Characteristic of the vast majority of cells. The main function is the oxidation of organic compounds and the production of ATP molecules from the released energy. The small mitochondrion is the main energy station of the entire body.

Origin of mitochondria

Today, there is a very popular opinion among scientists that mitochondria did not appear in the cell independently during evolution. Most likely, this happened due to the capture by a primitive cell, which at that time was not capable of independently using oxygen, of a bacterium that could do this and, accordingly, was an excellent source of energy. Such a symbiosis turned out to be successful and took hold in subsequent generations. This theory is supported by the presence of its own DNA in mitochondria.

How are mitochondria structured?

Mitochondria have two membranes: outer and inner. The main function of the outer membrane is to separate the organelle from the cell cytoplasm. It consists of a bilipid layer and proteins that penetrate it, through which the transport of molecules and ions necessary for work is carried out. While smooth, the inner one forms numerous folds - cristae, which significantly increase its area. The inner membrane is largely composed of proteins, including respiratory chain enzymes, transport proteins, and large ATP synthetase complexes. It is in this place that ATP synthesis occurs. Between the outer and inner membranes there is an intermembrane space with its inherent enzymes.

The inner space of mitochondria is called the matrix. Here are located the enzyme systems for the oxidation of fatty acids and pyruvate, enzymes of the Krebs cycle, as well as the hereditary material of mitochondria - DNA, RNA and the protein synthesizing apparatus.

What are mitochondria needed for?

The main function of mitochondria is the synthesis of a universal form of chemical energy - ATP. They also take part in the tricarboxylic acid cycle, converting pyruvate and fatty acids into acetyl-CoA and then oxidizing it. In this organelle, mitochondrial DNA is stored and inherited, encoding the reproduction of tRNA, rRNA and some proteins necessary for the normal functioning of mitochondria.

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

Structure

Mitochondria consist of three interconnected components:

• outer membrane;
• inner membrane;
• matrix.

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

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

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

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

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

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

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

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

Rice. 1. The structure of mitochondria.

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

Meaning

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

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

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

Where does it happen?	Substances	Processes
Cytoplasm		As a result of glycolysis, it decomposes into two molecules of pyruvic acid, which enter the matrix
		An acetyl group is cleaved, which attaches to coenzyme A (CoA), forming acetyl-coenzyme-A (acetyl-CoA), and a molecule of carbon dioxide is released. Acetyl-CoA can also be formed from fatty acids in the absence of carbohydrate synthesis
	Acetyl-CoA	Enters the Krebs cycle or the citric acid cycle (tricarboxylic acid cycle). The cycle begins with the formation of citric acid. Next, as a result of seven reactions, two molecules of carbon dioxide are formed, NADH and FADH2
	NADH and FADH2	When oxidized, NADH decomposes into NAD +, two high-energy electrons (e –) and two H + protons. The electrons are transferred to the respiratory chain, containing three enzyme complexes, on the inner membrane. The passage of an electron through the complexes is accompanied by the release of energy. At the same time, protons are released into the intermembrane space. Free protons tend to return to the matrix, which creates an electrical potential. As the voltage increases, H+ rush inward through ATP synthase, a special protein. Proton energy is used to phosphorylate ADP and synthesize ATP. H+ combines with oxygen to form water.

Rice. 3. The process of cellular respiration.

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

What have we learned?

From the biology lesson we learned about the structural features of mitochondria and briefly examined the functions and process of cellular respiration. Thanks to the work of mitochondria, pyruvic acid, formed during glycolysis, and fatty acids are oxidized to carbon dioxide and water. As a result of cellular respiration, energy is released, which is spent on the vital functions of the body.

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ABOUT THE COMPLEX IN SIMPLE LANGUAGE.

This topic is complex and complex, immediately affecting huge amount 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 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 carry out 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 release.

A series of oxidative processes in mitochondria that allow the energy potential of an electron to be transferred is called "intracellular respiration" or often "breathing chain", since the electron is transferred along the chain from atom to atom until it reaches its final destination, the 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 coherent 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 general concept 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 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 presence of molecular oxygen carried out inside mitochondria aerobic glycolysis within 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. Comparison of the energy balance of a cell with developed mitochondria and cells where they are not developed shows(with sufficient oxygen) the difference in the complete use of glucose energy inside the cell is almost 20 times!

