Structure and functions of mitochondria. Mitochondria in muscle cells

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

general characteristics

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

Due to their rather large size, the organelles are clearly visible in a light microscope. The maximum length is 10 microns, the diameter does not exceed 1 micron.

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

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

TOP 4 articleswho are reading along with this

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

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

Structure

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

Rice. 2. Internal structure of mitochondria.

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

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

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

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

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

Rice. 3. Plastids.

What have we learned?

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

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• Mitochondria are tiny inclusions in cells that were originally thought to be inherited from bacteria. In most cells there are up to several thousand of them, which is from 15 to 50 percent of the cell volume. They are the source of more than 90 percent of your body's energy.
• Your mitochondria have a huge impact on health, especially cancer, so optimizing mitochondrial metabolism may be at the heart of effective cancer treatment

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From Dr. Mercola

Mitochondria: You May Not Know What They Are, But They Are vital for Your health. Rhonda Patrick, PhD, is a biomedical scientist who has studied the interactions between mitochondrial metabolism, abnormal metabolism, and cancer.

Part of her work involves identifying early biomarkers of disease. For example, DNA damage is an early biomarker of cancer. She then tries to determine which micronutrients help repair this DNA damage.

She also researched mitochondrial function and metabolism, which is something I've recently become interested in. If, after listening to this interview, you want to learn more about this, I recommend starting with Dr. Lee Know's book, Life - The Epic Story of Our Mitochondria.

Mitochondria have a profound impact on health, especially cancer, and I am beginning to believe that optimizing mitochondrial metabolism may lie at the heart of effective cancer treatment.

The importance of optimizing mitochondrial metabolism

Mitochondria are tiny organelles that we were originally thought to have inherited from bacteria. There are almost none in red blood cells and skin cells, but in germ cells there are 100,000 of them, but in most cells there are from one to 2,000. They are the main source of energy for your body.

In order for organs to function properly, they need energy, and this energy is produced by mitochondria.

Since mitochondrial function underlies everything that happens in the body, optimizing mitochondrial function, and preventing mitochondrial dysfunction by getting all the essential nutrients and precursors required by mitochondria, is extremely important for health and disease prevention.

Thus, one of the universal characteristics of cancer cells is a serious impairment of mitochondrial function, in which the number of functional mitochondria is radically reduced.

Dr. Otto Warburg was a physician with a degree in chemistry and a close friend of Albert Einstein. Most experts recognize Warburg as the greatest biochemist of the 20th century.

In 1931, he received the Nobel Prize for his discovery that cancer cells use glucose as a source of energy production. This was called the “Warburg effect” but, unfortunately, this phenomenon is still ignored by almost everyone.

I am convinced that a ketogenic diet, which radically improves mitochondrial health, can help most cancers, especially when combined with a glucose scavenger such as 3-bromopyruvate.

How mitochondria produce energy

To produce energy, mitochondria need oxygen from the air you breathe and fat and glucose from the food you eat.

These two processes - breathing and eating - are coupled to each other in a process called oxidative phosphorylation. It is used by mitochondria to produce energy in the form of ATP.

Mitochondria have a series of electron transport chains through which they transfer electrons from the reduced form of the food you eat to combine with oxygen from the air you breathe to ultimately form water.

This process drives protons across the mitochondrial membrane, recharging ATP (adenosine triphosphate) from ADP (adenosine diphosphate). ATP transports energy throughout the body

But this process produces byproducts such as reactive oxygen species (ROS), which damage cells and mitochondrial DNA, then transferring them to the DNA of the nucleus.

Thus, a compromise occurs. By producing energy, the body getting old due to the destructive aspects of ROS that arise in the process. The rate at which the body ages depends largely on how well the mitochondria function and the amount of damage that can be compensated for by optimizing diet.

The role of mitochondria in cancer

When cancer cells appear, reactive oxygen species produced as a byproduct of ATP production send a signal that triggers the process of cell suicide, also known as apoptosis.

Since cancer cells are formed every day, this is a good thing. By killing damaged cells, the body gets rid of them and replaces them with healthy ones.

Cancer cells, however, are resistant to this suicide protocol—they have built-in defenses against it, as explained by Dr. Warburg and subsequently by Thomas Seyfried, who has deeply researched cancer as a metabolic disease.

As Patrick explains:

“One of the mechanisms of action of chemotherapy drugs is the formation of reactive oxygen species. They create damage, and this is enough to push the cancer cell towards death.

