General and specific metabolic pathways. The main biochemical pathways of microbiological transformation of pollutants

Introduction to Metabolism (Biochemistry)

Metabolism or metabolism is a set of chemical reactions in the body that provide it with the substances and energy necessary for life. The metabolic process, accompanied by the formation of simpler compounds from complex ones, is denoted by the term catabolism. A process going in the opposite direction and leading, ultimately, to the formation of a complex product from relatively simpler ones - anabolism. Anabolic processes are accompanied by energy consumption, catabolic - release.

Anabolism and catabolism are not simple reversals of reactions. Anabolic pathways must differ from the pathways of catabolism at least one of the enzymatic reactions in order to be independently regulated, and by controlling the activity of these enzymes, the total rate of decomposition and synthesis of substances is regulated. The enzymes that determine the speed of the entire process as a whole are called key enzymes.

Moreover, the path followed by the catabolism of a particular molecule may be unsuitable for its synthesis for energy reasons. For example, the breakdown of glucose to pyruvate in the liver is a process consisting of 11 successive steps catalyzed by specific enzymes. It would seem that the synthesis of glucose from pyruvate should be a simple reversal of all these enzymatic stages of its breakdown. At first glance, this way seems to be both the most natural and the most economical. However, in reality, the biosynthesis of glucose (gluconeogenesis) in the liver proceeds differently. It includes only 8 of the 11 enzymatic stages involved in its decay, and the 3 missing stages are replaced in it by a completely different set of enzymatic reactions, characteristic only of this biosynthetic pathway. In addition, the reactions of catabolism and anabolism are often separated by membranes and occur in different cell compartments.

Table 8.1. Compartmentalization of some metabolic pathways in the hepatocyte

Compartment	Metabolic pathways
Cytosol	Glycolysis, many reactions of gluconeogenesis, activation of amino acids, synthesis of fatty acids
Plasma membrane	Volatile transport systems
	DNA replication, synthesis of various types of RNA
Ribosomes	Protein synthesis
Lysosomes	Isolation of hydrolytic enzymes
Golgi complex	Plasma membrane and secretory vesicle formation
Microsomes	Localization of catalase and amino acid oxidases
Endoplasmic reticulum	Lipid synthesis
Mitochondria	Tricarboxylic acid cycle, tissue respiration chain, fatty acid oxidation, oxidative phosphorylation

Metabolism has 4 functions:

1.supply the body with chemical energy obtained from the breakdown of energy-rich nutrients;

2. the transformation of nutrients into building blocks that are used in the cell for the biosynthesis of macromolecules;

3. assembly of macromolecular (biopolymers) and supramolecular structures of a living organism, plastic and energetic maintenance of its structure;

4. synthesis and destruction of those biomolecules that are necessary for the performance of specific functions of the cell and the body.

A metabolic pathway is a sequence of chemical transformations of a particular substance in the body. The intermediate products formed during the conversion are called metabolites, and the last compound of the metabolic pathway is the final product. An example of a metabolic pathway is glycolysis, the synthesis of cholesterol.

The metabolic cycle is a metabolic pathway, one of the end products of which is identical to one of the compounds involved in this process. The most important metabolic cycles in the human body are the tricarboxylic acid cycle (Krebs cycle) and the ornithine cycle of urea formation.

Almost all metabolic reactions are ultimately linked, since the product of one enzymatic reaction serves as a substrate for another, which in this process plays the role of the next stage. Thus, metabolism can be represented as an extremely complex network of enzymatic reactions. If the flow of nutrients in any one part of this network is reduced or disrupted, then in response, changes can occur in another part of the network, so that this first change is somehow balanced or compensated. Moreover, both catabolic and anabolic reactions are adjusted so that they proceed most economically, that is, with the least expenditure of energy and substances. For example, the oxidation of nutrients in the cell occurs at a rate just enough to meet its energy needs at the moment.

Specific and general pathways of catabolism

There are three stages in catabolism:

1. Polymers are converted into monomers (proteins - into amino acids, carbohydrates into monosaccharides, lipids - into glycerol and fatty acid). The chemical energy is then dissipated in the form of heat.

2. Monomers are converted into common products, overwhelmingly into acetyl-CoA. Chemical energy is partly dissipated in the form of heat, partly accumulated in the form of reduced coenzyme forms (NADH, FADH2), partly stored in the high-energy bonds of ATP (substrate phosphorylation).

The 1st and 2nd stages of catabolism refer to specific pathways that are unique to the metabolism of proteins, lipids and carbohydrates.

3. The final stage of catabolism is reduced to the oxidation of acetyl-CoA to CO 2 and H 2 O in the reactions of the tricarboxylic acid cycle (Krebs cycle) - a common pathway of catabolism. Oxidative reactions the general pathways of catabolism are associated with the chain of tissue respiration. In this case, energy (40–45%) is stored in the form of ATP (oxidative phosphorylation).

As a result of specific and general pathways of catabolism, biopolymers (proteins, carbohydrates, lipids) decompose to CO 2, H 2 O and NH 3, which are the main end products of catabolism.

Metabolites in normal and pathological conditions

In a living cell, hundreds of metabolites are formed every second. However, their concentrations are maintained at a certain level, which is a specific biochemical constant or reference value. In diseases, there is a change in the concentration of metabolites, which is the basis of biochemical laboratory diagnostics. Normal metabolites include glucose, urea, cholesterol, total serum protein, and a number of others. The exit of the concentration of these substances beyond the physiological norms (increase or decrease) indicates a violation of their metabolism in the body. Moreover, a number of substances in the body healthy person is found only in certain biological fluids, which is due to the specifics of their metabolism. For example, serum proteins normally do not pass through the renal filter and are therefore not found in urine. But with inflammation of the kidneys (glomerulonephritis), proteins (primarily albumin) penetrate the capsule of the glomerulus, appear in the urine - proteinuria and are interpreted as pathological components of urine.

Pathological metabolites are myeloma proteins (Bens-Jones proteins), paraproteins in Waldenstrom macroglobulinemia, accumulation of abnormal glycogen in glycogenosis, various fractions of complex lipids in sphingolipidoses, etc. They are found only in diseases and are not typical for a healthy organism.

Metabolic Study Levels

Metabolism study levels:

1. The whole organism.

2. Isolated organs (perfused).

3. Tissue sections.

4. Cell cultures.

5. Tissue homogenates.

6. Isolated cellular organelles.

7. Molecular level (purified enzymes, receptors, etc.).

Quite often, radioactive isotopes (3 H, 32 P, 14 C, 35 S, 18 O) are used to study metabolism, which are used to mark substances introduced into the body. Then you can trace the cellular localization of these substances, determine the half-life and their metabolic pathways.

Rice. 8.1. Scheme of specific and general pathways of catabolism

Chapter 9. Biological membranes

The cell is a biological system, the basis of which is made up of membrane structures that separate the cell from the external environment, form its compartments (compartments), and also ensure the intake and removal of metabolites, the perception and transmission of signals and are the structural organizers of metabolic pathways.

The coordinated functioning of membrane systems - receptors, enzymes, transport mechanisms helps maintain cell homeostasis and at the same time quickly respond to changes in the external environment.

Membranes are non-covalent supramolecular structures. Proteins and lipids in them are held together by many non-covalent interactions (cooperative in nature).

The main functions of membranes include:

1.the separation of the cell from the environment and the formation of intracellular compartments (compartments);

2. control and regulation of the transport of a huge variety of substances through membranes (selective permeability);

3. participation in the provision of intercellular interactions;

4. perception and transmission of a signal into the cell (reception);

5. localization of enzymes;

6. energy transforming function.

Membranes are asymmetric in structural and functional respects (carbohydrates are always localized outside and they are not present on the inner side of the membrane). These are dynamic structures: their constituent proteins and lipids can move in the plane of the membrane (lateral diffusion). However, there is also a transition of proteins and lipids from one side of the membrane to the other (transverse diffusion, flip-flop), which is extremely slow. The mobility and fluidity of membranes depend on its composition: the ratio of saturated and unsaturated fatty acids, as well as cholesterol. The membrane fluidity is the lower, the higher the saturation of fatty acids in phospholipids and the more content cholesterol. In addition, self-assembly is characteristic of the membranes.

General properties of cell membranes:

1. readily permeable to water and neutral lipophilic compounds;

2. less permeable to polar substances (sugars, amides);

3. Poorly permeable to small ions (Na +, Cl -, etc.);

4. high electrical resistance is characteristic;

5. asymmetry;

6. can spontaneously restore integrity;

7. liquidity.

Chemical composition of membranes.

Membranes are composed of lipid and protein molecules, the relative amount of which varies widely in different membranes. Carbohydrates are contained in the form of glycoproteins, glycolipids and constitute 0.5% -10% of membrane substances. According to the liquid-mosaic model of the membrane structure (Sanger and Nicholson, 1972), the membrane is based on a double lipid layer, in the formation of which phospholipids and glycolipids are involved. The lipid bilayer is formed by two rows of lipids, the hydrophobic radicals of which are hidden inward, and the hydrophilic groups are facing outward and in contact with the aqueous medium. Protein molecules seem to be dissolved in the lipid bilayer and relatively freely "float in the lipid sea in the form of icebergs on which glycocalyx trees grow."

Membrane lipids.

Membrane lipids are amphiphilic molecules, i.e. the molecule contains both hydrophilic groups (polar heads) and aliphatic radicals (hydrophobic tails), which spontaneously form a bilayer in which the lipid tails are facing each other. The thickness of one lipid layer is 2.5 nm, of which 1 nm is for the head and 1.5 nm for the tail. There are three main types of lipids present in membranes: phospholipids, glycolipids, and cholesterol. The average molar ratio of cholesterol / phospholipids is 0.3–0.4, but in the plasma membrane this ratio is much higher (0.8–0.9). The presence of cholesterol in the membranes reduces the mobility of fatty acids, reduces the lateral diffusion of lipids and proteins.

Phospholipids can be classified into glycerophospholipids and sphingophospholipids. The most common membrane glycerophospholipids are phosphatidylcholines and phosphatidylethanolamines. Each glycerophospholipid, for example phosphatidylcholine, is represented by several tens of phosphatidylcholines, differing from each other in the structure of fatty acid residues.

Glycerophospholipids account for 2–8% of all membrane phospholipids. The most common are phosphatidylinositols.

Specific phospholipids of the inner mitochondrial membrane - cardiolipins (diphosphatid glycerols), built on the basis of glycerol and two phosphatidic acid residues, account for about 22% of all phospholipids of mitochondrial membranes.

The myelin sheath of nerve cells contains significant amounts of sphingomyelins.

Membrane glycolipids are represented by cerebrosides and gangliosides, in which the hydrophobic part is represented by ceramide. Hydrophilic group - carbohydrate residue - attached by a glycosidic bond to the hydroxyl group of the first carbon atom of ceramide. Significant amounts of glycolipids are found in the membranes of brain cells, epithelium, and erythrocytes. Gangliosides of erythrocytes of different individuals differ in the structure of oligosaccharide chains and exhibit antigenic properties.