In humans, fibers skeletal muscles Can conditionally divided into three types based on mechanical and metabolic properties: - slow oxidative; - fast glycolytic; - fast oxidative-glycolytic.

Fast muscle fibers Designed for 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 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 on.

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.

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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 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 large number 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 - stock up nutrients, for example, 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

Mitochondria were discovered in animal cells in 1882, and in plants only in 1904 (in the anthers of water lilies). Biological functions were established after isolation and purification of the fraction by fractional centrifugation. They contain 70% protein and about 30% lipids, a small amount of RNA and DNA, vitamins A, B6, B12, K, E, folic and pantothenic acids, riboflavin, and various enzymes. Mitochondria have a double membrane, the outer one isolates the organelle from the cytoplasm, and the inner one forms cristae. The entire space between the membranes is filled with matrix (Fig. 13).

The main function of mitochondria is to participate in cellular respiration. The role of mitochondria in respiration was established in 1950-1951. The complex enzyme system of the Krebs cycle is concentrated on the outer membranes. When the substrates of respiration are oxidized, energy is released, which is immediately accumulated in the resulting molecules of ADP and mainly ATP during the process of oxidative phosphorylation occurring in the cristae. The energy stored in high-energy compounds is subsequently used to satisfy all the needs of the cell.

The formation of mitochondria in a cell occurs continuously from microbodies; their occurrence is most often associated with the differentiation of membrane structures of the cell. They can be restored in the cell by dividing and budding. Mitochondria are not long-lived; their lifespan is 5-10 days.

Mitochondria are the “power” stations of the cell. They concentrate energy, which is stored in energy “accumulators” - ATP molecules, and is not dissipated in the cell. Violation of the mitochondrial structure leads to disruption of the respiration process and, ultimately, to pathology of the body.

Golgi apparatus.Golgi apparatus(synonym - dictyosomes) are stacks of 3-12 flattened, closed disks surrounded by a double membrane, called cisternae, from the edges of which numerous vesicles (300-500) are laced. The width of the tanks is 6-90 A, the thickness of the membranes is 60-70 A.

The Golgi apparatus is the center for the synthesis, accumulation and release of polysaccharides, in particular cellulose, and is involved in the distribution and intracellular transport of proteins, as well as in the formation of vacuoles and lysosomes. In plant cells, it was possible to trace the participation of the Golgi apparatus in the emergence of the middle plate and the growth of the cell pecto-cellulose membrane.

The Golgi apparatus is most developed during the period active life cells. As she ages, it gradually atrophies and then disappears.

Lysosomes.Lysosomes- rather small (about 0.5 microns in diameter) rounded bodies. They are covered with a protein-lipoid membrane. Lysosomes contain numerous hydrolytic enzymes that perform the function of intracellular digestion (lysis) of protein macromolecules, nucleic acids, and polysaccharides. Their main function is the digestion of individual sections of the cell protoplast (autophagy - self-devouring). This process occurs through phagocytosis or pinocytosis. The biological role of this process is twofold. Firstly, it is protective, since during a temporary lack of reserve products, the cell maintains life due to constitutional proteins and other substances, and secondly, there is a release from excess or worn-out organelles (plastids, mitochondria, etc.) The lysosome membrane prevents the release of enzymes into the cytoplasm , otherwise it would all be digested by these enzymes.

In a dead cell, lysosomes are destroyed, enzymes end up in the cell and all its contents are digested. All that remains is the pecto-cellulose shell.

Lysosomes are products of the activity of the Golgi apparatus, vesicles detached from it, in which this organelle accumulated digestive enzymes.

Spherosomes- round protein-lipoid bodies 0.3-0.4 microns. In all likelihood, they are derivatives of the Golgi apparatus or endoplasmic reticulum. They resemble lysosomes in shape and size. Since spherosomes contain acid phosphatase, they are probably related to lysosomes. Some authors believe that spherosomes and lysosomes are equivalent to each other, but most likely only in origin and form. There is an assumption about their participation in the synthesis of fats (A. Frey-Wissling).

