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Great. In their structure, they are usually spherical 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. 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 cytoskeleton of the eukaryotic cell for movement. In plant and animal cells, three types of mitochondrial organelles simultaneously exist in approximately equal quantities: young protomitochondria, mature mitochondria and old postmitochondria, degrading into lipofuscin granules.
Mitochondria 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 lipids interspersed with proteins (2:1 ratio). A special role is played by porin, a channel-forming protein: it forms holes in the outer membrane with a diameter of 2-3 nm, through which small molecules and ions weighing up to 5 kDa can penetrate. Large molecules can only cross the outer membrane through active transport through mitochondrial membrane transport proteins. The outer membrane is characterized by the presence of enzymes: monooxygenase, acyl-CoA synthetase and phospholipase A2. 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.
Intermembrane space
The intermembrane space is the space between the outer and inner membranes of the mitochondrion. Its thickness is 10-20 nm. Since the outer membrane of the mitochondrion is permeable to small molecules and ions, their concentration in the periplasmic space differs little from that in the cytoplasm. On the contrary, large proteins require specific signal peptides for transport from the cytoplasm to the periplasmic space; therefore, the protein components of the periplasmic space and the cytoplasm are different. One of the proteins contained not only in the inner membrane, but also in the periplasmic space is cytochrome c.
Inner membrane
The energy potential (energy reserve) in the ubiquinol molecule is significantly lower than in the NADH molecule, and the difference in such energy is temporarily stored in the form of an electrochemical proton gradient. The latter arises as a result of the fact that the transfer of electrons through the prosthetic groups of complex I, leading to a decrease in the energy potential of the electrons, is accompanied by the transmembrane transfer of two protons from the matrix into the intermembrane space of the mitochondrion.
Reduced ubiquinol migrates in the plane of the membrane, where it reaches the second enzyme of the respiratory chain - complex III (cytochrome bc 1 ). The latter is a dimer with a molecular weight of more than 300 kDa, formed from eight polypeptide chains and containing iron atoms both in the form of iron-sulfur centers and in the form of complexes with hemes b(I), b(II) and c 1 - complex heterocyclic molecules with four nitrogen atoms located at the corners of the metal-binding square. Complex III catalyzes the oxidation of two ubiquinols to ubiquinones, reducing two molecules of cytochrome c (a heme-containing transporter located in the intermembrane space). The four protons that are split off from ubiquinols are released into the intermembrane space, continuing the formation of an electrochemical gradient.
The last step is catalyzed by complex IV (cytochrome c-oxidase) with a molecular weight of about 200 kDa, consisting of 10-13 polypeptide chains and, in addition to two different hemes, also including several copper atoms tightly bound to proteins. In this case, the electrons taken from the reduced cytochrome c, passing through the iron and copper atoms in complex IV, they reach the oxygen bound in the active center of this enzyme, which leads to the formation of water.
Thus, the overall reaction catalyzed by the enzymes of the respiratory chain is the oxidation of NADH with oxygen to form water. Essentially, this process consists of a stepwise transfer of electrons between metal atoms present in the prosthetic groups of protein complexes of the respiratory chain, where each subsequent complex has a higher electron affinity than the previous one. In this case, the electrons themselves are transferred along the chain until they combine with molecular oxygen, which has the greatest affinity for electrons. The energy released in this case is stored in the form of an electrochemical (proton) gradient on both sides of the inner mitochondrial membrane. It is believed that during the transport of electron pairs through the respiratory chain, from three to six protons are pumped.
The final stage of mitochondrial functioning is the generation of ATP, carried out by a special macromolecular complex with a molecular weight of 500 kDa built into the inner membrane. This complex, called ATP synthase, catalyzes the synthesis of ATP by converting the energy of the transmembrane electrochemical gradient of hydrogen protons into the energy of the high-energy bond of the ATP molecule.
ATP synthase
In structural and functional terms, ATP synthase consists of two large fragments, designated by the symbols F 1 and F 0. 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. Like tightly packed orange slices, successive α and β subunits form a structure characterized by a third-order symmetry axis with a rotation angle of 120°. 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 by the symbol δ and is located on the outside of F 1 .
The membrane part of ATP synthase, called the coupling factor F0, is a hydrophobic protein complex that penetrates the membrane through and has two hemichannels inside for the passage of hydrogen protons. In total, the F 0 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 F 1 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 hydrophobic α-helices connected to each other by a short hydrophilic loop oriented towards F 1, and together they form a single ensemble in the shape of a cylinder immersed in the membrane. The γ subunit protruding from the F 1 complex towards F 0 is precisely immersed inside this cylinder and is quite firmly attached to it.
Thus, in the ATP synthase molecule, two groups of protein subunits can be distinguished, which can be likened to two parts of a motor: rotor and stator. The “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. The “rotor”, mobile relative to this structure, consists of subunits γ and ε, which, noticeably protruding from the complex (αβ) 3, are connected to a ring of subunits immersed in the membrane c.
The ability to synthesize ATP is a property of a single complex F 0 F 1, associated with the transfer of hydrogen protons through F 0 to F 1, in the latter of which the catalytic centers that convert ADP and phosphate into an ATP molecule are located. The driving force for the operation of ATP synthase is the proton potential created on the inner mitochondrial membrane as a result of the operation of the electron transport chain.
The force driving the “rotor” of ATP synthase occurs when the potential difference between the outer and inner sides of the membrane reaches > 220 mV 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 pathway includes the following structural elements:
- Two non-coaxially located “half-channels”, the first of which ensures the supply of protons from the intermembrane space to the essential functional groups F0, and the other ensures their exit into the mitochondrial matrix;
- Ring of subunits c, each of which in its central part contains a protonated carboxyl group, 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 catalytic activity of ATP synthase 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 catalytic subunits β, 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 discrete jumps of 120°, each of which is accompanied by the formation of one ATP molecule.
