Practical lesson No. 15.

Assignment for lesson No. 15.

Topic: ENERGY EXCHANGE.

Relevance of the topic.

Biological oxidation is a set of enzymatic processes occurring in each cell, as a result of which molecules of carbohydrates, fats and amino acids are ultimately broken down into carbon dioxide and water, and the released energy is stored by the cell in the form of adenosine triphosphoric acid (ATP) and then used in the life of the body ( biosynthesis of molecules, cell division process, muscle contraction, active transport, heat production, etc.). The doctor should be aware of the existence of hypoenergetic states, in which ATP synthesis is reduced. In this case, all vital processes that occur using energy stored in the form of macroergic bonds of ATP suffer. The most common cause of hypoenergetic conditions is tissue hypoxia, associated with a decrease in oxygen concentration in the air, disruption of the cardiovascular and respiratory systems, and anemia of various origins. In addition, hypoenergetic states can be caused by hypovitaminosis associated with a violation of the structural and functional state of enzyme systems involved in the process of biological oxidation, as well as starvation, which leads to the absence of substrates for tissue respiration. In addition, in the process of biological oxidation, reactive oxygen species are formed, which trigger the processes peroxidation lipids of biological membranes. It is necessary to know the body's defense mechanisms against these forms (enzymes, drugs that have a membrane-stabilizing effect - antioxidants).

Educational and educational goals:

The general goal of the lesson: to instill knowledge about the course of biological oxidation, which results in the formation of up to 70-8% of energy in the form of ATP, as well as the formation of reactive oxygen species and their damaging effects on the body.

Private goals: to be able to determine peroxidase in horseradish and potatoes; muscle succinate dehydrogenase activity.

1. Incoming knowledge control:

1.1. Tests.

1.2. Oral survey.

2. Main questions of the topic:

2.1. The concept of metabolism. Anabolic and catabolic processes and their relationship.

2.2. Macroergic compounds. ATP is a universal battery and source of energy in the body. ATP-ADP cycle. Energy charge of the cell.

2.3. Metabolic stages. Biological oxidation (tissue respiration). Features of biological oxidation.

2.4. Primary acceptors of hydrogen protons and electrons.

2.5. Organization of the respiratory chain. Carriers in the respiratory chain (CRE).

2.6. Oxidative phosphorylation of ADP. The mechanism of coupling of oxidation and phosphorylation. Oxidative phosphorylation ratio (P/O).

2.7. Respiratory control. Separation of respiration (oxidation) and phosphorylation (free oxidation).

2.8. Formation of toxic forms of oxygen in CPE and neutralization of hydrogen peroxide by the enzyme peroxidase.

Laboratory and practical work.

3.1. Method for determining peroxidase in horseradish.

3.2. Method for determining peroxidase in potatoes.

3.3. Determination of muscle succinate dehydrogenase activity and competitive inhibition of its activity.

Output control.

4.1. Tests.

4.2. Situational tasks.

5. Literature:

5.1. Lecture materials.

5.2. Nikolaev A.Ya. Biological chemistry.-M.: Higher School, 1989., pp. 199-212, 223-228.

5.3. Berezov T.T., Korovkin B.F. Biological chemistry. - M.: Medicine, 1990.P.224-225.

5.4. Kushmanova O.D., Ivchenko G.M. Guide to practical classes in biochemistry. - M.: Medicine, 1983, work. 38.

2. Main questions of the topic.

2.1. The concept of metabolism. Anabolic and catabolic processes and their relationship.

Living organisms are in constant and inextricable connection with the environment.

This connection is carried out in the process of metabolism.

Metabolism (metabolism) – the totality of all reactions in the body.

Intermediate metabolism (intracellular metabolism) - includes 2 types of reactions: catabolism and anabolism.

Catabolism– the process of breaking down organic substances into final products (CO 2 , H 2 O and urea). This process includes metabolites formed both during digestion and during the breakdown of the structural and functional components of cells.

The processes of catabolism in the cells of the body are accompanied by the consumption of oxygen, which is necessary for oxidation reactions. As a result of catabolic reactions, energy is released (exergonic reactions), which is necessary for the body to function.

Anabolism- synthesis of complex substances from simple ones. Anabolic processes use energy released during catabolism (endergonic reactions).

Sources of energy for the body are proteins, fats and carbohydrates. The energy contained in the chemical bonds of these compounds was transformed from solar energy during the process of photosynthesis.

Macroergic compounds. ATP is a universal battery and source of energy in the body. ATP-ADP cycle. Energy charge of the cell.

ATP– is a high-energy compound containing high-energy bonds; hydrolysis of the terminal phosphate bond releases about 20 kJ/mol of energy.

High-energy compounds include GTP, CTP, UTP, creatine phosphate, carbamoyl phosphate, etc. They are used in the body for the synthesis of ATP. For example, GTP + ADP à GDP + ATP

This process is called substrate phosphorylation– exorgonic reactions. In turn, all these high-energy compounds are formed by using the free energy of the terminal phosphate group of ATP. Finally, ATP energy is used to perform various types of work in the body:

Mechanical (muscle contraction);

Electrical (conducting nerve impulses);

Chemical (synthesis of substances);

Osmotic (active transport of substances across the membrane) – endergonic reactions.

Thus, ATP is the main, directly used energy donor in the body. ATP occupies a central position between endergonic and exergonic reactions.

The human body produces an amount of ATP equal to body weight, and every 24 hours all this energy is destroyed. 1 molecule of ATP “lives” in a cell for about a minute.

The use of ATP as an energy source is possible only under the condition of continuous synthesis of ATP from ADP due to the energy of oxidation of organic compounds. The ATP-ADP cycle is the primary mechanism for energy exchange in biological systems, and ATP is the universal “energy currency.”

