Processes that provide the cell with energy. Providing cells with energy. Energy sources. Cell wall functions

Energy is necessary for all living cells - it is used for various biological and chemical reactions flowing in the cell. Some organisms use energy sunlight for biochemical processes, these are plants (Fig. 1), while others use energy chemical bonds in substances obtained in the process of nutrition, these are animal organisms. The extraction of energy is carried out by splitting and oxidizing these substances, in the process of breathing, this breathing is called biological oxidation, or cellular respiration.

Rice. 1. The energy of sunlight

Cellular respiration- this is a biochemical process in the cell, proceeding with the participation of enzymes, as a result of which water and carbon dioxide are released, energy is stored in the form of high-energy bonds of ATP molecules. If this process takes place in the presence of oxygen, then it is called aerobic, but if it occurs without oxygen, then it is called anaerobic.

Biological oxidation includes three main stages:

1. Preparatory.

2. Anoxic (glycolysis).

3. Complete splitting organic matter(in the presence of oxygen).

Substances taken with food are broken down into monomers. This stage begins in the gastrointestinal tract or in the lysosomes of the cell. Polysaccharides break down into monosaccharides, proteins into amino acids, fats into glycerol and fatty acids. The energy released at this stage is dissipated in the form of heat. It should be noted that cells use carbohydrates for energy processes, and monosaccharides are better, and the brain can use only a monosaccharide - glucose for its work (Fig. 2).

Rice. 2. Preparatory stage

Glucose is broken down by glycolysis into two three-carbon molecules of pyruvic acid. The further fate of pyruvic acid depends on the presence of oxygen in the cell. If oxygen is present in the cell, then pyruvic acid passes into the mitochondria for complete oxidation to carbon dioxide and water (aerobic respiration). If there is no oxygen, then in animal tissues pyruvic acid turns into lactic acid. This stage takes place in the cytoplasm of the cell.

glycolysis- this is a sequence of reactions, as a result of which one molecule of glucose is split into two molecules of pyruvic acid, while energy is released, which is enough to convert two ADP molecules into two ATP molecules (Fig. 3).

Rice. 3. Anoxic stage

Oxygen is essential for the complete oxidation of glucose. At the third stage, pyruvic acid is completely oxidized in mitochondria to carbon dioxide and water, resulting in the formation of another 36 ATP molecules, since this stage occurs with the participation of oxygen, it is called oxygen, or aerobic (Fig. 4).

Rice. 4. Complete breakdown of organic matter

In total, 38 ATP molecules are formed from one glucose molecule in three stages, taking into account the two ATP obtained in the process of glycolysis.

Thus, we have considered the energy processes occurring in cells, characterized the stages of biological oxidation.

The respiration that occurs in the cell with the release of energy is often compared with the combustion process. Both processes occur in the presence of oxygen, release of energy and oxidation products - carbon dioxide and water. But, unlike combustion, respiration is an ordered process of biochemical reactions occurring in the presence of enzymes. During respiration, carbon dioxide arises as the end product of biological oxidation, and in the process of combustion, the formation of carbon dioxide occurs by direct combination of hydrogen with carbon. Also, during respiration, in addition to water and carbon dioxide, a certain amount of ATP molecules is formed, that is, respiration and combustion are fundamentally different processes (Fig. 5).

Rice. 5. Differences between breathing and combustion

Glycolysis is not only the main pathway for the metabolism of glucose, but also the main pathway for the metabolism of dietary fructose and galactose. Especially important in medicine is the ability of glycolysis to form ATP in the absence of oxygen. This makes it possible to maintain intensive work of the skeletal muscle in conditions of insufficient efficiency of aerobic oxidation. Tissues with increased glycolytic activity are able to remain active during periods of oxygen starvation. In the heart muscle, the possibilities for glycolysis are limited. It is difficult to tolerate impaired blood supply, which can lead to ischemia. Several diseases are known to be caused by insufficient activity of glycolysis enzymes, one of which is hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capacity of the citric acid cycle), which contributes to an increased synthesis of lactic acid in organs and tissues (Fig. 6).

Rice. 6. Hemolytic anemia

Elevated levels of lactic acid in the body can be a symptom of cancer. This metabolic feature is sometimes used to treat some forms of tumors.

Microbes are able to obtain energy in the process of fermentation. Fermentation has been known to people since time immemorial, for example, in the manufacture of wine, lactic acid fermentation was known even earlier (Fig. 7).

Rice. 7. Making wine and cheese

People consumed dairy products without suspecting that these processes are associated with the activity of microorganisms. The term "fermentation" was introduced by the Dutchman Van Helmont for processes that go with the release of gas. This was first proved by Louis Pasteur. Moreover, different microorganisms secrete different fermentation products. We will talk about alcoholic and lactic acid fermentation. Alcoholic fermentation is the process of oxidation of carbohydrates, which results in the formation of ethanol, carbon dioxide and energy is released. Brewers and winemakers have used the ability of certain types of yeast to stimulate fermentation, which turns sugars into alcohol. Fermentation is carried out mainly by yeasts, but also by some bacteria and fungi (Fig. 8).

Rice. 8. Yeast, flour mushrooms, fermentation products - kvass and vinegar

In our country, Saccharomyces yeast is traditionally used, in America - bacteria from the genus Pseudomonas, in Mexico, bacteria "mobile sticks" are used, in Asia, mucor fungi are used. Our yeasts tend to ferment hexoses (six-carbon monosaccharides) such as glucose or fructose. The process of alcohol formation can be represented as follows: from one glucose molecule, two alcohol molecules, two carbon dioxide molecules are formed, and two ATP molecules are released.

