Metabolism and its types

It ensures the constancy of the internal environment of the body in changing conditions of existence - homeostasis . Metabolism consists of two interrelated and mutually opposite processes. These are processes dissimilation , in which the breakdown of organic substances occurs and the released energy is used for the synthesis of ATP molecules, and the processes assimilation, in which the energy of ATP is used to synthesize its own compounds necessary for the body.

The process of dissimilation is also called catabolism and energy metabolism . And the processes of assimilation are also called anabolism and plastic metabolism . Such an abundance of synonyms for the same concept arose because metabolic reactions were studied by scientists of various specialties:

• biochemists,
• physiologists,
• cytology,
• genetics,
• molecular biologists.

But all the names and terms have taken root and are actively used by scientists.

Forms of energy supply to living organisms

For all living organisms on Earth, the Sun is the main source of energy. It is thanks to him that organisms satisfy their energy needs.

Organisms that can synthesize organic compounds from inorganic compounds are called autotrophs. They are divided into two groups. Some are able to use the energy of sunlight. These are photosynthetics or phototrophs. These are mainly green plants, cyanobacteria (blue-green algae).

Another group of autotrophs uses the energy that is released during chemical reactions. Such organisms are called chemotrophs or chemosynthetics.

Fungi, most animals and bacteria cannot synthesize organic substances themselves. Such organisms are called heterotrophs. For them, organic compounds synthesized by autotrophs serve as an energy source. Energy is used by living organisms for chemical, mechanical, thermal and electrical processes.

Preparatory stage of energy metabolism

Energy exchange is conventionally divided into three main stages. The first stage was called preparatory. At this stage, macromolecules are broken down to monomers under the influence of enzymes. In the course of reactions, a rather small amount of energy is released, which is dissipated in the form of heat.

Anoxic stage of energy metabolism

Anoxic (anaerobic) stage of energy metabolism occurs in cells. The monomers that were formed at the previous stage (glucose, glycerol, etc.) undergo further multi-stage cleavage without access to oxygen. The main thing at this stage is the process of splitting the glucose molecule into pyruvic or lactic acid molecules with the formation of two ATP molecules.

$C_6H_(12)O_6 + 2H_3PO_4 + 2ADP → 2C_3H_6O_3 + 2ATP + 2H_2O$

During this reaction (glycolysis reaction) about $200$ kJ of energy is released. However, not all of it is converted into heat. Part of it is used to synthesize two energy-rich (macroergic) phosphate bonds in ATP molecules. Glucose is also broken down during alcoholic fermentation.

$C_6H_(12)O_6 + 2H_3PO_4 + 2ADP → 2C_2H_5OH + 2CO_2 + 2ATP + 2H_2O$

In addition to alcohol, there are also such types of oxygen-free fermentation as butyric and lactic acid.

Oxygen stage of energy metabolism

At this stage, the compounds formed at the oxygen-free stage are oxidized to the final reaction products - carbon dioxide and water. English biochemist Adolph Krebs in $1937$ discovered the sequence of transformations of organic acids in the mitochondrial matrix. In his honor, the combination of these reactions was named the Krebs cycle.

Remark 1

The complete oxidation of lactic or pyruvic acid molecules formed during the anaerobic process to carbon dioxide and water is accompanied by the release of $2800$ kJ of energy. This amount is enough for the synthesis of $36$ ATP molecules ($18$ times more than at the previous stage).

The overall equation for the oxygen stage of energy metabolism looks like this:

$2C_3H_6O_3 + 6O_2 + 36ADP + 36H_3PO_4 → 6CO_2 + 42H_2O + 36ATP$

Summing up, we can write the total equation of energy exchange:

$C_6H_(12)O_6 + 6O_2 + 38ADP + 38H_3PO_4 → 6CO_2 + 44H_2O + 38ATP$

At the final stage, the products of metabolism are removed from the body.

Remember!

What is metabolism?

(from the Greek μεταβολή - “transformation, change”), or metabolism - a set of chemical reactions that occur in a living organism to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to environmental stimuli.

What two interrelated processes does it consist of?

Energy metabolism and plastic metabolism

Where in the human body is the breakdown of most of the organic substances that come with food?

Initially, in the digestive tract, then in cells and their organelles (mitochondria, cytoplasm).