I think the reason for this is that a cancer cell that is not using its mitochondria, that is, no longer producing reactive oxygen species, and suddenly you force it to use mitochondria, and you get a surge of reactive oxygen species (after all, that's what mitochondria do), and - boom, death, because the cancer cell is already ready for this death. She's ready to die."

Why is it good not to eat in the evening?

I've been a fan of intermittent fasting for quite some time now for a variety of reasons, longevity and health concerns of course, but also because it appears to provide powerful cancer prevention and treatment benefits. And the mechanism for this is related to the effect that fasting has on mitochondria.

As mentioned, a major side effect of the electron transfer that mitochondria engage in is that some leak out of the electron transport chain and react with oxygen to form superoxide free radicals.

Superoxide anion (the result of reducing oxygen by one electron), is a precursor to most reactive oxygen species and a mediator of oxidative chain reactions. Oxygen free radicals attack lipids in cell membranes, protein receptors, enzymes and DNA, which can kill mitochondria prematurely.

Some free radicals, in fact, are even beneficial, necessary for the body to regulate cellular functions, but problems arise with excessive formation of free radicals. Unfortunately, this is why the majority of the population develops most diseases, especially cancer. There are two ways to solve this problem:

• Increase antioxidants
• Reduce the production of mitochondrial free radicals

In my opinion, one of the most effective strategies for reducing mitochondrial free radicals is to limit the amount of fuel you put into your body. This is not at all controversial, as calorie restriction has consistently demonstrated many therapeutic benefits. This is one of the reasons intermittent fasting is effective because it limits the period of time in which food is consumed, which automatically reduces the amount of calories consumed.

This is especially effective if you don't eat a few hours before bed because this is your metabolically lowest state.

This may all seem overly complicated to non-experts, but one thing to understand is that since the body uses the fewest calories during sleep, you should avoid eating before bed, because excess fuel at this time will lead to the formation of excess amounts of free radicals that destroy tissue. accelerate aging and contribute to the occurrence of chronic diseases.

How else does fasting help healthy mitochondrial function?

Patrick also notes that part of the mechanism behind the effectiveness of fasting is that the body is forced to obtain energy from lipids and fat stores, which means that cells are forced to use their mitochondria.

Mitochondria are the only mechanism by which the body can create energy from fat. Thus, fasting helps activate mitochondria.

She also believes it plays a huge role in the mechanism by which intermittent fasting and the ketogenic diet kill cancer cells, and explains why some mitochondria-activating drugs can kill cancer cells. Again, this is because a surge of reactive oxygen species is formed, the damage from which decides the outcome of the matter, causing the death of cancer cells.

Nutrition of mitochondria

From a nutritional perspective, Patrick emphasizes the following nutrients and important co-factors necessary for the proper functioning of mitochondrial enzymes:

1. Coenzyme Q10 or ubiquinol (reduced form)
2. L-carnitine, which transports fatty acids into the mitochondria
3. D-ribose, which is the raw material for ATP molecules
4. Magnesium
5. All B vitamins, including riboflavin, thiamine and B6
6. Alpha Lipoic Acid (ALA)

As Patrick notes:

“I prefer to get as many micronutrients as possible from whole foods for a variety of reasons. Firstly, they form a complex with fibers, which facilitates their absorption.

In addition, in this case their correct ratio is ensured. You won't be able to get them in abundance. The ratio is exactly what you need. There are other components that are likely yet to be determined.

You have to be very vigilant in making sure you're eating a wide range of [foods] and getting the right micronutrients. I think taking a B complex supplement is helpful for this reason.

For this reason I accept them. Another reason is that as we age, we no longer absorb B vitamins as easily, mainly due to the increasing rigidity of cell membranes. This changes the way B vitamins are transported into the cell. They are water soluble, so they are not stored in fat. It is impossible to get poisoned by them. In extreme cases, you will urinate a little more. But I am sure that they are very useful."

Exercise can help keep mitochondria young

Exercise also promotes mitochondrial health because it gets your mitochondria working. As mentioned earlier, one of the side effects of increased mitochondrial activity is the creation of reactive oxygen species, which act as signaling molecules.

One of the functions they signal is the formation of more mitochondria. So when you exercise, the body responds by creating more mitochondria to meet increased energy demands.