Each cell has an electrical charge equal to

[ATP] + ½[ADP]

[ATP] + [ADP] + [AMP]

If the cell charge is 0.8-0.9, then the entire adenyl fund in the cell is presented in the form of ATP (the cell is saturated with energy and the process of ATP synthesis does not occur).

As energy is used, ATP is converted into ADP, the cell charge becomes equal to 0, and ATP synthesis automatically begins.

ANSWER: The cell is the elementary structural, functional and genetic unit of living things. A cell is an elementary unit of living development. The cell is capable of self-regulation, self-renewal and self-reproduction.

12. The total mass of mitochondria in relation to the mass of cells of various rat organs is: in the pancreas - 7.9%, in the liver - 18.4%, in the heart - 35.8%. Why do the cells of these organs have different mitochondrial content?

ANSWER: Mitochondria are the energy stations of the cell - ATP molecules are synthesized in them. The heart muscle needs a lot of energy to work, so its cells have the largest number of mitochondria. There is more in the liver than in the pancreas because it has a more intense metabolism.

How is the energy stored in ATP used?

ANSWER: ATP is a universal source of energy in the cells of all living organisms. ATP energy is spent on the synthesis and transport of substances, on cell reproduction, on muscle contraction, on conducting impulses, i.e. on the vital activity of cells, tissues, organs and the entire organism.

What properties of DNA confirm that it is the carrier of genetic information?

ANSWER: Ability to replicate (self-duplication), complementarity of two chains, ability to transcribe.

Describe the molecular structure of the outer plasma membrane of animal cells.

ANSWER: The plasma membrane is formed by two layers of lipids. Protein molecules can penetrate the plasma membrane or be located on its outer or inner surface. Carbohydrates can be attached to proteins externally, forming glycocalis.

By what characteristics do living organisms differ from inanimate bodies?

ANSWER: Signs of living things: metabolism and energy conversion, heredity and variability, adaptability to living conditions, irritability, reproduction, growth and development, self-regulation, etc.

What signs are characteristic of viruses?

What significance did the creation of the cell theory have for the formation of a scientific worldview?

ANSWER: The cell theory substantiated the relationship of living organisms, their common origin, and generalized knowledge about the cell as a unit of structure and vital activity of living organisms.

How does a DNA molecule differ from mRNA?

ANSWER: DNA has a double helix structure, and RNA has a single chain of nucleotides; DNA contains the sugar deoxyribose and nucleotides with the nitrogenous base thymine, and RNA contains the sugar ribose and nucleotides with the nitrogenous base uracil.

Why can't bacteria be classified as eukaryotes?

ANSWER: They do not have a nucleus, mitochondria, Golgi complex, or ER separated from the cytoplasm; they are not characterized by mitosis, meiosis, or fertilization. Hereditary information in the form of a circular DNA molecule.

Metabolism and energy

In which metabolic reactions is the starting material for the synthesis of carbohydrates water?

ANSWER: Photosynthesis.

What type of energy do heterotrophic living organisms consume?

ANSWER: Energy of oxidation of organic substances.

What type of energy do autotrophic organisms consume?

ANSWER: Phototrophs - light energy, chemotrophs - energy of oxidation of inorganic substances.

During which phase of photosynthesis does ATP synthesis occur?

ANSWER: In the light phase.

What substance serves as a source of oxygen during photosynthesis?

ANSWER: Water (as a result of photolysis - decomposition under the influence of light in the light phase, oxygen is released).

Why can't heterotrophic organisms create organic matter themselves?

ANSWER: Their cells do not have chloroplasts or chlorophyll.

ANSWER: The cell is a system because consists of many interconnected and interacting parts - organelles and other structures. This system is open, because substances and energy come into it from the environment, and metabolism takes place in it. The cell maintains a relatively constant composition due to self-regulation carried out at the genetic level. The cell is capable of responding to stimuli.

9. What is a research method? Give examples of biological research methods and situations in which they are used.

ANSWER: A method is a way of scientific knowledge of reality. There are biological research methods: description, observation, comparison, experiment, microscopy, centrifugation, hybridological, twin method, biochemical method, etc. Research methods are used only in certain cases and to achieve certain goals. For example, hybridology - used to study heredity in animal husbandry and crop production, but not used for humans. Centrifugation allows cell organelles to be isolated for study.

10. What is the role of the nucleus in a cell?

ANSWER: The cell nucleus contains chromosomes that carry hereditary information and controls the processes of metabolism and cell reproduction.

11. How is cell theory currently formulated?

13. How is the energy accumulated in ATP used?

14. What properties of DNA confirm that it is a carrier of genetic information?

ANSWER: Ability to replicate (self-duplication), complementarity of two chains, ability to transcribe.

Continuation. See No. 11, 12, 13, 14, 15, 16/2005

Biology lessons in science classes

Advanced planning, grade 10

Lesson 19. Chemical structure and biological role of ATP

Equipment: tables on general biology, diagram of the structure of the ATP molecule, diagram of the relationship between plastic and energy metabolism.

I. Test of knowledge

Conducting a biological dictation “Organic compounds of living matter”

The teacher reads the abstracts under numbers, the students write down in their notebooks the numbers of those abstracts that match the content of their version.

Option 1 – proteins.
Option 2 – carbohydrates.
Option 3 – lipids.
Option 4 – nucleic acids.

1. In their pure form they consist only of C, H, O atoms.

2. In addition to C, H, O atoms, they contain N and usually S atoms.

3. In addition to C, H, O atoms, they contain N and P atoms.

4. They have a relatively small molecular weight.

5. The molecular weight can be from thousands to several tens and hundreds of thousands of daltons.

6. The largest organic compounds with a molecular weight of up to several tens and hundreds of millions of daltons.

7. They have different molecular weights - from very small to very high, depending on whether the substance is a monomer or a polymer.