Review questions and assignments

1. What is dissimilation? List its steps.

The set of splitting reactions of macromolecular compounds, which are accompanied by the release and storage of energy, is called energy exchange or dissimilation. Basically, energy is stored in the form of a universal energy-intensive compound - ATP.

1) Preparatory

2) Oxygen-free oxidation

3) Oxygen oxidation

2. What is the role of ATP in cell metabolism?

Adenosine triphosphoric acid (ATP) is a nucleotide consisting of a nitrogenous base (adenine), ribose sugar and three phosphoric acid residues (Fig. 53). ATP is the main energy molecule of the cell, a kind of energy accumulator. All processes in living organisms that require energy expenditure are accompanied by the conversion of an ATP molecule into ADP (adenosine diphosphoric acid). When the residue of phosphoric acid is split off, a large amount of energy is released - 40 kJ / mol. There are two such high-energy (so-called macroergic) bonds in the ATP molecule. Restoration of the ATP structure from ADP and phosphoric acid occurs in mitochondria and is accompanied by energy absorption.

3. What cell structures carry out ATP synthesis?

Mitochondria

4. Tell us about the energy metabolism in the cell using the breakdown of glucose as an example.

1) The preparatory stage of the breakdown of carbohydrates goes in the digestive tract to a simple carbohydrate - glucose, while little energy is released and it is dissipated in the body in the form of heat.

2) The oxygen-free stage of glucose breakdown is glycolysis (anaerobic oxidation). The stage takes place in the cytoplasm in the absence of free oxygen. Glucose C6H12O6 pyruvic acid (PVA) C3H4O3. Glucose is broken down to PVC with the release of 4ATP. 2ATP is then used in this step to further convert PVC to lactic acid. And as a result, in the second stage, 2ATP is released.

3) Oxygen oxidation - aerobic oxidation (or cellular respiration). The stage, as a result of which lactic acid is split under the action of molecular oxygen to the final decomposition products - carbon dioxide and water. Occurs in mitochondria on the respiratory chain of enzymes, which are located on the cristae of mitochondria. As a result of this stage, 36 ATP are released. Thus, in two stages - with the complete oxidation of 1 mol of glucose (1 molecule), 38 ATP (2ATP + 36ATP) is released. The final synthesis and supply of ATP is carried out in mitochondria - these organelles are called the energy centers of the cell.

6. Synonyms of the words "dissimilation" and "assimilation" are the terms "catabolism" and "anabolism". Explain the origin of these terms.

Catabolism (from the Greek Καταβολή, “dropping, destruction”) or energy metabolism, or dissimilation is a process of metabolic decay, decomposition into simpler substances (differentiation) or oxidation of a substance, usually proceeding with the release of energy in the form of heat and in the form ATP. Anabolism (from the Greek ἀναβολή, “rise”) is the name of all the processes of creating new substances, cells and tissues of the body. Examples of anabolism: the synthesis of proteins and hormones in the body, the creation of new cells, the accumulation of fats, the creation of new muscle fibers - this is all anabolism.

Think! Remember!

Since in cells all organic compounds are connected to each other by the main metabolites (PVK, acetyl-CoA) through which some organic substances can be converted into others in excess. For example, excess carbohydrates are converted into fats.

The energy that is released during the energy exchange goes to the processes in the plastic exchange. And the substances of plastic metabolism are split in energy metabolism.

3. Why, in your opinion, after hard physical work, in order to quickly relieve muscle pain, is it recommended to take a warm bath?

Muscle pain causes the accumulation of lactic acid during glycolysis, its concentration acts on the receptors, irritating them, causing a burning sensation. To remove this action, a rush of blood with oxygen is necessary, oxygen to break down lactic acid to the final decomposition products. One way is to take a warm bath. At the same time, the body warms up, the vessels expand and the blood with oxygen flows and nourishes all the muscles, thereby lactic acid is oxidized to carbon dioxide and water, pain in the muscles is relieved.

Question 1. What is dissimilation? List its steps.

Dissimilation, or energy metabolism, is a set of cleavage reactions of macromolecular compounds, which are accompanied by the release and storage of energy.

