Use of atf as energy accumulators. What substance is the energy accumulator in the cell? Incoming knowledge control

ATP is a universal accumulator of biological energy. Its role for all living things was formulated by Academician of the USSR Academy of Medical Sciences V.A. This rule is also true for muscle cells and brain cells, where energy is accumulated additionally.

In the Chinese tradition, there is the concept of four bigrams or four fundamental energies: transcendental energy, energy in the beginning, it is never spoken about in books, because it is omnipresent and without it nothing would exist; ...

The ATP molecule contains three phosphoric acid residues. The bonds between them (in the presence of the ATPase enzyme) are easily broken. When one molecule of phosphoric acid is cleaved from one ATP molecule, 40 kJ of energy is released, therefore the bonds are called high-energy (carrying a large amount of energy).

The transformation of energy chemically bound to ATP into mechanical (necessary for the implementation of muscle contraction), electrical, light, sound energy of osmosis and its other types, providing the synthesis of plastic substances in the cell, growth, development, the possibility of transmission of hereditary traits, is carried out in the head of the elementary particles of respiratory ensembles due to the presence in them, i.e., in the same particles where its synthesis takes place. The energy released during the decay of ATP is directly converted into biological energy, which is necessary for the synthesis of proteins, nucleotides and other organic compounds, without which the growth and development of the organism is impossible. Energy reserves in ATP are used for movement, generation of electricity, light, for performing any function of the cell and its organelles.

ATP stores in the cell are limited. In muscle fibers, they can provide energy for only 30-40 contractions, and in the cells of other tissues, they are even less. To replenish ATP reserves, its synthesis must constantly occur - from (ADP) and inorganic phosphate, which is carried out with the participation of the enzyme ATP synthetase. Therefore, the ratio between the concentrations of ATP and ADP (the activity of ATP synthetase) is of great importance for controlling the process of ATP synthesis. With a lack of ADP, due to the presence of ATPase in the active center, the hydrolysis of ATP will be accelerated, which, as noted, is associated with the oxidative process and depends on the state of the hydrogen and oxygen carriers.

The more NAD and less of its reduced form, the more oxidized cytochrome c and ADP, the higher the rate of ATP synthesis. Along with other enzymes and coenzymes, they act as the main regulators of the work of respiratory ensembles at the first stage of hydrogen transfer from the substrate NAD - NAD, at the second stage - the carrier of electrons to oxygen, cytochromes, and at the final stage - the ratio between ATP and ADP.

Universal biological energy accumulator. The light energy of the Sun and the energy contained in the consumed food are stored in the ATP molecules. The stock of ATP in the cell is small. So, in the muscle, the reserve of ATP is enough for 20-30 contractions. With increased, but short-term work, the muscles work exclusively due to the breakdown of the ATP contained in them. After the end of work, the person breathes hard - during this period, the breakdown of carbohydrates and other substances occurs (energy is accumulated) and the supply of ATP in the cells is restored.

18. CELL

EUKARYOTES (eukaryotes) (from the Greek eu - well, completely and karyon - the nucleus), organisms (everything except bacteria, including cyanobacteria), which, unlike prokaryotes, have a formed cell nucleus, delimited from the cytoplasm by a nuclear membrane. The genetic material is contained in chromosomes. Eukaryotic cells have mitochondria, plastids, and other organelles. The sexual process is characteristic.

19. CELL, an elementary living system, the basis of the structure and life of all animals and plants. Cells exist as independent organisms (e.g., protozoa, bacteria) and as part of multicellular organisms, in which there are germ cells that serve for reproduction, and body cells (somatic), different in structure and function (e.g., nerve, bone, muscle , secretory). Cell sizes vary from 0.1-0.25 microns (some bacteria) to 155 mm (in-shell ostrich eggs).

In humans, in the body of a newborn approx. 2 1012. In each cell, 2 main parts are distinguished: the nucleus and the cytoplasm, in which the organelles and inclusions are located. Plant cells are usually covered with a hard shell. Cell science - cytology.

PROKARYOTES (from Latin pro - forward, instead of Greek karyon - nucleus), organisms that, unlike eukaryotes, do not have a formed cell nucleus. The genetic material in the form of a circular DNA chain lies freely in the nucleotide and does not form true chromosomes. There is no typical sexual process. Prokaryotes include bacteria, including cyanobacteria (blue-green algae). In the system of the organic world, prokaryotes constitute a super-kingdom.

20. PLASMATIC DIAPHRAGM(cell membrane, plasmalemma), a biological membrane that surrounds the protoplasm of plant and animal cells. Participates in the regulation of metabolism between the cell and its environment.

21. CELL INCLUSIONS- accumulations of reserve nutrients: proteins, fats and carbohydrates.

22. GOLGY APPART(Golgi complex) (named after K. Golgi), a cell organoid involved in the formation of its metabolic products (various secrets, collagen, glycogen, lipids, etc.), in the synthesis of glycoproteins.

23 LYSOSOMES(from lys. and Greek soma - body), cellular structures containing enzymes capable of cleaving (lyzing) proteins, nucleic acids, polysaccharides. Participate in the intracellular digestion of substances entering the cell by phagocytosis and pinocytosis.