Ribosomes- very small organelles, their diameter is about 250A, they are almost spherical in shape. Some of them are attached to the outer membranes of the endoplasmic reticulum, some of them are in a free state in the cytoplasm. A cell can contain up to 5 million ribosomes. Ribosomes are found in chloroplasts and mitochondria, where they synthesize part of the proteins from which these organelles are built, and the enzymes that function in them.

The main function is the synthesis of specific proteins according to information coming from the nucleus. Their composition: protein and ribosomal ribonucleic acid (RNA) in equal proportions. Their structure is small and large subunits formed from ribonucleotide.

Microtubules.Microtubules- peculiar derivatives of the endoplasmic reticulum. Found in many cells. Their very name speaks of their shape - one or two parallel tubes with a cavity inside. External diameter within 250A. The walls of microtubules are made of protein molecules. Microtubules form spindle filaments during cell division.

Core

The nucleus was discovered in a plant cell by R. Brown in 1831. It is located in the center of the cell or near the cell membrane, but is surrounded on all sides by the cytoplasm. In most cases, there is one nucleus per cell; several nuclei are found in the cells of some algae and fungi. Green algae with a noncellular structure have hundreds of nuclei. Multinucleated cells of unarticulated laticifers. There are no nuclei in the cells of bacteria and blue-green algae.

The shape of the nucleus is most often close to the shape of a sphere or an ellipse. Depends on the shape, age and function of the cell. In a meristematic cell, the nucleus is large, round in shape and occupies 3/4 of the cell volume. In parenchymal cells of the epidermis, which have a large central vacuole, the nucleus has a lenticular shape and is moved along with the cytoplasm to the periphery of the cell. This is a sign of a specialized, but already aging cell. A cell without a nucleus can only live short time. Nuclear-free sieve tube cells are living cells, but they do not live long. In all other cases, anucleate cells are dead.

The core has a double shell, through the pores in which the contents
the nuclei (nucleoplasm) can communicate with the contents of the cytoplasm. The membranes of the nuclear membrane are equipped with ribosomes and communicate with the membranes of the endoplasmic reticulum of the cell. The nucleoplasm contains one or two nucleoli and chromosomes. Nucleoplasm is a colloidal sol system, reminiscent of thickened gelatin in consistency. The nucleus, according to domestic biochemists (Zbarsky I.B. et al.), contains four fractions of proteins: simple proteins - globulins 20%, deoxyribonucleoproteins - 70%, acidic proteins - 6% and residual proteins 4%. They are localized in the following nuclear structures: DNA proteins (alkaline proteins) - in chromosomes, RNA proteins (acidic proteins) - in nucleoli, partially in chromosomes (during the synthesis of messenger RNA) and in the nuclear membrane. Globulins form the basis of the nucleoplasm. Residual proteins (nature not specified) form the nuclear membrane.

The bulk of nuclear proteins are complex alkaline deoxyribonucleoproteins, which are based on DNA.

DNA molecule.DNA molecule– polynucleotide and consists of nucleotides. A nucleotide consists of three components: a sugar molecule (deoxyribose), a nitrogenous base molecule, and phosphoric acid molecules. Deoxyribose is connected to a nitrogenous base by a glycosidic bond, and to phosphoric acid by an ester bond. DNA contains various combinations There are only 4 types of nucleotides, differing from each other in nitrogenous bases. Two of them (adenine and guanine) belong to purine nitrogenous compounds, and cytosine and thymine belong to pyrimidine compounds. DNA molecules are not located in one plane, but consist of two helical strands, i.e. two parallel chains twisted around one another form one DNA molecule. They are held together by hydrogen bonds between nitrogenous bases, with the purine bases of one chain attaching the pyrimidine bases of the other (Fig. 14). The structure and chemistry of the DNA molecule was discovered by English (Crick) and American (Watson) scientists and made public in 1953. This moment is considered to be the beginning of the development of molecular genetics. The molecular weight of DNA is 4-8 million. The number of nucleotides ( various options) up to 100 thousand. The DNA molecule is very stable, its stability is ensured by the fact that throughout it has the same thickness - 20A (8A - the width of the pyrimidine base + 12A - the width of the purine base). If radioactive phosphorus is introduced into the body, the label will be detected in all phosphorus-containing compounds except DNA (Levi, Sikewitz).