Dissimilation in aerobic (oxygen-breathing) organisms occurs in three stages: preparatory - the splitting of high-molecular compounds to low-molecular ones without storing energy;

oxygen-free - partial oxygen-free breakdown of compounds, energy is stored in the form of ATP;

oxygen - the final breakdown of organic substances to carbon dioxide and water, energy is also stored in the form of ATP.

Dissimilation in anaerobic (not using oxygen) organisms occurs in two stages: preparatory and anoxic. In this case, organic substances are not completely decomposed and much less energy is stored.

Question 2. What is the role of ATP in cell metabolism?

ATP (adenosine triphosphoric acid) is a nucleotide consisting of a nitrogenous base (adenine), a five-carbon monosaccharide (ribose) and three residues of phosphoric acid. This is a universal macroergic compound found in a variety of cells, in which there are two high-energy bonds between phosphoric acid residues. When such a bond is broken, a phosphoric acid residue is cleaved off and a large amount of energy (40 kJ/mol) is released. In this case, ATP is converted to ADP. If there is a splitting off of the second residue of phosphoric acid, ADP will turn into AMP. All processes in living organisms that require energy expenditure are accompanied by the conversion of ATP molecules into ADP (or even AMP).

Question 3. What cell structures carry out the synthesis of ATP?

In eukaryotic cells, the synthesis of the bulk of ATP from ADP and phosphoric acid occurs in mitochondria and is accompanied by the absorption (storage) of energy. In plastids, ATP is formed as an intermediate product of the light stage of photosynthesis.

Question 4. Tell us about the energy metabolism in the cell using the breakdown of glucose as an example.

Energy metabolism in aerobic organisms occurs in three stages.

Preparatory. In the gastrointestinal tract and lysosomes of cells, under the action of digestive enzymes, polysaccharides are broken down to monosaccharides, in particular to glucose. The energy released in this case is not stored, but dissipated in the form of heat.

Oxygen-free. As a result of glycolysis, one molecule of glucose is split into two molecules of pyruvic acid:

C 6 Hi 2 0 6 -> 2C 3 H 4 0 3

At the same time, 60% of the released energy is converted into heat, and 40% is stored in the form of ATP. When one glucose molecule breaks down, 2 ATP molecules are formed. Then fermentation occurs in anaerobic organisms - alcohol (C 2 H 5 OH - ethyl alcohol) or lactic acid (C 3 H 6 0 3 - lactic acid). In aerobic organisms, the third stage of energy metabolism begins.

Oxygen. At this stage, the carbon and hydrogen contained in pyruvic acid combine with oxygen to form carbon dioxide and water. This releases a large amount of energy, most of which is stored in the form of ATP. When two molecules of pyruvic acid are oxidized, energy is released that allows the formation of 36 ATP molecules. This process takes place in mitochondria and is divided into two multistage stages (the Krebs cycle and oxidative phosphorylation).

The final equation of the oxygen dissimilation path:

C 6 H 12 0 6 + 6O 2 + 38ADP + 38F ->

energy exchange(catabolism, dissimilation) - a set of reactions of splitting organic substances, accompanied by the release of energy. The energy released during the breakdown of organic substances is not immediately used by the cell, but is stored in the form of ATP and other high-energy compounds. ATP is the universal energy source of the cell. ATP synthesis occurs in the cells of all organisms in the process of phosphorylation - the addition of inorganic phosphate to ADP.

At aerobic organisms (living in an oxygen environment) distinguish three stages of energy metabolism: preparatory, oxygen-free oxidation and oxygen oxidation; at anaerobic organisms (living in an oxygen-free environment) and aerobic organisms with a lack of oxygen - two stages: preparatory, oxygen-free oxidation.

Preparatory stage

It consists in the enzymatic breakdown of complex organic substances to simple ones: protein molecules - to amino acids, fats - to glycerol and carboxylic acids, carbohydrates - to glucose, nucleic acids - to nucleotides. The breakdown of high-molecular organic compounds is carried out either by enzymes of the gastrointestinal tract or by enzymes of lysosomes. All the released energy is dissipated in the form of heat. The resulting small organic molecules can be used as "building material" or can be further broken down.

Anoxic oxidation, or glycolysis

This stage consists in the further splitting of organic substances formed during the preparatory stage, occurs in the cytoplasm of the cell and does not need the presence of oxygen. The main source of energy in the cell is glucose. The process of oxygen-free incomplete breakdown of glucose - glycolysis.