The direct function of ATP synthesis is localized on the β-subunits of the F1 conjugating complex. In this case, the very first act in the chain of events leading to the formation of ATP is the binding of ADP and phosphate to the active center of the free β-subunit, which is in state 1. Due to the energy of an external source (proton current), conformational changes occur in the F 1 complex, in as a result of which ADP and phosphate become firmly bound to the catalytic center (state 2), where the formation of a covalent bond between them becomes possible, leading to the formation of ATP. At this stage of ATP synthase, the enzyme requires virtually no energy, which will be needed at the next stage to release the tightly bound ATP molecule from the enzymatic center. Therefore, the next stage of the enzyme’s operation is that, as a result of an energy-dependent structural change in the F 1 complex, the catalytic β-subunit containing a tightly bound ATP molecule passes into state 3, in which the connection of ATP with the catalytic center is weakened. As a result of this, the ATP molecule leaves the enzyme, and the β-subunit returns to its original state 1, which ensures the cycling of the enzyme.
The work of ATP synthase 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 synthase causes the rotation of individual subunits of the conjugation factor F 1 relative to other subunits of the enzyme complex, as a result of which this unique energy-producing device performs chemical work - synthesizes molecules ATP. Subsequently, ATP enters the cytoplasm of the cell, where it is spent on a wide variety of energy-dependent processes. Such a transfer is carried out by a special enzyme ATP/ADP translocase built into the mitochondrial membrane, which exchanges newly synthesized ATP for cytoplasmic ADP, which guarantees the safety of the adenyl nucleotide pool 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.
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Notes
Literature
- M. B. Berkinblit, S. M. Glagolev, V. A. Furalev. General biology. - M.: MIROS, 1999.
- D. Taylor, N. Green, W. Stout. Biology. - M.: MIR, 2006.
- E. Willett. Genetics without secrets. - M.: EKSMO, 2008.
- D. G. Deryabin. Functional cell morphology. - M.: KDU, 2005.
- Belyakovich A.G. Study of mitochondria and bacteria using tetrazolium salt p-NTP. - Pushchino: ONTI NCBI AN USSR, 1990.
- N. L. Vekshin. Fluorescence spectroscopy of biopolymers. Pushchino, Foton, 2009.
Links
- Chentsov Yu. S., 1997
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Excerpt characterizing Mitochondria
Platon Karataev must have been over fifty years old, judging by his stories about the campaigns in which he participated as a long-time soldier. He himself did not know and could not determine in any way how old he was; but his teeth, bright white and strong, which kept rolling out in their two semicircles when he laughed (which he often did), were all good and intact; There was not a single gray hair in his beard or hair, and his whole body had the appearance of flexibility and, especially, hardness and endurance.His face, despite the small round wrinkles, had an expression of innocence and youth; his voice was pleasant and melodious. But the main feature of his speech was its spontaneity and argument. He apparently never thought about what he said and what he would say; and because of this, the speed and fidelity of his intonations had a special irresistible persuasiveness.
His physical strength and agility were such during the first time of captivity that it seemed that he did not understand what fatigue and illness were. Every day, in the morning and in the evening, when he lay down, he said: “Lord, lay it down like a pebble, lift it up into a ball”; in the morning, getting up, always shrugging his shoulders in the same way, he said: “I lay down and curled up, got up and shook myself.” And indeed, as soon as he lay down, he immediately fell asleep like a stone, and as soon as he shook himself, he immediately, without a second of delay, took up some task, like children, getting up, taking up their toys. He knew how to do everything, not very well, but not badly either. He baked, steamed, sewed, planed, and made boots. He was always busy and only at night allowed himself conversations, which he loved, and songs. He sang songs, not as songwriters sing, who know that they are being listened to, but he sang like birds sing, obviously because he needed to make these sounds just as it is necessary to stretch or disperse; and these sounds were always subtle, gentle, almost feminine, mournful, and at the same time his face was very serious.
Having been captured and grown a beard, he apparently threw away everything alien and soldierly that had been imposed on him and involuntarily returned to his former, peasant, folk mindset.
“A soldier on leave is a shirt made from trousers,” he used to say. He was reluctant to talk about his time as a soldier, although he did not complain, and often repeated that throughout his service he was never beaten. When he spoke, he mainly spoke from his old and, apparently, dear memories of “Christian”, as he pronounced it, peasant life. The sayings that filled his speech were not those, mostly indecent and glib sayings that soldiers say, but they were those folk sayings that seem so insignificant, taken in isolation, and which suddenly take on the meaning of deep wisdom when they are spoken opportunely.
Often he said the exact opposite of what he had said before, but both were true. He loved to talk and spoke well, decorating his speech with endearments and proverbs, which, it seemed to Pierre, he himself was inventing; but the main charm of his stories was that in his speech the simplest events, sometimes the very ones that Pierre saw without noticing them, took on the character of solemn beauty. He loved to listen to fairy tales that one soldier told in the evenings (all the same ones), but most of all he loved to listen to stories about real life. He smiled joyfully as he listened to such stories, inserting words and making questions that tended to clarify for himself the beauty of what was being told to him. Karataev had no attachments, friendship, love, as Pierre understood them; but he loved and lived lovingly with everything that life brought him to, and especially with a person - not with some famous person, but with those people who were before his eyes. He loved his mongrel, he loved his comrades, the French, he loved Pierre, who was his neighbor; but Pierre felt that Karataev, despite all his affectionate tenderness towards him (with which he involuntarily paid tribute to Pierre’s spiritual life), would not for a minute be upset by separation from him. And Pierre began to feel the same feeling towards Karataev.
Platon Karataev was for all the other prisoners the most ordinary soldier; his name was Falcon or Platosha, they mocked him good-naturedly and sent him for parcels. But for Pierre, as he appeared on the first night, an incomprehensible, round and eternal personification of the spirit of simplicity and truth, that is how he remained forever.
Platon Karataev knew nothing by heart except his prayer. When he gave his speeches, he, starting them, seemed not to know how he would end them.
When Pierre, sometimes amazed at the meaning of his speech, asked him to repeat what he had said, Plato could not remember what he had said a minute ago - just as he could not tell Pierre his favorite song in words. It said: “darling, little birch and I feel sick,” but the words didn’t make any sense. He did not understand and could not understand the meaning of words taken separately from speech. His every word and every action was a manifestation of an activity unknown to him, which was his life. But his life, as he himself looked at it, had no meaning as a separate life. She made sense only as a part of the whole, which he constantly felt. His words and actions poured out of him as uniformly, necessarily, and directly as a scent is released from a flower. He could not understand either the price or the meaning of a single action or word.
