected to each other using intermitochondrial contacts (MMK). The latter are formed by outer mitochondrial membranes tightly adjacent to each other, as a result of which the intermembrane space in this zone has an increased electron density (many negatively charged particles). MMC are especially abundant in cardiac muscle cells, where they link multiple individual mitochondria into a coordinated working cooperative system.

Structure.

Outer membrane.

The outer membrane of the mitochondria is about 7 nm thick, does not form invaginations or folds, and is closed on itself. The outer membrane accounts for about 7% of the surface area of ​​all membranes of cellular organelles. The main function is to separate mitochondria from the cytoplasm. The outer membrane of the mitochondrion consists of a double fatty layer (like a cell membrane) and proteins that penetrate it. Proteins and fats in equal proportions by weight.
Plays a special role porin - channel-forming protein.
It forms holes in the outer membrane with a diameter of 2-3 nm, through which small molecules and ions can penetrate. Large molecules can only cross the outer membrane through active transport through mitochondrial membrane transport proteins. The outer membrane of the mitochondrion can interact with the membrane of the endoplasmic reticulum; it plays an important role in the transport of lipids and calcium ions.

Inner membrane.

The inner membrane forms numerous comb-like folds - crista,
significantly increasing its surface area and, for example, in liver cells constitutes about a third of all cell membranes. a characteristic feature of the composition of the inner membrane of mitochondria is the presence in it cardiolopina - a special complex fat that contains four fatty acids at once and makes the membrane absolutely impermeable to protons (positively charged particles).

Another feature of the inner mitochondrial membrane is a very high protein content (up to 70% by weight), represented by transport proteins, respiratory chain enzymes, as well as large enzyme complexes that produce ATP. The inner membrane of the mitochondria, unlike the outer one, does not have special openings for the transport of small molecules and ions; on it, on the side facing the matrix, there are special ATP-producing enzyme molecules, consisting of a head, a stalk and a base. When protons pass through them, atf is created.
At the base of the particles, filling the entire thickness of the membrane, are the components of the respiratory chain. The outer and inner membranes touch in some places; there is a special receptor protein that promotes the transport of mitochondrial proteins encoded in the nucleus into the mitochondrial matrix.

Matrix.

Matrix- space limited by the internal membrane. The matrix (pink substance) of the mitochondria contains enzyme systems for the oxidation of pyruvate of fatty acids, as well as enzymes such as tricarboxylic acids (cell respiration cycle). In addition, mitochondrial DNA, RNA, and the mitochondria’s own protein-synthesizing apparatus are also located here.

pyruvates (salts of pyruvic acid)- important chemical compounds in biochemistry. They are the end product of glucose metabolism during its breakdown.

Mitochondrial DNA.

Several differences from nuclear DNA:

- Mitochondrial DNA is circular, unlike nuclear DNA, which is packaged into chromosomes.

- It is impossible to exchange similar sections between different evolutionary variants of mitochondrial DNA of the same species.

And so the entire molecule changes only through slow mutation over thousands of years.

- Code mutations in mitochondrial DNA can occur independently of nuclear DNA.

Mutation of the nuclear DNA code occurs mainly during cell division, but mitochondria divide independently of the cell, and can receive a mutation of the code separately from the nuclear DNA.

- The structure of mitochondrial DNA itself is simplified, because many of the component DNA reading processes have been lost.

- transport RNAs have the same structure. but mitochondrial RNAs are involved only in the synthesis of mitochondrial proteins.

Having its own genetic apparatus, the mitochondrion also has its own protein synthesizing system, a feature of which in animal and fungal cells are very small ribosomes.

Functions.

Energy generation.

The main function of mitochondria is the synthesis of ATP, a universal form of chemical energy in any living cell.

This molecule can be formed in two ways:

- through a reaction in which the energy released at certain oxidative stages of fermentation is stored in the form of ATP.

- thanks to the energy released during the oxidation of organic substances in the process of cellular respiration.