The loss of electrons is called oxidation, the acquisition is called reduction, while the electron donor is oxidized, the acceptor is reduced.

It should be noted that biological oxidation in cells can occur both with the participation of oxygen:

A + O 2 → AO 2,

and without his participation, due to the transfer of hydrogen atoms from one substance to another. For example, substance "A" is oxidized at the expense of substance "B":

AN 2 + B → A + BH 2

or due to electron transfer, for example, ferrous iron is oxidized to trivalent:

Fe 2+ → Fe 3+ + e -.

Glycolysis is a complex multi-step process that includes ten reactions. During this process, glucose dehydrogenation occurs, the coenzyme NAD + (nicotinamide adenine dinucleotide) serves as a hydrogen acceptor. As a result of a chain of enzymatic reactions, glucose is converted into two molecules of pyruvic acid (PVA), while a total of 2 ATP molecules and a reduced form of the hydrogen carrier NAD H 2 are formed:

C 6 H 12 O 6 + 2ADP + 2H 3 RO 4 + 2NAD + → 2C 3 H 4 O 3 + 2ATP + 2H 2 O + 2NAD H 2.

The further fate of PVC depends on the presence of oxygen in the cell. If there is no oxygen, yeast and plants undergo alcoholic fermentation, in which acetaldehyde is first formed, and then ethyl alcohol:

1. C 3 H 4 O 3 → CO 2 + CH 3 SON,
2. CH 3 SON + NAD H 2 → C 2 H 5 OH + OVER +.

In animals and some bacteria, with a lack of oxygen, lactic acid fermentation occurs with the formation of lactic acid:

C 3 H 4 O 3 + NAD H 2 → C 3 H 6 O 3 + OVER +.

As a result of glycolysis of one glucose molecule, 200 kJ are released, of which 120 kJ is dissipated in the form of heat, and 80% is stored in ATP bonds.

Oxygen oxidation, or respiration

It consists in the complete breakdown of pyruvic acid, occurs in mitochondria and with the obligatory presence of oxygen.

Pyruvic acid is transported to mitochondria (the structure and functions of mitochondria - lecture No. 7). Here, dehydrogenation (hydrogen elimination) and decarboxylation (carbon dioxide elimination) of PVC take place with the formation of a two-carbon acetyl group, which enters into a cycle of reactions called the Krebs cycle reactions. There is further oxidation associated with dehydrogenation and decarboxylation. As a result, three molecules of CO 2 are removed from the mitochondrion for each destroyed PVC molecule; five pairs of hydrogen atoms are formed associated with carriers (4NAD H 2, FAD H 2), as well as one ATP molecule.

The overall reaction of glycolysis and destruction of PVC in mitochondria to hydrogen and carbon dioxide is as follows:

C 6 H 12 O 6 + 6H 2 O → 6CO 2 + 4ATP + 12H 2.

Two ATP molecules are formed as a result of glycolysis, two - in the Krebs cycle; two pairs of hydrogen atoms (2NADHH2) were formed as a result of glycolysis, ten pairs - in the Krebs cycle.

The last step is the oxidation of hydrogen pairs with the participation of oxygen to water with simultaneous phosphorylation of ADP to ATP. Hydrogen is transferred to three large enzyme complexes (flavoproteins, coenzymes Q, cytochromes) of the respiratory chain located in the inner membrane of mitochondria. Electrons are taken from hydrogen, which are eventually combined with oxygen in the mitochondrial matrix:

O 2 + e - → O 2 -.

Protons are pumped into the intermembrane space of mitochondria, into the "proton reservoir". The inner membrane is impermeable to hydrogen ions, on the one hand it is charged negatively (due to O 2 -), on the other - positively (due to H +). When the potential difference across the inner membrane reaches 200 mV, protons pass through the channel of the ATP synthetase enzyme, ATP is formed, and cytochrome oxidase catalyzes the reduction of oxygen to water. So, as a result of the oxidation of twelve pairs of hydrogen atoms, 34 ATP molecules are formed.

All biosynthetic reactions involve the absorption of energy.