24. MITOCHONDRIUM surrounded by an outer membrane and, therefore, are already a compartment, being separated from the surrounding cytoplasm; in addition, the inner space of mitochondria is also subdivided into two compartments by an inner membrane. The outer membrane of mitochondria is very similar in composition to the membranes of the endoplasmic reticulum; the inner membrane of mitochondria, which forms folds (cristae), is very rich in proteins - perhaps this is one of the most protein-rich membranes in the cell; among them proteins of the "respiratory chain", which are responsible for the transfer of electrons; carrier proteins for ADP, ATP, oxygen, CO in some organic molecules and ions. Glycolysis products entering mitochondria from the cytoplasm are oxidized in the inner mitochondrial compartment.

Proteins responsible for the transfer of electrons are located in the membrane so that during the transfer of electrons protons are ejected to one side of the membrane - they enter the space between the outer and inner membranes and accumulate there. This gives rise to an electrochemical potential (due to differences in concentration and charges). This difference is supported by an important property of the inner mitochondrial membrane - it is impermeable to protons. That is, under normal conditions, protons by themselves cannot pass through this membrane. But it contains special proteins, or rather protein complexes, consisting of many proteins and forming a channel for protons. Protons pass through this channel under the action of the driving force of the electrochemical gradient. The energy of this process is used by an enzyme contained in the same protein complexes and capable of attaching a phosphate group to adenosine diphosphate (ADP), which leads to the synthesis of ATP.

Thus, mitochondria plays the role of a "power station" in the cell. The principle of ATP formation in chloroplasts of plant cells is generally the same - the use of a proton gradient and the conversion of the energy of the electrochemical gradient into the energy of chemical bonds.

25. PLASTIDS(from the Greek plastos - sculpted), cytoplasmic organelles of plant cells. Often they contain pigments that cause the color of the plastids. Higher plants have green plastids - chloroplasts, colorless - leukoplasts, differently colored - chromoplasts; in most algae, plastids are called chromatophores.

26. CORE is the most important part of the cell. It is covered with a two-membrane membrane with pores, through which some substances penetrate into the nucleus, while others enter the cytoplasm. Chromosomes are the main structures of the nucleus, carriers of hereditary information about the characteristics of the organism. It is transmitted in the process of division of the mother cell to daughter cells, and with reproductive cells - to daughter organisms. The nucleus is the site of the synthesis of DNA, mRNA. rRNA.

28. PHASES OF MITOSIS(prophase, meta-phase, anaphase, telophase) - a series of successive changes in the cell: a) spiralization of chromosomes, dissolution of the nuclear membrane and nucleolus; b) the formation of the spindle of division, the location of chromosomes in the center of the cell, the attachment of filaments of the spindle of division to them; c) the divergence of chromatids to the opposite poles of the cell (they become chromosomes);

d) the formation of a cell septum, the division of the cytoplasm and its organelles, the formation of a nuclear envelope, the appearance of two cells from one with the same set of chromosomes (46 each in the mother and daughter cells of a person).

In the process of biochemical transformations of substances, chemical bonds are broken, accompanied by the release of energy. It is free, potential energy that cannot be directly used by living organisms. It needs to be transformed. There are two universal forms of energy that can be used in a cell to do different kinds of work:

1) Chemical energy, energy of high-energy bonds of chemical compounds. Chemical bonds are called macroergic if, when they are broken, a large amount of free energy is released. Compounds with such connections are high-energy. The ATP molecule has high-energy bonds and has certain properties that determine its important role in the energy metabolism of cells:

· Thermodynamic instability;

· High chemical stability. Provides efficient energy storage because it prevents energy dissipation in the form of heat;

· The small size of the ATP molecule makes it easy to diffuse into various parts of the cell, where it is necessary to supply energy from the outside to perform chemical, osmotic or chemical work;

· The change in free energy during the hydrolysis of ATP has an average value, which allows it to perform energy functions in the best way, that is, to transfer energy from high-energy to low-energy compounds.

ATP is a universal accumulator of energy for all living organisms; energy is stored in ATP molecules for a very short time (the life span of ATP-1/3 of a second). It is immediately consumed to provide energy for all processes occurring at the moment. The energy contained in the ATP molecule can be used in reactions occurring in the cytoplasm (in most biosyntheses, as well as in some membrane-dependent processes).

2) Electrochemical energy (energy of the transmembrane potential of hydrogen) Δ. When electrons are transferred along the redox chain, in localized membranes of a certain type, called energy-generating or conjugating, an uneven distribution of protons occurs in space on both sides of the membrane, i.e. a transversely oriented or transmembrane hydrogen gradient Δ, measured in volts, appears on the membrane. the resulting Δ leads to the synthesis of ATP molecules. Energy in the form of Δ can be used in various energy-dependent processes localized on the membrane:

· For the absorption of DNA in the process of genetic transformation;

· For the transfer of proteins across the membrane;

· To ensure the movement of many prokaryotes;

· To ensure active transport of molecules and ions across the cytoplasmic membrane.

Not all of the free energy obtained during the oxidation of substances is converted into a form accessible to the cell and accumulates in ATP. Part of the resulting free energy is dissipated in the form of heat, less often light and electrical energy. If the cell stores more energy than it can spend on all energy-consuming processes, it synthesizes a large amount of high-molecular storage substances (lipids). If necessary, these substances undergo biochemical transformations and supply the cell with energy.