Mitochondria implement both of these pathways, the first of which is characteristic of the initial processes of oxidation and occurs in the matrix, and the second completes the processes of energy generation and is associated with the cristae of mitochondria.
At the same time, the uniqueness of mitochondria as energy-producing organelles of a eukaryotic cell determines precisely the second pathway of ATP generation, called “chemiosmotic coupling.”
In general, the entire process of energy production in mitochondria can be divided into four main stages, the first two of which occur in the matrix, and the last two on the cristae of mitochondria:

1) Conversion of pyruvate (the final product of the breakdown of glucose) and fatty acids received from the cytoplasm into the mitochondria into acetyl cola;

acetyl coa– an important compound in metabolism, used in many biochemical reactions. its main function is to deliver carbon atoms (c) with an acetyl group (ch3 co) into the cellular respiration cycle so that they are oxidized to release energy.

cellular respiration - a set of biochemical reactions occurring in the cells of living organisms, during which the oxidation of carbohydrates, fats and amino acids to carbon dioxide and water occurs.

2) Oxidation of acetyl-coa in the cellular respiration cycle, leading to the formation of nadn;

NADH– coenzyme acts as a carrier of electrons and hydrogen, which it receives from oxidized substances.

3) Transfer of electrons from nadn to oxygen through the respiratory chain;

4) Formation of ATP as a result of the activity of the membrane ATP-creating complex.

ATP synthetase.

ATP synthetase– station for the production of ATP molecules.

In structural and functional terms, ATP synthetase consists of two large fragments, designated by the symbols F1 and F0. The first of them (coupling factor F1) faces the mitochondrial matrix and protrudes noticeably from the membrane in the form of a spherical formation 8 nm high and 10 nm wide. It consists of nine subunits represented by five types of proteins. The polypeptide chains of three α subunits and the same number of β subunits are arranged in protein globules of similar structure, which together form a hexamer (αβ)3, which looks like a slightly flattened ball.

Subunit- is a structural and functional component of any particle
Polypeptides- organic compounds containing from 6 to 80-90 amino acid residues.
Globule– a state of macromolecules in which the vibration of the units is small.
Hexamer– a compound containing 6 subunits.

Like tightly packed orange slices, the successive α and β subunits form a structure characterized by symmetry around a 120° rotation angle. At the center of this hexamer is the γ subunit, which is formed by two extended polypeptide chains and resembles a slightly deformed curved rod about 9 nm long. In this case, the lower part of the γ subunit protrudes from the ball by 3 nm towards the membrane complex F0. Also located within the hexamer is a minor ε subunit associated with γ. The last (ninth) subunit is designated δ and is located on the outer side of F1.

Minor– single subunit.

The membrane part of ATP synthetase is a water-repellent protein complex that penetrates the membrane through and has two half-channels inside for the passage of hydrogen protons. In total, the F0 complex includes one protein subunit of the type A, two copies of the subunit b, as well as 9 to 12 copies of the small subunit c. Subunit A(molecular weight 20 kDa) is completely immersed in the membrane, where it forms six α-helical sections crossing it. Subunit b(molecular weight 30 kDa) contains only one relatively short α-helical region immersed in the membrane, and the rest of it protrudes noticeably from the membrane towards F1 and is attached to the δ subunit located on its surface. Each of 9-12 copies of a subunit c(molecular weight 6-11 kDa) is a relatively small protein of two water-repellent α-helices connected to each other by a short water-attracting loop oriented towards F1, and together they form a single ensemble having the shape of a cylinder immersed in the membrane . The γ subunit protruding from the F1 complex towards F0 is precisely immersed inside this cylinder and is quite firmly attached to it.
Thus, in the ATPase molecule, two groups of protein subunits can be distinguished, which can be likened to two parts of a motor: the rotor and the stator.

"Stator" is motionless relative to the membrane and includes a spherical hexamer (αβ)3 located on its surface and the δ subunit, as well as subunits a And b membrane complex F0.

Movable relative to this design "rotor" consists of subunits γ and ε, which, prominently protruding from the (αβ)3 complex, connect to a ring of subunits immersed in the membrane c.

The ability to synthesize ATP is a property of a single complex F0F1, combined with the transfer of hydrogen protons through F0 to F1, in the latter of which the reaction centers that convert ADP and phosphate into an ATP molecule are located. The driving force for the operation of ATP synthetase is the proton (positively charged) potential created on the inner mitochondrial membrane as a result of the operation of the electron (negatively charged) transport chain.
The force driving the “rotor” of ATP synthetase occurs when the potential difference between the outer and inner sides of the membrane reaches > 220 10−3 Volts and is provided by the flow of protons flowing through a special channel in F0, located at the boundary between subunits a And c. In this case, the proton transfer path includes the following structural elements:

1) Two “half-channels” located on different axes, the first of which ensures the supply of protons from the intermembrane space to the essential functional groups F0, and the other ensures their release into the mitochondrial matrix;

2) Ring of subunits c, each of which in its central part contains a protonated carboxyl group (COOH), capable of attaching H+ from the intermembrane space and releasing them through the corresponding proton channels. As a result of periodic displacements of subunits With, caused by the flow of protons through the proton channel, the γ subunit rotates, immersed in a ring of subunits With.