8. Consist of monosaccharides.

9. Consist of amino acids.

10. Consist of nucleotides.

11. They are esters of higher fatty acids.

12. Basic structural unit: “nitrogen base–pentose–phosphoric acid residue.”

13. Basic structural unit: “amino acids”.

14. Basic structural unit: “monosaccharide”.

15. Basic structural unit: “glycerol–fatty acid.”

16. Polymer molecules are built from identical monomers.

17. Polymer molecules are built from similar, but not quite identical monomers.

18. They are not polymers.

19. They perform almost exclusively energy, construction and storage functions, and in some cases – protective.

20. In addition to energy and construction, they perform catalytic, signaling, transport, motor and protective functions;

21. They store and transmit the hereditary properties of the cell and organism.

Option 1 – 2; 5; 9; 13; 17; 20.
Option 2 – 1; 7; 8; 14; 16; 19.
Option 3 – 1; 4; 11; 15; 18; 19.
Option 4– 3; 6; 10; 12; 17; 21.

II. Learning new material

1. Structure of adenosine triphosphoric acid

In addition to proteins, nucleic acids, fats and carbohydrates, a large number of other organic compounds are synthesized in living matter. Among them, an important role is played in the bioenergetics of the cell. adenosine triphosphoric acid (ATP). ATP is found in all plant and animal cells. In cells, adenosine triphosphoric acid is most often present in the form of salts called adenosine triphosphates. The amount of ATP fluctuates and averages 0.04% (on average there are about 1 billion ATP molecules in a cell). The largest amount of ATP is contained in skeletal muscles (0.2–0.5%).

The ATP molecule consists of a nitrogenous base - adenine, a pentose - ribose and three phosphoric acid residues, i.e. ATP is a special adenyl nucleotide. Unlike other nucleotides, ATP contains not one, but three phosphoric acid residues. ATP refers to macroergic substances - substances containing a large amount of energy in their bonds.

Spatial model (A) and structural formula (B) of the ATP molecule

The phosphoric acid residue is cleaved from ATP under the action of ATPase enzymes. ATP has a strong tendency to detach its terminal phosphate group:

ATP 4– + H 2 O ––> ADP 3– + 30.5 kJ + Fn,

because this leads to the disappearance of the energetically unfavorable electrostatic repulsion between adjacent negative charges. The resulting phosphate is stabilized due to the formation of energetically favorable hydrogen bonds with water. The charge distribution in the ADP + Fn system becomes more stable than in ATP. This reaction releases 30.5 kJ (breaking a normal covalent bond releases 12 kJ).

In order to emphasize the high energy “cost” of the phosphorus-oxygen bond in ATP, it is usually denoted by the sign ~ and called a macroenergetic bond. When one molecule of phosphoric acid is removed, ATP is converted to ADP (adenosine diphosphoric acid), and if two molecules of phosphoric acid are removed, ATP is converted to AMP (adenosine monophosphoric acid). The cleavage of the third phosphate is accompanied by the release of only 13.8 kJ, so that there are only two actual high-energy bonds in the ATP molecule.

2. ATP formation in the cell

The supply of ATP in the cell is small. For example, ATP reserves in a muscle are enough for 20–30 contractions. But a muscle can work for hours and produce thousands of contractions. Therefore, along with the breakdown of ATP to ADP, reverse synthesis must continuously occur in the cell. There are several pathways for ATP synthesis in cells. Let's get to know them.

1. Anaerobic phosphorylation. Phosphorylation is the process of ATP synthesis from ADP and low molecular weight phosphate (Pn). In this case, we are talking about oxygen-free processes of oxidation of organic substances (for example, glycolysis is the process of oxygen-free oxidation of glucose to pyruvic acid). Approximately 40% of the energy released during these processes (about 200 kJ/mol glucose) is spent on ATP synthesis, and the rest is dissipated as heat:

C 6 H 12 O 6 + 2ADP + 2Pn ––> 2C 3 H 4 O 3 + 2ATP + 4H.

2. Oxidative phosphorylation is the process of ATP synthesis using the energy of oxidation of organic substances with oxygen. This process was discovered in the early 1930s. XX century V.A. Engelhardt. Oxygen processes of oxidation of organic substances occur in mitochondria. Approximately 55% of the energy released in this case (about 2600 kJ/mol glucose) is converted into the energy of chemical bonds of ATP, and 45% is dissipated as heat.

Oxidative phosphorylation is much more effective than anaerobic synthesis: if during the process of glycolysis, only 2 ATP molecules are synthesized during the breakdown of a glucose molecule, then 36 ATP molecules are formed during oxidative phosphorylation.

3. Photophosphorylation– the process of ATP synthesis using the energy of sunlight. This pathway of ATP synthesis is characteristic only of cells capable of photosynthesis (green plants, cyanobacteria). The energy of solar light quanta is used by photosynthetics during the light phase of photosynthesis for the synthesis of ATP.

3. Biological significance of ATP

ATP is at the center of metabolic processes in the cell, being a link between the reactions of biological synthesis and decay. The role of ATP in a cell can be compared to the role of a battery, since during the hydrolysis of ATP the energy necessary for various vital processes is released (“discharge”), and in the process of phosphorylation (“charging”) ATP again accumulates energy.

Due to the energy released during ATP hydrolysis, almost all vital processes in the cell and body occur: transmission of nerve impulses, biosynthesis of substances, muscle contractions, transport of substances, etc.