ATP is the universal energy "currency" of the cell. One of the most amazing "inventions" of nature is the molecules of the so-called "high-energy" substances, in the chemical structure of which there are one or more bonds that serve as energy storage devices. Several similar molecules have been found in living nature, but only one of them is found in the human body - adenosine triphosphoric acid (ATP). It is a rather complex organic molecule to which 3 negatively charged residues of inorganic phosphoric acid PO are attached. It is these phosphorus residues that are associated with the organic part of the molecule by "high-energy" bonds, which are easily destroyed during a variety of intracellular reactions. However, the energy of these bonds is not dissipated in space in the form of heat, but is used for the movement or chemical interaction of other molecules. It is thanks to this property that ATP performs in the cell the function of a universal storage (accumulator) of energy, as well as a universal "currency". After all, almost every chemical transformation that takes place in a cell either absorbs or releases energy. According to the law of conservation of energy, the total amount of energy generated as a result of oxidative reactions and stored in the form of ATP is equal to the amount of energy that the cell can use for its synthetic processes and for performing any functions. As a "payment" for the ability to perform this or that action, the cell is forced to spend its supply of ATP. In this case, it should be especially emphasized: the ATP molecule is so large that it is not able to pass through the cell membrane. Therefore, ATP formed in one cell cannot be used by another cell. Each cell of the body is forced to synthesize ATP for its own needs in the quantities in which it is necessary to perform its functions.

Three sources of ATP resynthesis in the cells of the human body. Apparently, the distant ancestors of the cells of the human body existed many millions of years ago, surrounded by plant cells, which supplied them in excess with carbohydrates, and there was not enough oxygen or not at all. It is carbohydrates that are the most used component of nutrients for energy production in the body. And although most of the cells of the human body have acquired the ability to use proteins and fats as energy raw materials, some (for example, nerve, red blood, male reproductive cells) are capable of producing energy only through the oxidation of carbohydrates.

The processes of primary oxidation of carbohydrates - or rather, glucose, which is, in fact, the main oxidation substrate in cells - occur directly in the cytoplasm: it is there that enzyme complexes are located, due to which the glucose molecule is partially destroyed, and the released energy is stored in the form of ATP. This process is called glycolysis, it can take place in all cells of the human body without exception. As a result of this reaction, from one 6-carbon molecule of glucose, two 3-carbon molecules of pyruvic acid and two molecules of ATP are formed.

Glycolysis is a very fast but relatively ineffective process. The pyruvic acid formed in the cell after the completion of the glycolysis reactions is almost immediately converted into lactic acid and sometimes (for example, during heavy muscular work) in very large quantities is released into the blood, since it is a small molecule that can freely pass through the cell membrane. Such a massive release of acidic metabolic products into the blood disrupts homeostasis, and the body has to turn on special homeostatic mechanisms in order to cope with the consequences of muscle work or other active action.

The pyruvic acid formed as a result of glycolysis still contains a lot of potential chemical energy and can serve as a substrate for further oxidation, but this requires special enzymes and oxygen. This process takes place in many cells, which contain special organelles - mitochondria. The inner surface of mitochondrial membranes is composed of large lipid and protein molecules, including a large number of oxidative enzymes. The 3-carbon molecules formed in the cytoplasm, usually acetic acid (acetate), penetrate the mitochondria. There they are included in a continuously running cycle of reactions, during which carbon and hydrogen atoms are alternately split off from these organic molecules, which, when combined with oxygen, turn into carbon dioxide and water. In these reactions, a large amount of energy is released, which is stored in the form of ATP. Each molecule of pyruvic acid, having gone through a full cycle of oxidation in the mitochondria, allows the cell to receive 17 ATP molecules. Thus, the complete oxidation of 1 glucose molecule provides the cell with 2 + 17x2 = 36 ATP molecules. It is equally important that fatty acids and amino acids, that is, the constituents of fats and proteins, can also be included in the process of mitochondrial oxidation. Thanks to this ability, mitochondria make the cell relatively independent of what foods the body eats: in any case, the required amount of energy will be produced.

Some of the energy is stored in the cell in the form of creatine phosphate (CRP) molecules, smaller and more mobile than ATP. It is this small molecule that can quickly move from one end of the cell to the other - to where energy is most needed at the moment. KrF itself cannot give energy to the processes of synthesis, muscle contraction or the conduction of a nerve impulse: this requires ATP. But on the other hand, KrF is easily and practically without loss capable of giving all the energy contained in it to the adenazine diphosphate (ADP) molecule, which immediately turns into ATP and is ready for further biochemical transformations.

Thus, the energy expended in the course of cell functioning, i.e. ATP can be renewed due to three main processes: anaerobic (oxygen-free) glycolysis, aerobic (with the participation of oxygen) mitochondrial oxidation, and also due to the transfer of the phosphate group from KrF to ADP.

The creatine phosphate source is the most powerful, since the reaction of KrF with ADP proceeds very quickly. However, the stock of CRF in the cell is usually small - for example, muscles can work with maximum effort due to CRF for no more than 6-7 s. This is usually enough to trigger the second most powerful - glycolytic - energy source. In this case, the resource of nutrients is many times greater, but as work progresses, an increasing tension of homeostasis occurs due to the formation of lactic acid, and if such work is performed by large muscles, it cannot last more than 1.5-2 minutes. But during this time, mitochondria are almost completely activated, which are able to burn not only glucose, but also fatty acids, the supply of which in the body is almost inexhaustible. Therefore, the aerobic mitochondrial source can work for a very long time, however, its power is relatively low - 2-3 times less than the glycolytic source, and 5 times less than the power of creatine phosphate.