Thus, the unifying activity of ATP synthetase is directly related to the rotation of its “rotor”, in which the rotation of the γ subunit causes a simultaneous change in the conformation of all three unifying β subunits, which ultimately ensures the functioning of the enzyme. In this case, in the case of ATP formation, the “rotor” rotates clockwise at a speed of four revolutions per second, and such rotation itself occurs in precise jumps of 120°, each of which is accompanied by the formation of one ATP molecule.
The work of ATP synthetase is associated with the mechanical movements of its individual parts, which makes it possible to classify this process as a special type of phenomenon called “rotational catalysis.” Just as the electric current in the winding of an electric motor drives the rotor relative to the stator, the directed transfer of protons through ATP synthetase causes the rotation of individual subunits of the conjugation factor F1 relative to other subunits of the enzyme complex, as a result of which this unique energy-producing device performs chemical work - synthesizes ATP molecules . Subsequently, ATP enters the cell cytoplasm, where it is spent on a wide variety of energy-dependent processes. This transfer is carried out by a special enzyme, ATP/ADP translocase, built into the mitochondrial membrane.

ADP translocase- a protein that penetrates the inner membrane, which exchanges newly synthesized ATP for cytoplasmic ADP, which guarantees the safety of the fund inside the mitochondria.

Mitochondria and heredity.

Mitochondrial DNA is inherited almost exclusively through the maternal line. Each mitochondria has several sections of nucleotides in DNA that are identical in all mitochondria (that is, there are many copies of mitochondrial DNA in the cell), which is very important for mitochondria that are unable to repair DNA from damage (a high frequency of mutations is observed). Mutations in mitochondrial DNA are the cause of a number of hereditary human diseases.

3d model

Discovery

With English voice acting

A little about cell respiration and mitochondria in a foreign language

Building structure

Mitochondria are organelles the size of bacteria (about 1 x 2 microns). They are found in large numbers in almost all eukaryotic cells. Typically, a cell contains about 2000 mitochondria, the total volume of which is up to 25% of the total cell volume. The mitochondrion is bounded by two membranes - a smooth outer one and a folded inner one, which has a very large surface. The folds of the inner membrane penetrate deeply into the mitochondrial matrix, forming transverse septa - cristae. The space between the outer and inner membranes is usually called the intermembrane space. The mitochondrion is the cells' only source of energy. Located in the cytoplasm of every cell, mitochondria are comparable to “batteries” that produce, store and distribute the energy necessary for the cell.

Human cells contain on average 1,500 mitochondria. They are especially numerous in cells with intense metabolism (for example, in muscle or liver).

Mitochondria are mobile and move in the cytoplasm depending on the needs of the cell. Due to the presence of their own DNA, they multiply and self-destruct regardless of cell division.

Cells cannot function without mitochondria; life is not possible without them.

Different types of cells differ from each other both in the number and shape of mitochondria and in the number of cristae. Mitochondria in tissues with active oxidative processes, for example in the heart muscle, have especially many cristae. Variations in mitochondrial shape, which depend on their functional state, can also be observed in tissues of the same type. Mitochondria are variable and plastic organelles.

Mitochondrial membranes contain integral membrane proteins. The outer membrane contains porins, which form pores and make the membrane permeable to substances with a molecular weight of up to 10 kDa. The inner membrane of mitochondria is impermeable to most molecules; the exceptions are O2, CO2, H20. The inner membrane of mitochondria is characterized by an unusually high protein content (75%). These include transport carrier proteins), enzymes, components of the respiratory chain and ATP synthase. In addition, it contains an unusual phospholipid, cardiolipin. The matrix is ​​also enriched with proteins, especially enzymes of the citrate cycle. Mitochondria are the “power station” of the cell, since due to the oxidative degradation of nutrients they synthesize most of the ATP (ATP) needed by the cell. A mitochondrion consists of an outer membrane, which is its shell, and an inner membrane, the site of energy transformations. The inner membrane forms numerous folds that promote intense energy conversion activity.