Having received news from Nicholas that her brother was with the Rostovs in Yaroslavl, Princess Marya, despite her aunt’s dissuasions, immediately got ready to go, and not only alone, but with her nephew. Whether it was difficult, not difficult, possible or impossible, she did not ask and did not want to know: her duty was not only to be near her perhaps dying brother, but also to do everything possible to bring him her son, and she stood up drive. If Prince Andrei himself did not notify her, then Princess Marya explained it either by the fact that he was too weak to write, or by the fact that he considered this long journey too difficult and dangerous for her and for his son.
Within a few days, Princess Marya got ready to travel. Her crews consisted of a huge princely carriage, in which she arrived in Voronezh, a britzka and a cart. Traveling with her were M lle Bourienne, Nikolushka and her tutor, an old nanny, three girls, Tikhon, a young footman and a haiduk, whom her aunt had sent with her.
It was impossible to even think about going the usual route to Moscow, and therefore the roundabout route that Princess Marya had to take: to Lipetsk, Ryazan, Vladimir, Shuya, was very long, due to the lack of post horses everywhere, very difficult and near Ryazan, where, as they said the French were showing up, even dangerous.
During this difficult journey, M lle Bourienne, Desalles and Princess Mary's servants were surprised by her fortitude and activity. She went to bed later than everyone else, got up earlier than everyone else, and no difficulties could stop her. Thanks to her activity and energy, which excited her companions, by the end of the second week they were approaching Yaroslavl.
During her recent stay in Voronezh, Princess Marya experienced the best happiness of her life. Her love for Rostov no longer tormented or worried her. This love filled her entire soul, became an inseparable part of herself, and she no longer fought against it. Lately, Princess Marya became convinced—although she never clearly told herself this in words—she became convinced that she was loved and loved. She was convinced of this during her last meeting with Nikolai, when he came to announce to her that her brother was with the Rostovs. Nicholas did not hint in a single word that now (if Prince Andrei recovered) the previous relationship between him and Natasha could be resumed, but Princess Marya saw from his face that he knew and thought this. And, despite the fact that his attitude towards her - cautious, tender and loving - not only did not change, but he seemed to rejoice in the fact that now the kinship between him and Princess Marya allowed him to more freely express his friendship and love to her, as he sometimes thought Princess Marya. Princess Marya knew that she loved for the first and last time in her life, and felt that she was loved, and was happy and calm in this regard.
But this happiness on one side of her soul not only did not prevent her from feeling grief for her brother with all her might, but, on the contrary, this peace of mind in one respect gave her a greater opportunity to fully surrender to her feelings for her brother. This feeling was so strong in the first minute of leaving Voronezh that those accompanying her were sure, looking at her exhausted, desperate face, that she would certainly get sick on the way; but it was precisely the difficulties and worries of the journey, which Princess Marya took on with such activity, that saved her for a while from her grief and gave her strength.
As always happens during a trip, Princess Marya thought only about one journey, forgetting what was its goal. But, approaching Yaroslavl, when what could lie ahead of her was revealed again, and not many days later, but this evening, Princess Marya’s excitement reached its extreme limits.
When the guide sent ahead to find out in Yaroslavl where the Rostovs were standing and in what position Prince Andrei was, met a large carriage entering at the gate, he was horrified when he saw the terribly pale face of the princess, which leaned out of the window.
“I found out everything, your Excellency: the Rostov men are standing on the square, in the house of the merchant Bronnikov.” “Not far away, just above the Volga,” said the hayduk.
Princess Marya looked fearfully and questioningly at his face, not understanding what he was telling her, not understanding why he did not answer the main question: what about brother? M lle Bourienne asked this question for Princess Marya.
- What about the prince? – she asked.
“Their Lordships are standing with them in the same house.”
“So he is alive,” thought the princess and quietly asked: what is he?
“People said they were all in the same situation.”
What did “everything in the same position” mean, the princess did not ask and only briefly, glancing imperceptibly at the seven-year-old Nikolushka, who was sitting in front of her and rejoicing at the city, lowered her head and did not raise it until the heavy carriage, rattling, shaking and swaying, did not stop somewhere. The folding steps rattled.
The doors opened. On the left there was water - a large river, on the right there was a porch; on the porch there were people, servants and some kind of ruddy girl with a large black braid who was smiling unpleasantly, as it seemed to Princess Marya (it was Sonya). The princess ran up the stairs, the girl feigning a smile said: “Here, here!” - and the princess found herself in the hallway in front of an old woman with an oriental face, who quickly walked towards her with a touched expression. It was the Countess. She hugged Princess Marya and began to kiss her.
- Mon enfant! - she said, “je vous aime et vous connais depuis longtemps.” [My child! I love you and have known you for a long time.]
Despite all her excitement, Princess Marya realized that it was the countess and that she had to say something. She, without knowing how, uttered some polite French words, in the same tone as those spoken to her, and asked: what is he?
“The doctor says there is no danger,” said the countess, but while she was saying this, she raised her eyes upward with a sigh, and in this gesture there was an expression that contradicted her words.
- Where is he? Can I see him, can I? - asked the princess.
- Now, princess, now, my friend. Is this his son? - she said, turning to Nikolushka, who was entering with Desalles. “We can all fit in, the house is big.” Oh, what a lovely boy!
The Countess led the Princess into the living room. Sonya was talking to m lle Bourienne. The Countess caressed the boy. The old count entered the room, greeting the princess. The old count has changed enormously since the princess last saw him. Then he was a lively, cheerful, self-confident old man, now he seemed like a pitiful, lost man. While talking to the princess, he constantly looked around, as if asking everyone whether he was doing what was necessary. After the ruin of Moscow and his estate, knocked out of his usual rut, he apparently lost consciousness of his significance and felt that he no longer had a place in life.
Despite the excitement in which she was, despite the desire to see her brother as quickly as possible and the annoyance that at this moment, when she only wanted to see him, she was being occupied and feignedly praising her nephew, the princess noticed everything that was happening around her, and felt the need to temporarily submit to this new order into which she was entering. She knew that all this was necessary, and it was difficult for her, but she was not annoyed with them.