Features of the organization of energy production in various tissues of the body. Different tissues have different saturation of mitochondria. The least of them is in bones and white fat, most of all - in brown fat, liver and kidneys. There are quite a few mitochondria in nerve cells. Muscles do not have a high concentration of mitochondria, but due to the fact that skeletal muscles are the most massive tissue of the body (about 40% of the body weight of an adult), it is the needs of muscle cells that largely determine the intensity and direction of all energy metabolism processes. IA Arshavsky called it "the energy rule of skeletal muscles."

With age, two important components of energy metabolism change at once: the ratio of the masses of tissues with different metabolic activity changes, as well as the content of the most important oxidative enzymes in these tissues. As a result, energy metabolism undergoes rather complex changes, but in general its intensity decreases with age, and quite significantly.

Energy exchange

Energy exchange is the most integral function of the body. Any syntheses, the activity of any organ, any functional activity will inevitably affect energy metabolism, since according to the conservation law, which has no exceptions, any act associated with the transformation of matter is accompanied by the expenditure of energy.

Energy consumption organism consists of three unequal parts of basal metabolism, energy supply of functions, as well as energy consumption for growth, development and adaptive processes. The relationship between these parts is determined by the stage of individual development and specific conditions (Table 2).

Basal metabolism- this is the minimum level of energy production, which always exists, regardless of the functional activity of organs and systems, and is never equal to zero. Basal metabolism consists of three main types of energy expenditure: the minimum level of functions, futile cycles, and reparative processes.

The minimum requirement of the body for energy. The question of the minimum level of functions is quite obvious: even in conditions of complete rest (for example, restful sleep), when no activating factors act on the body, it is necessary to maintain a certain activity of the brain and endocrine glands, liver and gastrointestinal tract, heart and blood vessels , respiratory muscles and lung tissue, tonic and smooth muscles, etc.

Futile cycles. It is less known that millions of cyclic biochemical reactions continuously occur in every cell of the body, as a result of which nothing is produced, but a certain amount of energy is required to carry out them. These are the so-called futile cycles, processes that preserve the "fighting capacity" of cellular structures in the absence of a real functional task. Like a spinning top, futile cycles give stability to the cell and all its structures. The energy expenditure to maintain each of the futile cycles is small, but there are many of them, and as a result, this translates into a fairly noticeable share of basal energy expenditures.

Reparative processes. Numerous complexly organized molecules involved in metabolic processes sooner or later begin to be damaged, losing their functional properties or even acquiring toxic ones. Continuous "repair and restoration work" is required, removing damaged molecules from the cell and synthesizing new ones, identical to the old ones, in their place. Such reparative processes occur constantly in every cell, since the lifetime of any protein molecule usually does not exceed 1-2 weeks, and there are hundreds of millions of them in any cell. Environmental factors - unfavorable temperature, increased radiation background, exposure to toxic substances and much more - can significantly shorten the life of complex molecules and, as a result, increase the tension of reparative processes.

The minimum level of functioning of the tissues of a multicellular organism. The functioning of a cell is always a certain outside work... For a muscle cell, this is its contraction, for a nerve cell - the production and conduction of an electrical impulse, for a glandular cell - the production of secretions and the act of secretion, for an epithelial cell - pinocytosis or another form of interaction with the surrounding tissues and biological fluids. Naturally, any work cannot be carried out without the expenditure of energy for its implementation. But any work, in addition, leads to a change in the internal environment of the body, since the waste products of an active cell may be not indifferent to other cells and tissues. Therefore, the second echelon of energy consumption when performing a function is associated with the active maintenance of homeostasis, which sometimes consumes a very significant part of the energy. Meanwhile, not only does the composition of the internal environment change in the course of performing functional tasks, but also structures often change, and often in the direction of destruction. So, with the contraction of skeletal muscles (even of low intensity), muscle fiber breaks always occur, i.e. the integrity of the form is violated. The body has special mechanisms for maintaining the constancy of shape (homeomorphosis), which ensure the fastest restoration of damaged or altered structures, but this again consumes energy. And, finally, it is very important for a developing organism to preserve the main tendencies of its development, regardless of which functions have to be activated as a result of exposure to specific conditions. Maintaining the invariability of the direction and channels of development (homeoresis) is another form of energy consumption when activating functions.

For a developing organism, an important article of energy consumption is growth and development itself. However, for any, including a mature organism, the processes of adaptive rearrangements are no less energy-intensive in volume and are essentially very similar. Here, energy expenditures are aimed at activating the genome, destroying obsolete structures (catabolism) and synthesis (anabolism).

The costs of basal metabolism and the costs of growth and development decrease significantly with age, while the costs of performing functions become qualitatively different. Since it is methodologically extremely difficult to separate the basal energy expenditure and energy expenditure on the processes of growth and development, they are usually considered together under the name "BX".

Age-related dynamics of the basal metabolic rate. Since the time of M. Rubner (1861) it is well known that in mammals, as the body weight increases, the intensity of heat production per unit mass decreases; while the amount of exchange calculated per unit surface remains constant ("surface rule"). These facts still do not have a satisfactory theoretical explanation, and therefore empirical formulas are used to express the relationship between body size and metabolic rate. For mammals, including humans, the formula of M. Kleiber is most often used now:

M = 67.7 P 0 75 kcal / day,

where M is the heat production of the whole organism, and P is the body weight.