C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2 + 2ATP

Compared to respiration, such a process is less energetically beneficial than aerobic processes, but allows you to maintain life in the absence of oxygen. At lactic acid fermentation one molecule of glucose forms two molecules of lactic acid, and two molecules of ATP are released, this can be described by the equation:

C 6 H 12 O 6 → 2C 3 H 6 O 3 + 2ATP

The process of formation of lactic acid is very close to the process of alcoholic fermentation, glucose, as in alcoholic fermentation, is broken down to pyruvic acid, then it passes not into alcohol, but into lactic acid. Lactic acid fermentation is widely used for the production of dairy products: cheese, cottage cheese, curdled milk, yoghurts (Fig. 9).

Rice. 9. Lactic acid bacteria and products of lactic acid fermentation

In the process of cheese formation, first lactic acid bacteria are involved, which produce lactic acid, then propionic acid bacteria convert lactic acid into propionic acid, due to this, cheeses have a rather specific sharp taste. Lactic acid bacteria are used in the preservation of fruits and vegetables, lactic acid is used in the confectionery industry and the manufacture of soft drinks.

Bibliography

1. Mamontov S.G., Zakharov V.B., Agafonova I.B., Sonin N.I. Biology. General patterns. - Bustard, 2009.

2. Ponomareva I.N., Kornilova O.A., Chernova N.M. Fundamentals of General Biology. Grade 9: A textbook for students in grade 9 educational institutions / Ed. prof. I.N. Ponomareva. - 2nd ed., revised. - M.: Ventana-Graf, 2005.

3. Pasechnik V.V., Kamensky A.A., Kriksunov E.A. Biology. Introduction to general biology and ecology: Textbook for grade 9, 3rd ed., stereotype. - M.: Bustard, 2002.

1. Website "Biology and Medicine" ()

3. Internet site "Medical Encyclopedia" ()

Homework

1. What is biological oxidation and its stages?

2. What is glycolysis?

3. What are the similarities and differences between alcoholic and lactic acid fermentation?

When you get acquainted with the fundamental works of mankind, you often find yourself thinking that with the development of science, there are more questions than answers. In the 1980s and 1990s, molecular biology and genetics expanded our understanding of cells and cellular interactions. A whole class of cellular factors that regulate intercellular interaction has been isolated. This is important for understanding the functioning of the multicellular human body and especially the cells of the immune system. But every year biologists discover more and more of these intercellular factors and it becomes more and more difficult to recreate a picture of a whole organism. Thus, there are more questions than there are answers.

The inexhaustibility of the human body and limited opportunities its studies lead to the conclusion about the need for immediate and subsequent research priorities. Such a priority today is the energy of the cells of a living human body. Insufficient knowledge about energy production and energy exchange of cells in the body becomes an obstacle to serious scientific research.

The cell is the basic structural unit of the body: all organs and tissues are made up of cells. It is difficult to count on the success of drugs or non-drug methods if they are developed without sufficient knowledge about cell energy and intercellular energy interaction. Enough examples can be given where widely used and recommended remedies are harmful to health.

The substantive approach is dominant in healthcare. Substance is substance. The logic of healing is extremely simple: provide the body with the necessary substances (water, food, vitamins, trace elements, and, if necessary, drugs) and remove metabolic products from the body (excrement, excess fats, salts, toxins, etc.). The expansion of medicines continues to triumph. New generations of people in many countries are becoming voluntary participants in a large-scale experiment. The drug industry demands new patients. However, there are fewer and fewer healthy people.

The creator of a popular drug guide was once asked about how many drugs he personally had to try. None, was the answer. Apparently, this intelligent man had a brilliant knowledge of cell biochemistry and was able to use this knowledge to good use in life.

Imagine a miniature particle of living matter, in the form of an ellipsoid, disk, ball, approximately 8-15 microns (µm) in diameter, which at the same time is the most complex self-regulating system. An ordinary living cell is called differentiated, as if emphasizing that the many elements that make up its composition are clearly separated relative to each other. The concept of "undifferentiated cell", as a rule, belongs to a modified, for example, a cancer cell. Differentiated cells differ not only in structure, internal metabolism, but also in specialization, for example, kidney, liver, and heart cells.

In general, a cell consists of three components: cell membrane, cytoplasm, nucleus. The composition of the cell membrane, as a rule, includes a three-, four-layer membrane and an outer shell. The two layers of the membrane are composed of lipids (fats), the bulk of which are unsaturated fats - phospholipids. The cell membrane has a very complex structure and diverse functions. The potential difference on both sides of the membrane can be several hundred millivolts. The outer surface of the membrane contains a negative electrical charge.

Typically, a cell has one nucleus. Although there are cells that have two or more nuclei. The function of the nucleus is to store and transmit hereditary information, for example, during cell division, as well as to control all physiological processes in the cell. The nucleus contains DNA molecules that carry the genetic code of the cell. The nucleus is enclosed in a two-layer membrane.