Cholesterol is present in all membranes of animal cells. Its molecule consists of a rigid hydrophobic core and a flexible hydrocarbon chain, the only hydroxyl group being the polar head.

Functions of membrane lipids.

Phospho- and glycolipids of membranes, in addition to participating in the formation of the lipid bilayer, perform a number of other functions. Membrane lipids form the environment for the functioning of membrane proteins, which assume a native conformation in it.

Some membrane lipids are precursors of secondary messengers in the transmission of hormonal signals. So phosphatidylinositol diphosphate under the action of phospholipase C is hydrolyzed to diacylglycerol and inositol triphosphate, which are secondary hormone mediators.

A number of lipids are involved in the fixation of anchored proteins. An example of an anchored protein is acetylcholinesterase, which binds to the postsynaptic membrane to phosphatylinositol.

Membrane proteins.

Membrane proteins are responsible for the functional activity of membranes and account for from 30 to 70%. Membrane proteins differ in their position in the membrane. They can penetrate deeply into the lipid bilayer or even permeate it - integral proteins, in various ways attach to the membrane - surface proteins, or covalently contact it - anchored proteins. Surface proteins are almost always glycosylated. Oligosaccharide residues protect the protein from proteolysis, are involved in ligand recognition and adhesion.

Proteins localized in the membrane perform structural and specific functions:

1.transport;

2. enzymatic;

3. receptor;

4. antigenic.

Membrane transport mechanisms

There are several ways of transporting substances through the membrane:

1. Simple diffusion Is the transfer of small neutral molecules along the concentration gradient without the expenditure of energy and carriers. Small non-polar molecules such as O 2, steroids, and thyroid hormones pass most easily by simple diffusion through the lipid membrane. Small polar uncharged molecules - CO 2, NH 3, H 2 O, ethanol and urea - also diffuse at a sufficient rate. Diffusion of glycerol is much slower, and glucose is practically unable to pass through the membrane on its own. For all charged molecules, regardless of size, the lipid membrane is impermeable.

2. Facilitated diffusion- transfer of a substance along a concentration gradient without energy consumption, but with a carrier. Typical for water-soluble substances. Facilitated diffusion is different from simple more speed transfer and saturation ability. There are two types of facilitated diffusion:

Transport through special channels formed in transmembrane proteins (for example, cation-selective channels);

Using proteins-translocases, which interact with a specific ligand, ensure its diffusion along the concentration gradient (ping-pong) (transfer of glucose into erythrocytes using the GLUT-1 transporter protein).

Kinetically, the transfer of substances by facilitated diffusion resembles an enzymatic reaction. For translocases, there is a saturating concentration of the ligand, at which all the binding sites of the protein with the ligand are occupied, and the proteins work at maximum speed. Therefore, the rate of transport of substances by facilitated diffusion depends not only on the concentration gradient of the transferred substance, but also on the number of carrier beks in the membrane.

Simple and easy diffusion belongs to passive transport, since it takes place without energy consumption.

3. Active transport- transport of a substance against a concentration gradient (uncharged particles) or an electrochemical gradient (for charged particles), which requires energy consumption, most often ATP. There are two types of it: primary active transport uses the energy of ATP or redox potential and is carried out with the help of transport ATP-ases. The most common in the plasma membrane of human cells are Na +, K + - ATP-ase, Ca 2+ -ATP-ase, H + -ATP-ase.

With secondary active transport, an ion gradient is used, created on the membrane due to the work of the system primarily active transport(absorption of glucose by intestinal cells and reabsorption of glucose and amino acids from primary urine by kidney cells, carried out by the movement of Na + ions along the concentration gradient).

Transfer of macromolecules across the membrane. Transport proteins provide the transport of small polar molecules across the cell membrane, but they cannot transport macromolecules, such as proteins, nucleic acids, polysaccharides, or individual particles.

The mechanisms by which cells can assimilate such substances or remove them from the cell are different from the mechanisms of transport of ions and polar compounds.

1. Endocytosis. This is the transfer of a substance from the environment to the cell along with a part of the plasma membrane. Through endocytosis (phagocytosis), cells can engulf large particles such as viruses, bacteria, or cell fragments. The absorption of liquid and substances dissolved in it by means of small bubbles is called pinocytosis.

2. Exocytosis... Macromolecules, such as blood plasma proteins, peptide hormones, digestive enzymes, are synthesized in cells and then secreted into the intercellular space or blood. But the membrane is impermeable to such macromolecules or complexes; their secretion occurs by exocytosis. The body has both regulated and unregulated pathways of exocytosis. Unregulated secretion is characterized by the continuous synthesis of secreted proteins. An example is the synthesis and secretion of collagen by fibroblasts to form the extracellular matrix.

For regulated secretion, storage of exported molecules in transport vesicles is characteristic. With the help of regulated secretion, the release of digestive enzymes occurs, as well as the secretion of hormones and neurotransmitters.

Chapter 10. Energy exchange. Biological oxidation

Living organisms from the point of view of thermodynamics are open systems. Energy exchange is possible between the system and the environment, which occurs in accordance with the laws of thermodynamics. Each organic compound entering the body has a certain amount of energy (E). Some of this energy can be used to do useful work. This energy is called free energy (G). The direction of the chemical reaction is determined by the DG value. If this value is negative, then the reaction proceeds spontaneously. Such reactions are called exergonic. If DG is positive, then the reaction will proceed only when free energy is supplied from the outside - these are endergonic reactions. V biological systems thermodynamically unfavorable endergonic reactions can proceed only due to the energy of exergonic reactions. Such reactions are called energetically coupled.

The most important function of many biological membranes is the transformation of one form of energy into another. Membranes with such functions are called energy converting membranes. Any membrane that performs an energy function is capable of converting the chemical energy of oxidizable substrates or ATP into electrical energy, namely, into a transmembrane electrical potential difference (DY) or into the energy of a difference in the concentrations of substances contained in solutions separated by a membrane, and vice versa. Among the energy-converting membranes with greatest value, can be called the inner membrane of mitochondria, the outer cytoplasmic membrane, membranes of lysosomes and the Golgi complex, sarcoplasmic reticulum. The outer membrane of mitochondria and the nuclear membrane cannot convert one form of energy into another.

The transformation of energy in a living cell is described by the following general scheme:

Energy resources → ΔμI → work

where ΔμI is the transmembrane difference in electrochemical potentials of ion I. Consequently, the processes of energy utilization and the performance of work due to it turn out to be coupled through the formation and use of ΔμI. Therefore, this ion can be called a conjugating ion. The main conjugating ion in the eukaryotic cell is H +, and, accordingly, ΔμH + is the main convertible form of energy storage. The second most important conjugating ion is Na + (ΔμNa +). While Ca 2+, K + and Cl - are not used to do any work.

Biological oxidation is the process of dehydrogenation of a substrate using intermediate hydrogen carriers and its final acceptor. If oxygen acts as the final acceptor, the process is called aerobic oxidation or tissue respiration, if the final acceptor is not oxygen - anaerobic oxidation. Anaerobic oxidation is of limited importance in the human body. The main function of biological oxidation is to provide the cell with energy in an accessible form.

Tissue respiration is the process of oxidation of hydrogen by oxygen to water by enzymes of the tissue respiration chain. It proceeds as follows:

A substance is oxidized if it donates electrons or simultaneously electrons and protons (hydrogen atoms), or adds oxygen. The ability of a molecule to donate electrons to another molecule is determined by the redox potential (redox potential). Any compound can donate electrons only to a substance with a higher redox potential. The oxidizing agent and the reducing agent always form a conjugate pair.

There are 2 types of oxidizable substrates:

1. Pyridine-dependent - alcohol or aldehyde - isocitrate, α-ketoglutarate, pyruvate, malate, glutamate, β-hydroxyacyl-CoA, β-hydroxybutyrate, - NAD-dependent dehydrogenases are involved in their dehydrogenation.

2. flavin-dependent - are derivatives of hydrocarbons - succinate, acyl-CoA, glycerol-3-phosphate, choline - during dehydrogenation they transfer hydrogen to FAD-dependent dehydrogenases.

The tissue respiration chain is a sequence of carriers of hydrogen protons (H +) and electrons from the oxidized substrate to oxygen, localized on the inner mitochondrial membrane.

Rice. 10.1. Circuit diagrams

CTD components:

1. NAD-dependent dehydrogenases dehydrogenate pyridine-dependent substrates and accept 2ē and one H +.

2. FAD (FMN) - dependent dehydrogenases accept 2 hydrogen atoms (2H + and 2ē). FMN-dependent dehydrogenase dehydrates only NADH, while FAD-dehydrogenases oxidize flavin-dependent substrates.

3. Fat-soluble carrier ubiquinone (coenzyme Q, CoQ) - freely moves across the mitochondrial membrane and accepts two hydrogen atoms and turns into CoQH 2 (reduced form - ubiquinol).

4. The system of cytochromes - carries only electrons. Cytochromes are iron-containing proteins, the prosthetic group of which resembles heme in structure. In contrast to heme, the iron atom in cytochrome can reversibly pass from the two - to the trivalent state (Fe 3+ + ē → Fe 2+). This ensures the participation of cytochrome in the transport of electrons. Cytochromes act in ascending order of their redox potential and are located in the respiratory chain as follows: b-c 1 -c-a-a 3. The latter two work in association as one enzyme, cytochrome oxidase aa 3. Cytochrome oxidase consists of 6 subunits (2 - cytochrome a and 4 - cytochrome a 3). In addition to iron, cytochrome a 3 contains copper atoms and it transfers electrons directly to oxygen. At the same time, the oxygen atom is charged negatively and acquires the ability to interact with protons to form metabolic water.

Iron-sulfur proteins (FeS) - contain non-heme iron and are involved in redox processes proceeding according to the one-electron mechanism and are associated with flavoproteins and cytochrome b.

Structural organization of the tissue respiration chain

The components of the respiratory chain in the inner membrane of mychochondria form complexes:

1. Complex I (NADH-CoQH 2 -reductase) - accepts electrons from mitochondrial NADH and transports them to CoQ. Protons are transported to the intermembrane space. FMN and iron-sulfur proteins are intermediate acceptors and carriers of protons and electrons. Complex I separates the flow of electrons and protons.

2. Complex II - succinate - CoQ - reductase - includes FAD-dependent dehydrogenases and iron-sulfur proteins. It transports electrons and protons from flavin-dependent substrates to ubiquinone, with the formation of the intermediate FADH 2.

Ubiquinone easily moves across the membrane and transfers electrons to the III complex.

3. Complex III - KoQH 2 - cytochrome c - reductase - contains cytochromes b and c 1, as well as iron-sulfur proteins. The functioning of KoQ with the III complex leads to the separation of the flow of protons and electrons: protons from the matrix are pumped into the intermembrane space of mitochondria, and electrons are transported further along the CTD.