Aging is inevitable. But your biological age can be very different from your chronological age, and mitochondria have a lot in common with biological aging. Patrick cites recent research that shows how people can age biologically Very at different paces.

The researchers measured more than a dozen different biomarkers, such as telomere length, DNA damage, LDL cholesterol, glucose metabolism and insulin sensitivity, at three points in people's lives: ages 22, 32 and 38.

“We found that someone aged 38 could biologically look 10 years younger or older, based on biological markers. Despite the same age, biological aging occurs at completely different rates.

Interestingly, when these people were photographed and their photographs were shown to passers-by and asked to guess the chronological age of the people depicted, people guessed the biological age, not the chronological age.”

So, regardless of your actual age, how old you look corresponds to your biological biomarkers, which are largely determined by your mitochondrial health. So while aging can't be avoided, you have a lot of control over how you age, and that's a lot of power. And one of the key factors is keeping mitochondria in good working order.

According to Patrick, “youth” is not so much chronological age, but how old you feel and how well your body works:

“I want to know how to optimize my mental performance and my athletic performance. I want to prolong my youth. I want to live to be 90. And when I do, I want to surf in San Diego the same way I did in my 20s. I wish I didn't fade away as quickly as some people. I like to delay this decline and prolong my youth as long as possible, so that I can enjoy life as much as possible.”

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

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

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

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

ABOUT THE COMPLEX IN SIMPLE LANGUAGE.

This topic is complex and complex, immediately affecting a huge number of biochemical processes occurring in our body. But let’s still try to figure out what mitochondria are and how they work.

And so, mitochondria are one of the most important components of a living cell. In simple terms, we can say that this is the energy station of the cell. Their activity is based on the oxidation of organic compounds and the generation of electrical potential (energy released during the breakdown of the ATP molecule) to effect muscle contraction.

We all know that the work of our body occurs in strict accordance with the first law of thermodynamics. Energy is not created in our body, but only transformed. The body only chooses the form of energy transformation, without producing it, from chemical to mechanical and thermal. The main source of all energy on planet Earth is the Sun. Coming to us in the form of light, the energy is absorbed by the chlorophyll of plants, where it excites the electron of the hydrogen atom and thus gives energy to living matter.

We owe our life to the energy of a small electron.

The work of the mitochondrion consists of a stepwise transfer of hydrogen electron energy between metal atoms present in groups of protein complexes of the respiratory chain (electron transport chain of proteins), where each subsequent complex has a higher affinity for the electron, attracting it than the previous one, until the electron not to combine with molecular oxygen, which has the highest electron affinity.

Each time an electron is transferred along a circuit, energy is released which is accumulated in the form of an electrochemical gradient and is then realized in the form of muscle contraction and heat generation.

The series of oxidative processes in the mitochondrion that allows the energy potential of an electron to be transferred is called “intracellular respiration” or often the “respiratory chain”, since the electron is passed along the chain from atom to atom until it reaches its final destination, an oxygen atom.

Mitochondria need oxygen to transfer energy through the process of oxidation.

Mitochondria consume up to 80% of the oxygen we inhale.

Mitochondria is a permanent cell structure located in its cytoplasm. The size of a mitochondrion is usually between 0.5 and 1 µm in diameter. It has a granular structure in shape and can occupy up to 20% of the cell volume. This permanent organic structure of a cell is called an organelle. Organelles also include myofibrils - the contractile units of the muscle cell; and the cell nucleus is also an organelle. In general, any permanent cell structure is an organelle.

Mitochondria were discovered and first described by the German anatomist and histologist Richard Altmann in 1894, and the name of this organelle was given by another German histologist K. Bend in 1897. But only in 1920, again, the German biochemist Otto Wagburg, proved that the processes of cellular respiration are associated with mitochondria.

There is a theory according to which mitochondria appeared as a result of the capture by primitive cells, cells that themselves could not use oxygen to generate energy, of protogenote bacteria that could do this. Precisely because the mitochondrion was previously a separate living organism, it still has its own DNA.

Mitochondria previously represented an independent living organism.

During evolution, progenotes transferred many of their genes to the formed nucleus, thanks to increased energy efficiency, and ceased to be independent organisms. Mitochondria are present in all cells. Even the sperm has mitochondria.

It is thanks to them that the tail of the sperm is set in motion, which carries out its movement. But there are especially many mitochondria in those places where energy is needed for any life processes. And these are, of course, primarily muscle cells.