The cytoplasm makes up the bulk of the cell and is a cell fluid with organelles and inclusions located in it. Organelles are permanent components of the cytoplasm that perform specific important functions. Of these, we are most interested in the mitochondria, which are sometimes called the powerhouses of the cell. Each mitochondrion has two membrane systems: outer and inner. The outer membrane is smooth, lipids and proteins are equally represented in it. The inner membrane belongs to the most complex types of membrane systems in the human body. It contains many folds, called scallops (cristae), due to which the membrane surface increases significantly. This membrane can be represented as a set of mushroom-shaped outgrowths directed into the inner space of the mitochondria. There are 10 to 4-10 to 5 such outgrowths per mitochondria.

In addition, another 50-60 enzymes are present in the inner mitochondrial membrane, total number molecules different types reaches 80. All this is necessary for chemical oxidation and energy metabolism. Among the physical properties of this membrane, one should note the high electrical resistance, which is characteristic of the so-called conjugating membranes, which are capable of accumulating energy like a good capacitor. The potential difference on both sides of the inner mitochondrial membrane is about 200-250 mV.

One can imagine how complex a cell is if, for example, a hepatocyte liver cell contains about 2000 mitochondria. But there are many other organelles in the cell, hundreds of enzymes, hormones and other complex substances. Each organelle has its own set of substances; certain physical, chemical and biochemical processes are carried out in it. Substances in the cytoplasmic space are in the same dynamic state; they constantly exchange with organelles and with the external environment of the cell through its membrane.

I apologize to the Non-Specialist Reader for the technical details, but it is useful to know these ideas about the cell for every person who wants to be healthy. We must admire this miracle of nature and at the same time take into account the weaknesses of the cell when we treat. I have observed when ordinary analgin led to tissue edema in a young healthy person. It is amazing how, without thinking, with what ease others swallow pills!

The understanding of the complexity of cellular functioning will not be complete if we do not talk about the energy of cells. Energy in the cell is spent on performing various work: mechanical - the movement of fluid, the movement of organelles; chemical - synthesis of complex organic substances; electrical - the creation of a difference in electrical potentials on plasma membranes; osmotic - the transport of substances into the cell and back. Without setting ourselves the task of listing all the processes, we confine ourselves to the well-known statement: without sufficient energy supply, the full functioning of the cell cannot be achieved.

Where does the cell get the energy it needs? According to scientific theories, the chemical energy of nutrients (carbohydrates, fats, proteins) is converted into the energy of macroergic (containing a lot of energy) bonds of adenosine triphosphate (ATP). These processes are carried out in the mitochondria of cells mainly in the tricarboxylic acid cycle (Krebs cycle) and during oxidative phosphorylation. The energy stored in ATP is easily released when macroergic bonds are broken, as a result, energy consumption in the body is provided.

However, these ideas do not allow for an objective assessment of the quantitative and qualitative characteristics of energy supply and energy exchange in tissues, as well as the state of cell energy and intercellular interaction. Attention should be paid to the most important question (G. N. Petrakovich), which cannot be answered by the traditional theory: due to what factors is intercellular interaction carried out? After all, ATP is formed and consumed, releasing energy, inside the mitochondria.

Meanwhile, there are enough reasons to doubt the well-being of the energy supply of organs, tissues, cells. It can even be directly stated that a person is not very perfect in this respect. This is evidenced by the fatigue that many experience every day, and which begins to annoy a person from childhood.

The calculations show that if the energy in the human body were produced due to these processes (the Krebs cycle and oxidative phosphorylation), then at a low load, the energy deficit would be 30-50%, and at a high load - more than 90%. This is confirmed by the studies of American scientists, who came to the conclusion that the mitochondria are not functioning properly in terms of providing a person with energy.

Questions about the energy of cells and tissues would probably have remained on the side of the road for a long time, along which theoretical and practical medicine is slowly moving, if two events had not occurred. It's about about the New Hypothesis of Respiration and the discovery of Endogenous Respiration.

The ability to photosynthesis is the main feature of green plants. Plants, like all living organisms, must eat, breathe, remove waste, grow, multiply, respond to change environment . All this is provided by the work of the corresponding organs of the body. Usually, organs form organ systems that work together to ensure the performance of one or another function of a living organism. Thus, a living organism can be represented as a biosystem. Each organ in a living plant performs a specific job. Root absorbs water from the soil with minerals and strengthens the plant in the soil. The stem carries the leaves towards the light. Water moves along the stem, as well as mineral and organic substances. In the chloroplasts of the leaf, in the light, organic substances are formed from inorganic substances, which they feed on. cells all organs plants. Leaves evaporate water.

If the work of any one organ of the body is disturbed, then this can cause a disruption in the work of other organs and the whole organism. If, for example, water stops flowing through the root, then the whole plant may die. If the plant does not produce enough chlorophyll in the leaves, then it will not be able to synthesize a sufficient amount of organic substances for its vital activity.

Thus, the vital activity of the organism is ensured by the interconnected work of all organ systems. Vitality is all the processes that take place in the body.

Through nutrition, the body lives and grows. In the process of nutrition, the necessary substances are absorbed from the environment. They are then absorbed into the body. Plants absorb water and minerals from the soil. The above-ground green organs of plants absorb carbon dioxide from the air. Water and carbon dioxide are used by plants to synthesize organic substances, which are used by the plant to renew body cells, grow and develop.

During respiration, gas exchange takes place. Oxygen is absorbed from the environment, and carbon dioxide and water vapor are released from the body. Oxygen is essential for all living cells to produce energy.