4. Complex IV - cytochrome a - cytochrome oxidase - contains cytochrome oxidase and transports electrons to oxygen from the intermediate cytochrome c carrier, which is a mobile component of the chain.

There are 2 types of CTD:

1. Full chain - pyridine-dependent substrates enter into it and transfer hydrogen atoms to NAD-dependent dehydrogenases

2. Incomplete (shortened or reduced) CTD in which hydrogen atoms are transferred from FAD-dependent substrates, bypassing the first complex.

Oxidative phosphorylation of ATP

Oxidative phosphorylation is the process of ATP formation, coupled with the transport of electrons along the tissue respiration chain from the oxidized substrate to oxygen. Electrons always tend to move from electronegative systems to electropositive ones; therefore, their transport along the CTD is accompanied by a decrease in free energy. In the respiratory chain, at each stage, the decrease in free energy occurs stepwise. In this case, three regions can be distinguished in which the transfer of electrons is accompanied by a relatively large decrease in free energy. These stages are able to provide energy ATP synthesis, since the amount of released free energy is approximately equal to the energy required for the synthesis of ATP from ADP and phosphate.

A number of hypotheses have been put forward to explain the mechanisms of conjugation of respiration and phosphorylation.

Mechanochemical or conformational (Green Boyer's).

In the process of transfer of protons and electrons, the conformation of enzyme proteins changes. They pass into a new, energy-rich conformational state, and then, upon returning to the original conformation, release energy for the synthesis of ATP.

Chemical conjugation hypothesis (Lipman).

In the conjugation of respiration and phosphorylation, "conjugating" substances are involved. They accept protons and electrons and interact with H 3 PO 4. At the moment of donation of protons and electrons, the bond with phosphate becomes high-energy and the phosphate group is transferred to ADP with the formation of ATP by substrate phosphorylation. The hypothesis is logical, but the "conjugating" substances have not yet been identified.

Chemiosmotic hypothesis by Peter Mitchell (1961)

The main postulates of this theory:

1.the inner mitochondrial membrane is impermeable to H + and OH - ions;

2. due to the energy of electron transport through the I, III and IV complexes of the respiratory chain, protons are pumped out of the matrix;

3. the electrochemical potential arising on the membrane is an intermediate form of energy storage;

4.The return of protons to the mitochondrial matrix through the proton channel of ATP synthase is the energy supplier for the synthesis of ATP according to the scheme

ADP + H 3 PO 4 → ATP + H 2 O

Evidence for the chemiosmotic theory:

1. there is an H + gradient on the inner membrane and it can be measured;

2. the creation of the H + gradient in mitochondria is accompanied by the synthesis of ATP;

3. ionophores (uncouplers) that destroy the proton gradient inhibit the synthesis of ATP;

4. inhibitors that block the transport of protons along the proton channels of ATP synthase, inhibit the synthesis of ATP.

ATP synthase structure

ATP synthase is an integral protein of the inner mitochondrial membrane. It is located in close proximity to the respiratory chain and is designated as the V complex. ATP synthase consists of 2 subunits designated as F 0 and F 1. The hydrophobic complex F 0 is immersed in the inner mitochondrial membrane and consists of several protomers, which form a channel through which protons are transferred into the matrix. The F 1 subunit appears in the mitochondrial matrix and consists of 9 protomers. Moreover, three of them bind the subunits F 0 and F 1, forming a kind of stem and are sensitive to oligomycin.

The essence of the chemioosmotic theory: due to the energy of electron transfer along the CTD, protons move through the inner mitochondrial membrane into the intermembrane space, where an electrochemical potential (ΔμH +) is created, which leads to a conformational transformation of the active center of ATP synthase, as a result of which reverse transport of protons becomes possible through the proton channels of ATP synthase. When the protons return back, the electrochemical potential is transformed into the energy of the high-energy ATP bond. The formed ATP is transferred to the cytosol of the cell with the help of the translocase carrier protein, and ADP and FN enter the matrix instead.

Phosphorylation coefficient (P / O) is the number of inorganic phosphate atoms included in the ATP molecule, per one atom of absorbed oxygen used.

Phosphorylation points are areas in the respiratory chain where the energy of electron transport is used to generate a proton gradient, and then, during phosphorylation, is stored in the form of ATP:

1. 1 point - between pyridine-dependent and flavin-dependent dehydrogenases; 2 point - between cytochromes b and c 1; 3 point - between cytochromes a and a 3.

2. Consequently, during the oxidation of NAD-dependent substrates, the P / O ratio is equal to 3, since electrons from NADH are transported with the participation of all CTD complexes. Oxidation of FAD-dependent substrates bypasses the first complex of the respiratory chain and P / O is equal to 2.

Energy metabolism disorders

All living cells constantly need ATP to carry out various activities. Violation of any stage of metabolism, leading to the cessation of ATP synthesis, is fatal to the cell. Tissues with high energy requirements (central nervous system, myocardium, kidneys, skeletal muscles and liver) are the most vulnerable. Conditions in which the synthesis of ATP is reduced are combined with the term "hypoenergetic". The reasons for these conditions can be divided into two groups:

Alimentary - starvation and hypovitaminosis B2 and PP - there is a disruption in the supply of oxidizable substrates to CTD or the synthesis of coenzymes.

Hypoxic - occur when the delivery or utilization of oxygen in the cell is impaired.

Regulation of CTD.

It is carried out using respiratory control.

Respiratory control is the regulation of the rate of electron transfer along the respiratory chain by the ATP / ADP ratio. The smaller this ratio, the more intense respiration is and the more actively ATP is synthesized. If ATP is not used, and its concentration in the cell increases, then the flow of electrons to oxygen stops. Accumulation of ADP increases substrate oxidation and oxygen uptake. The respiratory control mechanism is characterized by high accuracy and is important, since as a result of its action, the rate of ATP synthesis corresponds to the cell's energy requirements. ATP reserves in the cell do not exist. The relative concentrations of ATP / ADP in tissues vary within narrow limits, while the energy consumption of the cell can change tens of times.

American biochemist D. Chance proposed to consider 5 states of mitochondria, in which the rate of their respiration is limited by certain factors:

1. Lack of SH 2 and ADP - breathing rate is very low.

2. Lack of SH 2 in the presence of ADP - the speed is limited.

3. There is SH 2 and ADP - breathing is very active (limited only by the rate of transport of ions through the membrane).

4. Lack of ADP in the presence of SH 2 - breathing is inhibited (state of respiratory control).

5. Lack of oxygen, in the presence of SH 2 and ADP - the state of anaerobiosis.

Mitochondria in a resting cell are in state 4, in which the rate of respiration is determined by the amount of ADP. During intensive work, they can be in state 3 (the possibilities of the respiratory chain are being exhausted) or 5 (lack of oxygen) - hypoxia.

CTD inhibitors are drugs that block the transfer of electrons along the CTD. These include: barbiturates (amytal), which block the transport of electrons through the I complex of the respiratory chain, the antibiotic antimycin blocks the oxidation of cytochrome b; carbon monoxide and cyanides inhibit cytochrome oxidase and block the transport of electrons to oxygen.

Inhibitors of oxidative phosphorylation (oligomycin) are substances that block the transport of H + along the proton channel of ATP synthase.

Uncouplers of oxidative phosphorylation (ionophores) are substances that suppress oxidative phosphorylation without affecting the process of electron transfer along the CTD. The mechanism of action of uncouplers is that they are fat-soluble (lipophilic) substances and have the ability to bind protons and transfer them through the inner mitochondrial membrane into the matrix, bypassing the proton channel of ATP synthase. The energy released in this case is dissipated in the form of heat.

Artificial uncouplers - dinitrophenol, vitamin K derivatives (dicumarol), some antibiotics (valinomycin).

Natural uncouplers are lipid peroxidation products, long-chain fatty acids, high doses of iodine-containing thyroid hormones, thermogenin proteins.

The thermoregulatory function of tissue respiration is based on the separation of respiration and phosphorylation. Mitochondria of brown adipose tissue produce more heat, since the protein thermogenin present in them uncouples oxidation and phosphorylation. It is essential in maintaining the body temperature of newborns.

In contrast to the diversity of the macrocosm (the world of large creatures visible to the naked eye), the world of microbes is characterized by relative uniformity. Currently existing more than 3000 different types of bacteria, but their appearance is divided into 3 main forms:

Spherical or elliptical (cocci) in size from 1 to 2 microns (Fig. 1.3). Cocci belong to the simplest form of bacteria; they can connect with each other, forming diplococci (two each), tetra-cocci (four each) and streptococci (chains); - rod-shaped or cylindrical in size from 1 to 5 micro (Fig. 1.4). They are also able to connect with each other in pairs and in a chain and give a wide variety of forms of bacteria (diplobacterium, diplobacillus, streptobacillus, streptobacterium); - Crimped or spirillae in sizes from 1 to 30 microns.

Microorganisms-destructors... The leading role in the transformation and mineralization of organic xenobiotics belongs to chemoorganotrophic (heterotrophic) microorganisms, especially bacteria that synthesize various enzyme systems.

Of the bacteria that break down organic xenobiotics, in terms of frequency of occurrence, the number of species (about 30) and the spectrum of degradable compounds, pseudomonads occupy the first place.

The biodegradable activity of a community of microorganisms depends on its composition, growth rate and exchange of nutrients and genetic material between species. The accumulated metabolites can be toxic to one component of the community and can be absorbed by other microorganisms, which together accelerates the decomposition process (detoxification phenomenon).

Taking into account the methods of obtaining biological objects - destructors of xenobiotics, two variants of biological purification and bioremediation are possible. The first option is for areas with old pollution, where wild, aboriginal microflora that can transform them almost always lives. Such contamination can be removed in situ(on site) without the introduction of biological products. In this case, biodegradation is limited by environmental factors and the properties of pollution, such as the oxygen content in the environment, the solubility of the pollutant, etc. The second option is to preliminarily obtain a biologically active strain, accumulate viable cells, which are introduced in the form of a biological product into the contaminated environment. This option is advisable to apply in the northern regions and when processing places with non-old pollution;

The ability of microorganisms to destroy a xenobiotic or other pollutant depends on the presence in cells of genes that determine the synthesis of enzymes involved in the degradation of the compound. Construction of recombinant strains - destructors of xenobiotics consists in combining several genes or their blocks responsible for the primary metabolism of compounds. The advantage of such a combination is that genetically modified microorganisms (GMMOs) can synthesize various enzyme systems, which makes it possible to efficiently and quickly destroy a wide range of chemical contaminants.

Biological wastewater treatment. Schematic diagrams of treatment facilities. Basic principles of work, methods and construction of aerobic and anaerobic biological wastewater treatment and industrial waste processing.