However, age-related changes in basal metabolism cannot always be described using this equation. During the first year of life, heat production does not decrease, as would be required by the Kleiber equation, but remains at the same level or even slightly increases. Only at the age of one year is approximately the metabolic rate achieved (55 kcal / kg · day), which is "supposed" according to the Kleiber equation for an organism weighing 10 kg. Only from the age of 3 years, the intensity of the basal metabolism begins to gradually decrease, and reaches the level of an adult - 25 kcal / kg · day - only by the period of puberty.

Energy cost of growth and development processes. Often, increased basal metabolic rate in children is associated with growth costs. However, accurate measurements and calculations carried out in recent years have shown that even the most intense growth processes in the first 3 months of life do not require more than 7-8% of the daily energy consumption, and after 12 months they do not exceed 1%. Moreover, the highest level of energy consumption of the child's body was noted at the age of 1 year, when the rate of its growth becomes 10 times lower than at the age of six months. Those stages of ontogenesis, when the growth rate decreases, and significant qualitative changes occur in organs and tissues, due to the processes of cell differentiation, turned out to be much more "energy-intensive". Special studies of biochemists have shown that in tissues that enter the stage of differentiation processes (for example, in the brain), the content of mitochondria sharply increases, and, consequently, oxidative metabolism and heat production increase. The biological meaning of this phenomenon is that in the process of cell differentiation, new structures, new proteins and other large molecules are formed, which the cell could not produce before. Like any new business, this requires special energy costs, while growth processes are an established "batch production" of protein and other macromolecules in the cell.

In the process of further individual development, a decrease in the intensity of the basal metabolism is observed. At the same time, it turned out that the contribution of various organs to the basal metabolic rate changes with age. For example, the brain (making a significant contribution to the basal metabolic rate) in newborns is 12% of the body weight, and in an adult - only 2%. Internal organs also grow unevenly, which, like the brain, have a very high level of energy metabolism even at rest - 300 kcal / kg day. At the same time, muscle tissue, the relative amount of which almost doubles during postnatal development, is characterized by a very low level of metabolism at rest - 18 kcal / kg day. In an adult, the brain accounts for about 24% of the basal metabolic rate, the liver - 20%, the heart - 10%, and skeletal muscle - 28%. In a one-year-old child, the brain accounts for 53% of the basal metabolism, the liver contributes about 18%, and skeletal muscles account for only 8%.

Rest exchange in school-age children. Basal metabolism can be measured only in the clinic: this requires special conditions. But rest exchange can be measured in every person: it is enough for him to be in a fasting state and to be in muscle rest for several tens of minutes. Quiescent exchange is slightly higher than basic exchange, but this difference is not fundamental. The dynamics of age-related changes in resting metabolism is not reduced to a simple decrease in metabolic rate. Periods characterized by a rapid decrease in metabolic rate are replaced by age intervals in which resting metabolism is stabilized.

At the same time, a close relationship is found between the nature of the change in metabolic intensity and the growth rate (see Fig. 8 on p. 57). The bars in the figure show the relative annual growth in body weight. It turns out that the greater the relative growth rate, the more significant the decrease in the intensity of rest metabolism during this period.

One more feature is visible in the presented figure - clear sex differences: girls in the studied age interval are about a year ahead of boys in terms of changes in growth rates and metabolic intensity. At the same time, a close relationship is found between the intensity of rest exchange and the growth rate of children during the half-height jump - from 4 to 7 years. In the same period, the change of milk teeth to permanent ones begins, which can also serve as one of the indicators of morphological and functional maturation.

In the process of further development, the decrease in the intensity of the basal metabolism continues, and now in close connection with the processes of puberty. In the early stages of puberty, the metabolic rate in adolescents is about 30% higher than in adults. A sharp decrease in the indicator begins at stage III, when the gonads are activated, and continues until the onset of puberty. As you know, the pubertal growth spurt also coincides with the achievement of stage III of puberty, i.e. and in this case, the regularity of the decrease in the metabolic rate remains during the periods of the most intensive growth.

Boys in their development during this period lag behind girls by about 1 year. In strict accordance with this fact, the intensity of metabolic processes in boys is always higher than in girls of the same calendar age. These differences are small (5-10%), but they are stable throughout the entire period of puberty.

Thermoregulation

Thermoregulation, i.e. maintaining a constant temperature of the core of the body, is determined by two main processes: heat production and heat transfer. Heat production (thermogenesis) depends, first of all, on the intensity of metabolic processes, while heat transfer is determined by thermal insulation and a whole complex of rather complexly organized physiological mechanisms, including vasomotor reactions, the activity of external respiration and sweating. In this regard, thermogenesis is referred to the mechanisms of chemical thermoregulation, and the methods of changing heat transfer - to the mechanisms of physical thermoregulation. With age, both those and other mechanisms change, as well as their importance in maintaining a stable body temperature.

Age-related development of thermoregulatory mechanisms. Purely physical laws lead to the fact that as the mass and absolute dimensions of the body increase, the contribution of chemical thermoregulation decreases. So, in newborns, the value of thermoregulatory heat production is approximately 0.5 kcal / kg h hail, and in an adult - 0.15 kcal / kg h hail.