In the process of metabolism, substances that are unnecessary for the body are formed, which are released into the environment.

When a plant reaches a certain size and the age required for its species, if it is in sufficiently favorable environmental conditions, then it begins to reproduce. As a result of reproduction, the number of individuals increases.

Unlike the vast majority of animals, plants grow throughout their lives.

The acquisition of new properties by organisms is called development.

Nutrition, respiration, metabolism, growth and development, as well as reproduction are influenced by the environmental conditions of the plant. If they are not favorable enough, then the plant may grow and develop poorly, its vital processes will be suppressed. Thus, the vital activity of plants depends on the environment.

Question 3_Cell membrane, its functions, composition, structure. Primary and secondary shell.

The cell of any organism is an integral living system. It consists of three inextricably linked parts: membrane, cytoplasm and nucleus. The cell shell directly interacts with the external environment and interacts with neighboring cells (in multicellular organisms). cell membrane. The cell membrane has a complex structure. It consists of an outer layer and a plasma membrane located under it. In plants, as well as in bacteria, blue-green algae and fungi, a dense membrane, or cell wall, is located on the surface of the cells. In most plants, it consists of fiber. The cell wall plays an extremely important role: it is an outer frame, a protective shell, provides turgor plant cells: water, salts, molecules of many organic substances pass through the cell wall.

Cell wall or wall - a rigid shell of the cell, located outside the cytoplasmic membrane and performing structural, protective and transport functions. Found in most bacteria, archaea, fungi and plants. Animals and many protozoa do not have a cell wall.

Cell wall functions:

1. The transport function provides selective regulation of the metabolism between the cell and the external environment, the entry of substances into the cell (due to the semipermeability of the membrane), as well as the regulation of the water balance of the cell

1.1. Transmembrane transport (i.e. across the membrane):
- Diffusion
- Passive transport = facilitated diffusion
- Active = selective transport (with the participation of ATP and enzymes).

1.2. Transport in membrane packaging:
- Exocytosis - release of substances from the cell
- Endocytosis (phago- and pinocytosis) - absorption of substances by the cell

2) Receptor function.
3) Support ("skeleton")- maintains the shape of the cell, gives strength. This is mainly a function of the cell wall.
4) Cell isolation(its living contents) from the environment.
5) protective function.
6) contact with neighboring cells. Association of cells into tissues.

The life cycle of a cell clearly demonstrates that the life of a cell breaks down into a period of interkinesis and mitosis. During interkinesis, all vital processes are actively carried out, except for division. Let's focus on them first. The main life process of a cell is metabolism.

On the basis of it, the formation of specific substances, growth, cell differentiation, as well as irritability, movement and self-reproduction of cells occur. In a multicellular organism, the cell is part of the whole. Therefore, the morphological features and nature of all vital processes of the cell are formed under the influence of the organism and the external environment. The body exerts its influence on cells mainly through the nervous system, as well as through the action of hormones of the endocrine glands.

Metabolism is a certain order of the transformation of substances, leading to the preservation and self-renewal of the cell. In the process of metabolism, on the one hand, substances enter the cell, which are processed and are part of the cell body, and on the other hand, substances that are decay products are removed from the cell, that is, the cell and the environment exchange substances. Chemically, metabolism is expressed in chemical reactions following one after another in a certain order. Strict order in the course of the transformation of substances is provided by protein substances - enzymes that play the role of catalysts. Enzymes are specific, that is, they act in a certain way only on certain substances. Under the influence of enzymes, a given substance of all possible transformations changes many times faster in only one direction. The new substances formed as a result of this process change further under the influence of other, equally specific enzymes, etc.

The driving principle of metabolism is the law of unity and struggle of opposites. Indeed, the metabolism is determined by two contradictory and at the same time common processes - assimilation and dissimilation. The substances received from the external environment are processed by the cell and turn into substances characteristic of this cell (assimilation). Thus, the composition of its cytoplasm, nucleus organelles is updated, trophic inclusions are formed, secrets, hormones are produced. The processes of assimilation are synthetic, they go on with the absorption of energy. The source of this energy is the processes of dissimilation. As a result, their previously formed organic substances are destroyed, and energy is released and products are formed, some of which are synthesized into new cell substances, while others are excreted from the cell (excretions). The energy released as a result of dissimilation is used in assimilation. Thus, assimilation and dissimilation are two, although different, but closely related aspects of metabolism.

The nature of metabolism is different not only in different animals, but even within the same organism in different organs and tissues. This specificity is manifested in the fact that the cells of each organ are able to assimilate only certain substances, build specific substances of their body from them, and release quite certain substances into the external environment. Along with the metabolism, energy is also exchanged, that is, the cell absorbs energy from the external environment in the form of heat, light and, in turn, releases radiant and other types of energy.

Metabolism is composed of a number of private processes. The main ones are:

1) penetration of substances into the cell;

2) their "processing" with the help of nutrition and respiration processes (aerobic and anaerobic);

3) the use of products of "processing" for various synthetic processes, an example of which may be the synthesis of proteins and the formation of a secret;

4) removal of waste products from the cell.