“This is my niece,” said the count, introducing Sonya. “You don’t know her, princess?”
The princess turned to her and, trying to extinguish the hostile feeling towards this girl that had risen in her soul, kissed her. But it became difficult for her because the mood of everyone around her was so far from what was in her soul.
- Where is he? – she asked again, addressing everyone.
“He’s downstairs, Natasha is with him,” Sonya answered, blushing. - Let's go find out. I think you are tired, princess?
Tears of annoyance came to the princess's eyes. She turned away and was about to ask the countess again where to go to him, when light, swift, seemingly cheerful steps were heard at the door. The princess looked around and saw Natasha almost running in, the same Natasha who she had not liked so much on that long-ago meeting in Moscow.
But before the princess had time to look at this Natasha’s face, she realized that this was her sincere companion in grief, and therefore her friend. She rushed to meet her and, hugging her, cried on her shoulder.
As soon as Natasha, who was sitting at Prince Andrey’s bedside, found out about Princess Marya’s arrival, she quietly left his room with those quick, as it seemed to Princess Marya, seemingly cheerful steps and ran towards her.
On her excited face, when she ran into the room, there was only one expression - an expression of love, boundless love for him, for her, for everything that was close to her loved one, an expression of pity, suffering for others and a passionate desire to give herself all for in order to help them. It was clear that at that moment there was not a single thought about herself, about her relationship to him, in Natasha’s soul.
The sensitive Princess Marya understood all this from the first glance at Natasha’s face and cried with sorrowful pleasure on her shoulder.
“Come on, let’s go to him, Marie,” Natasha said, taking her to another room.
Princess Marya raised her face, wiped her eyes and turned to Natasha. She felt that she would understand and learn everything from her.
“What...” she began to ask, but suddenly stopped. She felt that words could neither ask nor answer. Natasha's face and eyes should have spoken more and more clearly.
Natasha looked at her, but seemed to be in fear and doubt - to say or not to say everything that she knew; she seemed to feel that before those radiant eyes, penetrating into the very depths of her heart, it was impossible not to tell the whole, the whole truth as she saw it. Natasha's lip suddenly trembled, ugly wrinkles formed around her mouth, and she covered her face with her hands, sobbing.
Princess Marya understood everything.
But she still hoped and asked in words she didn’t believe in:
- But how is his wound? In general, what is his position?
“You, you... will see,” Natasha could only say.
They sat downstairs near his room for some time in order to stop crying and come to him with calm faces.
– How did the whole illness go? How long ago has he gotten worse? When did it happen? - asked Princess Marya.
Natasha said that at first there was a danger from a fever and from suffering, but at Trinity this passed, and the doctor was afraid of one thing - Antonov’s fire. But this danger also passed. When we arrived in Yaroslavl, the wound began to fester (Natasha knew everything about suppuration, etc.), and the doctor said that suppuration could proceed properly. There was a fever. The doctor said that this fever is not so dangerous.
“But two days ago,” Natasha began, “suddenly it happened...” She held back her sobs. “I don’t know why, but you will see what he has become.”
- Are you weak? Have you lost weight?.. - asked the princess.
- No, not that, but worse. You will see. Oh, Marie, Marie, he's too good, he can't, can't live... because...
When Natasha opened his door with her usual movement, letting the princess pass first, Princess Marya already felt ready sobs in her throat. No matter how much she prepared or tried to calm down, she knew that she would not be able to see him without tears.
Princess Marya understood what Natasha meant with the words: this happened two days ago. She understood that this meant that he had suddenly softened, and that this softening and tenderness were signs of death. As she approached the door, she already saw in her imagination that face of Andryusha, which she had known since childhood, tender, meek, touching, which he so rarely saw and therefore always had such a strong effect on her. She knew that he would say quiet, tender words to her, like those her father had told her before his death, and that she would not bear it and would burst into tears over him. But, sooner or later, it had to be, and she entered the room. The sobs came closer and closer to her throat, while with her myopic eyes she discerned his form more and more clearly and looked for his features, and then she saw his face and met his gaze.
He was lying on the sofa, covered with pillows, wearing a squirrel fur robe. He was thin and pale. One thin, transparent white hand held a handkerchief; with the other, with quiet movements of his fingers, he touched his thin, overgrown mustache. His eyes looked at those entering.
Seeing his face and meeting his gaze, Princess Marya suddenly moderated the speed of her step and felt that her tears had suddenly dried up and her sobs had stopped. Catching the expression on his face and gaze, she suddenly became shy and felt guilty.
“What is my fault?” – she asked herself. “The fact that you live and think about living things, and I!..” answered his cold, stern gaze.
There was almost hostility in his deep, out-of-control, but inward-looking gaze as he slowly looked around at his sister and Natasha.
He kissed his sister hand in hand, as was their habit.
- Hello, Marie, how did you get there? - he said in a voice as even and alien as his gaze. If he had screamed with a desperate cry, then this cry would have terrified Princess Marya less than the sound of this voice.
- And did you bring Nikolushka? – he said also evenly and slowly and with an obvious effort of recollection.
– How is your health now? - said Princess Marya, herself surprised at what she was saying.
“This, my friend, is something you need to ask the doctor,” he said, and, apparently making another effort to be affectionate, he said with just his mouth (it was clear that he did not mean what he was saying): “Merci, chere amie.” , d'etre venue. [Thank you, dear friend, for coming.]
Princess Marya shook his hand. He winced slightly when she shook her hand. He was silent and she didn't know what to say. She understood what happened to him in two days. In his words, in his tone, especially in this look - a cold, almost hostile look - one could feel the alienation from everything worldly, terrible for a living person. He apparently now had difficulty understanding all living things; but at the same time it was felt that he did not understand the living, not because he was deprived of the power of understanding, but because he understood something else, something that the living did not and could not understand and that absorbed him completely.
- Yes, that’s how strange fate brought us together! – he said, breaking the silence and pointing at Natasha. - She keeps following me.