With a decrease in ambient temperature, a newborn child can increase heat production to almost the same values ​​as an adult - up to 4 kcal / kg h. However, due to low thermal insulation (0.15 deg m 2 h / kcal), the range of chemical thermoregulation in a newborn child is very small - no more than 5 °. It should be taken into account that the critical temperature ( Th), at which thermogenesis is turned on, is +33 ° С for a full-term baby, and by the adult state it decreases to +27 ... + 23 ° С. However, in clothes, the thermal insulation of which is usually 2.5 KLO, or 0.45 deg-m2 , i.e. in conditions that do not require additional costs for maintaining body temperature.

Only during the dressing procedure, in order to prevent cooling, the child of the first months of life should turn on sufficiently powerful mechanisms of heat production. Moreover, children of this age have special, specific, mechanisms of thermogenesis that are absent in adults. In response to cooling, an adult begins to tremble, including the so-called "contractile" thermogenesis, that is, additional heat production in skeletal muscles (cold tremors). The structural features of the child's body make such a mechanism of heat production ineffective, therefore, in children, the so-called "non-contractile" thermogenesis is activated, localized not in skeletal muscles, but in completely other organs.

These are internal organs (first of all, the liver) and special brown adipose tissue, saturated with mitochondria (hence its brown color) and having high energy capabilities. The activation of heat production of brown fat in a healthy child can be seen by an increase in skin temperature in those parts of the body where brown fat is located more superficially - the interscapular region and the neck. By the change in temperature in these areas, one can judge the state of the child's thermoregulation mechanisms, the degree of his hardening. The so-called "hot back of the head" of a child in the first months of life is associated precisely with the activity of brown fat.

During the first year of life, the activity of chemical thermoregulation decreases. In a 5-6 month old child, the role of physical thermoregulation increases markedly. With age, the bulk of brown fat disappears, but even up to 3 years of age, the reaction of the largest part of brown fat, the interscapular, remains. There are reports that in adults working in the North, outdoors, brown adipose tissue continues to function actively. Under normal conditions, in a child over 3 years old, the activity of non-contractile thermogenesis is limited, and the dominant role in increasing heat production when chemical thermoregulation is activated begins to play a specific contractile activity of skeletal muscles - muscle tone and muscle tremors. If such a child finds himself in a normal room temperature (+20 ° C) in shorts and a T-shirt, heat production is activated in 80 cases out of 100.

Strengthening growth processes during the half-growth leap (5-6 years) leads to an increase in the length and surface area of ​​the limbs, which provides a regulated heat exchange between the body and the environment. This, in turn, leads to the fact that, starting from 5.5-6 years (especially clearly in girls), significant changes in the thermoregulatory function occur. The thermal insulation of the body increases, and the activity of chemical thermoregulation is significantly reduced. This method of regulating body temperature is more economical, and it is this method that becomes predominant in the course of further age development. This period of thermoregulation development is sensitive for hardening procedures.

With the onset of puberty, the next stage in the development of thermoregulation begins, which manifests itself in a disorder of the emerging functional system. In 11-12-year-old girls and 13-year-old boys, despite the continuing decrease in the intensity of rest exchange, the corresponding adjustment of vascular regulation does not occur. Only in adolescence, after the completion of puberty, the possibilities of thermoregulation reach a definitive level of development. Increasing the thermal insulation of the tissues of one's own body makes it possible to dispense with the inclusion of chemical thermoregulation (i.e., additional heat production) even when the temperature of the environment drops by 10-15 ° C. Such a reaction of the body is naturally more economical and efficient.

Nutrition

All substances necessary for the human body, which are used to produce energy and build their own body, come from the environment. As the child grows up, by the end of the first year of life, more and more switches to independent nutrition, and after 3 years, the child's nutrition is not much different from that of an adult.

Structural components of nutrients. Human food can be of plant and animal origin, but regardless of this, it consists of the same classes of organic compounds - proteins, fats and carbohydrates. Actually, these same classes of compounds mainly constitute the body of the person himself. At the same time, there are differences between animal and plant foods, and they are quite important.

Carbohydrates... The most abundant component of plant food is carbohydrates (most often in the form of starch), which form the basis of the energy supply of the human body. For an adult, you need to get carbohydrates, fats and proteins in a ratio of 4: 1: 1. Since metabolic processes in children are more intensive, and mainly due to the metabolic activity of the brain, which feeds almost exclusively on carbohydrates, children should receive more carbohydrate food - in a ratio of 5: 1: 1. In the first months of life, the child does not receive plant foods, but breast milk contains relatively a lot of carbohydrates: it is about the same fat as cow's milk, contains 2 times less protein, but 2 times more carbohydrates. The ratio of carbohydrates, fats and proteins in human milk is approximately 5: 2: 1. Artificial formula for feeding babies in the first months of life is prepared on the basis of approximately half-diluted cow's milk with the addition of fructose, glucose and other carbohydrates.

