The processes of assimilation and dissimilation in the body. Assimilation and dissimilation as the basis for self-renewal of biological systems. Definition, essence, meaning. The breathing process has two parts.

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 reactions energy metabolism a 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 sunlight energy into energy chemical compounds. Photosynthesis 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 occur 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 - the synthesis of organic substances due to energy 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 final 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. characteristic feature 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. It's about 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, is inextricably linked with it. the most important property 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, 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 concept of dissimilation. Wikipedia treats this term as loss of specificity 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, a central place is occupied by complex reactions dissimilation - 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 decomposition reactions 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:

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;
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:

The process of gas exchange in the respiratory system of multicellular organisms and in tissues;
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 in different organisms these stages can proceed in different ways.

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

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;
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);
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.

Assimilation in biology is a process that plays an important role in the digestive system of a living organism. What is it? Let's say you ate a meal today to get some energy. But have you ever wondered how food gets from the plate into the cells? After you eat something, your body starts to break down the food during digestion, absorbing the nutrients and distributing them to the cells during assimilation, where they are used for growth and repair.

What happens after eating?

To understand what digestion and assimilation is in biology, let's first look at how we digest ordinary food. Let's take a cheeseburger as an example. During chewing, food is soaked, crushed and turned into a bolus, which then travels through the esophagus to the stomach, where already strong acids and enzymes break it apart.

Carbohydrates and proteins (bun and meat) begin to be digested before anyone else. Further in the small intestine, fats (cheese) begin to break down into their individual components, called fatty acids. At this point, the digestion of the cheeseburger is complete. Now it's time to assimilate the nutrients that have entered your body.

Nutrient absorption

Nutrient absorption takes place in the small intestine, which is lined with small projections called microvilli. These important cells take nutrients from the intestines and pump them into the blood, which delivers them to the body. To understand this process, let's look at how carbohydrates are digested specifically.

By the time the carbohydrates in a hamburger bun reach the small intestine, they are broken down into a sugar known as glucose. Microvilli contain small pumps that suck it out of the intestinal lumen and move it to its epithelial cells. However, for sugar to reach the rest of the body, it must enter the blood stream. The other side of the intestinal epithelial cells has another pump that directs glucose to the blood vessels that surround the intestines.

Too much glucose in the blood can cause serious problems, so some of it is taken to the liver for storage. The cells of this vital important body store excess sugar as glycogen. From there, glucose is delivered to all cells in the body, which use it to create cellular energy, or ATP, needed to meet all the needs of cells and the body as a whole. Nutrients are not the only thing needed to keep the body healthy. Sufficient water intake is very important.

Assimilation in biology - what is it?

Biological absorption is a combination of two processes during which nutrients are supplied to the cells. The first involves the absorption of vitamins, minerals and other chemical substances from food. In the human body, this is done through physical (oral chewing and gastric foaming) and chemical breakdown (enzymes and acids). The second process, which is called bioassimilation, is the chemical change of substances in the blood, liver, or cellular secretions.

Assimilation and dissimilation in biology

Dissimilation in biology is the process of decomposition of organic compounds (proteins, fats, carbohydrates, etc.) into simple substances. The unity of assimilation and dissimilation ensures the exchange of matter and energy, which is the cornerstone of life and ensures the continuity of renewal of organic matter throughout the entire life cycle of the organism.

Dissimilation in plant and animal organisms

Dissimilation in plants is central to the metabolism of a number of processes, including respiration and glycolysis. The release of energy and the usable result of these processes is necessary for the existence of vital signs. Among the end products of dissimilation, the leading positions are occupied by water, gaseous carbon dioxide and ammonia.

If in animals these products are excreted from the outside in the process of accumulation, then in plants carbon dioxide (not in full measure) and ammonia are used for the biosynthesis of organic matter and are the starting material for assimilation. The intensity of dissimilation processes in plants varies depending on the ontogeny stage of the organism and depends on some other factors.

Examples of biological assimilation

The main source of energy for all life on the planet is solar radiation. All organisms living on Earth can be divided into autotrophic and heterotrophic. The first group is predominantly green plants capable of converting radiant energy from the sun and, through photosynthesis, obtaining organic compounds from inorganic substances.