The totality of biosynthesis reactions is called plastic exchange or assimilation (Latin "similis" - similar). The meaning of this process is that food substances entering the cell from the external environment, which differ sharply from the substance of the cell, become the substances of the cell as a result of chemical transformations.

splitting reactions. Complex substances break down into simpler ones, high-molecular ones into low-molecular ones. Proteins are broken down into amino acids, starch into glucose. These substances are split into even lower molecular weight compounds, and in the end, very simple, energy-poor substances are formed - CO2 and H2O. Splitting reactions in most cases are accompanied by the release of energy. The biological significance of these reactions is to provide the cell with energy. Any form of activity—movement, secretion, biosynthesis, etc.—needs the expenditure of energy.

The totality of the cleavage reaction is called the energy exchange of the cell or dissimilation. Dissimilation is directly opposite to assimilation: as a result of splitting, substances lose their similarity with the substances of the cell.

Plastic and energy exchanges (assimilation and dissimilation) are inextricably linked. On the one hand, biosynthesis reactions require the expenditure of energy, which is drawn from cleavage reactions. On the other hand, for the implementation of energy metabolism reactions, constant biosynthesis of enzymes serving these reactions is necessary, since in the process of work they wear out and are destroyed.

The complex systems of reactions that make up the process of plastic and energy exchanges are closely connected not only with each other, but also with the external environment. From the external environment, food substances enter the cell, which serve as a material for plastic exchange reactions, and in the splitting reactions, the energy necessary for the functioning of the cell is released from them. Substances that can no longer be used by the cell are released into the external environment.

The totality of all enzymatic reactions of the cell, i.e. the totality of plastic and energy exchanges (assimilation and dissimilation), interconnected and with the external environment, is called the exchange of substances and energy. This process is the main condition for maintaining the life of the cell, the source of its growth, development and functioning .

19. Metabolism and energy in the cell. Photosynthesis, chemosynthesis. The process of assimilation (basic reactions). Metabolism is a unity of assimilation and dissimilation. Dissimilation is an exothermic process, i.e. the process of releasing energy due to the breakdown of cell substances. Substances formed during dissimilation also undergo further transformations. Assimilation is the process of assimilation of substances entering the cell with specific substances characteristic of this cell. Assimilation is an endothermic process that requires energy. The source of energy is previously synthesized substances that have undergone decay in the process of dissimilation. Photosynthesis is the process of converting the energy of sunlight into the energy of chemical compounds. Photosynthesis- this is the process of formation of organic substances (glucose, and then starch) from inorganic substances, in chloroplasts in the light with the release of oxygen. Photosynthesis proceeds in 2 phases: light and shadow. The light phase proceeds in the light. During the light phase, chlorophyll is excited by absorbing a quantum of light. In the light phase, photolysis of water occurs, followed by the release of oxygen into the atmosphere. In addition, the following processes take place in the light phase of photosynthesis: the accumulation of hydrogen protons, the synthesis of ATP from ADP, the addition of H + to a special carrier NADP

TOTAL LIGHT REACTION:

The formation of ATP and NADP * H, the release of O2 into the atmosphere.

dark phase(CO2 fixation cycle, Calvin cycle) takes place in the stroma of the chloroplast. The following processes take place in the dark phase

ATP and NADP*H are taken from the light reaction

From the atmosphere - CO2

1)CO2 fixation

2) Formation of glucose

3) Starch formation

FINAL EQUATION:

6CO2 + 6H2O - (chlorophyll, light) - С6H12O6 + 6O2

Chemosynthesis is the synthesis of organic substances due to the energy of chemical reactions. Chemosynthesis is carried out by bacteria. The main reactions of photosynthesis: 1) sulfur oxidation: 2H2S + O2 = 2H20 + 2S

2S + O2 + 2H2O = 2H2SO4 2) nitrogen oxidation: 2NH3 + 3O2 = 2HNO2 + 2H2O 2HNO2 + O2 = HNO3 3) oxygen oxidation 2H2 + O2 = 2H2O 4) iron oxidation: 4FeCO3 + O2 + 6H2O = 4Fe(OH)3 + 4CO2