DNA molecules are carriers of heredity, because their structure encodes information about the synthesis of specific proteins that determine the properties of the organism. Changes can occur under the influence of mutagenic factors (radioactive radiation, potent chemical agents - alkaloids, alcohols, etc.).

RNA molecule.Ribonucleic acid (RNA) molecules significantly fewer DNA molecules. These are single chains of nucleotides. There are three types of RNA: ribosomal, the longest, forming numerous loops, information (template) and transport, the shortest. Ribosomal RNA is localized in the ribosomes of the endoplasmic reticulum and makes up 85% of the total RNA of the cell.

Messenger RNA in its structure resembles a clover leaf. Its amount is 5% of the total RNA in the cell. It is synthesized in the nucleoli. Its assembly occurs in chromosomes during interphase. Its main function is the transfer of information from DNA to ribosomes, where protein synthesis occurs.

Transfer RNA, as has now been established, is a whole family of compounds related in structure and biological function. Each living cell according to a rough estimate, contains 40-50 individual transfer RNAs and their total number in nature, if we take into account species differences, it is enormous. (Academician V. Engelhardt). They are called transport because their molecules are involved in transport services for the intracellular process of protein synthesis. By combining with free amino acids, they deliver them to the ribosomes into the protein chain under construction. These are the smallest RNA molecules, consisting of an average of 80 nucleotides. Localized in the cytoplasmic matrix and make up about 10% of cellular RNA

RNA contains four nitrogenous bases, but unlike DNA, the RNA molecule contains uracil instead of thymine.

Structure of chromosomes. Chromosomes were first discovered at the end of the 19th century by the classics of cytology Fleming and Strasburger (1882, 1884), and the Russian cell researcher I.D. Chistyakov discovered them in 1874.

Basic structural element chromosis - nucleus. They have different shape. These are either straight or curved rods, oval bodies, balls, the sizes of which vary.

Depending on the location of the centromere, straight, equal-armed and unequal-armed chromosomes are distinguished. The internal structure of chromosomes is shown in Fig. 15, 16. It should be noted that deoxyribonucleoprotein is a monomer of the chromosome.

The chromosome contains 90-92% deoxyribonucleoproteins, of which 45% is DNA and 55% is protein (histone). The chromosome also contains small amounts of RNA (messenger).

Chromosomes also have a clearly defined transverse structure - the presence of thickened areas - disks, which back in 1909. were called genes. This term was proposed by the Danish scientist Johansen. In 1911, the American scientist Morgan proved that genes are the main hereditary units and they are distributed in chromosomes in a linear order and, therefore, the chromosome has qualitatively different sections. In 1934, the American scientist Paynter proved the discontinuity of the morphological structure of chromosomes and the presence of disks in chromosomes, and disks are places where DNA accumulates. This served as the beginning of the creation of chromosomal maps, which indicated the location (locus) of the gene that determines a particular trait of the organism. A gene is a section of a DNA double helix that contains information about the structure of a single protein. This is a section of the DNA molecule that determines the synthesis of one protein molecule. DNA is not directly involved in protein synthesis. It only contains and stores information about the structure of the protein.

The DNA structure, consisting of several thousand sequentially located 4 nucleotides, is the code of heredity.

Heredity code. Protein synthesis. The first message on the DNA code was made by the American biochemist Nirenberg in 1961 in Moscow at the international biochemical congress. The essence of the DNA code is as follows. Each amino acid corresponds to a section of a DNA chain consisting of three adjacent nucleotides (triplet). So, for example, a section consisting of T-T-T (a triplet of 3 thymine-containing nucleotides) corresponds to the amino acid lysine, a triplet A (adenine) - C (cytosine) - A (adenine) - cysteine, etc. Let us assume that a gene is represented by a chain of nucleotides arranged in the following order: A-C-A-T-T-T-A-A-C-C-A-A-G-G-G. By breaking this series into triplets, we can immediately decipher which amino acids and in what order will be located in the synthesized protein.