III. Consolidation of knowledge

Solving biological problems

Task 1. When we run fast, we breathe quickly, and increased sweating occurs. Explain these phenomena.

Problem 2. Why do freezing people start stamping and jumping in the cold?

Task 3. In the famous work of I. Ilf and E. Petrov “The Twelve Chairs”, among many useful tips one can find the following: “Breathe deeply, you are excited.” Try to justify this advice from the point of view of the energy processes occurring in the body.

IV. Homework

Start preparing for the test and test (dictate the test questions - see lesson 21).

Lesson 20. Generalization of knowledge in the section “Chemical organization of life”

Equipment: tables on general biology.

I. Generalization of knowledge of the section

Students work with questions (individually) followed by checking and discussion

1. Give examples of organic compounds, which include carbon, sulfur, phosphorus, nitrogen, iron, manganese.

2. How can you distinguish a living cell from a dead one based on its ionic composition?

3. What substances are found in the cell in undissolved form? What organs and tissues do they contain?

4. Give examples of macroelements included in the active sites of enzymes.

5. What hormones contain microelements?

6. What is the role of halogens in the human body?

7. How do proteins differ from artificial polymers?

8. How do peptides differ from proteins?

9. What is the name of the protein that makes up hemoglobin? How many subunits does it consist of?

10. What is ribonuclease? How many amino acids does it contain? When was it synthesized artificially?

11. Why is the rate of chemical reactions without enzymes low?

12. What substances are transported by proteins across the cell membrane?

13. How do antibodies differ from antigens? Do vaccines contain antibodies?

14. What substances do proteins break down into in the body? How much energy is released? Where and how is ammonia neutralized?

15. Give an example of peptide hormones: how are they involved in the regulation of cellular metabolism?

16. What is the structure of the sugar with which we drink tea? What three other synonyms for this substance do you know?

17. Why is the fat in milk not collected on the surface, but rather in the form of a suspension?

18. What is the mass of DNA in the nucleus of somatic and germ cells?

19. How much ATP is used by a person per day?

20. What proteins do people use to make clothes?

Primary structure of pancreatic ribonuclease (124 amino acids)

II. Homework.

Continue preparing for the test and test in the section “Chemical organization of life.”

Lesson 21. Test lesson on the section “Chemical organization of life”

I. Conducting an oral test on questions

1. Elementary composition of the cell.

2. Characteristics of organogenic elements.

3. Structure of the water molecule. Hydrogen bonding and its significance in the “chemistry” of life.

4. Properties and biological functions of water.

5. Hydrophilic and hydrophobic substances.

6. Cations and their biological significance.

7. Anions and their biological significance.

8. Polymers. Biological polymers. Differences between periodic and non-periodic polymers.

9. Properties of lipids, their biological functions.

10. Groups of carbohydrates, distinguished by structural features.

11. Biological functions of carbohydrates.

12. Elementary composition of proteins. Amino acids. Peptide formation.

13. Primary, secondary, tertiary and quaternary structures of proteins.

14. Biological function of proteins.

15. Differences between enzymes and non-biological catalysts.

16. Structure of enzymes. Coenzymes.

17. Mechanism of action of enzymes.

18. Nucleic acids. Nucleotides and their structure. Formation of polynucleotides.

19. Rules of E. Chargaff. The principle of complementarity.

20. Formation of a double-stranded DNA molecule and its spiralization.

21. Classes of cellular RNA and their functions.

22. Differences between DNA and RNA.

23. DNA replication. Transcription.

24. Structure and biological role of ATP.

25. Formation of ATP in the cell.

II. Homework

Continue preparing for the test in the section “Chemical organization of life.”

Lesson 22. Test lesson on the section “Chemical organization of life”

I. Conducting a written test

Option 1

1. There are three types of amino acids - A, B, C. How many variants of polypeptide chains consisting of five amino acids can be built. Please indicate these options. Will these polypeptides have the same properties? Why?

2. All living things consist mainly of carbon compounds, and the carbon analogue, silicon, the content of which in the earth’s crust is 300 times greater than carbon, is found only in very few organisms. Explain this fact in terms of the structure and properties of the atoms of these elements.

3. ATP molecules labeled with radioactive 32P at the last, third phosphoric acid residue were introduced into one cell, and ATP molecules labeled with 32P at the first residue closest to ribose were introduced into the other cell. After 5 minutes, the content of inorganic phosphate ion labeled with 32P was measured in both cells. Where will it be significantly higher?

4. Research has shown that 34% of the total number of nucleotides of this mRNA is guanine, 18% is uracil, 28% is cytosine and 20% is adenine. Determine the percentage composition of the nitrogenous bases of double-stranded DNA, of which the indicated mRNA is a copy.

Option 2

1. Fats constitute the “first reserve” in energy metabolism and are used when the reserve of carbohydrates is exhausted. However, in skeletal muscles, in the presence of glucose and fatty acids, the latter are used to a greater extent. Proteins are always used as a source of energy only as a last resort, when the body is starving. Explain these facts.

2. Ions of heavy metals (mercury, lead, etc.) and arsenic are easily bound by sulfide groups of proteins. Knowing the properties of sulfides of these metals, explain what will happen to the protein when combined with these metals. Why are heavy metals poisons for the body?

3. In the oxidation reaction of substance A into substance B, 60 kJ of energy is released. How many ATP molecules can be maximally synthesized in this reaction? How will the rest of the energy be used?

4. Studies have shown that 27% of the total number of nucleotides of this mRNA is guanine, 15% is uracil, 18% is cytosine and 40% is adenine. Determine the percentage composition of the nitrogenous bases of double-stranded DNA, of which the indicated mRNA is a copy.