20. Metabolism in the cell. dissimilation process. The main stages of energy metabolism. Metabolism is a unity of assimilation and dissimilation. during dissimilation, are also subjected to further transformations. Assimilation is the process of assimilation of substances entering the cell with specific substances characteristic of this cell. Assimilation is an endothermic process that requires energy. The source of energy is previously synthesized substances that have undergone decay in the process of dissimilation. Dissimilation is an exothermic process, i.e. the process of releasing energy due to the breakdown of cell substances. Substances formed All the functions performed by the cell require the expenditure of energy, which is released in the process of dissimilation. The biological significance of dissimilation is reduced not only to the release of energy needed by the cell, but often to the destruction of substances harmful to the body. The entire process of dissimilation, or energy metabolism, consists of 3 stages: preparatory, oxygen-free and oxygen. In the preparatory stage, under the action of enzymes, the polymers are degraded to monomers. So, proteins are broken down into amino acids, polysaccharides - into monosaccharides, fats - into glycerol and fatty acids. In the preparatory phase, little energy is released and is usually dissipated in the form of heat. 2) Anoxic or anaerobic stage. Let's take glucose as an example. In the anaerobic stage, glucose is decomposed to lactic acid: C6H12O6 + 2ADP + H3RO4 = 2C3H6O3 + 2H2O + 2ATP (lactic acid) 3) Oxygen stage. At the oxygen stage, substances are oxidized to CO2 and H2O. With the access of oxygen, pyruvic acid penetrates into the mitochondria and undergoes oxidation: С3H6O3 + 6O2-6CO2 + 6H2O + 36ATP Total equation: C6H12O6 + 6O2-6CO2 + 6H2O + 38ATP

Dissimilation is a complex of chemical reactions in which there is a gradual decay of complex organic substances to simpler ones. This process is accompanied by the release of energy, a significant part of which is used in the synthesis of ATP.

Dissimilation in biology

Dissimilation is the opposite process of assimilation. Nucleic acids, proteins, fats and carbohydrates act as initial substances to be decomposed. And the end products are water, carbon dioxide and ammonia. In the body of animals, decay products are excreted as they gradually accumulate. And in plants, carbon dioxide is partially released, and ammonia is used in full in the process of assimilation, serving as the starting material for the biosynthesis of organic compounds.

The relationship of dissimilation and assimilation allows the tissues of the body to be constantly updated. For example, within 10 days, half of the albumin cells in human blood are renewed, and in 4 months all red blood cells are regenerated. The ratio of the intensity of two opposite metabolic processes depends on many factors. This is the stage of development of the organism, and age, and the physiological state. In the course of growth and development, assimilation prevails in the body, as a result, new cells, tissues and organs are formed, their differentiation occurs, that is, body weight increases. In the presence of pathologies and during starvation, the process of dissimilation prevails over assimilation, and the body decreases in weight.

All organisms can be divided into two groups, depending on the conditions in which dissimilation occurs. These are aerobes and anaerobes. The former require free oxygen for life, the latter do not need it. In anaerobes, dissimilation proceeds by fermentation, which is an oxygen-free enzymatic breakdown of organic substances to simpler ones. For example, lactic acid or alcoholic fermentation.

The breakdown of organic matter in aerobes is carried out in three steps. At the same time, several specific enzymatic reactions occur on each of them.

The first stage is preparatory. The main role at this stage belongs to the digestive enzymes located in the gastrointestinal tract in multicellular organisms. In unicellular organisms, lysosome enzymes. During the first stage, proteins break down into amino acids, fats form glycerol and fatty acids, polysaccharides break down into monosaccharides, nucleic acids into nucleotides.

glycolysis

The second stage of dissimilation is glycolysis. It flows without oxygen. The biological essence of glycolysis is that it is the beginning of the breakdown and oxidation of glucose, resulting in the accumulation of free energy in the form of 2 ATP molecules. This occurs in the course of several consecutive reactions, the final result of which is the formation of two pyruvate molecules and the same amount of ATP from one glucose molecule. It is in the form of adenosine triphosphoric acid that part of the energy released as a result of glycolysis is stored, the rest is subject to dissipation in the form of heat. Chemical reaction of glycolysis: C6H12O6 + 2ADP + 2P → 2C3H4O3 + 2ATP.

Under conditions of oxygen deficiency in plant cells and in yeast cells, pyruvirate is split into two substances: ethyl alcohol and carbon dioxide. This is alcoholic fermentation.