Specific DNA: The most remarkable feature of mitochondria is that they have their own DNA: mitochondrial DNA. Regardless of nuclear DNA, each mitochondrion has its own genetic apparatus. As its name suggests, mitochondrial DNA (mtDNA) is found inside mitochondria, small structures located in the cytoplasm of the cell, unlike nuclear DNA, which is packaged into chromosomes inside the nucleus . Mitochondria are present in most eukaryotes and have a single origin, it is believed, from one ancient bacterium, which at the dawn of evolution was once absorbed by the cell and turned into its component part, which was “entrusted” with very important functions. Mitochondria are often called the “energy stations” of cells for the reason that they produce adenosine triphosphoric acid (ATP), the chemical energy of which the cell can use almost everywhere, just as a person uses the energy of fuel or electricity for his own purposes. And in the same way, the production of fuel and electricity requires a considerable amount of human labor and the coordinated work of a large number of specialists; the production of ATP inside the mitochondria (or “cellular respiration”, as it is called) uses a huge amount of cellular resources, including “fuel” in the form of oxygen and some organic substances, and of course involves the participation of hundreds of proteins in this process, each of which performs its own specific functions.

To call this process simply “complex” will probably not be enough, because it is directly or indirectly connected with most other metabolic processes in the cell, due to the fact that evolution has endowed each “cog” of this mechanism with many additional functions. The basic principle is to create conditions when inside the mitochondrial membrane it becomes possible to add another phosphate to the ADP molecule, which is “energetically” unrealistic under normal conditions. Conversely, the subsequent use of ATP is the ability to break this bond, releasing energy that the cell can use for its many purposes. The structure of the mitochondrial membrane is very complex; it includes a large number of proteins of various types, which are combined into complexes, or, as they say, “molecular machines” that perform strictly defined functions. Biochemical processes occurring inside the mitochondrial membrane (tricarboxylic cycle, etc.) take in glucose as an input, and produce carbon dioxide and NADH molecules as output products, which are capable of splitting off a hydrogen atom, transferring it to membrane proteins. In this case, a proton is transferred to the outside of the membrane, and the electron is ultimately taken by an oxygen molecule on the inside. When the potential difference reaches a certain value, protons begin to move into the cell through special protein complexes, and combining with oxygen molecules (which have already received an electron), they form water, and the energy of moving protons is used in the formation of ATP. Thus, the input of the whole process is carbohydrates (glucose) and oxygen, and the output is carbon dioxide, water and a supply of “cellular fuel” - ATP, which can be transported to other parts of the cell.

As mentioned above, the mitochondrion inherited all these functions from its ancestor - an aerobic bacterium. Since a bacterium is an independent single-celled organism, inside it there is a DNA molecule that contains sequences that determine the structure of all the proteins of a given organism, that is, directly or indirectly, all the functions it performs. When a protomitochondrial bacterium and an ancient eukaryotic cell (also a bacterium by origin) merged, the new organism received two different DNA molecules - nuclear and mitochondrial, which, apparently, initially encoded two completely independent life cycles. However, inside a new single cell such an abundance of metabolic processes turned out to be unnecessary, since they largely duplicated each other. The gradual mutual adaptation of the two systems led to the replacement of most mitochondrial proteins with the eukaryotic cell's own proteins, capable of performing similar functions. As a result, sections of the mitochondrial DNA code that previously performed certain functions became non-coding and were lost over time, leading to the reduction of the molecule. Due to the fact that some forms of life, such as fungi, have very long (and fully functioning!) chains of mitochondrial DNA, we can judge the history of the simplification of this molecule quite reliably by observing how, over the course of millions of years, certain or different branches of the Tree of Life were lost. its other functions. Modern chordates, including mammals, have mtDNA ranging from 15,000 to 20,000 nucleotides in length, the remaining genes of which are located very closely together. Only a little more than 10 proteins and only two types of structural RNA are encoded in the mitochondrion itself; everything else that is required for cellular respiration (more than 500 proteins) is provided by the nucleus. Perhaps the only subsystem that has been preserved entirely is transfer RNA, the genes of which still lie in mitochondrial DNA. Transfer RNAs, each of which includes a three-nucleotide sequence, serve for the synthesis of proteins, with one side “reading” the three-letter codon specifying the future protein, and with the other adding a strictly defined amino acid; the correspondence between trinucleotide sequences and amino acids is called the “translation table” or “genetic code”. Mitochondrial transfer RNAs are involved only in the synthesis of mitochondrial proteins and cannot be used by the nucleus because small differences have accumulated between the nuclear and mitochondrial codes over millions of years of evolution.