The plasmalemma plays an important role in the penetration of substances, as well as in the removal of substances from the cell. Both of these processes can be considered from the physicochemical and morphological point of view. Permeability is due to passive and active transfer. The first occurs due to the phenomena of diffusion and osmosis. However, substances can enter the cell contrary to these laws, which indicates the activity of the cell itself and its selectivity. It is known, for example, that sodium ions are pumped out of the cell, even if their concentration in the external environment is higher than in the cell, while potassium ions, on the contrary, are pumped into the cell. This phenomenon is described under the name "sodium-potassium pump" and is accompanied by the expenditure of energy. The ability to penetrate into the cell decreases as the number of hydroxyl groups (OH) in the molecule increases when an amino group (NH2) is introduced into the molecule. Organic acids penetrate more easily than inorganic acids. Ammonia penetrates especially quickly from alkalis. For permeability, the size of the molecule is also important. The permeability of a cell changes depending on the reaction, temperature, lighting, age and physiological state of the cell itself, and these reasons can increase the permeability of some substances and at the same time weaken the permeability of others.

The morphological picture of the permeability of substances from the environment is well traced and is carried out by phagocytosis (phagein - to eat) and pinocytosis (pynein - to drink). The mechanisms of both seem to be similar and differ only quantitatively. With the help of phagocytosis, larger particles are captured, and with the help of pinocytosis, smaller and less dense ones. First, the substances are adsorbed by the surface of the plasmalemma covered with mucopolysaccharides, then, together with it, they sink deep into, and a bubble is formed, which then separates from the plasmalemma (Fig. 19). The processing of infiltrated substances is carried out in the course of processes resembling digestion and culminating in the formation of relatively simple substances. Intracellular digestion begins with the fact that phagocytic or pinocytic vesicles fuse with primary lysosomes, which contain digestive enzymes, and a secondary lysosome, or digestive vacuole, is formed. In them, with the help of enzymes, the decomposition of substances into simpler ones occurs. This process involves not only lysosomes, but also other components of the cell. Thus, mitochondria provide the energy side of the process; channels of the cytoplasmic reticulum can be used to transport processed substances.

Intracellular digestion ends with the formation, on the one hand, of relatively simple products, from which they are synthesized again. complex substances(proteins, fats, carbohydrates), which are used to renew cellular structures or form secrets, and on the other hand, products to be removed from the cell as excretions. Examples of the use of processed products are protein synthesis and the formation of secrets.

Rice. 19. Scheme of pinocytosis:

L - formation of a pinocytic canal (1) and pinocytic vesicles (2). Arrows show the direction of plasmalemma invagination. B-Zh - successive stages of pinocytosis; 3 - adsorbed particles; 4 - particles captured by cell outgrowths; 5 - cell plasma membrane; D, E, B - successive stages of pinocytotic vacuole formation; G - food particles are released from the vacuole shell.

Protein synthesis is carried out on ribosomes and conditionally occurs in four stages.

The first step involves the activation of amino acids. Their activation occurs in the cytoplasmic matrix with the participation of enzymes (aminoacyl - RNA synthetases). About 20 enzymes are known, each of which is specific for only one amino acid. Activation of an amino acid is carried out when it is combined with an enzyme and ATP.

As a result of the interaction, pyrophosphate is cleaved from ATP, and the energy that is in the connection between the first and second phosphate groups is completely transferred to the amino acid. The amino acid activated in this way (aminoacyladenylate) becomes reactive and acquires the ability to combine with other amino acids.

The second stage is the binding of the activated amino acid to transfer RNA (t-RNA). In this case, one t-RNA molecule attaches only one molecule of the activated amino acid. The same enzyme is involved in these reactions as in the first stage, and the reaction ends with the formation of a complex of t-RNA and an activated amino acid. The tRNA molecule consists of a double helix closed at one end. The closed (head) end of this helix is ​​represented by three nucleotides (anticodon), which determine the attachment of this t-RNA to a specific site (codon) of a long messenger RNA (i-RNA) molecule. An activated amino acid is attached to the other end of the tRNA (Fig. 20). For example, if a tRNA molecule has a UAA triplet at the head end, then only the amino acid lysine can be attached to its opposite end. Thus, each amino acid has its own specific t-RNA. If the three terminal nucleotides in different tRNAs are the same, then its specificity is determined by the sequence of nucleotides in another part of the tRNA. The energy of the activated amino acid attached to the tRNA is used to form peptide bonds in the polypeptide molecule. The activated amino acid is transported by tRNA through the hyaloplasm to the ribosomes.

The third stage is the synthesis of polypeptide chains. The messenger RNA, leaving the nucleus, stretches through the small subunits of several ribosomes of a certain polyribosome, and the same synthesis processes are repeated in each of them. During the broach, the laying of that mole

Rice. 20. Scheme of polypeptide synthesis on ribosomes by means of i-RNA and t-RNA: /, 2 - ribosome; 3 - t-RNA carrying anticodons at one end: ACC, AUA. Ayv AGC, and at the other end, respectively, amino acids: tryptophan, roller, lysine, serine (5); 4-n-RNA, in which the codes are located: UGG (tryptophan)» URU (valine). UAA (lysine), UCG (serine); 5 - synthesized polypeptide.

A t-RNA coule, the triplet of which corresponds to the code word of the m-RNA. Then the code word shifts to the left, and with it the t-RNA attached to it. The amino acid brought by it is connected by a peptide bond with the previously brought amino acid of the synthesizing polypeptide; t-RNA is separated from i-RNA, translation (writing off) of i-RNA information occurs, that is, protein synthesis. Obviously, two t-RNA molecules are attached to ribosomes at the same time: one at the site carrying the synthesized polypeptide chain, and the other at the site to which the next amino acid is attached before it falls into its place in the chain.