Princess Marya listened and did not understand what he was saying. He, the sensitive, gentle Prince Andrei, how could he say this in front of the one he loved and who loved him! If he had thought about living, he would not have said this in such a coldly insulting tone. If he didn’t know that he would die, then how could he not feel sorry for her, how could he say this in front of her! There was only one explanation for this, and that was that he didn’t care, and it didn’t matter because something else, something more important, was revealed to him.
The conversation was cold, incoherent and interrupted constantly.
“Marie passed through Ryazan,” said Natasha. Prince Andrei did not notice that she called his sister Marie. And Natasha, calling her that in front of him, noticed it herself for the first time.
- Well then? - he said.
“They told her that Moscow was completely burned down, as if...
Natasha stopped: she couldn’t speak. He obviously made an effort to listen, but still could not.
“Yes, it burned down, they say,” he said. “This is very pathetic,” and he began to look forward, absentmindedly straightening his mustache with his fingers.
– Have you met Count Nikolai, Marie? - Prince Andrei suddenly said, apparently wanting to please them. “He wrote here that he really liked you,” he continued simply, calmly, apparently unable to understand all the complex meaning that his words had for living people. “If you fell in love with him too, it would be very good... for you to get married,” he added somewhat more quickly, as if delighted by the words that he had been looking for for a long time and finally found. Princess Marya heard his words, but they had no other meaning for her, except that they proved how terribly far he was now from all living things.
- What to say about me! – she said calmly and looked at Natasha. Natasha, feeling her gaze on her, did not look at her. Again everyone was silent.
“Andre, do you want...” Princess Marya suddenly said in a shuddering voice, “do you want to see Nikolushka?” He thought about you all the time.
Prince Andrei smiled faintly for the first time, but Princess Marya, who knew his face so well, realized with horror that it was not a smile of joy, not tenderness for her son, but of quiet, gentle mockery of what Princess Marya used, in her opinion. , the last resort to bring him to his senses.
– Yes, I’m very happy about Nikolushka. He is healthy?
When they brought Nikolushka to Prince Andrei, who was looking at his father in fear, but was not crying, because no one was crying, Prince Andrei kissed him and, obviously, did not know what to say to him.
When Nikolushka was taken away, Princess Marya went up to her brother again, kissed him and, unable to resist any longer, began to cry.
He looked at her intently.
– Are you talking about Nikolushka? - he said.
Princess Marya, crying, bowed her head affirmatively.
“Marie, you know Evan...” but he suddenly fell silent.
- What are you saying?
- Nothing. There’s no need to cry here,” he said, looking at her with the same cold gaze.
When Princess Marya began to cry, he realized that she was crying that Nikolushka would be left without a father. With great effort he tried to return to life and was transported to their point of view.
“Yes, they must find it pathetic! - he thought. “How simple it is!”
“The birds of the air neither sow nor reap, but your father feeds them,” he said to himself and wanted to say the same to the princess. “But no, they will understand it in their own way, they will not understand! What they cannot understand is that all these feelings that they value are all ours, all these thoughts that seem so important to us are that they are not needed. We can't understand each other." - And he fell silent.
Prince Andrei's little son was seven years old. He could barely read, he didn't know anything. He experienced a lot after this day, acquiring knowledge, observation, and experience; but if he had then possessed all these later acquired abilities, he could not have understood better, more deeply the full meaning of that scene that he saw between his father, Princess Marya and Natasha than he understood it now. He understood everything and, without crying, left the room, silently approached Natasha, who followed him out, and shyly looked at her with thoughtful, beautiful eyes; his raised, rosy upper lip trembled, he leaned his head against it and began to cry.
From that day on, he avoided Desalles, avoided the countess who was caressing him, and either sat alone or timidly approached Princess Marya and Natasha, whom he seemed to love even more than his aunt, and quietly and shyly caressed them.
Princess Marya, leaving Prince Andrei, fully understood everything that Natasha’s face told her. She no longer spoke to Natasha about the hope of saving his life. She alternated with her at his sofa and did not cry anymore, but prayed incessantly, turning her soul to that eternal, incomprehensible, whose presence was now so palpable over the dying man.
Prince Andrei not only knew that he would die, but he felt that he was dying, that he was already half dead. He experienced a consciousness of alienation from everything earthly and a joyful and strange lightness of being. He, without haste and without worry, awaited what lay ahead of him. That formidable, eternal, unknown and distant, the presence of which he never ceased to feel throughout his entire life, was now close to him and - due to the strange lightness of being that he experienced - almost understandable and felt.
Before, he was afraid of the end. He experienced this terrible, painful feeling of fear of death, of the end, twice, and now he no longer understood it.
The first time he experienced this feeling was when a grenade was spinning like a top in front of him and he looked at the stubble, at the bushes, at the sky and knew that death was in front of him. When he woke up after the wound and in his soul, instantly, as if freed from the oppression of life that held him back, this flower of love, eternal, free, independent of this life, blossomed, he was no longer afraid of death and did not think about it.
The more he, in those hours of suffering solitude and semi-delirium that he spent after his wound, thought about the new beginning of eternal love that had been revealed to him, the more he, without feeling it himself, renounced earthly life. Everything, to love everyone, to always sacrifice oneself for love, meant not loving anyone, meant not living this earthly life. And the more he was imbued with this principle of love, the more he renounced life and the more completely he destroyed that terrible barrier that, without love, stands between life and death. When, at first, he remembered that he had to die, he said to himself: well, so much the better.
But after that night in Mytishchi, when the one he desired appeared in front of him in a semi-delirium, and when he, pressing her hand to his lips, cried quiet, joyful tears, love for one woman imperceptibly crept into his heart and again tied him to life. Both joyful and anxious thoughts began to come to him. Remembering that moment at the dressing station when he saw Kuragin, he now could not return to that feeling: he was tormented by the question of whether he was alive? And he didn't dare ask this.
His illness took its own physical course, but what Natasha called: this happened to him happened to him two days before Princess Marya’s arrival. This was the last moral struggle between life and death, in which death won. It was the unexpected consciousness that he still valued the life that seemed to him in love for Natasha, and the last, subdued fit of horror in front of the unknown.
It was in the evening. He was, as usual after dinner, in a slight feverish state, and his thoughts were extremely clear. Sonya was sitting at the table. He dozed off. Suddenly a feeling of happiness overwhelmed him.