To be continued

How exactly is energy stored in ATP(adenosine triphosphate), and how is it used to perform some useful work? It seems incredibly complex that some abstract energy suddenly receives a material carrier in the form of a molecule located inside living cells, and that it can be released not in the form of heat (which is more or less understandable), but in the form of the creation of another molecule. Typically, textbook authors limit themselves to the phrase “energy is stored in the form of a high-energy bond between parts of the molecule, and is released when this bond is broken, performing useful work,” but this does not explain anything.

In the most general terms, these manipulations with molecules and energy occur like this: first. Or they are created in chloroplasts in a chain of similar reactions. This requires energy obtained from the controlled combustion of nutrients directly inside the mitochondria or the energy of photons from sunlight falling on a chlorophyll molecule. ATP is then delivered to those places in the cell where some work needs to be done. And when one or two phosphate groups are split off from it, energy is released, which does this work. In this case, ATP breaks down into two molecules: if only one phosphate group is split off, then ATP turns into ADF(adenosine diphosphate, differing from adenosine triphosphate only in the absence of the same separated phosphate group). If ATP gives up two phosphate groups at once, then more energy is released, and what remains from ATP is adenosine MONOphosphate ( AMF).

Obviously, the cell also needs to carry out the reverse process, converting ADP or AMP molecules into ATP so that the cycle can repeat. But these “blank” molecules can calmly float next to the phosphates they lack for conversion into ATP, and never combine with them, because such a combination reaction is energetically unfavorable.

What is the “energy benefit” of a chemical reaction is quite easy to understand if you know about second law of thermodynamics: In the Universe, or in any system isolated from the rest, disorder can only increase. That is, complexly organized molecules sitting in a cell in orderly order, in accordance with this law, can only be destroyed, forming smaller molecules or even breaking up into individual atoms, because then there will be noticeably less order. To understand this idea, you can compare a complex molecule to a Lego airplane. Then the small molecules into which the complex one breaks down will be associated with individual parts of this plane, and the atoms with individual Lego cubes. Looking at a neatly assembled airplane and comparing it to a jumbled pile of parts, it becomes clear why complex molecules contain more order than small ones.

Such a decay reaction (of molecules, not of an airplane) will be energetically favorable, which means it can occur spontaneously, and energy will be released during decay. Although in fact, the splitting of the aircraft will be energetically beneficial: despite the fact that the parts themselves will not split off from each other and an outside force in the form of a kid who wants to use these parts for something else will have to work on uncoupling them, he will spend on turning the plane into a chaotic pile of parts the energy received from eating highly ordered food. And the more tightly the parts stick together, the more energy will be spent, including released in the form of heat. Result: a piece of bun (the source of energy) and the plane were turned into a disordered mass, the air molecules around the child heated up (and therefore moved more randomly) - there was more chaos, that is, the splitting of the plane is energetically beneficial.

To summarize, we can formulate the following rules following from the second law of thermodynamics:

1. When the amount of order decreases, energy is released and energetically favorable reactions occur

2. As the amount of order increases, energy is absorbed and energy-consuming reactions occur

At first glance, such an inevitable movement from order to chaos makes it impossible for the reverse processes, such as the construction of a calf, undoubtedly very orderly compared to chewed grass, from a single fertilized egg and nutrient molecules absorbed by the mother cow.

But still, this happens, and the reason for this is that living organisms have one feature that allows them to both support the desire of the Universe for entropy and build themselves and their offspring: they combine two reactions into one process, one of which is energetically beneficial and the other energy-consuming. By combining two reactions in this way, it is possible to ensure that the energy released during the first reaction more than covers the energy costs of the second. In the example of an airplane, taking it apart separately is energy-consuming, and without an external source of energy in the form of a bun destroyed by the boy’s metabolism, the airplane would stand forever.

It’s like sledding down a hill: first, when a person absorbs food, he stores energy obtained as a result of energetically beneficial processes of splitting highly ordered chicken into molecules and atoms in his body. And then he spends this energy pulling the sled up the mountain. Moving a sled from the bottom to the top is energetically unprofitable, so it will never roll there spontaneously; this requires some kind of external energy. And if the energy received from eating chicken is not enough to overcome the climb, then the process of “sledding down the mountain top” will not happen.

It is energy-consuming reactions ( energy-consuming reaction ) increase the amount of order by absorbing the energy released during the conjugate reaction. And the balance between the release and consumption of energy in these coupled reactions must always be positive, that is, their combination will increase the amount of chaos. An example of an increase entropy(disorder) ( entropy[‘entrə pɪ]) is the release of heat during an energy-producing reaction ( energy supply reaction): particles of a substance adjacent to the reacting molecules receive energetic shocks from the reacting ones, begin to move faster and more chaotically, pushing in turn other molecules and atoms of this and neighboring substances.

Let's return once again to obtaining energy from food: a piece of Banoffee Pie is much more orderly than the resulting mass that ends up in the stomach as a result of chewing. Which in turn consists of large, more ordered molecules than those into which the intestines break it down. And they, in turn, will be delivered to the cells of the body, where individual atoms and even electrons will be torn from them... And at each stage of increasing chaos in a single piece of cake, energy will be released, which is captured by the organs and organelles of the happy eater, storing it in in the form of ATP (energy-intensive), used for the construction of new necessary molecules (energy-intensive) or for heating the body (also energy-intensive). As a result of this, in the system “man - Banoffee Pie - Universe” there was less order (due to the destruction of the cake and the release of thermal energy by the organelles processing it), but in an individual human body there was more happiness in order (due to the emergence of new molecules, parts of organelles and whole cellular organs).