Classification of biological cleaning methods. Biological methods purification is used to purify household and industrial wastewater (Figure 2.1) from many dissolved organic and some inorganic substances(hydrogen sulfide, sulfides, ammonia, nitrates, etc.). The cleaning process is based on the ability of microorganisms to use these substances for nutrition. Contacting organic substances, microorganisms partially destroy them, converting them into water, carbon dioxide, nitrite, sulfations, etc. Organic substances for microorganisms are a source of carbon. The destruction of organic matter by microorganisms is called biochemical oxidation.

Anaerobic microbiological processes are carried out during the mineralization of both dissolved organic matter and the solid phase of wastewater. Anaerobic processes proceed at a slower pace, without oxygen, and are mainly used to ferment sediments. The aerobic cleaning method is based on the use of aerobic groups of microorganisms, for the life of which a constant flow of oxygen and a temperature of 20-40 ° C are required.

The availability of any substance to biological oxidation can be estimated by the value of the biochemical index, which is understood as the ratio of the values ​​of the total BOD (BOD complete) and COD. The biochemical index is a parameter necessary for the calculation and operation of industrial biological facilities for wastewater treatment. When the value of the biochemical index is equal to or more than 0.5, the substances are susceptible to biochemical oxidation. The value of the biochemical indicator varies widely for different groups of wastewater. Industrial waste water has a low rate (0.05 - 0.3), domestic waste water - over 0.5.

Biological wastewater treatment facilities. The main structures for biochemical treatment are aerotanks and secondary sedimentation tanks.

An aeration tank is an apparatus with constantly flowing waste water, in the entire thickness of which aerobic microorganisms develop, consuming the substrate, i.e. "pollution" of this wastewater. Biological wastewater treatment in aerotanks occurs as a result of the vital activity of activated sludge microorganisms. Waste water is continuously mixed and aerated until it is saturated with oxygen in the air. Activated sludge is a suspension of microorganisms capable of flocculation.

There is also a classification of aeration tanks according to the magnitude of the "load" on activated sludge: high-load (aeration tanks for incomplete cleaning), conventional and low-load (extended aeration aeration tanks). The aeration system is of great importance in the construction of aeration tanks. Aeration systems are designed to supply and distribute oxygen or air in the aeration tank, as well as to maintain the activated sludge in suspension.

Mixing aeration tanks(aeration tanks of complete mixing, Fig. 2, handout material) are characterized by a uniform supply of source water and activated sludge along the length of the structure and a uniform discharge of the sludge mixture. Complete mixing of wastewater with a sludge mixture in them ensures equalization of sludge concentrations and rates of the biochemical oxidation process, therefore, mixing aeration tanks are more suitable for purification of concentrated industrial wastewater (BOD total up to 1000 mg / l) with sharp fluctuations in their consumption, composition and amount of contamination ...

Aeration tanks-displacers... Unlike other types of aeration tanks (mixing aeration tanks and intermediate type aeration tanks), propellant aeration tanks (Fig. 2, handout) are structures in which the treated wastewater gradually moves from the inlet to the outlet. At the same time, there is practically no active mixing of the incoming wastewater with the previously received one. The processes taking place in these structures are characterized by a variable reaction rate, since the concentration of organic pollutants decreases as the water flows. Aeration tanks-displacers are very sensitive to changes in the concentration of organic substances in the incoming water, especially to the salvo of toxic substances with wastewater, therefore, such structures are recommended to be used for the treatment of urban and industrial wastewater similar in composition to domestic wastewater.

Dispersed inlet aeration tanks(Fig. 2, handout) waste water is intermediate between mixers and displacers; they are used for the purification of mixtures of industrial and municipal wastewater.

Aeration tanks can be combined with free-standing secondary sedimentation tanks or combined into a block when rectangular shape both structures in plan. The most compact are the combined structures - aeration tanks-sedimentation tanks. Abroad, this type of structure with a round shape with mechanical aerators was called an air accelerator. Combining an aeration tank with a sludge tank allows to increase the recirculation of the sludge mixture without the use of special pumping stations, improve the oxygen regime in the sump and increase the sludge dose to 3-5 g / l, respectively, increasing the oxidizing capacity of the structure.

Variety settling aeration tank- the air accelerator is a round structure. Clarified wastewater enters the lower part of the aeration zone, where air is supplied pneumatically or pneumatically mechanically, which ensures the process of biochemical oxidation, and also creates a circulating movement of liquid in this zone and suction of the sludge mixture from the circulation zone of the settler. From the aeration zone, the sludge mixture through flooded adjustable overflow windows enters the air separator and then into the circulation zone of the settler. A significant part of the sludge mixture through the slot returns to the aeration zone, and the discharged purified wastewater through the layer of suspended sludge enters the settling zone.

Secondary sedimentation tanks are part of biological treatment facilities are located in the technological scheme immediately after the biooxidants and serve to separate activated sludge from biologically treated water coming out of aeration tanks, or to retain the biological film coming with water from biofilters. The efficiency of the secondary sedimentation tanks determines the final effect of water purification from suspended solids. For technological schemes of biological wastewater treatment in aeration tanks, secondary sedimentation tanks to some extent also determine the volume of aeration facilities, which depends on the concentration of return sludge and the degree of its recirculation, the ability of the settling tanks to effectively separate highly concentrated sludge mixtures.

The sludge mixture coming from the aeration tanks to the secondary sedimentation tanks is a heterogeneous (multiphase) system in which biologically purified waste water serves as a dispersion medium, and the main component of the dispersed phase is activated sludge pops, formed in the form of a complex three-level cellular structure surrounded by exocellular biopolymer material. composition.

Anaerobic treatment is used to remove pollutants from wastewater, as the first stage of wastewater treatment with a high concentration of organic pollutants (BOD n> 4-5 g / l), as well as for processing activated sludge, other sludge and solid waste. Many solid waste contains cellulose, which is more readily degradable anaerobically to biogas than aerobic oxidation.

In the course of methane generation (methanogenesis) - an anaerobic process with the formation of methane - organic pollution is converted into biogas, containing mainly CH 4 and CO2. It can be used as fuel. The amount of emitted biogas is sufficient not only to compensate for energy costs for anaerobic decomposition, but also for use by third-party consumers - in boilers or heaters for generating steam and hot water, in stationary gas generators for generating electricity with heat recovery, in technological processes of thermal drying and incineration of sludge, and dr.

Biocenoses and bio chemical processes with anaerobic cleaning. Formation of cenoses... Anaerobic biocenoses in wastewater treatment can be floccules, biofilms, and sludge granules. They develop in ecosystems dominated by anoxygenic and anaerobic conditions, in which the processes of fermentation, anoxygenic oxidation (anaerobic respiration) and methane formation take place.

Anoxygenic oxidation of organic substrates includes denitrification and sulfate reduction processes that occur in the presence of NO 3, - NO 2 -, S0 4 2 - ions and, as a rule, in the absence of oxygen. These processes are used to remove nitrogen and sulfur compounds from wastewater.

The main process that takes place under anaerobic conditions and is used to decompose and remove organic pollution and waste is methanogenesis. In the process of methane generation (often called "methane fermentation"), organic substrates and impurities are decomposed, and effluents are disinfected and detoxified. In nature, this process takes place in various environments with anaerobic conditions, in the rumen of ruminants, in termite mounds.

Methane generation is a complex, multistage process in which the initial organic matter successively transform into simpler ones with the transition of a significant part of carbon into methane and carbon dioxide and into sludge liquid. Methane decomposition includes three stages of anaerobic fermentation (Figure 5.1): hydrolysis, acidic (acidogenic), acetogenic and the fourth, methanogenic stage (gas generation stage).

The first stage of fermentation is attended by hydrolytic microorganisms with cellulolytic, proteolytic, amylolytic, lipolytic, ammonifying activities. The nitrates and sulfates contained in the medium are reduced by denitrifying bacteria and sulfate reducers. As a result of enzymatic hydrolysis of cellulose and hemicellulose, proteins, fats and other components are hydrolyzed to form fatty acids, glycerol, peptides, amino acids, mono- and disaccharides and in small amounts acetic acid, methanol, ammonia, hydrogen. Bacteria are involved in hydrolysis pp. Clostridium, Bacillus, as well as Bacteroides, Butyrivibrio, Cellobacterium, Eubacterium, Bifidobacterium, Lactobacillus, Selenomonas. At the acidogenic stage, various fermentation saws take place: alcoholic, butyric acid, acetone-butyl, propionic and others, during which acidogenic bacteria ferment the resulting hydrolysis products, such as glucose, to organic acids:

Consuming mono- and oligosaccharides, amino acids and other intermediate hydrolysis products, these bacteria thereby prevent inhibition by the hydrolysis products of hydrolytic enzymes involved in the first phase of fermentation.

As a result of splitting in the first two stages, 70-80% of the resulting organic products are higher fatty acids, up to 20% - acetate and 3-5% - hydrogen. Other products include isobutyric, phenylacetic, benzoic, indolylbenzoic acids, NH 4 +, H, S, butanol, propanol, CO2, etc.

At the acetogenic stage of fermentation, heteroacetogenic bacteria (acetogens) pp. Clostridium, Syntrophus and others convert organic acids, for example, propionic and butyric, other acidogenesis products into acetic acid:

The main role in methane decomposition is played by the final stage, which is performed by strict anaerobes - methane-forming bacteria. They are more sensitive to environmental conditions. The generation time of methanogen cells is several days. Their activity is maximum at a pH of the medium from 6.8 to 7.5. At lower and high values pH development of methanogens slows down or stops altogether.

The reaction product of the methanogenic stage is CH 4. Its formation is possible in two ways. Methanogenic bacteria-lithotrophs (pp. Methanococcus, Methanobacterium, Methanospirillum, Methanomicrobium, Methanogenium, Methanothermus, Methanobrevibacter) consume H2 and CO2 as a substrate, as well as CO2 and formate:

C0 2 + 4H 2 → CH 4 + 2H 2 0

4НСООН → СН 4 + ЗС0 2 + 2Н, 0

4CO + 2H 2 0 → CH 4 + 3C0 2

Acetotrophic microorganisms (pp. Methanosarcina, Melhanosaeta, Methanoplanus) use acetate, methanol, methylamine:

CH 3 COOH → CH 4 + CО 2

4СН 3 ОН → ЗСН 4 + С0 2 + 2Н 2 0

4CH 3 NH 2 + 2H 2 0 → CH 4 + 4NH 3 + CO

Due to the destruction of organic acids, the pH of the medium rises, the reaction of the medium becomes silky, therefore the methanogenic stage is sometimes called "alkaline fermentation".

When acetic acid decomposes, 70-75% of methane is formed, and the remaining 25-30% - as a result of synthesis from carbon dioxide and hydrogen and other reactions. The ratio of the final products in the process of methane fermentation depends on the composition of the medium, the conditions of fermentation and the microflora present.

The discovery in the mid-1970s was a major stimulus for the development of many of the modern methods of anaerobic purification. the ability of microorganisms that are part of the methanogenic community to form aggregates - granules (pellets) during growth in an anaerobic reactor under conditions of an upward flow (Fig. 5.2 handout).