Let us also mention that the structure of mitochondrial DNA itself has been significantly simplified, since many components of the DNA transcription (reading) process have been lost, as a result of which the need for special structuring of the mitochondrial code has disappeared. Polymerase proteins that perform transcription (reading) and replication (doubling) of mitochondrial DNA are encoded not in it itself, but in the nucleus.

The main and immediate cause of the diversity of life forms is mutations of the DNA code, that is, the replacement of one nucleotide with another, the insertion of nucleotides and their deletion. Like nuclear DNA mutations, mtDNA mutations mainly occur during the multiplication of the molecule - replication. However, mitochondrial division cycles are independent of cell division, and therefore mutations in mtDNA can occur independently of cell division. In particular, there may be some minor differences between mtDNA located in different mitochondria within the same cell, as well as between mitochondria in different cells and tissues of the same organism. This phenomenon is called heteroplasmy. There is no exact analogue of heteroplasmy in nuclear DNA: an organism develops from a single cell containing a single nucleus, where the entire genome is represented by a single copy. Later, during the life of an individual, various tissues can accumulate the so-called. somatic mutations, but all copies of the genome ultimately come from one. The situation with the mitochondrial genome is somewhat different: a mature egg contains hundreds of thousands of mitochondria, which, as they divide, can quickly accumulate small differences, with the entire set of variants being inherited by a new organism after fertilization. Thus, if discrepancies between nuclear DNA variants of different tissues are caused only by somatic (lifetime) mutations, then differences in mitochondrial DNA are caused by both somatic and germinal (germline) mutations.

Another difference is that the mitochondrial DNA molecule is circular, while nuclear DNA is packaged into chromosomes, which can (with some degree of convention) be considered as linear sequences of nucleotides.

Finally, the last feature of mitochondrial DNA that we will mention in this introductory section is its inability to recombine. In other words, the exchange of homologous (i.e., similar) regions is impossible between different evolutionary variants of mitochondrial DNA of the same species, and therefore the entire molecule changes only through slow mutation over thousands of years. In all chordates, mitochondria are inherited only from the mother, so the evolutionary tree of mitochondrial DNA corresponds to genealogy in the direct female line. However, this feature is not unique; in various evolutionary families, certain nuclear chromosomes are also not subject to recombination (having no pairs) and are inherited only from one of the parents. So. for example, the Y chromosome in mammals can only be passed on from father to son. Mitochondrial DNA is inherited only through the maternal line and is passed down from generation to generation exclusively by women. This special form of inheritance of the mitochondrial genome has made it possible to create a family tree of different human ethnic groups, locating our common ancestors in Ethiopia about 200,000 years ago. Possessing extraordinary abilities to adapt, with increasing Energy requirements Mitochondria are also able to multiply independently of cell division. This phenomenon is possible thanks to mitochondrial DNA. Mitochondrial DNA is transmitted exclusively by women. Mitochondrial DNA is not inherited according to Mendelian laws, but according to the laws of cytoplasmic inheritance. During fertilization, the sperm that penetrates the egg loses its flagellum, which contains all the mitochondria. Only the mitochondria contained in the mother's egg are transferred to the embryo. Thus, cells inherit their only source of energy from the mother's mitochondria. Mitochondria: the powerhouse of the cell. A unique source of energy. In everyday life, there are various ways to extract energy and use it for domestic needs: solar panels, nuclear power plants, wind power plants... The cell has only one solution for extracting, converting and storing energy: mitochondria. Only the mitochondrion can convert various types of energy into ATP, the energy used by the cell.
Cellular Energy Conversion Process Mitochondria use 80% of the oxygen we breathe to convert potential energy into energy usable by the cell. During the oxidation process, a large amount of energy is released, which is stored by mitochondria in the form of ATP molecules.