“Oh, she came in!” - he thought.
Indeed, sitting in Sonya’s place was Natasha, who had just entered with silent steps.
Since she began following him, he had always experienced this physical sensation of her closeness. She sat on an armchair, sideways to him, blocking the light of the candle from him, and knitted a stocking. (She learned to knit stockings since Prince Andrei told her that no one knows how to take care of the sick like old nannies who knit stockings, and that there is something soothing in knitting a stocking.) Thin fingers quickly fingered her from time to time the clashing spokes, and the pensive profile of her downcast face was clearly visible to him. She made a movement and the ball rolled off her lap. She shuddered, looked back at him and, shielding the candle with her hand, with a careful, flexible and precise movement she bent, raised the ball and sat down in her previous position.
He looked at her without moving, and saw that after her movement she needed to take a deep breath, but she did not dare to do this and carefully took a breath.
In the Trinity Lavra they talked about the past, and he told her that if he were alive, he would forever thank God for his wound, which brought him back to her; but since then they never spoke about the future.
“Could it or could it not have happened? - he thought now, looking at her and listening to the light steel sound of the knitting needles. - Was it really only then that fate brought me so strangely together with her that I might die?.. Was the truth of life revealed to me only so that I could live in a lie? I love her more than anything in the world. But what should I do if I love her? - he said, and he suddenly groaned involuntarily, according to the habit that he acquired during his suffering.
Hearing this sound, Natasha put down the stocking, leaned closer to him and suddenly, noticing his glowing eyes, walked up to him with a light step and bent down.
- You are not asleep?
- No, I’ve been looking at you for a long time; I felt it when you came in. No one like you, but gives me that soft silence... that light. I just want to cry with joy.
Covered with two membranes. The outer membrane is smooth, the inner one has inward growths - cristae, they increase the area of the inner membrane in order to place as many enzymes of cellular respiration on it as possible.
The internal environment of the mitochondria is called the matrix. It contains circular DNA and small (70S) ribosomes, due to which mitochondria independently make part of their proteins, which is why they are called semi-autonomous organelles. (The theory of symbiogenesis holds that previously mitochondria and plastids were free bacteria that were engulfed by a large cell but not digested.)
Function: mitochondria take part in cellular respiration (they are the “energy stations of the cell”).
Oxygen breathing (medium difficulty)
1. Glycolysis
Occurs in the cytoplasm. Glucose is oxidized to two molecules of pyruvic acid (PVA), releasing energy that is stored in 2 ATP and energy-rich electron carriers.
2. Oxidation of PVC in the mitochondrial matrix
PVC is completely oxidized to carbon dioxide, releasing energy that is stored in 2 ATP and energy-rich electrons on the carriers.
3. Respiratory chain
Occurs on the inner membrane of mitochondria. The energy-rich electrons obtained in the previous stages give up their energy, resulting in the formation of 34 ATP.
Mitochondria
Mitochondria are rod-shaped or oval-shaped structures (Greek. mitos- a thread, chondros- granule). They are found in all animal cells (excluding mature red blood cells): in higher plants, algae and protozoa. They are absent only in prokaryotic bacteria.
These organelles were first discovered and described at the end of the last century by Altman. Somewhat later, these structures were called mitochondria. In 1948, Hogeboom pointed out the importance of mitochondria as the center of cellular respiration, and in 1949, Kennedy and Lehninger established that a cycle of oxidative phosphorylation occurs in mitochondria. Thus, it was proven that mitochondria serve as a place for generating energy.
Mitochondria are visible in a conventional light microscope using special staining methods. In a phase contrast microscope and in a “dark field” they can be observed in living cells.
Structure, dimensions, shape mitochondria are very variable. This depends primarily on the functional state of the cells. For example, it has been established that in the motor neurons of flies that fly continuously for 2 hours, a huge number of spherical mitochondria appear, while in flies with glued wings the number of mitochondria is much smaller and they are rod-shaped (L. B. Levinson). In shape they can be thread-like, rod-shaped, rounded and dumbbell-shaped, even within the same cell.
Mitochondria are localized in the cell, as a rule, either in those areas where energy is consumed, or near accumulations of substrate (for example, lipid droplets), if any.
A strict orientation of mitochondria is found along the flagella of spermatozoa, in striated muscle tissue, where they are located along myofibrils, in the epithelium of the renal tubules they are localized in invaginations of the basement membrane, etc.
The number of mitochondria in cells has organ characteristics, for example, the liver cells of rats contain from 100 to 2500 mitochondria, and the cells of the collecting ducts of the kidney - 300, in the sperm of various animal species from 20 to 72, in the giant amoeba Chaos chaos their number reaches 500,000. The sizes of mitochondria range from 1 to 10 microns.
The ultramicroscopic structure of mitochondria is the same, regardless of their shape and size. They are covered with two lipoprotein membranes: outer and inner. Between them there is an intermembrane space.
Invaginations of the inner membrane that protrude into the body of mitochondria are called Christami. The arrangement of cristae in mitochondria can be transverse or longitudinal. The shape of the cristae can be simple or branched. Sometimes they form a complex network. In some cells, for example, in the cells of the zona glomerulosa of the adrenal gland, the cristae look like tubes. The number of cristae is directly proportional to the intensity of oxidative processes occurring in mitochondria. For example, in the mitochondria of cardiomyocytes there are several times more of them than in the mitochondria of hepatocytes. The space enclosed by the inner membrane constitutes the inner chamber of the mitochondria. In it, between the cristae, there is a mitochondrial matrix - a relatively electron-dense substance.
Inner membrane proteins are synthesized by mitoribosomes, and outer membrane proteins are synthesized by cytoribosomes.
“The outer membrane of mitochondria is similar in many respects to the membranes of the ER. It is poor in oxidative enzymes. There are few of them in the membrane space. But the inner membrane and mitochondrial matrix are literally saturated with them. Thus, enzymes of the Krebs cycle and fatty acid oxidation are concentrated in the mitochondrial matrix. In the inner The electron transport chain, phosphorylation enzymes (formation of ATP from ADP), and numerous transport systems are localized in the membrane.