Methanogenic bacteria Methanosaeta concilii (Methanothrix soehngenii) and Methanosarcina spp. Play a special role in the formation and functioning of granules. Bacteria p. Methanosaeta form brush-like and ball-like structures (Fig. 5.3), within which microcolonies of Methanosarcina bacteria are grouped (Fig. 5.4). Due to this, aggregates are formed in the form of dense, easily settling granules with a size of 1-5 mm.

Traditional structures include septitanks, clarifiers, decomposers, contact reactors, anaerobic lagoons, digesters, anaerobic biofilters with an upward fluid flow (see handout, Fig. 3.5).

A septic tank (septic tank) is an apparatus consisting of two parts: a settling and a septic tank (Fig. 6.1). In the first part, the water is clarified due to its movement at a low speed, and in the second part, located under the first, there is decomposition of the sediment during its storage for 6-12 months. The settling and septic parts of the septic tank are not separated from each other. The duration of the stay of water in the septic tank is 3-4 days. Septic tanks are used if the amount of wastewater does not exceed 25 m 3 / day.

Separators are often used for fermentation of activated sludge from secondary sedimentation tanks, sediment from primary sedimentation tanks and foam in order to accumulate sediment, reduce its volume, bad smell and the amount of pathogenic microflora. Septic tanks are the most common treatment facilities for individual households, since they can work autonomously and do not need power.

Clarifiers-decomposers, which can be considered as a type of septitenk, are used at wastewater treatment plants with a throughput of up to 30,000 m 5 / day. In fig. .2 shows the design of the clarifier - the digester, made in the form of a combined structure, consisting of the clarifier, concentrically located inside the digester.

The method of anaerobic purification in a contact reactor was one of the first, widely used in industry since the early 1930s, in particular, for the treatment of effluents from sugar, alcohol and yeast industries. Compared to the septitenk, the contact reactor is much more efficient, since it provides for the mixing of the medium with the anaerobic sludge and maintains a higher concentration of sludge due to the return of its part from the secondary settling tank (see handout for lecture 3, Fig. 3.5), i.e. similarly how this is implemented in an aeration tank with a secondary clarifier. To increase the separation efficiency, the sludge liquid in front of the secondary clarifier can be additionally degassed (in a separate vessel) or cooled. During degassing, the gas is removed mechanically (hydraulically) or by vacuum. Cooling slows down the processes of methane formation and, as a result, the formation of new bubbles, which improves the sedimentation properties of anaerobic sludge.

The traditional and most common apparatus for carrying out anaerobic decomposition are digestion tanks. They are used for the fermentation of wastewater with a high concentration of pollutants and the decomposition of organic waste, in particular, activated sludge from treatment plants.

Digester tanks operate with heating, as a rule, in a periodic mode of loading waste or waste water, with continuous sampling of biogas and discharge of solid sludge as the process is completed. They are made from steel, concrete, plastics, bricks; they differ in the shape of the tank, the number of fermentation chambers, the method of loading and unloading the substrate, the methods of heating and mixing.

Large volume digesters are made in the form of vertical cylindrical or ellipsoidal tanks with forced mixing of the fermented mass; they are designed for an excess gas pressure of up to 5 kPa. Small biogas plants can be cylindrical horizontal or vertical mechanically stirred bioreactors, partially or completely buried in the ground to reduce heat loss. Bioreactors must be designed to allow complete emptying of the tank, so the bottom is often tapered, hemispherical or conical.

Digester tanks with a fixed non-flooded overlap have a disadvantage typical of structures with rigid ceilings - the inconstancy of the pressure inside the reactor. When unloading the sediment, a vacuum may form inside the digester, and the pressure may rise during loading. This leads to the destruction of structures, the formation of cracks.

Advantages of the digester with a floating ceiling: 1) explosion safety, since regardless of the filling of the digester, a positive gas pressure is maintained in it, which excludes the possible ingress of air into the structure; 2) according to the position of the floating ceiling, loading and unloading dosage can be carried out; 3) the fight against crust formation is facilitated.

The role of stirring and temperature control In metatenki. Metantenki of all types can operate in mesophilic (20-45 ° C, usually 30-35 ° C) and thermophilic (50-60 ° C) temperature regimes. The mode of fermentation is selected taking into account the methods of subsequent processing and disposal of sludge, as well as sanitary requirements. The mesophilic regime is used more often, since it is less energy-consuming and more economically profitable, allows the existence of a larger number of types of microorganisms and therefore is more stable, less sensitive to changes in environmental conditions; Sludge in this mode after processing is dewatered better in comparison with the thermophilic process. However, under the thermophilic regime, the rate of decomposition of organic compounds is higher (approximately 2 times) and the degree of their decomposition is higher, almost complete deworming of sediments is achieved, which is important if the sediments are used as a recultivator or fertilizer for the soil. The duration of fermentation in the mesophilic mode is 20-30 days, in the thermophilic mode - about 10 days. The calorific value of gas with thermophilic fermentation is 5% lower than with mesophilic one.

For a more complete methane generation process, it is necessary to thoroughly mix the contents of the digester to ensure uniform distribution of the reactor contents, the necessary conditions for mass and heat transfer, to minimize sticking, foam and crust formation, the formation of bottom sediment, and remove gases. For mixing in the digester, mechanical mixers, circulation pumps, hydraulic elevators, or a combination of these systems are used.

Optimum concentration of suspended solids in the digester, at which a high intensity of methane formation is observed, is in the range of 2-10%. At a concentration of solid particles above 10-12%, mixing of the medium becomes difficult, and this leads to a decrease in gas evolution. In such cases, special designs of bioreactors are used to ensure the required level of mixing.

Methane formation proceeds at a maximum rate at pH from 6 to 8. When the pH drops below 5.5 (in the case of "acidification" of the digester), the activity of methanogenic bacteria ceases. As a rule, the pH is not adjusted due to the high buffering capacity of the medium. But when the medium is acidic, the best neutralizing agent is a NaHCO 3 solution.

The process of methanogenesis slows down in the presence of various detergents (at a concentration of about 15 mg / l), antibiotics and other substances. Of the anionic surfactants, alkyl sulfates, chlorine sulfanol, decompose relatively completely and slightly inhibit the fermentation process; difficult to decompose and strongly inhibit the fermentation of sulfanols.

Anaerobic reactors are resistant to long interruptions in the supply of waste water, changes chemical composition incoming effluents, which makes it possible to effectively use them for the treatment of effluents from seasonal industries, as well as in low-load modes. In the case of a decrease in methanogenic activity, to restore it, it is possible to reduce the rate of substrate supply, alkalize the medium with chemicals, dilute the effluent with water, and remove toxic compounds by pretreating the effluent.

Bacterial leaching chemical elements from ores, concentrates and rocks, ore dressing, biosorption of metals from solutions. Removal of sulfur from oil and coal. Enhanced oil recovery. Removal of methane from coal seams. Suppression of biocorrosion of oil products.

Research on bacterial oxidation of iron and leaching of metals began after the isolation in the 50s of the 20th century from the acidic drainage waters of a coal mine of microorganisms capable of participating in the oxidation of ferrous iron to ferric iron - bacteria Acidithiobaccilus ferrooxidans (formerly called Thiobaccilus ferrooxidans). Bacteria participating in the leaching of metals are chemoautotrophic by type of nutrition, catalyzing chemical redox reactions to obtain energy and assimilating carbon dioxide for constructive cell metabolism, i.e. eating autonomously, without the use of organic matter.

Heap bioleaching of sulphide ores.

V last years vat bacterial leaching of concentrates or ores began to be used to prepare refractory raw materials for cyanidation. There are already more than a dozen industrial enterprises practicing this technology in the world, but the capital costs for this technology are very high, therefore, they are not justified for small and medium-sized fields.

The use of strictly acidophilic bacteria assumes that the pH of the pulp or solution is 2 or less. If bacteria A. ferrooxidans are used for leaching, then the process of biological oxidation of minerals can proceed in two ways: these bacteria not only oxidize sulfur compounds, but are also capable of oxidizing ferrous forms of iron to oxide forms to obtain energy. The processing time depends on the composition of the sulfide ore, the shape and distribution of the metal in the ore, and the amount of sulfur available to microorganisms. There are also a number of narrower problems, for example, the toxicity of high concentrations of mined heavy precious metals for certain species or strains of leaching microorganisms.

Thus, one of the approaches to the improvement and development of technology and methods of bioleaching is the selection of bacteria and archaea that are resistant to the toxicity of metals. Other criteria for the selection of crops are: ease of working with them in industrial conditions, activity in the oxidation of mineral compounds, relation to pH, temperature, aeration regime and the ability to stimulate their activity by introducing additional substances.

Currently, a number of genera (groups subdivided according to properties and systematic position) of bacteria and archaea (two super kingdoms of microorganisms) are known, whose representatives are capable of leaching metals by oxidizing sulfides: Acidothiobacillus, Halothiobacillus, Thiobacillus, Leptospirillum, Acidiphilium, Sulrofobacillus, Ferrobacillus , Metallosphaera and Acidianus. Thus, the development of bioleaching technologies can rely both on changes in the organization of the process (optimization of aeration, temperature regime, pretreatment of mineral raw materials, etc.), and on the selection of new microbial cultures - with a higher activity or easier to build up biomass, or with a wider range of pH, temperature, etc. Traditional leaching with acidic solutions has led to the fact that the search for new cultures of microorganisms is focused specifically on acidophilic and superacidophilic organisms.

^ 20.biochemical basis of the quality of strength and the ways of its development

Muscle strength is usually understood as the ability to overcome external resistance, or to counteract it through muscle tension.

Speed-strength qualities mainly depend on the energy supply of working muscles and on their structural and morphological features, largely predetermined genetically.

The manifestation of strength and speed is characteristic of physical activity performed in the zone of maximum and submaximal power. Consequently, the anaerobic pathways of ATP resynthesis - creatine-phosphate and glycolytic - are predominantly involved in the energy supply of speed-strength qualities.

Resynthesis of ATP develops most rapidly due to the creatine phosphate reaction. It reaches its maximum within 1–2 s after the start of work. The maximum power of this method of ATP formation exceeds the rate of the glycolytic and aerobic pathways of ATP synthesis by 1.5 and 3 times, respectively. It is due to the creatine phosphate pathway of ATP resynthesis that muscle loads are performed with the greatest strength and speed. In turn, the value of the maximum rate of the creatine phosphate reaction depends on the content of creatine phosphate in muscle cells and the activity of the enzyme creatine kinase. It is possible to increase the reserves of creatine phosphate and the activity of creatine kinase through the use of physical exercises, leading to a rapid depletion of creatine phosphate in the muscles.