The number of possible combinations of 4 available nucleotides in threes is 4×64. Based on these relationships, the number of different triplets is more than enough to provide information on the synthesis of numerous proteins that determine both the structure and functions of the body. For protein synthesis, an exact copy of this information is sent to the ribosomes in the form of messenger RNA. In addition to mRNA, it is involved in decoding and synthesis large number molecules of various transport ribonucleic acids (tRNA), ribosomes and a number of enzymes. Each of the 20 amino acids binds to T-RNA - molecule to molecule. Each of the 20 amino acids has its own tRNA. tRNA has chemical groups that can “recognize” their amino acid, selecting it from the available amino acids. This happens with the help of special enzymes. Having recognized its amino acid, t-RNA enters into a connection with it. A ribosome is attached to the beginning of the chain (molecule) of i-RNA, which, moving along the i-RNA, connects with each other into a polypeptide chain exactly those amino acids, the order of which is encrypted by the nucleotide sequence of this I-RNA. As a result, a protein molecule is formed, the composition of which is encoded in one of the genes.

Nucleoli- an integral structural part of the core. These are spherical bodies. They are very changeable, changing their shape and structure, appearing and disappearing. There are one or two of them. For every plant certain number. The nucleoli disappear as the cell prepares to divide and then reappear; they appear to be involved in the synthesis of ribonucleic acids. If the nucleolus is destroyed by a focused beam of X-rays or ultraviolet rays, cell division is inhibited.

The role of the nucleus in the life of a cell. The nucleus serves as the control center of the cell; it directs cellular activity and contains carriers of heredity (genes) that determine the characteristics of a given organism. The role of the nucleus can be revealed if, using microsurgical techniques, it is removed from the cell and the consequences of this are observed. A series of experiments proving its important role in the regulation of cell growth were carried out by Gemmerling on the single-celled green alga Acetobularia. This seaweed reaches a height of 5 cm, looks like a mushroom, and has something like “roots” and “legs”. It ends at the top with a large disc-shaped “hat”. The cell of this algae has one nucleus, located in the basal part of the cell.

Hammerling found that if the stem is cut, the lower part continues to live and the cap is completely regenerated after the operation. The upper part, deprived of the nucleus, survives for some time, but eventually dies without being able to restore the lower part. Therefore, the acetobularia nucleus is essential for the metabolic reactions underlying growth.

The nucleus contributes to the formation of the cell membrane. This can be illustrated by experiments with the algae Voucheria and Spyrogyra. By releasing the contents of the cells from the cut threads into the water, we can obtain lumps of cytoplasm with one, several nuclei, or without nuclei. In the first two cases, the cell membrane formed normally. In the absence of a core, the shell was not formed.

In experiments by I.I. Gerasimov (1890) with spirogyra, it was found that cells with a double nucleus double the length and thickness of the chloroplast. In nuclear-free cells, the process of photosynthesis continues, assimilation starch is formed, but at the same time the process of its hydrolysis is damped, which is explained by the absence of hydrolytic enzymes, which can be synthesized in ribosomes only according to the information from the DNA of the nucleus. The life of a protoplast without a nucleus is incomplete and short-lived. In the experiments of I.I. Gerasimov, the nuclear-free cells of Spirogyra lived for 42 days and died. One of the most important functions of the nucleus is to supply the cytoplasm with ribonucleic acid necessary for protein synthesis in the cell. Removal of the nucleus from the cell leads to a gradual decrease in the RNA content in the cytoplasm and a slowdown in protein synthesis in it.

The most important role of the nucleus is in transmitting characteristics from cell to cell, from organism to organism, and does this during the process of division of the nucleus and the cell as a whole.

Cell division. Cells reproduce by division. In this case, from one cell two daughter cells are formed with the same set of hereditary material contained in the chromosomes as the mother cell. In somatic cells, chromosomes are represented by two, so-called homologous chromosomes, which contain allelic genes (carriers of opposite characteristics, for example, white and red color of pea petals, etc.), characteristics of two parental pairs. In this regard, in the somatic cells of the plant body there is always a double set of chromosomes, designated 2n. Chromosomes have distinct individuality. The quantity and quality of chromosomes is a characteristic feature of each species. Thus, in strawberry cells the diploid set of chromosomes is 14, (2n), in apple cells - 34, in Jerusalem artichoke - 102, etc.