The fourth stage is the removal of the polypeptide chain from the ribosome and the formation of a spatial configuration characteristic of the synthesized protein. Finally, the protein molecule that has completed its formation becomes independent. tRNA can be used for repeated synthesis, while mRNA is destroyed. The duration of the formation of a protein molecule depends on the number of amino acids in it. It is believed that the addition of one amino acid lasts 0.5 seconds.

The synthesis process requires the expenditure of energy, the source of which is ATP, which is formed mainly in the mitochondria and in a small amount in the nucleus, and with increased cell activity also in the hyaloplasm. In the nucleus in the hyaloplasm, ATP is not formed on the basis of oxidation process, as in mitochondria, but on the basis of glycolysis, that is, an anaerobic process. Thus, the synthesis is carried out due to the coordinated work of the nucleus, hyaloplasm, ribosomes, mitochondria and the granular cytoplasmic reticulum of the cell.

The secretory activity of the cell is also an example of the coordinated work of a number of cellular structures. Secretion is the production by a cell of special products that in a multicellular organism are most often used in the interests of the whole organism. So, saliva, bile, gastric juice and other secrets serve to process food into

Rice. 21. Scheme of one of the possible ways of secretion synthesis in the cell and its excretion:

1 - secret in the kernel; 2 - exit of the pro-secret from the kernel; 3 - accumulation of prosecret in the cistern of the cytoplasmic reticulum; 4 - separation of the tank with a secret from the cytoplasmic reticulum; 5 - lamellar complex; 6 - a drop of secret in the area of ​​the lamellar complex; 7- mature secretion granule; 8-9 - successive stages of secretion; 10 - secret outside the cell; 11 - cell plasmalemma.

Digestive organs. Secrets can be formed either only by proteins (a number of hormones, enzymes), or consist of glycoproteins (mucus), ligu-proteins, glycolipoproteins, less often they are represented by lipids (fat of milk and sebaceous glands) t or inorganic substances (hydrochloric acid of the fundic glands).

In secretory cells, two ends can usually be distinguished: basal (facing the pericapillary space) and apical (facing the space where the secretion is secreted). In the arrangement of the components of the secretory cell, zoning is observed, and from the basal to the apical ends (poles), they form the following row: granular cytoplasmic reticulum, nucleus, lamellar complex, secretion granules (Fig. 21). The plasmalemma of the basal and apical poles often carries microvilli, as a result of which the surface for the entry of substances from the blood and lymph through the basal pole and the removal of the finished secret through the apical pole increases.

With the formation of a secret of a protein nature (pancreas), the process begins with the synthesis of proteins specific for the secret. Therefore, the nucleus of secretory cells is rich in chromatin, has a well-defined nucleolus, thanks to which all three types of RNA are formed that enter the cytoplasm and participate in protein synthesis. Sometimes, apparently, secretion synthesis begins in the nucleus and ends in the cytoplasm, but most often in the hyaloplasm and continues in the granular cytoplasmic reticulum. The tubules of the cytoplasmic reticulum play an important role in the accumulation of primary products and their transport. In this regard, there are many ribosomes in the secretory cells and the cytoplasmic reticulum is well developed. Sections of the cytoplasmic reticulum with the primary secret are torn off and directed to the lamellar complex, passing into its vacuoles. Here the formation of secretory granules occurs.

In this case, a lipoprotein membrane is formed around the secret, and the secret itself matures (loses water), becoming more concentrated. The finished secret in the form of granules or vacuoles leaves the lamellar complex and is released through the apical pole of the cells. Mitochondria provide energy for this entire process. Secrets of a non-protein nature are apparently synthesized in the cytoplasmic reticulum and in some cases even in mitochondria (lipid secrets). The secretion process is regulated by the nervous system. In addition to constructive proteins and secrets, as a result of metabolism in the cell, substances of a trophic nature (glycogen, fat, pigments, etc.) can be formed, energy is produced (radiant, thermal and electrical biocurrents).

The metabolism is completed with the release into the external environment of a number of substances that, as a rule, are not used by the cell and are often

Even harmful to her. The removal of substances from the cell is carried out, as well as the intake, on the basis of passive physical and chemical processes (diffusion, osmosis), and by active transfer. The morphological picture of excretion often has a character opposite to that of phagocytosis. The excreted substances are surrounded by a membrane.

The resulting vesicle approaches the cell membrane, comes into contact with it, then breaks through, and the contents of the vesicle are outside the cell.

Metabolism, as we have already said, also determines other vital manifestations of the cell, such as cell growth and differentiation, irritability, and the ability of cells to reproduce themselves.

Cell growth is an external manifestation of metabolism, expressed in an increase in cell size. Growth is possible only if, in the process of metabolism, assimilation prevails over dissimilation, and each cell grows only up to a certain limit.

Cell differentiation is a series of qualitative changes that proceed differently in different cells and are determined by the environment and the activity of DNA sections called genes. As a result, different-quality cells of various tissues arise, and in the future, the cells undergo age-related changes that are little studied. However, it is known that cells become depleted of water, protein particles become larger, which entails a decrease in the total surface of the dispersed phase of the colloid and, as a consequence, a decrease in the intensity of metabolism. Therefore, the vital potential of the cell decreases, oxidative, reduction and other reactions slow down, the direction of some processes changes, due to which various substances accumulate in the cell.