Fats. Vegetable food is rarely rich in fats, but the components contained in vegetable fats are essential for the human body. Unlike animal fats, vegetable fats contain many so-called polyunsaturated fatty acids. These are long-chain fatty acids, in the structure of which there are double chemical bonds. Such molecules are used by human cells to build cell membranes, in which they have a stabilizing role, protecting cells from invasion of aggressive molecules and free radicals. Due to this property, vegetable fats have anticancer, antioxidant and antiradical activity. In addition, a large amount of valuable vitamins of groups A and E are usually dissolved in vegetable fats. Another advantage of vegetable fats is the absence of cholesterol in them, which can be deposited in human blood vessels and cause their sclerotic changes. Animal fats, on the other hand, contain a significant amount of cholesterol, but practically do not contain vitamins and polyunsaturated fatty acids. However, animal fats are also essential for the human body, as they are an important component of energy supply, and in addition, they contain lipokinins, which help the body to absorb and process its own fat.

Proteins. Plant and animal proteins also differ significantly in their composition. Although all proteins are made up of amino acids, some of these essential building blocks can be synthesized by the cells of the human body, while others cannot. These latter are few, only 4-5 species, but they cannot be replaced by anything, therefore they are called essential amino acids. Plant food contains almost no essential amino acids - only legumes and soybeans contain a small amount of them. Meanwhile, these substances are widely represented in meat, fish and other animal products. The lack of some essential amino acids has a dramatic negative effect on the dynamics of growth processes and on the development of many functions, and most significantly on the development of the child's brain and intelligence. For this reason, children who suffer from long-term malnutrition at an early age often remain mentally disabled for life. That is why children should in no way be restricted in the use of animal food: at least milk and eggs, as well as fish. Apparently, this circumstance is connected with the fact that children under 7 years old, according to Christian traditions, should not observe fasting, that is, refuse animal food.

Macro and microelements. Foodstuffs contain almost all chemical elements known to science, with the possible exception of radioactive and heavy metals, as well as inert gases. Some elements, such as carbon, hydrogen, nitrogen, oxygen, phosphorus, calcium, potassium, sodium and some others, are included in all food products and enter the body in very large quantities (tens and hundreds of grams per day). Such substances are usually referred to as macronutrients. Others are found in food in microscopic amounts, which is why they are called micronutrients. These are iodine, fluorine, copper, cobalt, silver and many other elements. Iron is often referred to as trace elements, although its amount in the body is quite large, since iron plays a key role in the transfer of oxygen within the body. A deficiency in any of the micronutrients can cause serious illness. Lack of iodine, for example, leads to the development of severe thyroid disease (called goiter). Lack of iron leads to iron deficiency anemia - a form of anemia that negatively affects the child's performance, growth and development. In all such cases, nutritional correction is necessary, the inclusion of foods containing missing elements in the diet. So, iodine is found in large quantities in seaweed - kelp, in addition, iodized table salt is sold in stores. Iron is found in beef liver, apples and some other fruits, as well as in children's toffee "Hematogen" sold in pharmacies.

Vitamins, vitamin deficiency, metabolic diseases. Vitamins are organic molecules of medium size and complexity and are not normally produced by the cells of the human body. We have to get vitamins from food, since they are necessary for the work of many enzymes that regulate biochemical processes in the body. Vitamins are very unstable substances, so cooking over a fire almost completely destroys the vitamins it contains. Only raw foods contain vitamins in noticeable quantities, so vegetables and fruits are the main source of vitamins for us. Animals of prey, as well as the indigenous people of the North, who live almost exclusively on meat and fish, get enough vitamins from raw animal products. There are practically no vitamins in fried and boiled meat and fish.

Lack of vitamins manifests itself in various metabolic diseases, which are collectively called vitamin deficiency. About 50 vitamins have now been discovered, and each of them is responsible for its own "site" of metabolic processes, respectively, and diseases caused by vitamin deficiency, there are several dozen. Scurvy, beriberi, pellagra and other diseases of this kind are widely known.

Vitamins are divided into two large groups: fat-soluble and water-soluble. Water-soluble vitamins are found in large quantities in vegetables and fruits, and fat-soluble vitamins are more often found in seeds and nuts. Olive, sunflower, corn, and other vegetable oils are important sources of many fat-soluble vitamins. However, vitamin D (anti-rachitis) is found mainly in fish oil, which is obtained from the liver of cod and some other marine fish.

In the middle and northern latitudes, by spring, the amount of vitamins preserved from autumn in plant foods decreases sharply, and many people - residents of northern countries - experience vitamin deficiency. Salted and sauerkraut foods (cabbage, cucumbers and some others), which are high in many vitamins, help to overcome this condition. In addition, vitamins are produced by the intestinal microflora, therefore, with normal digestion, a person is supplied with many essential B vitamins in sufficient quantities. In children of the first year of life, the intestinal microflora has not yet been formed, therefore, they should receive a sufficient amount of mother's milk, as well as fruit and vegetable juices as sources of vitamins.

The daily requirement for energy, proteins, vitamins. The amount of food eaten per day directly depends on the rate of metabolic processes, since food must fully compensate for the energy spent on all functions (Fig. 13). Although the intensity of metabolic processes in children older than 1 year old decreases with age, an increase in their body weight leads to an increase in the total (gross) energy consumption. Accordingly, the need for essential nutrients also increases. The lookup tables below (Tables 3-6) show the approximate daily intake of nutrients, vitamins, and essential minerals by children. It should be emphasized that the tables give the mass of pure substances without taking into account the water included in any food, as well as organic substances not related to proteins, fats and carbohydrates (for example, cellulose, which makes up the bulk of vegetables).