40 kg are converted per day. ATP Energy in a cell can take many forms. The principle of operation of the cellular mechanism is the conversion of potential energy into energy that can be directly used by the cell. Potential types of energy enter the cell through nutrition in the form of carbohydrates, fats and proteins. Cellular energy consists of a molecule called ATP: Adenosine triphosphate. It is synthesized as a result of the transformation of carbohydrates, fats and proteins inside the mitochondria. During the day, the equivalent of 40 kg of ATP is synthesized and decomposed in the adult human body. The following metabolic processes are localized in mitochondria: the conversion of pyruvate into acetyl-CoA, catalyzed by the pyruvate dehydrogenase complex: citrate cycle; respiratory chain associated with ATP synthesis (the combination of these processes is called “oxidative phosphorylation”); the breakdown of fatty acids by oxidation and partly the urea cycle. Mitochondria also supply the cell with products of intermediate metabolism and act, along with the ER, as a depot of calcium ions, which, with the help of ion pumps, maintains the Ca2+ concentration in the cytoplasm at a constant low level (below 1 µmol/l).

The main function of mitochondria is the capture of energy-rich substrates (fatty acids, pyruvate, the carbon skeleton of amino acids) from the cytoplasm and their oxidative breakdown with the formation of CO2 and H2O, coupled with the synthesis of ATP. Reactions of the citrate cycle lead to the complete oxidation of carbon-containing compounds (CO2) and the formation of reducing compounds equivalents, mainly in the form of reduced coenzymes. Most of these processes occur in the matrix. Respiratory chain enzymes that reoxidize reduced coenzymes are localized in the inner mitochondrial membrane. NADH and the enzyme-linked FADH2 are used as electron donors to reduce oxygen and form water. This highly exergonic reaction is multistep and involves the transfer of protons (H+) through the inner membrane from the matrix into the intermembrane space. As a result, an electrochemical gradient is created on the inner membrane. In mitochondria, the electrochemical gradient is used to synthesize ATP from ADP (ADP) and inorganic phosphate (Pi) catalyzed by ATP synthase. The electrochemical gradient is also the driving force behind a number of transport systems
215).http://www.chem.msu.su/rus/teaching/kolman/212.htm

The presence of its own DNA in mitochondria opens new avenues in research into the problem of aging, which may be related to the stability of mitochondria. In addition, mutation of mitochondrial DNA in known degenerative diseases (Alzheimer, Parkinson...) suggests that they may play a special role in these processes. Due to the constant sequential division of mitochondria aimed at producing energy, their DNA “wears out” . The supply of mitochondria in good shape is depleted, reducing the only source of cellular energy. Mitochondrial DNA is 10 times more sensitive to free radicals than nuclear DNA. Mutations caused by free radicals lead to mitochondrial dysfunction. But compared to the cell, the self-healing system of mitochondrial DNA is very weak. When damage to mitochondria is significant, they self-destruct. This process is called "autophagy".

In 2000, it was proven that mitochondria accelerate the process of photoaging. Areas of skin that are regularly exposed to sunlight have significantly higher rates of DNA mutations than areas that are protected. A comparison of biopsies (taking skin samples for analysis) from an area of ​​skin exposed to ultraviolet rays and a protected area shows that mitochondrial mutations due to UV exposure radiation causes chronic oxidative stress. Cells and mitochondria are forever linked: the energy supplied by mitochondria is necessary for cell activity. Maintaining mitochondrial activity is essential for better cellular activity and improved skin quality, especially facial skin that is too often exposed to UV rays.

Conclusion:

Damaged mitochondrial DNA within a few months gives rise to more than 30 similar mitochondria, i.e. with the same damage.

Weakened mitochondria cause a state of energy starvation in “host cells”, which results in a disruption of cellular metabolism.

Restoring the functions of metachondria and limiting the processes leading to aging is possible with the use of coenzyme Q10. As a result of the experiments, a slowdown in the aging process and an increase in life expectancy in some multicellular organisms was established as a result of the introduction of CoQ10 supplements.

Q10 (CoQ10) is the “spark plug” of the human body: just as a car cannot run without a starting spark, the human body cannot do without CoQ10. It is the most important component of mitochondria, producing the energy that cells need to divide, move, contract, and perform all other functions. CoQ10 also plays an important role in the production of adenosine triphosphate (ATP), the energy that powers all processes in the body. Moreover, CoQ10 is a very important antioxidant that protects cells from damage.

Although our bodies can produce CoQ10, they do not always produce enough of it. Since the brain and heart are among the most active tissues in the body, CoQ10 deficiency negatively affects them the most and can lead to serious problems with these organs. CoQ10 deficiency can be caused by a variety of reasons, including poor nutrition, genetic or acquired defects, and increased tissue demand, for example. Cardiovascular diseases, including high cholesterol levels and high blood pressure, also require increased tissue levels of CoQ10. Additionally, because CoQ10 levels decline with age, people over 50 may need more of it. Many studies have shown that a number of medications (primarily lipid-lowering drugs such as statins) reduce CoQ10 levels.