The amount of energy released during glycolysis is not enough for those organisms that breathe oxygen. That is why in the body of animals and humans, during heavy physical exertion, lactic acid is synthesized in the muscles, which serves as a reserve source of energy and accumulates in the form of lactate. A characteristic feature of this process is the appearance of pain in the muscles.

Dissimilation is a very complex process, and the third oxygen stage also consists of two successive reactions. We are talking about the Krebs cycle and oxidative phosphorylation.

During oxygen respiration, pyruvirate is oxidized to the final products, which are CO2 and H2O. This releases energy stored in the form of 36 ATP molecules. Then the same energy provides the synthesis of organic substances in the plastic volume. Evolutionarily, the emergence of this stage is associated with the accumulation of molecular oxygen in the atmosphere and the appearance of aerobic organisms.

The site of oxidative phosphorylation (cellular respiration) is the inner membranes of mitochondria, inside which there are carrier molecules that transport electrons to molecular oxygen. The energy generated at this stage is partially dissipated in the form of heat, while the rest goes to the formation of ATP.

Dissimilation in biology is an energy exchange, the reaction of which looks like this: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38ATP.

Thus, dissimilation is a set of reactions that occur due to organic substances that were previously synthesized by the cell, and free oxygen that came from the external environment during respiration.

Assimilation, anabolism(lat. Assimilo - I liken - likening, merging, assimilation) - in biology - the processing and use by organisms of substances coming from the environment.

Assimilation and the opposite process, dissimilation, are inextricably linked with it, underlie the most important property of living matter - metabolism. The nature of these continuous processes determines the vitality and development of the organism.

Through assimilation, the organism builds its body at the expense of the environment; growth of an organism is possible if assimilation prevails over dissimilation.

essence assimilation basically comes down to the synthesis of all substances necessary for the life of the organism in a certain way, which has developed in the process of evolution. So, in autotrophic organisms, during assimilation, complex organic compounds are synthesized from inorganic ones, for example, during photosynthesis, carbohydrates are assimilated by green plants from carbon dioxide in the air and water. In heterotrophic organisms that feed only on substances of plant and animal origin, synthesis during assimilation is preceded by their splitting and processing.

Features of organisms acquired in the process of evolution determine the nature of assimilation, but changes in assimilation, in turn, affect the nature of organisms, changing their heredity.

When light quanta hit chlorophyll, chlorophyll molecules are excited. Excited electrons pass through the electron chain on the membrane to ATP synthesis. At the same time, the splitting of water molecules occurs. H + ions combine with reduced NADP (PS1) at the expense of chlorophyll electrons; the resulting energy goes to the synthesis of ATP. O 2 ions donate electrons to chlorophyll (FS2) and turn into free oxygen: H 2 O + NADP + hν → NADPH + H + + 1 / 2O 2 + 2ATP

dark phase Dark phase - fixation of C, synthesis of C 6 H 12 O 6. The energy source is ATP. In the stroma of chromoplasts (where ATP, NADPH and H + come from thylakoids gran and CO 2 from the air), cyclic reactions take place, resulting in CO 2 fixation, its reduction of H (due to NADPH + H +) and the synthesis of C 6 H 12 About 6:

CO 2 + NADPH + H + + 2ATP → 2ADP + C 6 H 12 O 6

Dissimilation in biology refers to the reverse process of assimilation. In other words, this is the stage of metabolism in the body, at which the destruction of complex organic compounds occurs with the production of simpler ones. There are several different definitions of the concept of dissimilation. Wikipedia interprets this term as the loss of specificity of complex substances and the destruction of complex organic compounds to simpler ones. A synonym for this concept is catabolism.

In the metabolism in a living cell, the central place is occupied by complex dissimilation reactions - respiration, fermentation, glycolysis. The result of these biological processes is the release of energy, which is contained in complex molecules. This energy is partially transformed into the energy of adenosine triphosphate (ATP). The end products of dissimilation in all living cells are carbon dioxide, ammonia and water. Plant cells were able to partially use these substances for assimilation. Animal organisms remove these decay products to the outside.

According to the nature of the participation of oxygen molecules in catabolism reactions, all organisms are usually divided into aerobic, that is, proceeding with the participation of oxygen, and anaerobic (oxygen-free).