For this purpose, short-term exercises performed with maximum power are used. The use of an interval training method, consisting of a series of such exercises, gives a good effect. The athlete is offered a series of 4-5 exercises of maximum power, lasting 8-10 seconds. Rest between exercises in each series is 20–30 s. The rest period between series is 5–6 minutes.

The implementation of high-speed and power loads in the submaximal power zone is provided with energy mainly due to glycolytic resynthesis of ATP. The possibilities of this method for obtaining ATP are due to intramuscular glycogen stores, the activity of enzymes involved in this process, and the body's resistance to lactic acid formed from glycogen. Therefore, for the development of speed-strength abilities based on glycolytic energy supply, training is used that meets the following requirements. First, training should lead to a sharp decrease in muscle glycogen content, followed by its supercompensation. Secondly, during training, lactic acid must accumulate in the muscles and in the blood for the subsequent development of the body's resistance to it.

Rest intervals, both between individual exercises and between exercise series, are clearly insufficient to restore glycogen stores, and as a result, during training, muscle glycogen content gradually decreases to very low values, which is a prerequisite for the occurrence of pronounced supercompensation.

The structural and morphological features of muscles, which determine the possibilities of manifestation of strength and speed, relate to the structure of both individual muscle fibers and the muscle as a whole. The speed-strength qualities of an individual muscle fiber depend on the number of contractile elements - myofibrils - and on the development of the sarcoplasmic reticulum containing calcium ions. The sarcoplasmic reticulum is also involved in the conduction of nerve impulses inside the muscle cell. The content of myofibrils and the development of the sarcoplasmic reticulum are not the same in muscle fibers of different types. Depending on the predominance of certain methods of ATP formation, chemical composition and microscopic structure, there are three main types of muscle fibers: tonic, phasic and transitional. These types of fibers also differ in their excitability, timing, speed and strength of contraction, and duration of functioning.

Tonic fibers contain a relatively large number of mitochondria, they contain a lot of myoglobin, but few contractile elements - myofibrils. The main mechanism of ATP resynthesis in such muscle fibers is aerobic. Therefore, they shrink slowly, develop little power, but they can shrink. long time.

Phase fibers have many myofibrils, a well-developed sarcoplasmic reticulum, and many nerve endings are suitable for them. Collagen fibers are well developed in them, which contributes to their rapid relaxation. In their sarcoplasm, the concentrations of creatine phosphate and glycogen are significant, the activity of creatine kinase and glycolysis enzymes is high. The relative number of mitochondria in white fibers is much less, the content of myoglobin in them is low, so they have a pale color. The energy supply of white muscle fibers is carried out through the creatine phosphate reaction and glycolysis. The combination of anaerobic pathways for ATP resynthesis with a large number of myofibrils allows fibers of this type to develop a high speed and strength of contraction. However, due to the rapid depletion of creatine phosphate and glycogen stores, the operating time of these fibers is limited.

Transitional muscle fibers in their structure and properties occupy an intermediate position between tonic and phasic.

Even from such a brief enumeration of the differences between the types of muscle fibers, it follows that for the manifestation of strength and speed, white fibers and transitional fibers close to them in structure are more preferable. Therefore, the more pronounced speed-power qualities, all other things being equal, are possessed by those muscles in which the ratio between the muscle fibers is shifted towards whites.

The ratio between different types of fibers in skeletal muscle is not the same. So, the muscles of the forearm, the biceps brachii, the muscles of the head and others contain mainly physical fibers. The muscles of the trunk, rectus abdominis, and rectus femus mainly contain tonic fibers. Hence, it is easy to understand why these muscle groups differ significantly in properties such as excitability, speed, strength, endurance.

The relationship between the different types of muscle cells in each person is genetically predetermined. However, using physical activity of a certain nature, it is possible to purposefully cause a change in the spectrum of muscle fibers. Through the application strength exercises there is a shift in this spectrum towards the predominance of white fibers having a larger diameter compared to red and transitional ones, which ultimately leads to hypertrophy of the trained muscles. The main reason for hypertrophy in this case is an increase in the content of contractile elements in muscle cells - myofibrils. Therefore, muscle hypertrophy caused by strength loads belongs to the myofibrillar type.

Physical activity used for the development of muscle hypertrophy of the myofibrillar type, at the biochemical level, should lead to damage to myofibrils with their subsequent supercompensation. For this purpose, various weight exercises are used.

To develop strength, a repetitive exercise method is often used with a tension of 80–90% of maximum strength. The most effective resistance is 85% of maximum strength. In this case, the number of repetitions "to failure" is usually 7-8. Each exercise is performed in series, the number of which ranges from 5 to 10, with a rest interval between them of several minutes. The exercise speed is determined by the training goal. For a predominant increase in muscle mass, exercises are performed at a slow to moderate pace. For the simultaneous development of strength and speed, the exercises are carried out in an explosively smooth mode: the initial phase of the movement is performed at high speed, and it ends as smoothly as possible. Therefore, in speed-strength types, athletes during the period of strength training should abandon the slow performance of strength exercises, since in this case the muscles' ability to quickly contract is lost.

Recovery time after speed-strength training is 2-3 days. However, by changing the muscle groups to which the loads are directed, training sessions can be carried out at shorter rest intervals.

A prerequisite for effective strength training is a complete, protein-rich diet, since myofibrils are composed exclusively of proteins. There is evidence that ultraviolet radiation contributes to the development of muscle hypertrophy. It is assumed that under the influence of ultraviolet radiation, the formation of male sex hormones, which stimulate the synthesis of proteins in the body, increases.

21 Biochemical bases of speed (speed) as a quality of motor activity

Speed ​​as a motor quality is the ability of a person to perform a motor action in the minimum for given conditions a period of time with a certain frequency and impulsivity. On the question of the nature of this quality, there is no unanimity of views among specialists. Some suggest that the physiological basis of speed is the lability of the neuromuscular apparatus. Others believe that the mobility of nervous processes plays an important role in the manifestation of speed. Numerous studies have proven that speed is a complex motor quality of a person.

The main forms of human quickness manifestation are the time of the motor reaction, the time of the fastest possible fulfillment of a single movement, the time of the fulfillment of the movement with the maximum frequency, the time of the complete motor act fulfillment. There is also one more form of quickness manifestation (“high-speed qualities”) - a quick start of movement (what is called “sharpness” in sports practice). In practice, the speed of integral motor acts (running, swimming, etc.) is of the greatest importance, rather than the elementary forms of manifestation of speed, although the speed of integral movement only indirectly characterizes the speed of a person.

Skeletal muscle is a complex system that converts chemical energy into mechanical work and heat. The main components of muscle fiber are proteins: actin and myosin.

When making quick movements, muscle contraction requires a large amount of energy per unit time with a deficiency of oxygen, therefore, anaerobic processes of ATP hydrolysis play the main role in this.

Hydrolysis of ATP in the ATPase center of the myosin head is accompanied by a change in the conformation of the latter and its transfer to a new, high-energy state. Re-attachment of the myosin head to a new center on the actin filament again leads to rotation of the head, which is provided by the energy behind it. In each cycle of connection and disconnection of the myosin head with actin, one ATP molecule is cleaved for each bridge. The rate of rotation is determined by the speed of the cleavage of ATP. Obviously, fast phasic fibers consume significantly more ATP per unit time and retain less chemical energy during tonic loading than slow fibers. Thus, in the process of chemomechanical transformation, ATP provides the separation of the myosin head and actin filament and energetics for further interaction of the myosin head with another part of the actin filament. These reactions are possible at calcium concentrations above 106 mol / l.

The level of development of speed ultimately determines success in the vast majority of sports. Even a marathon runner should probably run his distance faster while maintaining a high "cruising" speed (by "cruising" speed is meant the average speed of the course). And the success of a weightlifter depends on how fast he is able to perform the required movement.

The speed is determined by:

a) by measuring the speed of movement in response to a certain signal with reactionometers of various designs;

b) by the number of movements for a set time with an unloaded limb or trunk within the limits of a certain amplitude;

c) by the time it takes to overcome the established short distance (for example, running 20, 30 m);

d) by the speed of performing a single movement in a complex action, for example, pushing off in jumps, movement of the shoulder girdle and hand in throwing, hitting in boxing, the initial movement of a short-distance runner, movements of a gymnast, etc.

All manifestations of speed are effectively developed when playing basketball. You can also recommend a handball, table tennis, outdoor games with a fast-changing game situation and fast movement. The main task in the development of speed is that the athlete does not prematurely specialize in any one exercise of a high-speed nature, so as not to include a large volume of the same type of repetition of this exercise. Therefore, it is so important that athletes use speed exercises as often as possible in the form of a competition or game. The training program should include a significant amount of such high-speed exercises as sprint running from the start and from the run, running with acceleration, long and high jumps with extremely fast take-off, throwing lightweight shells, outdoor and sports games, extremely quickly performed acrobatic exercises, and a variety of special preparatory exercises.

Correct determination of the dosage of speed exercises is of great importance for fostering quickness and increasing the speed of movements. Those that are performed at maximum intensity are highly effective and fatiguing agents. The same applies to exercises aimed at increasing the speed of movement. Therefore, exercises performed at maximum speed should be used often, but in a relatively small amount. The duration of the rest intervals is due to the degree of excitability of the central nervous system and restoration of indicators of vegetative functions associated with the elimination of oxygen deficiency. Training work for the development of speed should be completed as soon as the athlete's subjective feelings or the stopwatch readings indicate a decrease in the set or maximum speed.

22.biochemical basis of the quality of endurance to prolonged loads and the ways of its development

Endurance is the most important motor quality, on the level of development of which the achievements of the athlete largely depend. Endurance can be defined as the time at a given power level before fatigue occurs.

In accordance with the nature of the work performed, general and special endurance are distinguished. Overall endurance reflects the athlete's ability to perform non-specific loads. Such loads, for example, for a football player can be cross-country, cross-country skiing, swimming, outdoor games, etc., as well as performing physical work of a household nature. Special endurance characterizes the performance of physical activities specific to a particular sport and requiring technical, tactical and psychological preparation athlete.

Of paramount importance for the manifestation of endurance is the level of development of the molecular mechanisms of the formation of ATP - a direct source of energy for ensuring muscle contraction and relaxation

Depending on the method of energy supply of the work performed, alactate, lactate and aerobic endurance are distinguished. The terms alactate, lactate and aerobic components of endurance are often used.

Alactate endurance is characterized by the longest working time in the zone of maximum power. Depending on the type of load, one can distinguish speed, speed o-power and power alactate endurance. The main source of energy during muscular work of maximum power is the creatine phosphate reaction. Therefore, the development of alactate endurance is due to intramuscular stores of creatine phosphate. As already noted, white muscle fibers are richer in creatine phosphate. In this regard, muscles with a predominance of white fibers have greater alactate endurance. The content of creatine phosphate in muscles can be significantly increased using specific exercises. The principle of building such a training in an interval mode was described above, when considering the energy supply of speed-strength qualities.