In addition to protein and lipids, the composition of mitochondrial membranes includes RNA and DNA, the latter has genetic specificity and differs in its physicochemical properties from nuclear DNA.
Electron microscopic studies revealed that the surface of the outer membrane is covered with small spherical elementary particles. The inner membrane and cristae contain similar elementary particles on “legs,” the so-called mushroom bodies. They consist of three parts: a spherical head (diameter 90-100 A°), a cylindrical leg, 5 nm long and 3-4 nm wide, and a base measuring 4 by 11 nm. Mushroom body heads are associated with phosphorylation, and the heads are then found to contain an enzyme with ATP-ide activity.
In the intermembrane space there is a substance with a lower electron density than the matrix. It provides communication between membranes and supplies auxiliary coenzyme catalysts for enzymes located in both membranes.
It is now known that the outer membrane of mitochondria is highly permeable to substances with low molecular weight, in particular protein compounds. The inner membrane of mitochondria is selectively permeable. It is practically impermeable to anions (Cl -1, Br -1, SO 4 -2, HCO 3 -1, Sn +2, Mg +2 cations, a number of sugars and most amino acids, while Ca 2+, Mn 2+, phosphate , polycarboxylic acids easily penetrate through it. There is evidence of the presence in the inner membrane of several carriers specific to certain groups of penetrating anions and cations. Active transport of substances through membranes is carried out using the energy of the ATPase system or the electrical potential generated on the membrane as a result of work. respiratory chain. Even ATP synthesized in mitochondria can be released using a transporter (coupled transport).
The mitochondrial matrix is represented by a fine-grained electron-dense substance. It contains mitoribosomes, fibrillar structures consisting of DNA molecules and granules with a diameter of more than 200A ◦ formed by salts: Ca 3 (PO 4), Ba 3 (PO 4) 2, Mg 3 (PO 4). It is believed that the granules serve as a reservoir of Ca +2 and Mg +2 ions. Their number increases with changes in the permeability of mitochondrial membranes.
The presence of DNA in mitochondria ensures the participation of mitochondria in the synthesis of RNA and specific proteins, and also indicates the existence of cytoplasmic inheritance. Each mitochondria contains, depending on its size, one or several DNA molecules (from 2 to 10). The molecular weight of mitochondrial DNA is about (30-40) * 10 6 in protozoa, yeast, and fungi. In higher animals there are about (9–10) * 10 6.
Its length in yeast is approximately 5 microns, in plants - 30 microns. The amount of genetic information contained in mitochondrial DNA is small: it consists of 15-75 thousand base pairs, which can encode on average 25-125 protein chains with a molecular weight of about 40,000.
Mitochondrial DNA differs from nuclear DNA in a number of features: it has a higher synthesis rate (5-7 times), it is more resistant to the action of DNase, it is a double-circular molecule, contains more guanine and cytosine, is denatured at a higher temperature and is easier to restore. However, not all mitochondrial proteins are synthesized by the mitochondrial system. Thus, the synthesis of cytochrome C and other enzymes is provided by the information contained in the nucleus. Vitamins A, B2, B12, K, E, as well as glycogen are localized in the mitochondrial matrix.
Mitochondrial function consists in the formation of energy necessary for the life of cells. Various compounds can serve as a source of energy in the cell: proteins, fats, carbohydrates. However, the only substrate that is immediately included in energy processes is glucose.
Biological processes, as a result of which energy is generated in mitochondria, can be divided into 3 groups: Group I - oxidative reactions, including two phases: anaerobic (glycolysis) and aerobic. Group II - dephosphorylation, ATP breakdown and energy release. Group III - phosphorylation associated with the oxidation process.
The process of glucose oxidation initially occurs without the participation of oxygen (anaerobically or glycolytically) to pyruvic or lactic acid.
However, only a small amount of energy is released. Subsequently, these acids are involved in oxidation processes that occur with the participation of oxygen, i.e., they are aerobic. As a result of the oxidation process of pyruvic and lactic acid, called the Krebs cycle, carbon dioxide, water and a large amount of energy are formed.
The resulting energy is not released in the form of heat, which would lead to overheating of cells and death of the entire organism, but is accumulated in a form convenient for storage and transport in the form of adenosine triphosphoric acid (ATP). ATP synthesis occurs from ADP and phosphoric acid and is therefore called phosphorylation.
In healthy cells, phosphorylation is coupled with oxidation. In diseases, conjugation can become uncoupled, so the substrate is oxidized, but phosphorylation does not occur, and oxidation turns into heat, and the ATP content in cells decreases. As a result, the temperature rises and the functional activity of cells decreases.
So, the main function of mitochondria is to produce almost all the energy of the cell and the synthesis of components necessary for the activity of the organelle itself, enzymes of the “respiratory ensemble”, phospholipids and proteins occurs.
Another aspect of the activity of mitochondria is their participation in specific syntheses, for example, in the synthesis of steroid hormones and individual lipids. In the oocytes of various animals, accumulations of yolk form in the mitochondria, and they lose their basic system. Spent mitochondria can also accumulate excretion products.
In some cases (liver, kidneys), mitochondria are capable of accumulating harmful substances and poisons that enter the cell, isolating them from the main cytoplasm and partially blocking the harmful effects of these substances. Thus, mitochondria are capable of taking on the functions of other cell organelles when this is required to fully ensure a particular process under normal conditions or under extreme conditions.
Biogenesis of mitochondria. Mitochondria are renewable structures with a rather short life cycle (in rat liver cells, for example, the half-life of mitochondria covers about 10 days). Mitochondria are formed as a result of the growth and division of previous mitochondria. Their division can occur in three ways: constriction, budding of small sections and the emergence of daughter mitochondria inside the mother. The division (reproduction) of mitochondria is preceded by the reproduction of its own genetic system - mitochondrial DNA.
So, according to the views of most researchers, the formation of mitochondria occurs mainly through self-reproduction de novo.
The structure and function of mitochondria is a rather complex issue. The presence of an organelle is characteristic of almost all nuclear organisms - both autotrophs (plants capable of photosynthesis) and heterotrophs, which are almost all animals, some plants and fungi.