Mitosis (karyokinesis)– division of somatic cells was first described by E. Russov (1872) and I.D. Chistyakov (1874). Its essence lies in the fact that from the mother cell, by division, two daughter cells with the same set of chromosomes are formed. The cell cycle consists of interphase and mitosis itself. Using the microautoradiography method, it was established that the longest and most complex is the interphase - the period of the “resting” nucleus, because During this period, nuclear material doubles. Interphase is divided into three phases:

Q1 - presynthetic (its duration is 4-6 hours);

S - synthetic (10-20 hours);

Q2 - postsynthetic (2-5 hours).

During the Q1 phase, preparations are made for DNA reduplication. And in the S phase, DNA reduplication occurs; the cell doubles its DNA supply. In the Q2 phase, enzymes and structures necessary to initiate mitosis are formed. Thus, in interphase, DNA molecules in chromosomes are split into two identical strands, and messenger RNAs are assembled on their matrix. The latter carries information about the structure of specific proteins into the cytoplasm, and in the nucleus, each of the DNA strands completes the missing half of its molecule. In this process of duplication (reduplication) appears unique feature DNA, which consists of the ability of DNA to accurately reproduce itself. The resulting daughter DNA molecules are automatically obtained as exact copies of the parent molecule, because during reduplication, complementary (A-T; G-C; etc.) bases from the environment are added to each half.

During the prophase of mitotic division, the duplicated chromosomes become noticeable. In metaphase, they are all located in the equatorial zone, arranged in one row. Spindle filaments (from microtubules connecting to each other) are formed. The nuclear membrane and nucleolus disappear. Thickened chromosomes are split lengthwise into two daughter chromosomes. This is the essence of mitosis. It ensures precise distribution of duplicated DNA molecules between daughter cells. Thus, it ensures the transmission of hereditary information encrypted in DNA.

In anaphase, the daughter chromosomes begin to move to opposite poles. The first fragments of the cell membrane (phragmoblast) appear in the center.

During telophase, the formation of nuclei in daughter cells occurs. The contents of the mother cell (organelle) are distributed among the resulting daughter cells. The cell membrane is fully formed. This ends cytokinesis (Fig. 17).

Meiosis - reduction division was discovered and described in the 90s of the last century by V.I. Belyaev. The essence of division is that from a somatic cell containing a 2n (double, diploid) set of chromosomes, four haploid cells are formed, with “n”, a half set of chromosomes. This type of division is complex and consists of two stages. The first is reduction by chromosis. Duplicate chromosomes are located in the equatorial zone in pairs (two parallel homologous chromosomes). At this moment, conjugation (coupling) with chromosis, crossing over (crossover) can occur and, as a result, an exchange of sections of chromosis can occur. As a result of this, some of the genes of paternal chromosomes pass into the composition of maternal chromosomes and vice versa. The appearance of both chromosomes does not change as a result of this, but their qualitative composition becomes different. Paternal and maternal heredity are redistributed and mixed.

In the anaphase of meiosis, homologous chromosomes, with the help of spindle threads, disperse to the poles, at which, after a short period of rest (the threads disappear, but the partition between new nuclei is not formed), the process of mitosis begins - metaphase, in which all the chromosomes are located in the same plane and their longitudinal splitting occurs to daughter chromosomes. During anaphase of mitosis, with the help of a spindle, they disperse to the poles, where four nuclei are formed and, ultimately, four haploid cells. In the cells of some tissues, during their development, under the influence of certain factors, incomplete mitosis occurs and the number of chromosomes in the nuclei doubles due to the fact that they do not diverge to the poles. As a result of such disturbances of a natural or artificial nature, tetraploid and polyploid organisms arise. With the help of meiosis, sex cells are formed - gametes, as well as spores, elements of sexual and asexual reproduction of plants (Fig. 18).

Amitosis is direct division of the nucleus. During amitosis, the spindle does not form and the nuclear membrane does not disintegrate, as during mitosis. Previously, amitosis was considered a primitive form of division. It has now been established that it is associated with the degradation of the body. It is a simplified version of a more complex nuclear fission. Amitosis occurs in the cells and tissues of the nucellus, endosperm, tuber parenchyma, leaf petioles, etc.