Biochemical assessment of alactate endurance can be given by determining the daily urinary excretion of creatinine. This indicator characterizes the total reserves of creatine phosphate in the body. The increase in alactate endurance is usually accompanied by an increase in the daily excretion of creatinine. Another criterion characterizing the development of alactate endurance is the alactate oxygen debt, measured after completion of the maximum power work.

Lactate endurance characterizes the performance of physical activity in the zone of submaximal power. The main source of energy when working at this power is the anaerobic breakdown of muscle glycogen to lactic acid, called glycolysis. Possibilities of the glycolytic method of obtaining ATP largely depend on the reserves of muscle glycogen. The higher the working concentration of glycogen in the muscles, the longer it will be used in glycolysis. It follows that muscles with a predominance of white fibers, rich in creatine phosphate and glycogen, also have a pronounced lactate endurance. Another factor that determines lactate endurance is the resistance of muscle cells and the whole organism to an increase in acidity due to the accumulation of lactate in muscles and in the blood.

Based on this dependence, training aimed at developing lactate endurance is structured so as to ensure the fulfillment of two tasks. First, due to the physical activity performed in the muscles, the glycogen content should increase. Secondly, training sessions should lead to the emergence of resistance to lactate accumulation and acidity.

For this purpose, exercises are used that cause, on the one hand, a significant depletion of muscle glycogen reserves, which is a prerequisite for its subsequent supercompensation, and on the other hand, leading to the formation of large amounts of lactic acid. These are physical activities of submaximal power, performed in an interval or repetitive mode. Training of this type is described above, when considering the energy supply of speed-strength qualities. Depending on the nature of the applied loads, it is possible to predominantly develop the strength or speed component of lactate endurance.

The leading biochemical indicator of the manifestation of lactate endurance during work is the accumulation of lactate in the blood. Determination of the concentration of lactic acid in the blood is carried out after performing physical work of submaximal power "to failure". High level the concentration of lactic acid in the blood indicates the use of large amounts of muscle glycogen for energy during work and the development of resistance to an increase in acidity.

The same information can be obtained by determining the change in acid-base balance in the blood after submaximal loads. In this case, high lactate endurance corresponds to a significant shift in the pH of the blood to the acidic side. Another indicator of the development of lactate endurance is the lactate oxygen debt, measured after performing work of submaximal power "to failure". The higher the value of this indicator, the greater the contribution of anaerobic breakdown of glycogen to the energy supply of the work done. In athletes with good physical fitness, the lactate oxygen debt can reach 18–20 liters.

In sports practice, alactate and lactate endurance is very often combined into anaerobic endurance.

Aerobic endurance is manifested through sustained, moderate-intensity exercise, which is primarily supplied with energy from aerobic oxidation. The contribution of anaerobic energy production is limited only by the initial period of activation. In sports literature, the term "endurance" often refers to aerobic endurance.

Aerobic endurance is determined by three main factors: the body's reserves of available energy sources, the delivery of oxygen to the working muscles, and the development of mitochondrial oxidation in the working muscles.

The commonly used energy sources are carbohydrates, fatty acids, ketone bodies and amino acids. Due to the long duration of aerobic work, these energy substrates are delivered to the muscles by blood, since the muscle cells' own energy resources are consumed at the beginning of work.

The liver plays a significant role in providing the muscles with energy sources. It is here, during the performance of long-term loads, that glycogen breaks down to glucose, which then enters the skeletal muscles and other organs involved in providing muscle activity with the blood flow. Another process that takes place in the liver during work is the oxidation of fatty acids, accompanied by the formation of ketone bodies, which are also important sources of energy. In addition, other chemical processes occur in the liver during work that contribute to the performance of muscle work. In connection with such an important role of the liver in ensuring physical work in sports practice, hepatoprotectors are used - pharmacological agents that improve the functioning of the liver and accelerate recovery processes in it.

Oxygen delivery to the muscles is carried out by the cardiorespiratory system. Therefore, for the manifestation of aerobic endurance, the functional state of the cardiovascular and respiratory systems, the oxygen capacity of the blood, due to the number of erythrocytes and the content of hemoglobin in them, are extremely important.

The development of aerobic endurance is also largely determined by the state of neuro-hormonal regulation. The leading role in this regulation is played by the adrenal glands, which release catecholstins and glucocorticoids into the bloodstream - hormones that cause the body to restructure, aimed at creating optimal conditions for muscle activity. For the manifestation of aerobic endurance, the ability of the adrenal glands to maintain an increased concentration of these hormones in the bloodstream for a long time is important.

Intramuscular factors responsible for aerobic endurance are the size and number of mitochondria - intracellular structures in which ATP synthesis occurs with the participation of oxygen, as well as the content of myoglobin, a muscle protein that provides oxygen transport to mitochondria inside muscle fibers. As already noted, red muscle fibers are characterized by a higher content of mitochondria and myoglobin. This implies that higher aerobic endurance is observed in muscles with a predominance of red fibers.

Aerobic endurance is less specific than anaerobic endurance. This is due to the fact that it is largely limited by various extramuscular factors: the functional state of the cardiorespiratory system, liver and neuro-hormonal regulation, oxygen capacity of the blood, reserves in the body of readily available energy sources. Therefore, an athlete with a good level of aerobic endurance can show it not only in the type of activity where he received specialized training, but also in other types of aerobic work. For example, a qualified soccer player might show good result in long distance running.

The multifactorial nature of aerobic endurance requires the use of a complex of various training means, since each specific lesson, causing a rather versatile effect on the body, still predominantly improves one side of the functional capabilities. As a result, training aimed at developing aerobic endurance should ensure an increase in the efficiency of the cardiorespiratory system, promote an increase in the number of erythrocytes in the blood and the content of hemoglobin in them, an increase in the concentration of myoglobin in muscle cells, and better provision of working organs with energy substrates.

For this purpose, various options for repeated and interval training are used, as well as continuous long-term work of uniform or variable power.

As an example of the construction of training sessions aimed at developing aerobic endurance, we can cite the so-called circulatory interval training. This method consists in alternating short-term exercises of low intensity and duration from 30 to 90 seconds with intervals of rest of the same duration. Such work stimulates aerobic energy supply to muscular activity and leads to an improvement in the parameters of the cardiorespiratory system.

Myoglobin interval training can be used to increase muscle myoglobin levels. Athletes are offered very short loads of medium intensity, alternating with equally short rest periods. Performed short-term loads are mainly provided with oxygen, which is deposited in muscle cells in the form of a complex with myoglobin. A short rest between exercises is sufficient to replenish oxygen stores.

To increase the oxygen capacity of the blood, as well as to increase the concentration of myoglobin, training in mid-altitude conditions gives a good effect.

A feature of the development of aerobic endurance is the ability to use nonspecific exercises, and primarily outdoor games, which makes the training process varied and interesting.

Important information for assessing aerobic endurance can be obtained by determining the content and ratio in the blood of the main energy substrates during continuous work. In untrained people, there is a reciprocal relationship between blood glucose and fat mobilization products. The high concentration of glucose in the blood prevents the mobilization of fat from the depot. Therefore, in untrained people, an increase in the content of fatty acids, glycerol and ketone bodies in the blood is observed only against the background of a decrease in glucose concentration. In athletes who are well trained in an aerobic regime, powerful fat mobilization is noted against the background of not only normal, but also increased blood glucose levels. Increased utilization of fat and ketone bodies allows the body not only to preserve liver and blood carbohydrates, but also to slow down the consumption of muscle glycogen, a decrease in the concentration of which is one of the factors in the development of fatigue.

In conclusion, it should be noted that all components of endurance, along with the energy and structural factors discussed above, largely depend on technical, tactical and psychological training. Good technical training, correctly chosen tactics allow an athlete to use energy reserves economically and rationally, and thus to maintain performance longer. Due to high motivation, great willpower, an athlete can continue to perform work even in conditions of significant biochemical and functional changes in the body.

13.4.1. The reactions of the Krebs cycle belong to the third stage of nutrient catabolism and occur in the mitochondria of the cell. These reactions belong to the general pathway of catabolism and are characteristic of the breakdown of all classes of nutrients (proteins, lipids and carbohydrates).

The main function of the cycle is the oxidation of the acetyl residue with the formation of four molecules of reduced coenzymes (three NADH molecules and one FADH2 molecule), as well as the formation of a GTP molecule by substrate phosphorylation. The carbon atoms of the acetyl residue are released in the form of two CO2 molecules.

13.4.2. The Krebs cycle includes 8 consecutive stages, paying special attention to the reaction of substrate dehydrogenation:

Figure 13.6. Krebs cycle reactions, including the formation of α-ketoglutarate

a) condensation of acetyl-CoA with oxaloacetate, as a result of which citrate is formed (Fig. 13.6, reaction 1); therefore, the Krebs cycle is also called citrate cycle... In this reaction, the methyl carbon of the acetyl group reacts with the keto group of oxaloacetate; at the same time, the thioether bond is cleaved. In the reaction, CoA-SH is released, which can take part in the oxidative decarboxylation of the next pyruvate molecule. The reaction is catalyzed by citrate synthase, it is a regulatory enzyme, it is inhibited by high concentrations of NADH, succinyl-CoA, citrate.

b) the conversion of citrate to isocitrate through the intermediate formation of cis-aconitate. The citrate formed in the first reaction of the cycle contains a tertiary hydroxyl group and is not capable of oxidation under cell conditions. By the action of an enzyme aconitase there is a splitting off of a water molecule (dehydration), and then its addition (hydration), but in a different way (Fig. 13.6, reactions 2-3). As a result of these transformations, the hydroxyl group moves to a position favorable to its subsequent oxidation.

v) dehydrogenation of isocitrate followed by the release of the CO2 molecule (decarboxylation) and the formation of α-ketoglutarate (Fig. 13.6, reaction 4). This is the first redox reaction in the Krebs cycle to form NADH. Isocitrate dehydrogenase, catalyzing the reaction, is a regulatory enzyme that is activated by ADP. Excess NADH inhibits the enzyme.

Figure 13.7. Krebs cycle reactions starting with α-ketoglutarate.

G) oxidative decarboxylation of α-ketoglutarate, catalyzed by a multienzyme complex (Fig. 13.7, reaction 5), accompanied by the release of CO2 and the formation of a second NADH molecule. This reaction is analogous to the pyruvate dehydrogenase reaction. The inhibitor is the reaction product, succinyl-CoA.

e) substrate phosphorylation at the level of succinyl-CoA, during which the energy released during the hydrolysis of the thioether bond is stored in the form of a GTP molecule. Unlike oxidative phosphorylation, this process proceeds without the formation of an electrochemical potential of the mitochondrial membrane (Fig. 13.7, reaction 6).

e) dehydrogenation of succinate with the formation of fumarate and the FADH2 molecule (Fig. 13.7, reaction 7). The enzyme succinate dehydrogenase is tightly bound to the inner mitochondrial membrane.

g) hydration of fumarate, as a result of which a readily oxidizable hydroxyl group appears in the reaction product molecule (Fig. 13.7, reaction 8).

h) malate dehydrogenation leading to the formation of oxaloacetate and a third NADH molecule (Figure 13.7, reaction 9). The oxaloacetate formed in the reaction can be used again in the condensation reaction with the next acetyl-CoA molecule (Fig. 13.6, reaction 1). Therefore, this process is cyclical.