In muscle cells, mitochondria can be combined into groups of giant branched mitochondria connected to each other through intermitochondrial contacts, in which they create a coordinated working cooperative system. The space in such a zone has an increased electron density. New mitochondria are formed by simple division of previous organelles. The most “simple” energy supply mechanism available to all cells is most often called the general concept of glycolysis.

This is the process of sequential decomposition of glucose to pyruvic acid. If this process occurs without the participation of molecular oxygen or with its insufficient presence, then it is called anaerobic glycolysis. In this case, glucose is broken down not into final products, but into lactic and pyruvic acid, which then undergoes further transformations during fermentation. Therefore, the released energy is less, but the rate of energy production is faster. As a result of anaerobic glycolysis, from one molecule of glucose the cell receives 2 molecules of ATP and 2 molecules of lactic acid. This “basic” energy process can occur inside any cell without the participation of mitochondria.

In the presence of molecular oxygen, aerobic glycolysis occurs within the mitochondria as part of the “respiratory chain”. Pyruvic acid under aerobic conditions is involved in the tricarboxylic acid cycle or Krebs cycle. As a result of this multi-step process, 36 ATP molecules are formed from one glucose molecule. A comparison of the energy balance of a cell with developed mitochondria and cells where they are not developed shows (with a sufficient amount of oxygen) a difference in the completeness of the use of glucose energy inside the cell by almost 20 times!

In humans, skeletal muscle fibers can be divided into three types based on mechanical and metabolic properties: - slow oxidative; - fast glycolytic; - fast oxidative-glycolytic.

Fast twitch muscle fibers are designed to perform fast and hard work. For their reduction, they use mainly fast energy sources, namely criatine phosphate and anaerobic glycolysis. The mitochondrial content in these types of fibers is significantly less than in slow-twitch muscle fibers.

Slow-twitch muscle fibers perform slow contractions, but are able to work for a long time. They use aerobic glycolysis and energy synthesis from fats as energy. This provides much more energy than anaerobic glycolysis, but requires more time in return, since the chain of glucose degradation is more complex and requires the presence of oxygen, the transport of which to the site of energy conversion also takes time. Slow muscle fibers are called red because of myoglobin, a protein responsible for delivering oxygen into the fiber. Slow-twitch muscle fibers contain a significant number of mitochondria.

The question arises: how and with the help of what exercises can a branched network of mitochondria be developed in muscle cells? There are various theories and training methods and about them in the material at the link.

Characteristics, role and structure of mitochondria

Functions of mitochondria as organelles of aerobic eukaryotic cells - synthesis of ATP molecules(adenosine triphosphate) from ADP. Since ATP is a universal source of energy for all processes in the cell that involve energy consumption, they say that mitochondria perform function of energy supply, or energy generation.

Intermediate products of the oxidation of organic substances, oxygen, ADP, and phosphoric acid, enter the mitochondria from the cytoplasm. Carbon dioxide, water and ATP molecules are released back.

ATP molecules are formed not only in mitochondria. A small amount of them is synthesized in the cytoplasm during the process of glycolysis, which is observed in all living cells. As a result of glycolysis, a glucose molecule is decomposed into two pyruvate molecules. In aerobic prokaryotes, it is further oxidized in the presence of oxygen at invaginations of the cytoplasmic membrane. In eukaryotes, pyruvate enters the mitochondria.

Here pyruvate donates its acetyl group, containing two carbon atoms, to coenzyme A. In this case, the first CO2 molecule is released. Coenzyme A is converted to acetyl-coenzyme-A (acetyl-CoA).

Acetyl-CoA is obtained not only from pyruvate, but also from fatty acids and amino acids. So it doesn’t matter what kind of initial organic matter will be “burned” in the mitochondria to produce energy. Their functioning is universal in any case.

In the mitochondrial matrix, acetyl-CoA enters Krebs cycle, or the tricarboxylic acid cycle, where the acetyl group is oxidized and decomposed into two more CO2 molecules. Its hydrogen atoms join the coenzymes NAD+ and FAD+, forming their reduced forms - NAD H + H+ and FAD H + H+. It is their subsequent oxidation that will lead to the synthesis of ATP.

Although oxygen is not used in the Krebs cycle, in its absence the mitochondria ceases to perform its function already at this stage, as reaction products accumulate.