If we return to the ATP molecule, after all this thermodynamic digression, it becomes clear that in order to create it from its constituent parts (smaller molecules), it is necessary to expend energy obtained from energetically favorable reactions. One of the methods for its creation is described in detail, another (very similar) is used in chloroplasts, where instead of the energy of the proton gradient, the energy of photons emitted by the Sun is used.

There are three groups of reactions that produce ATP (see diagram on the right):

the breakdown of glucose and fatty acids into large molecules in the cytoplasm already makes it possible to obtain a certain amount of ATP (small, for one glucose molecule split at this stage there are only 2 ATP molecules obtained). But the main purpose of this stage is to create molecules used in the mitochondrial respiratory chain.
further cleavage of the molecules obtained at the previous stage in the Krebs cycle, occurring in the mitochondrial matrix, produces only one molecule of ATP, its main purpose is the same as in the previous paragraph.
finally, the molecules accumulated in the previous stages are used in the respiratory chain of mitochondria to produce ATP, and here a lot of it is released (more about this below).

If we describe all this in more detail, looking at the same reactions from the point of view of energy production and expenditure, we get this:

0. Food molecules are carefully burned (oxidized) in the primary cleavage that occurs in the cytoplasm of the cell, as well as in a chain of chemical reactions called the “Krebs cycle”, which already occurs in the mitochondrial matrix - energy-giving part of the preparatory stage.

As a result of coupling with these energetically favorable reactions of other, already energetically unfavorable reactions of creating new molecules, 2 ATP molecules and several molecules of other substances are formed - energy-consuming part of the preparatory stage. These incidentally formed molecules are carriers of high-energy electrons, which will be used in the mitochondrial respiratory chain at the next stage.

1. On the membranes of mitochondria, bacteria and some archaea, the energy-producing abstraction of protons and electrons from molecules obtained in the previous step (but not from ATP) occurs. The passage of electrons through the complexes of the respiratory chain (I, III and IV in the diagram on the left) is shown by yellow winding arrows, the passage of protons through these complexes (and therefore through the inner membrane of the mitochondrion) by red arrows.

Why can’t electrons simply be split off from the carrier molecule using a powerful oxidizing agent, oxygen, and use the released energy? Why transfer them from one complex to another, because in the end they come to the same oxygen? It turns out that the greater the difference in the ability to attract electrons from the electron-giving ( reducing agent) and electron-collector ( oxidizing agent) molecules involved in the electron transfer reaction, the greater the energy released during this reaction.

The difference in this ability between the electron and oxygen carrier molecules formed in the Krebs cycle is such that the energy released would be sufficient for the synthesis of several ATP molecules. But due to such a sharp drop in the energy of the system, this reaction would proceed with almost explosive power, and almost all the energy would be released in the form of undetectable heat, that is, it would actually be lost.

Living cells, on the other hand, divide this reaction into several small stages, first transferring electrons from weakly attractive carrier molecules to the slightly stronger attractive first complex in the respiratory chain, and from it to a slightly stronger attractive one. ubiquinone(or coenzyme Q-10), whose task is to drag electrons to the next, slightly stronger attracting respiratory complex, which receives its part of the energy from this failed explosion, using it to pump protons through the membrane.. And so on until the electrons finally meet oxygen, attracted to it, grabbing a couple of protons, and do not form a water molecule. This division of one powerful reaction into small steps allows almost half of the useful energy to be directed to doing useful work: in this case, creating proton electrochemical gradient, which will be discussed in the second paragraph.

Exactly how the energy of the transferred electrons helps the coupled energy-consuming reaction of pumping protons through the membrane is only now beginning to be elucidated. Most likely, the presence of an electrically charged particle (electron) affects the configuration of the place in the membrane-embedded protein where it is located: such that this change provokes a proton to be drawn into the protein and move through a protein channel in the membrane. The important thing is that, in fact, the energy obtained as a result of the abstraction of high-energy electrons from the carrier molecule and their final transfer to oxygen is stored in the form of a proton gradient.

2. The energy of protons accumulated as a result of events from point 1 on the outside of the membrane and tending to get to the inside consists of two unidirectional forces:

electrical(the positive charge of protons tends to move to the place of accumulation of negative charges on the other side of the membrane) and
chemical(as with any other substance, protons try to disperse evenly in space, spreading from places with a high concentration of them to places where there are few of them)

The electrical attraction of protons to the negatively charged side of the inner membrane is a much more powerful force than the tendency of protons to move to a site of lower concentration due to differences in proton concentration (this is indicated by the width of the arrows in the diagram above). The combined energy of these attractive forces is so great that it is enough to both move protons into the membrane and fuel the accompanying energy-consuming reaction: the creation of ATP from ADP and phosphate.

Let's take a closer look at why this requires energy, and how exactly the aspiration energy of protons is converted into the energy of a chemical bond between the two parts of the ATP molecule.

The ADP molecule (in the diagram on the right) does not want to acquire another phosphate group: the oxygen atom to which this group can attach is charged as negatively as the phosphate, which means they repel each other. And in general, ADP is not going to react; it is chemically passive. Phosphate, in turn, has its own oxygen atom attached to the phosphorus atom, which could become the site of connection between phosphate and ADP when creating the ATP molecule, so it cannot take the initiative either.

Therefore, these molecules must be linked by one enzyme, unfolded so that the bonds between them and the “extra” atoms are weakened and broken, and then the two chemically active ends of these molecules, on which the atoms experience a lack and excess of electrons, are brought to each other.