Given CoQ10's key role in mitochondrial function and cell protection, this coenzyme may be beneficial for a range of health problems. CoQ10 can benefit such a wide range of illnesses that there is no doubt about its importance as a nutrient. CoQ10 is not only a general antioxidant, but can also help with the following diseases:

Cardiovascular disease: high blood pressure, congestive heart failure, cardiomyopathy, protection during heart surgery, high cholesterol treated with medications, especially statins
Cancer (to enhance immune function and/or offset the side effects of chemotherapy)
Diabetes mellitus
Male infertility
Alzheimer's disease (prevention)
Parkinson's disease (prevention and treatment)
Periodontal disease
Macular degeneration

Animal and human studies have confirmed the benefits of CoQ10 for all of the above diseases, especially cardiovascular disease. In fact, studies have shown that 50 to 75 percent of people with various cardiovascular diseases suffer from CoQ10 deficiency in their heart tissue. Correcting this deficiency can often lead to dramatic results in patients with some type of heart disease. For example, CoQ10 deficiency has been shown to occur in 39 percent of patients with high blood pressure. This finding alone makes it necessary to take CoQ10 supplements. However, it appears that CoQ10's benefits extend beyond reversing cardiovascular disease.

A 2009 study published in the journal Pharmacology & Therapeutics suggests that the effects of CoQ10 on blood pressure are only noticeable 4 to 12 weeks after treatment, and the typical reduction in systolic and diastolic blood pressure in patients with high blood pressure is quite modest - within 10 percent.

Statin drugs, such as Crestor, Lipitor, and Zocor, work by inhibiting an enzyme that the liver needs to make cholesterol. Unfortunately, they also block the production of other substances necessary for the body to function, including CoQ10. This may explain the most common side effects of these drugs, especially fatigue and muscle pain. One large study, ENDOTACT, published in the International Journal of Cardiology in 2005, demonstrated that statin therapy significantly reduced plasma CoQ10 levels, but that this decline could be prevented by taking a 150 mg CoQ10 supplement. In addition, CoQ10 supplementation significantly improves the function of the lining of blood vessels, which is one of the key goals in the treatment and prevention of atherosclerosis.

In double-blind studies, it was demonstrated that taking CoQ10 supplements was quite beneficial for some patients with Parkinson's disease. All patients in these studies had the three core symptoms of Parkinson's disease - tremors, rigidity and slowness of movement - and had been diagnosed with the disease within the past five years.

A 2005 study published in the Archives of Neurology also showed a slowing of functional decline in Parkinson's disease patients who took CoQ10. After initial screening and baseline blood tests, patients were randomized into four groups. Three groups received CoQ10 at different doses (300 mg, 600 mg and 1200 mg per day) for 16 months, while the fourth group received a placebo. The group that took the 1,200 mg dose showed less deterioration in mental and motor function and the ability to carry out daily activities such as feeding or dressing themselves. The greatest effect was noted in everyday life. The groups that received 300 mg and 600 mg per day developed less disability than those in the placebo group, but the results for members of these groups were less dramatic than those who received the highest dosage of the drug. These results indicate that the beneficial effects of CoQ10 in Parkinson's disease can be achieved at the highest doses of the drug. None of the patients experienced any significant side effects.

Coenzyme Q10 is very safe. No serious side effects have ever been reported, even with long-term use. Because safety has not been demonstrated during pregnancy and lactation, CoQ10 should not be used during these periods unless a physician determines that the clinical benefits outweigh the risks. I generally recommend taking 100 to 200 mg of CoQ10 per day. For best absorption, softgels should be taken with food. At higher dosage levels, it is better to take the drug in divided doses rather than in one dose (200 mg three times a day is better than 600 mg all at once).

Mitochondria are microscopic membrane-bound organelles that provide the cell with energy. Therefore, they are called energy stations (battery) of cells.

Mitochondria are absent in the cells of simple organisms, bacteria, and entamoeba, which live without the use of oxygen. Some green algae, trypanosomes contain one large mitochondrion, and the cells of the heart muscle and brain have from 100 to 1000 of these organelles.