The modern understanding of the process of oxidative phosphorylation dates back to the pioneering work of Belitser and Kalkar. Kalkar found that aerobic phosphorylation is associated with respiration. Belitser studied in detail the stoichiometric relationship between the conjugated binding of phosphate and oxygen uptake and showed that the ratio of the number of inorganic phosphate molecules to the number of absorbed oxygen atoms

when breathing is not less than two. He also pointed out that the transfer of electrons from the substrate to oxygen is a possible source of energy for the formation of two or more ATP molecules per one atom of absorbed oxygen.

The NAD H molecule serves as an electron donor, and the phosphorylation reaction has the form

Briefly, this reaction is written as

The synthesis of three ATP molecules in reaction (15.11) occurs due to the transfer of two electrons of the NAD H molecule along the electron transport chain to the oxygen molecule. In this case, the energy of each electron decreases by 1.14 eV.

In the aquatic environment, with the participation of special enzymes, hydrolysis of ATP molecules occurs

The structural formulas of the molecules involved in reactions (15.12) and (15.13) are shown in Fig. 31.

Under physiological conditions, the molecules involved in reactions (15.12) and (15.13) are in different stages of ionization (ATP,). Therefore, chemical symbols in these formulas should be understood as a conditional notation of reactions between molecules in different stages of ionization. In connection with this, an increase in the free energy AG in reaction (15.12) and its decrease in reaction (15.13) depends on the temperature, ion concentration and on the pH value of the medium. Under standard conditions eV kcal / mol). If we introduce the appropriate corrections taking into account the physiological pH values ​​and the concentration of ions inside the cells, as well as the usual values ​​of the concentrations of ATP and ADP molecules and inorganic phosphate in the cytoplasm of cells, then for the free energy of hydrolysis of ATP molecules we obtain a value of -0.54 eV (-12.5 kcal / mol). The free energy of hydrolysis of ATP molecules is not constant. It may not be the same even in different places of the same cell, if these places differ in concentration.

Since the appearance of Lipman's pioneering work (1941), it has been known that ATP molecules in the cell play the role of a universal short-term storage and carrier of chemical energy used in most vital processes.

The release of energy in the process of hydrolysis of the ATP molecule is accompanied by the transformation of molecules

In this case, the cleavage of the bond indicated by the symbol leads to the elimination of the phosphoric acid residue. At the suggestion of Lipman, such a bond became known as the "energy-rich phosphate bond" or "high-energy bond." This name is extremely unfortunate. It does not at all reflect the energetics of the processes occurring during hydrolysis. The release of free energy is caused not by the breaking of one bond (such a break always requires energy expenditure), but by the rearrangement of all molecules participating in the reactions, the formation of new bonds and the rearrangement of the solvation shells during the reaction.

When the NaCl molecule dissolves in water, hydrated ions are formed.The gain in energy during hydration overlaps the energy consumption when the bond in the NaCl molecule is broken. It would be strange to attribute this energy gain to the "high-ergic bond" in the NaCl molecule.

As is known, during the fission of heavy atomic nuclei, a large amount of energy is released, which is not associated with the breaking of any high-ergic bonds, but is due to the rearrangement of fission fragments and a decrease in the Kulop repulsion energy between nucleons in each fragment.

Fair criticism of the concept of "macroergic connections" has been expressed more than once. Nevertheless, this concept has been widely implemented in the scientific literature. Big

Table 8

Structural formulas of phosphorylated compounds: a - phosphoenollyruvate; b - 1,3-diphosphoglycerate; c - creatine phosphate; - glucose-I-phosphate; - glucose-6-phosphate.

there is no trouble in this if the expression "high-energy phosphate bond" is used conventionally, as a short description of the entire cycle of transformations that occur in an aqueous solution with the corresponding presence of other ions, pH, etc.

So, the concept of phosphate bond energy, used by biochemists, conventionally characterizes the difference between the free energy of the initial substances and the free energy of the products of hydrolysis reactions, in which phosphate groups are split off. This concept should not be confused with the concept of chemical bond energy between two groups of atoms in a free molecule. The latter characterizes the energy required to break the bond.

The cells contain a number of phosphorylated compounds, the hydrolysis of which in the cytoplasm is associated with the release of free energy. The values ​​of the standard free energies of hydrolysis of some of these compounds are given in table. 8. The structural formulas of these compounds are shown in Fig. 31 and 35.

Large negative values ​​of the standard free energies of hydrolysis are due to the hydration energy of negatively charged hydrolysis products and the rearrangement of their electronic shells. From table. 8 it follows that the value of the standard free energy of hydrolysis of the ATP molecule occupies an intermediate position between "high-energy" (phosphoenolpyru-nat) and "low-energy" (glucose-6-phosphate) compounds. This is one of the reasons that the ATP molecule is a convenient universal carrier of phosphate groups.

With the help of special enzymes, ATP and ADP molecules communicate between high- and low-energy

phosphate compounds. For example, the enzyme pyruvate kinase transfers phosphate from phosphoenolpyruvate to ADP. As a result of the reaction, pyruvate and an ATP molecule are formed. Further, using the enzyme hexokinase, the ATP molecule can transfer the phosphate group to D-glucose, turning it into glucose-6-phosphate. The total product of these two reactions will be reduced to the transformation

It is very important that reactions of this type can proceed only through an intermediate stage, in which ATP and ADP molecules are necessarily involved.