The rest of living organisms, apart from some micro-organisms capable of obtaining energy by means of chemical reactions, assimilate already formed organic matter and use it as an energy source or as structural material for building organs. The time when the most active and intensive assimilation in biology occurs is the young age in animals and the growing season in plants.

Metabolism: the unity of two processes

Metabolism is a unity of two processes: assimilation and dissimilation. Assimilation is the sum of all the processes of creating living matter: the absorption by the cell of substances entering the body from the environment, the formation of more complex chemical compounds from simpler ones, and so on. Assimilation in biology is the process in which cells using different materials turn into living matter. Dissimilation is the destruction of living matter, decay, splitting of substances in cellular structures, in particular in protein compounds. Assimilation (examples in nature are photosynthesis, nitrogen fixation from the soil, absorption of nutrients during digestion) and dissimilation are inextricably linked. Assimilation is accompanied by an increase in destruction processes, which, in turn, prepare the ground for assimilation.

Topic: Assimilation and dissimilation. Metabolism. The purpose of the lesson: To introduce students to the concept of "metabolism in the body", assimilation, dissimilation, metabolism. Lesson objectives: Educational: to concretize knowledge about metabolism (metabolism) as a property of living organisms, to introduce the two sides of the exchange, to identify the general patterns of metabolism; to establish the connection of plastic and energy metabolism at different levels of organization of the living and their connection with environment. Developing: to form the ability to highlight the essence of the process in the material being studied; generalize and compare, draw conclusions; work with text, diagrams, other sources; implementation creativity students, development of independence. Educational: using the acquired knowledge, understand the prospects for the practical use of photosynthesis; understand the impact of metabolism on the preservation and promotion of health. Equipment: computer, projector, presentation. Type of lesson: learning new material. Forms of student work: independent work with a textbook individual work at the blackboard, frontal work.

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LESSON PLAN

Subject: Assimilation and dissimilation. Metabolism.

The purpose of the lesson:

To acquaint students with the concept of "metabolism in the body", assimilation, dissimilation, metabolism.

Lesson objectives:

Educational: to concretize knowledge about metabolism (metabolism) as a property of living organisms, to acquaint with the two sides of the exchange, to identify the general patterns of metabolism; to establish the connection of plastic and energy exchange at different levels of organization of the living and their connection with the environment.

Developing: to form the ability to highlight the essence of the process in the material being studied; generalize and compare, draw conclusions; work with text, diagrams, other sources;

realization of the creative potential of students, development of independence.

Educational: using the acquired knowledge, understand the prospects for the practical use of photosynthesis; understand the impact of metabolism on the preservation and promotion of health.

Equipment: computer, projector, presentation.

Lesson type: learning new material.

Forms of student work:independent work with a textbook, individual work at the blackboard, frontal work.

During the classes

Organizing time.

II. Repetition of material

Checking the correctness of filling in the table "Comparison of the structure of eukaryotic and prokaryotic cells." (Student answer at the blackboard.)
Frontal discussion on:

What is the role of the spore in prokaryotes? How is it different from eukaryotic spores?
Comparing the structure and life processes of eukaryotes and prokaryotes, highlight the signs that allow us to assume which cells are historically older and which are younger.
What are enzymes? What is their role in the body?
What is metabolism? Give examples of metabolism in the body.

III. Learning new material.

Task: compare two definitions, find if they are different or similar. How can you explain this?

Metabolism consists of two interrelated processes - anabolism and catabolism.

1. In the course of assimilation, complex molecules are synthesized from simple precursor molecules or from molecules of substances that come from the external environment.

2. The most important processes of assimilation are the synthesis of proteins and nucleic acids (typical of all organisms) and the synthesis of carbohydrates (only in plants, some bacteria and cyanobacteria).

3. In the process of assimilation during the formation of complex molecules, energy is accumulated, mainly in the form chemical bonds.

1. When chemical bonds are broken in the molecules of organic compounds, energy is released and stored in the form of ATP.

2. ATP synthesis in eukaryotes occurs in mitochondria and chloroplasts, and in prokaryotes - in the cytoplasm, on membrane structures.