At the cristae of mitochondria, electrons and hydrogen protons are separated. Electrons from NAD and FAD are transferred across the membrane through a chain of enzymes and coenzymes called respiratory chain. At the beginning of their journey, protons are transferred to the intermembrane space, to the outer side of the cristae.

The electrons are eventually transferred to the oxygen molecule, which becomes a negatively charged ion. An electrical potential is created between the outer and inner sides of the cristae, since one is charged positively and the other negatively. When a critical value is reached, H+ rushes through the channels of ATP synthetases and other enzymes to the inner side, where they combine with O2- to form water.

ATP synthetase is an enzyme that synthesizes ATP. In mitochondria, it is embedded in the cristae membrane and uses the energy of translocating protons to phosphorylate ADP.

The Krebs cycle and the respiratory chain are complex multi-step processes provided by a number of enzymes and coenzymes. Each requires separate consideration. In general terms, the functions of mitochondria are reduced to the synthesis of acetyl-CoA, the use of hydrogen atoms of the acetyl group to restore NAD and FAD, the separate transfer of electrons and protons of hydrogen to oxygen, and the use of the energy of the electrochemical gradient of protons for the synthesis of ATP.

Related articles:Structure of mitochondria, Stages of energy metabolism

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.

According to the symbiogenesis hypothesis mitochondria originated from aerobic bacteria that invaded another prokaryotic cell. These bacteria began to supply the cell with additional ATP molecules and receive nutrients from it. During the process of evolution, they lost their autonomy, transferring some of their genes to the nucleus and thus becoming a cellular organelle.

In cells, new mitochondria appear mainly by dividing previously existing ones, i.e. they are not synthesized anew, which resembles the process of reproduction and speaks in favor of symbiogenesis.

Structure and functions of mitochondria

Mitochondria consists of

two membranes - external and internal,

intermembrane space,

internal content - matrix,

Krist, which are outgrowths into the matrix of the inner membrane,

own protein synthesizing system: DNA, ribosomes, RNA,

proteins and their complexes, including a large number of enzymes and coenzymes,

other molecules and granules of various substances found in the matrix.

The outer and inner membranes perform different functions, so their chemical composition differs. The distance between membranes is up to 10 nm. The outer membrane of mitochondria is similar in structure to the plasmalemma surrounding the cell and primarily performs a barrier function, separating the contents of the organelle from the cytoplasm. Small molecules penetrate through it, the transport of large ones is selective. In some places, the outer membrane is connected to the ER, the channels of which open into the mitochondrion.

Enzymes are located on the inner membrane, mainly in its outgrowths - cristae, forming multienzymatic systems. Therefore, the chemical composition here is dominated by proteins rather than lipids. The number of cristae varies depending on the intensity of the processes. So there are a lot of them in muscle mitochondria.

In some places, the outer and inner membranes are connected to each other.

Mitochondria, like chloroplasts, have their own protein synthesizing system - DNA, RNA and ribosomes. The genetic apparatus is a ring molecule - a nucleoid, like in bacteria. The ribosomes of plant mitochondria are similar to bacterial ones; in animals, mitochondrial ribosomes are smaller not only than cytoplasmic ones, but also bacterial ones. Some of the necessary proteins are synthesized by mitochondria themselves, while the other part is obtained from the cytoplasm, since these proteins are encoded by nuclear genes.

The main function of mitochondria is to supply the cell with energy, which is extracted from organic compounds through numerous enzymatic reactions and stored in ATP. Some reactions involve oxygen, while others release carbon dioxide. Reactions occur both in the matrix (Krebs cycle) and on the cristae (oxidative phosphorylation).

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.

Mitochondria

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 + H2O (reaction is reversible)

The resulting water is removed enzymatically. This, along with other factors, facilitates the reaction from left to right.

Mitochondria

Plastids and mitochondria of a plant cell: structure, functions, structural features in connection with biological functions.

Mitochondria of a plant cell. Their structure and functions

Form− round or dumbbell-shaped bodies.

Dimensions− length 1-5 microns, diameter 0.4-0.5 microns.

Quantity per cage− from tens to 5,000.

Structure. They consist mainly of protein (60-65%) and lipids (30%). These are double-membrane organelles. The thickness of the outer and inner membranes is 5-6 nm each. The perimitochondrial space (the space between the membranes) is filled with a fluid such as serum. The inner membrane forms folds of various shapes − cristas. On the inner surface of the inner membrane there are mushroom-shaped particles - oxisomes containing oxidative enzymes. Internal contents of mitochondria − matrix. The matrix contains ribosomes and mitochondrial DNA (0.5%), which has a ring structure and is responsible for the synthesis of mitochondrial proteins. Mitochondria have all types of RNA (1%), divide independently of nuclear division, and in the cell are formed from preexisting mitochondria by fission or budding. The half-life of mitochondria is 5-10 days.