The irritability of a cell is its reaction to changes in the external environment, due to which the temporary contradictions that arise between the cell and the environment are eliminated, and the living structure is adapted to the already changed external environment.

In the phenomenon of irritability, the following points can be distinguished:

1) the impact of an environmental agent (for example, mechanical, chemical, radiation, etc.)

2) the transition of the cell to an active, that is, excitable, state, which manifests itself in a change in biochemical and biophysical processes inside the cell, and the permeability of the cell and oxygen uptake can increase, the colloidal state of its cytoplasm changes, electric currents of action appear, etc.;

3) the response of the cell to the influence of the environment, and in different cells the response manifests itself in different ways. Thus, a local change in metabolism occurs in the connective tissue, a contraction occurs in the muscular tissue, a secret is secreted in the glandular tissues (saliva, bile, etc.), a nerve impulse occurs in the nerve cells. area, spreads throughout the tissue. In a nerve cell, excitation can spread not only to other elements of the same tissue (resulting in the formation of complex excitable systems - reflex arcs), but also to transfer to other tissues. Thanks to this, the regulatory role of the nervous system is carried out. The degree of complexity of these reactions depends on the height of the organization of the animal. Depending on the strength and nature of the irritating agent, the following three types of irritability are distinguished: normal, paranecrosis, and necrotic. If the strength of the stimulus does not go beyond the usual, inherent in the environment in which the cell or the organism as a whole lives, then the processes that arise in the cell eventually eliminate the contradiction with the external environment, and the cell returns to its normal state. In this case, no violation of the cell structure visible under a microscope occurs. If the strength of the stimulus is great or it affects the cell for a long time, then a change in intracellular processes leads to a significant disruption of the function, structure and chemistry of the cell. Inclusions appear in it, structures are formed in the form of threads, clumps, nets, etc. The reaction of the cytoplasm shifts towards acidity, a change in the structure and physico-chemical properties of the cell disrupts the normal functioning of the cell, puts it on the verge of life and death. This condition Nasonov and Aleksandrov called paranecrotic* It is reversible and can result in cell restoration, but it can also lead to cell death. Finally, if the agent acts with a very strong force, the processes inside the cell are so severely disturbed that recovery is impossible and the cell dies. After this, a number of structural changes occur, that is, the cell enters a state of necrosis or necrosis.

Traffic. The nature of the movement inherent in the cell is very diverse. First of all, there is a continuous movement of the cytoplasm in the cell, which is obviously associated with the implementation of metabolic processes. Further, various cytoplasmic formations can move very actively in the cell, for example, cilia in the ciliated epithelium, mitochondria; makes motion and the nucleus. In other cases, the movement is expressed in a change in the length or volume of the cell, followed by its return to its original position. Such movement is observed in muscle cells, in muscle fibers and in pigment cells. Movement in space is also widespread. It can be carried out with the help of pseudopods, like an amoeba. This is how leukocytes and some cells of connective and other tissues move. Sperm have a special form of movement in space. Their translational movement occurs due to a combination of serpentine bends of the tail and rotation of the spermatozoa around the longitudinal axis. In relatively simply organized beings and in some cells of highly organized multicellular animals, movement in space is caused and directed by various agents of the external environment and is called taxis.

There are: chemotaxis, thigmotaxis and rheotaxis. Chemotaxis - movement towards chemicals or from them. Such taxis is detected by blood leukocytes, which move like amoeboids towards the bacteria that have entered the body, releasing certain substances, Tigmotaxis - movement towards or away from the touched solid body. For example, a light touch of food particles on an amoeba causes it to envelop them and then swallow them. Strong mechanical irritation can cause movement in the direction opposite to the irritating beginning. Rheotaxis - movement against the flow of a fluid. The ability for rheotaxis is possessed by sperm moving in the uterus against the current of mucus towards the egg cell.

The ability to self-reproduce is the most important property of living matter, without which life is impossible. Every living system is characterized by a chain of irreversible changes that end in death. If these systems did not give rise to new systems capable of starting the cycle over again, life would cease.

The function of self-reproduction of the cell is carried out by division, which is a consequence of the development of the cell. In the process of its vital activity, due to the predominance of assimilation over dissimilation, the mass of cells increases, but the volume of the cell increases faster than its surface. Under these conditions, the intensity of metabolism decreases, deep physicochemical and morphological restructuring of the cell occurs, and assimilation processes are gradually inhibited, which has been convincingly proven with the help of labeled atoms. As a result, the growth of the cell first stops, and then its further existence becomes impossible, and division occurs.

The transition to division is a qualitative leap, or a consequence of quantitative changes in assimilation and dissimilation, a mechanism for resolving contradictions between these processes. After cell division, as it were, they become rejuvenated, their life potential increases, since already due to a decrease in size, the proportion of the active surface increases, the metabolism in general and its assimilation phase in particular are intensified.

Thus, the individual life of a cell is made up of a period of interphase, characterized by an increased metabolism, and a period of division.

Interphase is divided with some degree of conventionality:

1) for the presynthetic period (Gj), when the intensity of assimilation processes gradually increases, but DNA reduplication has not yet begun;

2) synthetic (S), characterized by the height of synthesis, during which DNA doubling occurs, and

3) postsynthetic (G2), when DNA synthesis processes stop.