3. Dissimilation provides all biochemical processes in the cell with energy.

All living cells constantly need the energy necessary for the flow of various biological and chemical reactions in them. Some organisms use the energy of sunlight for these reactions (during photosynthesis), others use the energy of chemical bonds of organic substances that come with food. The extraction of energy from food substances is carried out in the cell by splitting and oxidizing them with oxygen supplied during respiration. Therefore, this process is calledbiological oxidation, or cellular respiration.

Biological oxidation involving oxygen is called aerobic , without oxygen anaerobic . The process of biological oxidation is multistage. At the same time, energy is accumulated in the cell in the form of ATP molecules and other organic compounds.

IV. Consolidation of the studied material.

What is assimilation? Give examples of synthesis reactions in a cell.
What is dissimilation? Give examples of decay reactions in a cell.
Prove that assimilation and dissimilation are two sides of a single process of metabolism and energy - metabolism.

Exercise. Establish a correspondence between the processes occurring in the cells of organisms and their belonging to assimilation or dissimilation:

Processes occurring in cells

Metabolism

1. Water evaporation

Assimilation is the totality of all complex creative processes occurring in cells, and hence in the whole organism. Assimilation is the accumulation of energy.
Dissimilation is a set of oxidative processes in which energy is released. It is this energy that is used in the future for the implementation of all vital functions of the body.

Thus, these two opposite processes are so interconnected with each other that the cessation of one of them entails the cessation of all metabolism, and hence life.

Despite such a strong relationship and interdependence, the processes of assimilation and dissimilation are not always mutually balanced. Age is key here.

The younger the human body, the more intense the processes of assimilation proceed in it. In older people, on the contrary, dissimilation prevails over assimilation. Especially intensive metabolism is observed in newborns and in adolescents during puberty.

All living organisms are capable of exchanging substances with the environment, absorbing from it the elements necessary for nutrition and releasing waste products. In the circulation of organic substances, the processes of synthesis and decay became the most significant.

Assimilation or plastic exchange is a set of synthesis reactions that take place with the expenditure of ATP energy. In the process of assimilation, they synthesize organic matter needed by the cell. provides growth, development, renewal of the body and the accumulation of reserves used as an energy source. From the point of view of thermodynamics, organisms are open systems, i.e., they can exist only with a continuous influx of energy from outside. Assimilation is balanced by the sum of dissimilation (decay) processes. Examples of such reactions are photosynthesis, protein biosynthesis, and DNA replication.

Amino acids -> Proteins

Glucose -> Polysaccharides

Glycerin + Fatty acid-> Fats

Nucleotides -> Nucleic acids

The other side of metabolism is dissimilation processes, as a result of which complex organic compounds break down into simple compounds, while their similarity with body substances is lost and energy is released, stored in the form of ATP, necessary for biosynthesis reactions. Therefore, dissimilation is also called energy exchange. The most important processes of energy metabolism are respiration and fermentation.

Proteins -> Amino acids

Polysaccharides -> Glucose

Fats -> Glycerol + Fatty acids

Nucleic acids -> Nucleotides

Metabolism ensures consistency chemical composition and the structure of all parts of the body and, as a result, the constancy of functioning in continuously changing environmental conditions.

Deoxyribonucleic acid, its structure and properties. DNA monomers. Methods for joining nucleotides. Nucleotide complementarity. Antiparallel polynucleotide chains. replication and repair.

The structure of the DNA molecule was deciphered in 1953 by Watson, Crick, Wilkins. These are two helical antiparallel (opposite end 3 / one strand is 5 / end another) polynucleotide chains. The monomers of DNA are nucleotides., each of them includes: 1) deoxyribose; 2) a phosphoric acid residue; 3) one of the four nitrogenous bases (adenine, thymine, guanine, cytosine).). In the cells of prokaryotic organisms (bacteria and archaea), a circular or linear DNA molecule, the so-called nucleoid attached to the inside of the cell membrane. DNA is a long polymer molecule made up of repeating blocks called nucleotides. Nucleotides are connected in a chain due to phosphorus-diester bonds between the deoxyribose of one residue and the phosphoric acid residue of another nucleotide. Nitrogenous bases attach to deoxyribose and form side radicals. Hydrogen bonds are established between the nitrogenous bases of DNA chains (2 between A and T, 3 between G and C). The strict correspondence of nucleotides to each other in paired DNA chains is called complementarity.