The main purpose of mitochondria is the oxidation of organic substances and the subsequent use of the energy released as a result of this process. For this reason, organelles also have a second (unofficial) name - the energy stations of the cell. They are sometimes called "catabolism plastids".
What are mitochondria
The term is of Greek origin. Translated, this word means “thread” (mitos), “grain” (chondrion). Mitochondria are permanent organelles that are of great importance for the normal functioning of cells and make the existence of the entire organism possible.
“Stations” have a specific internal structure, which changes depending on the functional state of the mitochondria. Their shape can be of two types - oval or oblong. The latter often has a branching appearance. The number of organelles in one cell ranges from 150 to 1500.
A special case is germ cells. Sperm contain only one spiral organelle, while female gametes contain hundreds of thousands more mitochondria. In a cell, organelles are not fixed in one place, but can move throughout the cytoplasm and combine with each other. Their size is 0.5 microns, their length can reach 60 microns, while the minimum is 7 microns.
Determining the size of one “energy station” is not an easy task. The fact is that when examined under an electron microscope, only part of the organelle gets into the section. It happens that a spiral mitochondrion has several sections that can be mistaken for separate, independent structures.
Only a three-dimensional image will make it possible to find out the exact cellular structure and understand whether we are talking about 2-5 separate organelles or one mitochondria with a complex shape.
Structural features
The mitochondrial shell consists of two layers: outer and inner. The latter includes various outgrowths and folds, which have a leaf-like and tubular shape.
Each membrane has a special chemical composition, a certain amount of certain enzymes and a specific purpose. The outer shell is separated from the inner shell by an intermembrane space 10-20 nm thick.
The structure of the organelle looks very clearly in the figure with captions.
Mitochondria structure diagram
Looking at the structure diagram, we can make the following description. The viscous space inside the mitochondrion is called the matrix. Its composition creates a favorable environment for the necessary chemical processes to occur in it. It contains microscopic granules that promote reactions and biochemical processes (for example, they accumulate glycogen ions and other substances).
The matrix contains DNA, coenzymes, ribosomes, t-RNA, and inorganic ions. ATP synthase and cytochromes are located on the surface of the inner layer of the shell. Enzymes contribute to processes such as the Krebs cycle (TCA cycle), oxidative phosphorylation, etc.
Thus, the main task of the organelle is performed by both the matrix and the inner side of the shell.
Functions of mitochondria
The purpose of “energy stations” can be characterized by two main tasks:
- energy production: oxidative processes are carried out in them with the subsequent release of ATP molecules;
- storage of genetic information;
- participation in the synthesis of hormones, amino acids and other structures.
The process of oxidation and energy production takes place in several stages:
Schematic drawing of ATP synthesis
It is worth noting: As a result of the Krebs cycle (citric acid cycle), ATP molecules are not formed, the molecules are oxidized and carbon dioxide is released. This is an intermediate step between glycolysis and the electron transport chain.
Table “Functions and structure of mitochondria”
What determines the number of mitochondria in a cell?
The prevailing number of organelles accumulates near those areas of the cell where the need for energy resources arises. In particular, a large number of organelles gather in the area where myofibrils are located, which are part of the muscle cells that ensure their contraction.
In male germ cells, the structures are localized around the axis of the flagellum - it is assumed that the need for ATP is due to the constant movement of the gamete tail. The arrangement of mitochondria in protozoa, which use special cilia for movement, looks exactly the same - the organelles accumulate under the membrane at their base.
As for nerve cells, the localization of mitochondria is observed near the synapses through which signals from the nervous system are transmitted. In cells that synthesize proteins, organelles accumulate in zones of ergastoplasm - they supply the energy that powers this process.
Who discovered mitochondria
The cellular structure acquired its name in 1897-1898 thanks to K. Brand. Otto Wagburg was able to prove the connection between the processes of cellular respiration and mitochondria in 1920.
Conclusion
Mitochondria are the most important component of a living cell, acting as an energy station that produces ATP molecules, thereby ensuring cellular life processes.
The work of mitochondria is based on the oxidation of organic compounds, resulting in the generation of energy potential.
Mitochondria- This double membrane organelle eukaryotic cell, whose main function is ATP synthesis– a source of energy for the life of the cell.
The number of mitochondria in cells is not constant, on average from several units to several thousand. Where synthesis processes are intense, there are more of them. The size of mitochondria and their shape also varies (round, elongated, spiral, cup-shaped, etc.). More often they have a round, elongated shape, up to 1 micrometer in diameter and up to 10 microns in length. They can move in the cell with the flow of cytoplasm or remain in one position. They move to places where energy production is most needed.
It should be borne in mind that in cells ATP is synthesized not only in mitochondria, but also in the cytoplasm during glycolysis. However, the efficiency of these reactions is low. The peculiarity of the function of mitochondria is that not only oxygen-free oxidation reactions occur in them, but also the oxygen stage of energy metabolism.
In other words, the function of mitochondria is to actively participate in cellular respiration, which includes many reactions of oxidation of organic substances, transfer of hydrogen protons and electrons, releasing energy that is accumulated in ATP.
Mitochondrial enzymes
Enzymes translocases The inner membrane of mitochondria carries out active transport of ADP and ATP.
In the structure of cristae, elementary particles are distinguished, consisting of a head, a stalk and a base. On heads consisting of enzyme ATPases, ATP synthesis occurs. ATPase ensures the coupling of ADP phosphorylation with reactions of the respiratory chain.
Components of the respiratory chain are located at the base of elementary particles in the thickness of the membrane.
The matrix contains most of Krebs cycle enzymes and fatty acid oxidation.
As a result of the activity of the electrical transport respiratory chain, hydrogen ions enter it from the matrix and are released on the outside of the inner membrane. This is carried out by certain membrane enzymes. The difference in the concentration of hydrogen ions on different sides of the membrane results in a pH gradient.
The energy to maintain the gradient is supplied by the transfer of electrons along the respiratory chain. Otherwise, hydrogen ions would diffuse back.
The energy from the pH gradient is used to synthesize ATP from ADP:
ADP + P = ATP + H 2 O (reaction is reversible)
The resulting water is removed enzymatically. This, along with other factors, facilitates the reaction from left to right.