Phosphorus (P +) and oxygen (O -) ions that fall into the field of mutual reach are bound by a strong covalent bond due to the fact that they jointly take possession of one electron that originally belonged to oxygen. This molecule processing enzyme is ATP synthase, and it receives the energy to change both its configuration and the relative position of ADP and phosphate from the protons passing through it. It is energetically favorable for protons to get to the oppositely charged side of the membrane, where, moreover, there are few of them, and the only path passes through the enzyme, the “rotor” of which the protons simultaneously rotate.

The structure of ATP synthase is shown in the diagram on the right. Its element rotating due to the passage of protons is highlighted in purple, and the moving picture below shows a diagram of its rotation and the creation of ATP molecules. The enzyme works almost like a molecular motor, converting electrochemical proton current energy in mechanical energy friction of two sets of proteins against each other: the rotating “leg” rubs against the stationary proteins of the “mushroom cap”, while the subunits of the “mushroom cap” change their shape. This mechanical deformation turns into energy of chemical bonds during ATP synthesis, when ADP and phosphate molecules are processed and unfolded in the manner necessary to form a covalent bond between them.

Each ATP synthase is capable of synthesizing up to 100 ATP molecules per second, and for every ATP molecule synthesized, about three protons must pass through the synthetase. Most of the ATP synthesized in cells is formed precisely in this way, and only a small part is the result of the primary processing of food molecules that occurs outside the mitochondria.

At any given time, a typical living cell contains approximately a billion ATP molecules. In many cells, all of this ATP is replaced (that is, used and created again) every 1-2 minutes. The average person at rest uses a mass of ATP every 24 hours approximately equal to his own mass.

In general, almost half of the energy released during the oxidation of glucose or fatty acids to carbon dioxide and water is captured and used for the energetically unfavorable reaction of ATP formation from ADP and phosphates. An efficiency factor of 50% is very good; for example, a car engine uses only 20% of the energy contained in the fuel for useful work. At the same time, the rest of the energy in both cases is dissipated in the form of heat, and just like some cars, animals constantly spend this excess (although not completely, of course) to warm up the body. During the reactions mentioned here, one molecule of glucose, gradually broken down into carbon dioxide and water, supplies the cell with 30 molecules of ATP.

So, everything is more or less clear about where the energy comes from and how exactly it is stored in ATP. It remains to understand how exactly the stored energy is released and what happens at the molecular-atomic level.

The covalent bond formed between ADP and phosphate is called high energy for two reasons:

when it breaks, a lot of energy is released
the electrons involved in creating this bond (that is, rotating around the oxygen and phosphorus atoms between which this bond is formed) are high-energy, that is, they are in “high” orbits around the atomic nuclei. And it would be energetically beneficial for them to jump to a lower level, releasing excess energy, but while they are in this very place, holding together oxygen and phosphorus atoms, it will not be possible to “jump”.

This desire of electrons to fall into a more convenient low-energy orbit ensures both the ease of destruction of a high-energy bond and the energy released in the form of a photon (which is the carrier of electromagnetic interaction). Depending on which molecules are substituted by the enzymes for the collapsing ATP molecule, and which particular molecule absorbs the photon emitted by the electron, different versions of events can occur. But every time the energy stored in the form of a high-energy bond will be used for some needs of the cell:

Scenario 1: the phosphate can be transferred to a molecule of another substance. In this case, high-energy electrons form a new bond, this time between the phosphate and the outermost atom of this recipient molecule. The condition for such a reaction to occur is its energetic benefit: in this new bond, the electron must have slightly less energy than when it was part of the ATP molecule, emitting some of the energy in the form of a photon outside.

The purpose of such a reaction is to activate the receptor molecule (in the diagram on the left it is indicated IN-OH): before the addition of phosphate, it was passive and could not react with another passive molecule A, but now she has a reserve of energy in the form of a high-energy electron, which means she can spend it somewhere. For example, to attach a molecule to itself A, which is impossible to attach without such a feint with the ears (that is, high energy of the connecting electron). The phosphate is then detached, having done its job.

This results in the following chain of reactions:

1. ATP+ passive molecule IN ➡️ ADF+ molecule active due to attached phosphate V-R

2. activated molecule V-R+ passive molecule A➡️connected molecules A-B+ split off phosphate ( R)

Both of these reactions are energetically favorable: each of them involves a high-energy bonding electron, which, when one bond is destroyed and another is built, loses part of its energy in the form of photon emission. As a result of these reactions, two passive molecules were combined. If we consider the reaction of connecting these molecules directly (passive molecule IN+ passive molecule A➡️connected molecules A-B), then it turns out to be energy-consuming and cannot happen. Cells “do the impossible” by coupling this reaction with the energetically favorable reaction of splitting ATP into ADP and phosphate during the two reactions described above. The detachment occurs in two stages, at each of which part of the energy of the bonding electron is spent on performing useful work, namely on creating the necessary bonds between two molecules, from which a third is obtained ( A-B), necessary for the functioning of the cell.

Scenario 2: phosphate can be split off simultaneously from an ATP molecule, and the released energy is captured by an enzyme or working protein and spent on performing useful work.

How can you detect something as imperceptible as a tiny disturbance in the electromagnetic field as an electron falls into a lower orbit? It’s very simple: with the help of other electrons and with the help of atoms capable of absorbing the photon released by the electron.

The atoms that make up molecules are held together into strong chains and rings (such a chain is represented by an unfolded protein in the picture on the right). And individual parts of these molecules are attracted to each other by weaker electromagnetic interactions (for example, hydrogen bonds or van der Waals forces), which allows them to form into complex structures. Some of these atomic configurations are very stable, and no disturbance of the electromagnetic field will shake them... will not shake them... in general, they are stable. And some are quite mobile, and a slight electromagnetic kick is enough for them to change their configuration (usually these are not covalent bonds). And it is precisely this kick that is given to them by the same arriving photon-carrier of the electromagnetic field, emitted by the electron that moved to a lower orbit when the phosphate was detached.