Structural features

Mitochondria are double-membrane organelles; they have outer and inner membranes, an intermembrane space between them, and a matrix.

Outer membrane. It is smooth, has no folds, and separates the internal contents from the cytoplasm. Its width is 7 nm and contains lipids and proteins. An important role is played by porin, a protein that forms channels in the outer membrane. They provide ion and molecular exchange.

Intermembrane space. The size of the intermembrane space is about 20 nm. The substance filling it is similar in composition to the cytoplasm, with the exception of large molecules that can penetrate here only through active transport.

Inner membrane. It is composed mainly of protein, only a third is allocated to lipid substances. A large number of proteins are transport proteins, since the inner membrane lacks freely passable pores. It forms many outgrowths - cristae, which look like flattened ridges. Oxidation of organic compounds to CO 2 in mitochondria occurs on the membranes of the cristae. This process is oxygen-dependent and is carried out under the action of ATP synthetase. The released energy is stored in the form of ATP molecules and is used as needed.

Matrix– the internal environment of mitochondria has a granular, homogeneous structure. In an electron microscope, you can see granules and filaments in balls that lie freely between the cristae. The matrix contains a semi-autonomous protein synthesis system - DNA, all types of RNA, and ribosomes are located here. But still, most of the proteins are supplied from the nucleus, which is why mitochondria are called semi-autonomous organelles.

Cell location and division

Hondriom is a group of mitochondria that are concentrated in one cell. They are located differently in the cytoplasm, which depends on the specialization of the cells. Placement in the cytoplasm also depends on the surrounding organelles and inclusions. In plant cells they occupy the periphery, since the mitochondria are pushed towards the membrane by the central vacuole. In renal epithelial cells, the membrane forms protrusions, between which there are mitochondria.

In stem cells, where energy is used equally by all organelles, mitochondria are randomly distributed. In specialized cells, they are mainly concentrated in areas of greatest energy consumption. For example, in striated muscles they are located near the myofibrils. In spermatozoa, they spirally cover the axis of the flagellum, since a lot of energy is needed to set it in motion and move the sperm. Protozoans that move using cilia also contain large numbers of mitochondria at their base.

Division. Mitochondria are capable of independent reproduction, having their own genome. Organelles are divided by constrictions or septa. The formation of new mitochondria in different cells differs in frequency; for example, in liver tissue they are replaced every 10 days.

Functions in the cell

1. The main function of mitochondria is the formation of ATP molecules.
2. Deposition of Calcium ions.
3. Participation in water exchange.
4. Synthesis of steroid hormone precursors.

Molecular biology is the science that studies the role of mitochondria in metabolism. They also convert pyruvate into acetyl-coenzyme A and beta-oxidation of fatty acids.

Table: structure and functions of mitochondria (briefly)
Structural elements	Structure	Functions
Outer membrane	Smooth shell, made of lipids and proteins	Separates the internal contents from the cytoplasm
Intermembrane space	There are hydrogen ions, proteins, micromolecules	Creates a proton gradient
Inner membrane	Forms protrusions - cristae, contains protein transport systems	Transfer of macromolecules, maintenance of proton gradient
Matrix	Location of Krebs cycle enzymes, DNA, RNA, ribosomes	Aerobic oxidation with the release of energy, the conversion of pyruvate to acetyl coenzyme A.
Ribosomes	Combined two subunits	Protein synthesis

Similarities between mitochondria and chloroplasts

The common properties of mitochondria and chloroplasts are primarily due to the presence of a double membrane.

Signs of similarity also include the ability to independently synthesize protein. These organelles have their own DNA, RNA, and ribosomes.

Both mitochondria and chloroplasts can divide by constriction.

They are also united by the ability to produce energy; mitochondria are more specialized in this function, but chloroplasts also produce ATP molecules during photosynthetic processes. Thus, plant cells have fewer mitochondria than animal cells, because chloroplasts partially perform the functions for them.

Let us briefly describe the similarities and differences:

• They are double-membrane organelles;
• the inner membrane forms protrusions: cristae are characteristic of mitochondria, and thillacoids are characteristic of chloroplasts;
• have their own genome;
• capable of synthesizing proteins and energy.

These organelles differ in their functions: mitochondria are intended for energy synthesis, cellular respiration occurs here, chloroplasts are needed by plant cells for photosynthesis.

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. The cristae define the third “compartment” of the 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.