Functions. Mitochondria are the centers of energy activity of cells. Aerobic respiration and oxidative phosphorelation systems function in mitochondria. The components of the electron transport chain and ATP synthetase complexes, which carry out the transport of electrons and protons and the synthesis of ATP, are localized in the inner membrane of mitochondria. The matrix contains systems for the oxidation of di- and tricarboxylic acids, a number of systems for the synthesis of lipids, amino acids, etc.

Mitochondria are able to move to places of increased energy consumption. They can associate with each other by close proximity or with the help of cords. During anaerobic respiration, mitochondria disappear.

Mitochondria have a round and oblong shape with a diameter of 0.4–0.5 μm and a length of 1–5 μm (Fig. 1.3).

The number of mitochondria varies from a few to 1,500–2,000 per plant cell.

Mitochondria are bounded by two membranes: outer and inner, the thickness of each of them is 5–6 nm. The outer membrane appears stretched, and the inner one forms folds called ridges (cristae) of various shapes. The space between the membranes, which also includes the internal space of the cristae, is called the intermembrane (perimitochondrial) space. It serves as a medium for the inner membrane and matrix of mitochondria.

Mitochondria generally contain 65–70% protein, 25–30% lipids, and small amounts of nucleic acids. Phospholipids (phosphatidylcholine and phosphatidylethanolamine) account for 70% of the total lipid content. The fatty acid composition is characterized by a high content of saturated fatty acids, which ensure the “rigidity” of the membrane.

The systems of aerobic respiration and oxidative phosphorylation are localized in mitochondria. As a result of respiration, organic molecules are broken down and energy is released and transferred to the ATP molecule.

Mitochondria contain proteins, RNA, DNA strands, ribosomes similar to bacterial ones, and various solutes. DNA exists in the form of circular molecules located in one or more nucleotides.

plastids, along with vacuoles and the cell membrane, they are characteristic components of plant cells. Each plastid is surrounded by its own shell, consisting of two elementary membranes. Inside plastids, a membrane system and a more or less homogeneous substance, the stroma, are distinguished. The internal structure of the chloroplast is quite complex. The stroma is permeated by a developed system of membranes in the form of flat vesicles called thylakoids. Thylakoids are collected in stacks - grana, resembling columns of coins.

Chloroplasts, in which photosynthesis occurs, contain chlorophylls and carotenoids. Size – 4–5 microns. One mesophyll cell of a leaf can contain 40–50 chloroplasts, and about 500,000 per mm2 of leaf. In the cytoplasm, chloroplasts are usually located parallel to the cell wall.

Chlorophylls and carotenoids are embedded in thylakoid membranes. The chloroplasts of green plants and algae often contain starch grains and small lipid (fat) droplets. Starch grains are temporary storage facilities for photosynthesis products. They can disappear from chloroplasts kept in the dark for only 24 hours and reappear within 3–4 hours after the plants are transferred to the light.

In isolated chloroplasts, RNA synthesis occurs, which is usually controlled only by chromosomal DNA. The formation of chloroplasts and the synthesis of the pigments contained in them are largely controlled by chromosomal DNA, which interacts with the DNA of chloroplasts in a poorly understood way. However, in the absence of their own DNA, chloroplasts do not form.

23. Ultrastructure of mitochondria, functions

They participate in the synthesis of amino acids and fatty acids and serve as a storage facility for temporary starch reserves.

Chromoplasts(from the Greek chroma - color) - pigmented plastids. Chromoplasts, varied in shape, do not contain chlorophyll, but synthesize and accumulate carotenoids, which give yellow, orange and other colors. Carrot roots and tomato fruits are colored by pigments that are found in chromoplasts.

Leukoplasts are a place of accumulation of a reserve substance - starch. There are especially many leukoplasts in the cells of potato tubers. In the light, leucoplasts can transform into chloroplasts (potato tubers turn green). In autumn, the chloroplasts transform into chromoplasts and green leaves, and the fruits turn yellow and red.

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

Functions of mitochondria

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

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

Mitochondrial DNA

Myochondrial division

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

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