REPAIR DNA- a special function of cells, which consists in the ability to repair chemical damage and breaks in DNA molecules damaged during normal DNA biosynthesis in the cell or as a result of exposure to physical or chemical agents. It is carried out by special enzyme systems of the cell. A number of hereditary diseases (eg, xeroderma pigmentosum) are associated with impaired repair systems. Each of the reparation systems includes the following components:

DNA helicase- an enzyme that "recognizes" chemically altered sites in the chain and breaks the chain near the damage; an enzyme that removes the damaged area;

DNA polymerase- an enzyme that synthesizes the corresponding section of the DNA chain instead of the deleted one;

DNA ligase is an enzyme that closes the last bond in the polymer chain and thereby restores its continuity.

Replication of DNA molecules occurs during the synthetic period of interphase. Each of the two chains of the "parent" molecule serves as a template for the "daughter". After replication, the newly synthesized DNA molecule contains one "maternal" strand, and the second - a "daughter", newly synthesized (semi-conservative method). For template synthesis of a new DNA molecule, it is necessary that the old molecule be despiralized and stretched. Replication begins at several locations in the DNA molecule. The section of a DNA molecule from the start of one replication to the start of another is called replicon . A prokaryotic cell contains one replicon, while a eukaryotic cell contains many replicons. The origin of replication is activated by primers (seeds) consisting of 100-200 base pairs. DNA enzyme - helicase unwinds and separates the parent helix DNA into 2 strands, on which, according to the principle of complementarity with the participation DNA polymerase enzyme assembles "daughter" strands of DNA. Enzyme DNA topoisomerase twists"daughter" DNA molecules. In each replicon, DNA polymerase can move along the "mother" strand in only one direction (3/ ⇒ 5/). Thus, the addition of complementary nucleotides of the daughter strands proceeds in opposite directions (anti-parallel). Replication in all replicons occurs simultaneously. Okazaki fragments and parts of "daughter" strands synthesized in different replicons are fused into a single strand enzyme ligase. Replication is characterized by semi-conservation, antiparallelism and discontinuity (Okazaki fragments).

The repair mechanism is based on the presence of two complementary chains in the DNA molecule. The distortion of the nucleotide sequence in one of them is detected by specific enzymes. Then the corresponding site is removed and replaced by a new one, synthesized on the second complementary DNA strand. Taku reparation is called excisional , those. with cut. It is carried out before the next replication cycle, so it is also called pre-replicative .

In the case when the excision repair system does not correct a change that has arisen in one DNA strand, during replication this change is fixed and it becomes the property of both DNA strands. This leads to the replacement of one pair of complementary nucleotides with another or to the appearance of breaks (gaps) in the newly synthesized chain against the altered regions. Post-replicative repair is carried out by recombination (exchange of fragments) between two newly formed DNA double helixes. An example is the restoration of the normal structure of DNA when thymine dimers (T-T) appear. The covalent bonds that arise between adjacent thymine residues make them incapable of binding to complementary nucleotides. As a result, breaks (gaps) that are recognized by repair enzymes appear in the newly synthesized DNA strand. Restoration of the integrity of the new polynucleotide chain of one of the daughter DNAs is carried out due to recombination with the corresponding normal maternal chain of the other daughter DNA. The gap formed in the parent chain is then filled by synthesis on the complementary polynucleotide chain. The often observed exchange of material between sister chromatids can be considered as a manifestation of such post-replicative repair, carried out by recombination between the strands of two daughter DNA molecules.

18. Replication of a DNA molecule. Replicon. Primer. Principles of DNA replication: semi-conservation, antiparallelism, discontinuity (Okazaki fragments). Replication phases: initiation, elongation, termination. Features of DNA replication in pro- and eukaryotes.

Ability to copy itself replication. This property is provided by a double-stranded structure. In the process of replication, a complementary chain is synthesized on each polynucleotide chain of the parent DNA molecule. This method of doubling molecules, in which each daughter molecule contains one parent and one newly synthesized chain, is called semi-conservative .