Anaerobic organisms carry out the processes of energy metabolism by fermentation, and aerobic organisms - by respiration.

Fermentation is a set of reactions of decomposition of organic molecules to simpler compounds, in which energy is released and ATP molecules are synthesized. Among other ways of obtaining energy, fermentation is considered the most inefficient: from 1 mol of glucose during lactic acid fermentation, 2 mol of ATP is obtained.

Two types of fermentation are most widely distributed in nature:

1. Lactic acid - includes the process of anaerobic breakdown of glucose with the formation of lactic acid. This type of fermentation is characteristic of lactic acid bacteria - they are responsible for the souring of milk. In a broader sense, the process of lactic acid fermentation is one of the stages of the respiration process in the vast majority of aerobic organisms, including humans;
2. Alcoholic fermentation is the process of anaerobic breakdown of glucose and is accompanied by the formation of carbon dioxide and ethyl alcohol. During this reaction, a certain amount of energy is released, which is spent on the synthesis of an ATP molecule. Alcoholic fermentation is most characteristic of fruits and other parts of the plant under anaerobic conditions.

Respiration in the context of the disclosed issue has a broader meaning than the usual process of gas exchange. In this case, respiration should be understood as a kind of dissimilation, which is realized in an environment containing oxygen molecules.

The breathing process has two parts:

1. The process of gas exchange in the respiratory system of multicellular organisms and in tissues;
2. The sequence of biochemical oxidation reactions that organic compounds undergo. As a result of these processes, water, ammonia and carbon dioxide are formed. The formation of some other simple compounds is possible - hydrogen sulfide, inorganic phosphorus compounds, etc.

For most people, a narrower interpretation of the process of respiration as gas exchange is customary.

The process of dissimilation in living cells consists of several stages. It should be noted that these stages may proceed differently in different organisms.

In aerobic organisms, the process of catabolism includes three main stages. Each stage proceeds with the participation of special enzymatic systems.

1. Initial stage or preparatory. In multicellular organisms, it is carried out in the cavity of the digestive tract. Digestive enzymes are directly involved in the process. In unicellular organisms, this stage proceeds with the participation of lysosomal enzymes. At the preparatory stage, proteins are broken down into amino acids. Fats break down into fatty acids and glycerol. Polysaccharides are cleaved at this stage to monosaccharides, and nucleic acids to nucleotides. In biology, such a process is usually called digestive;
2. The second stage of catabolism is glycolysis or anoxic. This stage is the initial stage of the breakdown of glucose molecules and the accumulation of energy in the form of ATP molecules. Glycolysis takes place in the cell cytoplasm. At this time, a sequence of chemical reactions is observed: one molecule of glucose is converted into two molecules of pyruvic acid (or pyruvate) and two molecules of ATP. Part of the released energy is stored in the form of ATP, the rest is dissipated in the form of heat. Under conditions of lack of oxygen in the cells of plants and yeast fungi, pyruvate molecules are split into carbon dioxide and ethanol (alcoholic fermentation);
3. The oxygen stage of catabolism consists, in turn, of two successive phases - the Krebs cycle and oxidative phosphorylation. Consider what stage of dissimilation is called oxygen. Here, the final splitting of pyruvate to the simplest constituents - water and carbon dioxide. During the oxidation of pyruvate, only 36 ATP molecules are formed. Of these, 34 molecules are formed as a result of a chain of reactions of the Krebs cycle and the remaining 2 as a result of oxidative phosphorylation. The evolutionary oxygen stage arose after a sufficient number of oxygen molecules accumulated in the earth's atmosphere and organisms with an aerobic type of metabolism appeared.

As a result of dissimilation reactions energy is obtained, which is subsequently used by the body for plastic metabolism.

The processes of oxidative phosphorylation occur on the inner mitochondrial membranes. These membranes have built-in carrier molecules. Their function is to deliver electrons to oxygen atoms. Some of the energy in this reaction is dissipated as heat.

As a result of glycolysis reactions, a small amount of energy is produced, which is not enough for the vital activity of organisms with an aerobic type of metabolism. This is the reason why lactic acid is formed in muscle cells with a lack of oxygen. This substance accumulates as lactate and causes muscle pain.