13.4.3. Thus, as a result of the described reactions, it undergoes complete oxidation acetyl residue CH3 -CO-... The number of acetyl-CoA molecules converted in mitochondria per unit time depends on the concentration of oxaloacetate. The main ways to increase the concentration of oxaloacetate in mitochondria (the corresponding reactions will be discussed later):

a) carboxylation of pyruvate - the addition of a CO2 molecule to pyruvate with the expenditure of ATP energy; b) deamination or transamination of aspartate - the cleavage of the amino group with the formation of a keto group in its place.

13.4.4. Some metabolites of the Krebs cycle can be used to synthesis building blocks for building complex molecules. Thus, oxaloacetate can be converted into the amino acid aspartate, and α-ketoglutarate into the amino acid glutamate. Succinyl-CoA takes part in the synthesis of heme - the prosthetic group of hemoglobin. Thus, the reactions of the Krebs cycle can participate both in the processes of catabolism and anabolism, that is, the Krebs cycle performs amphibolic function(see 13.1).

Carbohydrates, proteins and fats in the body are hydrolyzed, and the resulting hydrolysis products - monosaccharides, amino acids, fatty acids and glycerin undergo transformations, during which some of them are oxidized to carbon dioxide and water, which are products of oxidation of carbon and hydrogen. If a system in which each of the products of hydrolysis of biopolymers, which is a substrate for subsequent oxidation, had its own metabolic pathway, then such a system would be very cumbersome and unreliable. However, Nature has solved the problem of unification of metabolic pathways, organizing catabolic processes in such a way that at the intermediate stages of these processes, a minimum number of the same metabolites are formed, which are obtained during the oxidation of different substances. And, indeed, as can be seen from the diagram, most of the oxidation substrates are converted into pyruvic acid - pyruvate (C 3), and then into acetyl-CoA (C 2), and the latter can also be formed during the oxidation of pyruvate. Acetyl-CoA is completely oxidized in the tricarboxylic acid cycle (CTA - aka Krebs cycle or citrate cycle). The Krebs cycle is a common catabolic pathway for carbohydrates, proteins and fats. The energy released during catabolic reactions is partially dissipated in the form of heat, while most of it is consumed in anabolic reactions. Energy transfer is carried out using intermediates, the main one being ATP. Endergonic processes are the synthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate, as well as the synthesis of other substances with high-energy bonds. This process takes place due to the coupling of energy with catabolic reactions. The exergonic process is the hydrolysis of ATP and other triphosphates. Hydrolysis supplies the necessary energy for biosynthesis.

Below is a diagram of the conjugation of anabolic and catabolic processes:

S 1 oxidized substrate, ΔG< 0

ADP + phosphate ATP + H 2 O, ΔG< 0

Pairing

ATP + H 2 O → ADP + phosphate, ΔG< 0

S 2 biosynthetic product, ΔG> 0

Most of the ATP in the body is produced by oxidative phosphorylation which occurs in the electron transfer chain (CPE). The main substrates of this process are NAD * H and FAD * H 2, which are formed mainly in TCA, therefore one of the main tasks of catabolism is the synthesis of ATP - a kind of energy accumulator necessary for subsequent anabolic reactions. Most biosyntheses are of a reducing nature, since the products of biosynthesis are less oxidized compared to the initial substances. The role of the reducing agent in such processes is played by NAD * N. Thus, a limited number of compounds play a key role in metabolism. These are pyruvate and acetyl-CoA, which end in specific pathways of catabolism; ATP, hydrolysis products, to which energy is supplied for anabolic processes; NAD * H and FAD * H 2 are coenzymes, during the oxidation of which the main part of ATP is formed in the body.

Carbohydrate catabolism

The processes of carbohydrate metabolism in humans begin in the oral cavity, since the saliva contains the enzyme amylase, which is able to break down starch and glycogen to a disaccharide - maltose, which breaks down the latter to glucose with the enzyme maltase. The entry of glucose into the cells of various organs depends on the hormone insulin, which regulates the rate at which glucose is transported across the cell membranes. carriers - proteins.

The exchange of glucose in the cell begins with its phosphorylation:

Glucose + ATP glucose-6-phosphate + ADP

ATP → + ADP

Unlike free glucose, glucose-6-phosphate is not able to pass through cell membranes, therefore phosphorylated glucose is “locked” in the cell, and there it is stored in the form of glycogen - animal starch, which is synthesized from glucose-6-phosphate molecules.

Glucose catabolism in a cell can go in three main directions, which differ in the way the carbon skeleton of the molecule changes:

1. Dichotomous path, in which the C-C bond between the third and fourth carbon atoms is cleaved, and two trioses are obtained from one hexose molecule (C 6 → 2C 3).

2. Apotomic pathway (pentose phosphate), in which hexose is converted to pentose (C 6 → C 5) as a result of oxidation and elimination of one (first) carbon atom.

3.Glucuronic pathway, when oxidation and elimination of the sixth carbon atom occurs

The main pathway for the breakdown of glucose leading to the release of energy is the dichotomous path, and in this path, in turn, glucose can be oxidized and its energy obtained in two ways:

1.Independent anaerobic breakdown glucose to lactic acid - glycolysis.

glucose → 2-lactate + 134 kJ

Part of this energy is spent on the formation of two ATP molecules and the rest dissipates as heat.

2.Aerobic (oxygen dependent) breakdown of glucose to carbon dioxide and water

This is the reverse process of photosynthesis:

С 6 Н 12 О 6 + 6О 2 ↔ 6СО 2 + 6Н 2 О + 2850 kJ

60% of this energy is stored in the form of high-energy ATP bonds, that is, in a biologically available form. As can be seen from the above equations, the aerobic pathway is undoubtedly more beneficial in comparison with glycolysis, since it produces twenty times more ATP from the same amount of glucose. Aerobic breakdown is carried out by most body tissues with the exception of red blood cells. For malignant cells, the main way of obtaining energy is glycolysis. Muscles use glycolysis in case of heavy loads, when oxygen access is difficult and then lactic acid is formed in the stressed muscles.

The glucose glycolysis reaction chain includes eleven reactions, of which the first ten are common with aerobic decomposition, and the eleventh is the synthesis of lactic acid from pyruvic acid (PVA) using NAD * H. Let us consider sequentially the reactions during aerobic breakdown of glucose:

1 reaction is the phosphorylation of glucose, its activation.

2 reaction is isomerization, glucose-6-phosphate is converted to fructose-6-phosphate.

3 reaction - fructose-6-phosphate is phosphorylated to fructose-1,6-diphosphate.

The first three reactions represent the so-called preparatory stage, at this stage, the energy of ATP is still spent on phosphorylation reactions:

1

Glucose-6-phosphate

2- isomerization

ATF

fructose-6-phosphate 7 9 3-phosphoglycerate 10

2-phosphoglycerate common pathway

9 H 2 O ATP

The next stage is reactions glycolic oxyreduction, in which the six-carbon skeleton decays into two three-carbon ones and is oxidized to pyruvate.

4 reaction - fructose-1,6-diphosphate in its open acyclic form is decomposed by the enzyme aldolase into two three-carbon fragments: glyceraldehyde phosphate and dioxyacetone phosphate.

5 reaction - isomerization, conversion of dioxyacetone phosphate to glyceraldehyde phosphate.

Further catabolism occurs only through glyceraldehyde phosphate, two molecules of which in the 6th reaction are oxidized by NAD + to 1,3-diphosphoglycerate, and the energy released during this is stored in the form of ATP. In this case, oxidation of the aldehyde results in organic and phosphoric acid anhydride. Two molecules of 1,3-diphosphoglycerate are converted during hydrolysis into 3-phosphoglycerate, and then, in the 8th reaction, the phosphate group is transferred from position 3 to position 2.

9 reaction is the elimination of water to obtain phosphoenolpyruvate, and then a keto-enol transformation occurs, coupled with hydrolysis, when one molecule of phosphoric acid is cleaved from dioxyacetone phosphate and the enol form is converted into the keto form.

LIPID CATABOLISM

In higher animals and humans, lipids enter the stomach and leave it almost unaffected by the acidic environment. In the alkaline medium of the small intestine, lipids are hydrolyzed by lipases. Hydrolyzed lipids are absorbed into the bloodstream and transported to various organs for further metabolism.

Glycerin, fatty acids, mono- and diglycerides enter the bloodstream through the intestinal wall. In the blood, FAs are again esterified with glycerol, which is bound to blood proteins and transferred to adipose tissue or liver, where it is deposited. In the liver, hydrolysis takes place with the formation of fatty acids, which are oxidized to CO 2 and H 2 O. During oxidation, a large amount of energy is released.

The FA oxidation process includes many stages. FA is destroyed (synthesized) to C-C fragments (natural FAs consist of an even number of carbon atoms). During catabolism, FAs are first converted into thioesters with coenzyme A, with the release of ATP, then oxidized into unsaturated acids, FAD serves as an oxidizing agent.

C 15 H 31 COOH - palmitic acid

About HSKoA About FAD

CH 3 (CH 2) 12 CH 2 CH 2 C OH CH 3 (CH 2) 2 CH 2 CH 2 C SCoA

CH 2 (CH 2) 12 CH = CHS SCoA

The pathway of protein catabolism begins with hydrolysis (proteolysis) under the action of protease and peptidase enzymes.

Protein hydrolysis begins in the stomach under the action of the enzyme pepsin, this is facilitated by the acidic environment of gastric juice pH = 1-2 arises due to the release of gastric cells of hydrochloric acid.

In the small intestine at pH = 7.8-8.4, protein breakdown is catalyzed by pancreatic enzymes trypsin and chymitrypsin.

AK - a product of protein hydrolysis, coming from the gastrointestinal tract, is an important fund for replenishing the amino acid supply of cells and tissues. A limited supply of even one of the irreplaceable AAs from outside causes a sharp breakdown of the tissues' own proteins; AAs are used in the synthesis of their own proteins, nucleotides, porphyrins, etc.

An adult needs 100 g of protein per day. Proteins can be complete - all irreplaceable AAs are available and defective - not all irreplaceable AAs are available. During the day, 400 g of protein is decomposed and synthesized. All proteins are renewed in 35 days.

The state of protein metabolism can be judged by the nitrogen balance. Since the proteins of organs are distinguished by strict species and tissue specificity, a living organism is able to use the introduced protein only in a hydrolyzed state.

The absorption of AA through the membrane of the small intestine occurs under the action of glutathione. AK enter the bloodstream of the portal vein, then into the liver, where they undergo a number of transformations.