For replication to occur, the parent DNA strands must be separated from each other to become templates on which complementary strands of daughter molecules will be synthesized. With help helicase enzyme that breaks hydrogen bonds, the DNA double helix unwinds at the start of replication. The resulting single strands of DNA are bound by special destabilizing proteins that stretch the backbones of the chains, making their nitrogenous bases available for binding to complementary nucleotides located in the nucleoplasm. On each of the chains formed in the region of the replication fork, with the participation of the enzyme DNA polymerase complementary chains are synthesized.

Synthesis of the second DNA strand is carried out by short fragments ( fragments of Okazaki) also in the direction from the 5" to the 3" end. The synthesis of each such fragment is preceded by the formation of an RNA primer about 10 nucleotides long. Newly formed fragment with the help of an enzyme DNA ligases joins with the previous fragment after the removal of its RNA primer. Due to these features, the replication fork is asymmetric. Of the two synthesized daughter chains, one is built continuously, its synthesis is faster and this chain is called leading . Synthesis of the other chain is slower, as it is assembled from separate fragments that require the formation and then removal of the RNA primer. Therefore, such a circuit is called lagging (lagging behind). Although individual fragments are formed in the 5" → 3" direction, in general, this chain grows in the 3" → 5" direction. DNA replication in pro- and eukaryotes is basically similar, however, the rate of synthesis in eukaryotes is an order of magnitude lower than in prokaryotes. The reason for this may be the formation of eukaryotic DNA of sufficiently strong bonds with proteins, which hinders its despiralization, which is necessary for replicative synthesis.

primer- this is a short fragment of nucleic acid, complementary to a DNA or RNA target, serves as a seed for the synthesis of a complementary strand using DNA polymerase, as well as for DNA replication. The primer is necessary for DNA polymerases to initiate the synthesis of a new strand, from the 3' end of the primer. The DNA polymerase sequentially adds nucleotides complementary to the template strand to the 3' end of the primer.

Replicon- a unit of the process of replication of a section of the genome, to-ry is under the control of one point of initiation (beginning) of replication. From the point of initiation, replication goes in both directions, in some cases at an unequal speed. DNA replication- a key event in the course of cell division. It is important that by the time of division, the DNA is completely replicated and only once. This is provided by certain mechanisms of regulation of DNA replication. Replication takes place in three stages:

initiation of replication

elongation

termination of replication.

Replication is regulated mainly at the initiation stage. This is quite easy to implement, because replication can begin not from any DNA segment, but from a strictly defined one, called replication origin site. In the genome, there can be either only one or many such sites. The notion of replication initiation site is closely related to the notion of replicon. Replicon- this is a section of DNA that contains the site of replication initiation and replicates after the start of DNA synthesis from this site.

Replication begins at the site of replication initiation with the unwinding of the DNA double helix, forming replication fork is the site of direct DNA replication. Each site can form one or two replication forks, depending on whether replication is unidirectional or bidirectional. Bidirectional replication is more common. Some time after the start of replication, one can observe in an electron microscope replication eye- a region of the chromosome where DNA has already been replicated, surrounded by more extended regions of unreplicated DNA.

semi-conservative means that each daughter DNA consists of one template strand and one newly synthesized strand.

anti-parallelism DNA chains: the opposite direction of the two strands of the DNA double helix; one thread has a direction from 5" to 3", the other - from 3" to 5".

Each strand of DNA has a specific orientation. One end carries a hydroxyl group (-OH) attached to the 3" carbon in the sugar deoxyribose, at the other end of the chain there is a phosphoric acid residue in the 5" position of the sugar. Two complementary strands in a DNA molecule are located in opposite directions - antiparallel: one strand has a direction from 5 "to 3", the other - from 3" to 5". With a parallel orientation, opposite the 3 "-end of one strand would be the 3"-end of the other.

In prokaryotes one of the DNA strands breaks and one end of it is attached to the cell membrane, and the synthesis of daughter strands occurs at the opposite end. This synthesis of daughter strands of DNA is called the "rolling hoop". DNA replication is fast.