Changes in protein configuration as a result of the breakdown of ATP molecules are responsible for the most amazing events that occur in the cell. Surely those who are interested in cellular processes at least at the “I’ll watch their animation on YouTube” level have come across a video showing a protein molecule kinesin, literally walking, moving its legs, along the thread of the cellular skeleton, dragging the load attached to it.

It is the abstraction of phosphate from ATP that ensures this stepping, and this is how:

Kinesin ( kinesin) refers to a special type of proteins that tend to spontaneously change their conformation(mutual position of atoms in a molecule). Left alone, it randomly transitions from conformation 1, in which it is attached by one "foot" to the actin filament ( actin filament) - the thinnest thread forming cytoskeleton cells ( cytoskeleton), into conformation 2, thus taking a step forward and standing on two “legs”. From conformation 2, it is equally likely to go both to conformation 3 (puts the back leg to the front) and back to conformation 1. Therefore, kinesin does not move in any direction, it simply wanders aimlessly.

But everything changes as soon as it connects with the ATP molecule. As shown in the diagram on the left, the addition of ATP to kinesin, which is in conformation 1, leads to a change in its spatial position and it goes into conformation 2. The reason for this is the mutual electromagnetic influence of ATP and kinesin molecules on each other. This reaction is reversible because no energy was expended, and if ATP is detached from kinesin, it will simply raise its “leg”, remaining in place, and wait for the next ATP molecule.

But if it lingers, then due to the mutual attraction of these molecules, the bond holding the phosphate within ATP is destroyed. The energy released in this case, as well as the breakdown of ATP into two molecules (which have a different effect on kinesin atoms with their electromagnetic fields) lead to the fact that the conformation of kinesin changes: it “drags its back leg.” It remains to take a step forward, which is what happens when ADP and phosphate are detached, returning kinesin to its original conformation 1.

As a result of ATP hydrolysis, kinesin moves to the right, and as soon as the next molecule joins it, it will take another couple of steps, using the energy stored in it.

It is important that kinesin, which is in conformation 3 with ADP and phosphate attached, cannot return to conformation 2, taking a “step back”. This is explained by the same principle of compliance with the second law of thermoregulation: the transition of the “kinesin + ATP” system from conformation 2 to conformation 3 is accompanied by the release of energy, which means the reverse transition will be energy-consuming. For it to happen, you need to get energy from somewhere to combine ADP with phosphate, but in this situation there is nowhere to get it. Therefore, kinesin connected to ATP has a path open in only one direction, which allows it to do useful work of dragging something from one end of the cell to the other. Kinesin, for example, is involved in pulling apart the chromosomes of a dividing cell during mitosis(the process of division of eukaryotic cells). And muscle protein myosin runs along actin filaments, causing muscle contraction.

This movement can be very fast: some motor(responsible for various forms of cellular motility) proteins involved in gene replication race along the DNA strand at a speed of thousands of nucleotides per second.

They all move by hydrolysis ATP (destruction of a molecule with the addition of atoms taken from a water molecule to the resulting smaller molecules. Hydrolysis is shown on the right side of the diagram of the interconversion of ATP and ADP). Or due to hydrolysis GTF, which differs from ATP only in that it contains another nucleotide (guanine).

Scenario 3: the cleavage of two phosphate groups from ATP or another similar molecule containing a nucleotide at once leads to an even greater release of energy than when only one phosphate is cleaved. Such a powerful release makes it possible to create a strong sugar-phosphate backbone of DNA and RNA molecules:

1. In order for nucleotides to be able to join the DNA or RNA chain under construction, they need to be activated by attaching two phosphate molecules. This is an energy-consuming reaction carried out by cellular enzymes.

2. the enzyme DNA or RNA polymerase (not shown in the diagram below) attaches an activated nucleotide (GTP is shown in the diagram) to the polynucleotide under construction and catalyzes the cleavage of two phosphate groups. The released energy is used to create a bond between the phosphate group of one nucleotide and the ribose of another. The bonds created as a result are not high-energy, which means they are not easy to destroy, which is an advantage for building a molecule that contains or transmits the hereditary information of the cell.

In nature, only energetically favorable reactions can spontaneously occur, which is due to the second law of thermodynamics

However, living cells can combine two reactions, one of which produces slightly more energy than the other absorbs, and thus carry out energy-consuming reactions. Energy-consuming reactions are aimed at creating larger molecules, cellular organelles and whole cells, tissues, organs and multicellular living beings from individual molecules and atoms, as well as storing energy for their metabolism

Energy is stored through the controlled and gradual destruction of organic molecules (energy-producing process), coupled with the creation of energy-carrying molecules (energy-consuming process). Photosynthetic organisms thus store the energy of solar photons captured by chlorophyll.

Energy-carrying molecules are divided into two groups: those storing energy in the form of a high-energy bond or in the form of an attached high-energy electron. However, in the first group, high energy is provided by the same high-energy electron, so we can say that energy is stored in electrons driven to a high level, located in different molecules

The energy stored in this way is also released in two ways: the destruction of a high-energy bond or the transfer of high-energy electrons to gradually reduce their energy. In both cases, energy is released in the form of emission by an electron moving to a lower energy level of a particle carrying an electromagnetic field (photon) and heat. This photon is captured in such a way that useful work is done (formation of a molecule necessary for metabolism in the first case and pumping protons through the mitochondrial membrane in the second)

The energy stored in the proton gradient is used for ATP synthesis, as well as for other cellular processes that are left outside the scope of this chapter (I think no one is offended, given its size). And the synthesized ATP is used as described in the previous paragraph.