There are the following main types of division:

1) indirect division (mitosis, or karyokinesis);

2) meiosis, or reduction division, and

3) amitosis, or direct division.

This video lesson is devoted to the topic "Providing cells with energy." In this lesson, we will look at the energy processes in the cell and learn how cells are provided with energy. You will also learn what cellular respiration is, what stages it consists of. Discuss each of these steps in detail.

BIOLOGY 9 CLASS

Topic: Cellular level

Lesson 13

Stepanova Anna Yurievna

Ph.D., Assoc. MGUIE

Moscow

Today we will talk about providing cells with energy. Energy is used for various chemical reactions that take place in the cell. Some organisms use the energy of sunlight for biochemical processes - these are plants, while others use the energy of chemical bonds in substances obtained in the process of nutrition - these are animal organisms. Substances from food are extracted by splitting or biological oxidation in the process of cellular respiration.

Cellular respiration is a biochemical process in a cell that occurs in the presence of enzymes, as a result of which water and carbon dioxide are released, energy is stored in the form of macroenergetic bonds of ATP molecules. If this process takes place in the presence of oxygen, then it is called "aerobic". If it occurs without oxygen, then it is called "anaerobic".

Biological oxidation includes three main stages:

1. Preparatory,

2. Anoxic (glycolysis),

3. Complete breakdown of organic matter (in the presence of oxygen).

Preparatory stage. Substances taken with food are broken down into monomers. This stage begins in the gastrointestinal tract or in the lysosomes of the cell. Polysaccharides are broken down into monosaccharides, proteins into amino acids, fats into glycerols and fatty acids. The energy released at this stage is dissipated in the form of heat. It should be noted that cells use carbohydrates for energy processes, and preferably monosaccharides. And the brain can use for its work only the monosaccharide - glucose.

Glucose is broken down by glycolysis into two three-carbon molecules of pyruvic acid. Their further fate depends on the presence of oxygen in the cell. If oxygen is present in the cell, then pyruvic acid enters the mitochondria for complete oxidation to carbon dioxide and water (aerobic respiration). If there is no oxygen, then in animal tissues pyruvic acid turns into lactic acid. This stage takes place in the cytoplasm of the cell. Glycolysis produces only two ATP molecules.

Oxygen is essential for the complete oxidation of glucose. At the third stage in the mitochondria, pyruvic acid is completely oxidized to carbon dioxide and water. As a result, another 36 ATP molecules are formed.

In total, 38 ATP molecules are formed from one glucose molecule in three stages, taking into account the two ATP obtained in the process of glycolysis.

Thus, we have considered the energy processes occurring in cells. The stages of biological oxidation were characterized. This concludes our lesson, all the best to you, goodbye!

The difference between breathing and burning. The respiration that occurs in the cell is often compared to the combustion process. Both processes occur in the presence of oxygen, release of energy and oxidation products. But, unlike combustion, respiration is an ordered process of biochemical reactions occurring in the presence of enzymes. During respiration, carbon dioxide arises as the end product of biological oxidation, and in the process of combustion, the formation of carbon dioxide occurs by direct combination of hydrogen with carbon. Also during respiration, a certain amount of ATP molecules is formed. That is, respiration and combustion are fundamentally different processes.

biomedical significance. For medicine, not only the metabolism of glucose is important, but also fructose and galactose. Especially important in medicine is the ability to form ATP in the absence of oxygen. This makes it possible to maintain intensive work of the skeletal muscle in conditions of insufficient efficiency of aerobic oxidation. Tissues with increased glycolytic activity are able to remain active during periods of oxygen starvation. In the heart muscle, the possibilities for glycolysis are limited. It is difficult to tolerate impaired blood supply, which can lead to ischemia. Several diseases are known due to the lack of enzymes that regulate glycolysis:

Hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capacity of the citric acid cycle), which contributes to an increased synthesis of lactic acid in organs and tissues. Elevated levels of lactic acid in the body can be a symptom of cancer.

Fermentation. Microbes are able to obtain energy in the process of fermentation. Fermentation has been known to people since time immemorial, for example, in the manufacture of wine. Even earlier it was known about lactic acid fermentation. People consumed dairy products without suspecting that these processes are associated with the activity of microorganisms. This was first proved by Louis Pasteur. Moreover, different microorganisms secrete different fermentation products. Now we will talk about alcoholic and lactic acid fermentation. As a result, ethyl alcohol, carbon dioxide are formed and energy is released. Brewers and winemakers have used certain types of yeast to stimulate fermentation, which turns sugars into alcohol. Fermentation is carried out mainly by yeast, but also by some bacteria and fungi. Saccharomyces yeast is traditionally used in our country. In America - bacteria of the genus Pseudomonas. And in Mexico, bacteria "moving rods" are used. Our yeasts tend to ferment hexoses (six-carbon monosaccharides) such as glucose or fructose. The process of alcohol formation can be represented as follows: from one glucose molecule, two alcohol molecules, two carbon dioxide molecules and two ATP molecules are formed. This method is less profitable than aerobic processes, but allows you to maintain life in the absence of oxygen. Now let's talk about lactic acid fermentation. One molecule of glucose forms two molecules of lactic acid and two molecules of ATP are released. Lactic acid fermentation is widely used for the production of dairy products: cheese, curdled milk, yogurt. Lactic acid is also used in the manufacture of soft drinks.