The structure of ATP. ATP value
Continuation. See No. 11, 12, 13, 14, 15, 16/2005
Biology lessons in science classes
Advanced Planning, Grade 10
Lesson 19
Equipment: tables on general biology, a diagram of the structure of the ATP molecule, a diagram of the relationship between plastic and energy exchanges.
I. Knowledge Test
Conducting a biological dictation "Organic compounds of living matter"
The teacher reads the theses under the numbers, the students write down in the notebook the numbers of those theses that are suitable in content to their version.
Option 1 - proteins.
Option 2 - carbohydrates.
Option 3 - lipids.
Option 4 - nucleic acids.
1. In its 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 the 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: "nitrogenous 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 the same monomers.
17. Polymer molecules are built from similar, but not exactly identical, monomers.
18. Are not polymers.
19. They perform almost exclusively energy, construction and storage functions, in some cases - protective.
20. In addition to energy and construction, they perform catalytic, signal, transport, propulsion and protective function;
21. They store and transfer the hereditary properties of the cell and the body.
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. The 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 in the bioenergetics of the cell is played by adenosine triphosphate (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 found in skeletal muscles (0.2–0.5%).
The ATP molecule consists of a nitrogenous base - adenine, pentose - ribose and three residues of phosphoric acid, 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
From the composition of ATP under the action of ATPase enzymes, a residue of phosphoric acid is cleaved off. 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 neighboring negative charges. The resulting phosphate is stabilized by the formation of energetically favorable hydrogen bonds with water. The charge distribution in the ADP + Fn system becomes more stable than in ATP. As a result of this reaction, 30.5 kJ are released (when a conventional covalent bond is broken, 12 kJ is released).
In order to emphasize the high energy "cost" of the phosphorus-oxygen bond in ATP, it is customary to denote it with the sign ~ and call it a macroenergetic bond. When one molecule of phosphoric acid is cleaved off, ATP is converted to ADP (adenosine diphosphoric acid), and if two molecules of phosphoric acid are cleaved off, then 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 macroergic bonds in the ATP molecule.
2. Formation of ATP in the cell
The supply of ATP in the cell is small. For example, in a muscle, ATP reserves 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 the synthesis of ATP 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 of glucose) is spent on ATP synthesis, and the rest is dissipated in the form of heat:
C 6 H 12 O 6 + 2ADP + 2Fn -–> 2C 3 H 4 O 3 + 2ATP + 4H.
2. Oxidative phosphorylation- this is the process of ATP synthesis due to the energy of oxidation of organic substances with oxygen. This process was discovered in the early 1930s. 20th century V.A. Engelhardt. Oxygen processes of oxidation of organic substances proceed in mitochondria. Approximately 55% of the energy released in this case (about 2600 kJ / mol of glucose) is converted into the energy of chemical bonds of ATP, and 45% is dissipated in the form of heat.
Oxidative phosphorylation is much more efficient than anaerobic syntheses: if only 2 ATP molecules are synthesized during glycolysis during the breakdown of a glucose molecule, then 36 ATP molecules are formed during oxidative phosphorylation.
3. Photophosphorylation- the process of ATP synthesis due to the energy of sunlight. This pathway of ATP synthesis is characteristic only for cells capable of photosynthesis (green plants, cyanobacteria). The energy of sunlight quanta is used by photosynthetics in 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 the link between the reactions of biological synthesis and decay. The role of ATP in the cell can be compared with the role of a battery, since during the hydrolysis of ATP, the energy necessary for various life processes ("discharge") is released, and in the process of phosphorylation ("charging"), ATP again accumulates energy in itself.
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 running fast, we often breathe, there is increased sweating. Explain these phenomena.
Task 2. Why do freezing people start stomping and jumping in the cold?
Task 3. In the well-known work by I. Ilf and E. Petrov "The Twelve Chairs" among many useful tips you can also find this: "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 test questions - see lesson 21).
Lesson 20
Equipment: tables on general biology.
I. Generalization of the knowledge of the section
Work of students with questions (individually) with subsequent verification and discussion
1. Give examples of organic compounds that include carbon, sulfur, phosphorus, nitrogen, iron, manganese.
2. How can a living cell be distinguished from a dead one by ionic composition?
3. What substances are in the cell in an undissolved form? What organs and tissues do they include?
4. Give examples of macronutrients included in the active centers of enzymes.
5. What hormones contain trace elements?
6. What is the role of halogens in the human body?
7. How are proteins different from artificial polymers?
8. What is the difference between peptides and proteins?
9. What is the name of the protein that is part of hemoglobin? How many subunits does it consist of?
10. What is ribonuclease? How many amino acids are in it? When was it artificially synthesized?
11. Why is the rate of chemical reactions without enzymes low?
12. What substances are transported by proteins through the cell membrane?
13. How do antibodies differ from antigens? Do vaccines contain antibodies?
14. What substances break down proteins in the body? How much energy is released in this case? Where and how is ammonia neutralized?
15. Give an example of peptide hormones: how do they participate in the regulation of cellular metabolism?
16. What is the structure of sugar with which we drink tea? What other three synonyms for this substance do you know?
17. Why is fat in milk not collected on the surface, but is in 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 make clothes from?
Primary structure of pancreatic ribonuclease (124 amino acids)
II. Homework.
Continue preparation for the test and test in the section "Chemical organization of life."
Lesson 21
I. Conducting an oral test on questions
1. Elementary composition of the cell.
2. Characteristics of organogenic elements.
3. The structure of the water molecule. The hydrogen bond 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. The formation of peptides.
13. Primary, secondary, tertiary and quaternary structures of proteins.
14. Biological function of proteins.
15. Differences between enzymes and non-biological catalysts.
16. The structure of enzymes. Coenzymes.
17. The mechanism of action of enzymes.
18. Nucleic acids. Nucleotides and their structure. The 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. The formation of ATP in the cell.
II. Homework
Continue preparation for the test in the section "Chemical organization of life."
Lesson 22
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. Specify these options. Will these polypeptides have the same properties? Why?
2. All living things mainly consist of carbon compounds, and the analogue of carbon is silicon, the content of which in earth's crust 300 times more than carbon, found in only a 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 another 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. Studies have 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 specified mRNA is a mold.
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 as a source of energy are always used 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 the sulfides of these metals, explain what happens to the protein when combined with these metals. Why are heavy metals poisonous to 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% 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 specified mRNA is a mold.
To be continued
This molecule plays an extremely important role in metabolism, the compound is known as a universal source of energy in all processes occurring in a living organism.
Answer
Main source of energy for the cell are nutrients: carbohydrates, fats and proteins, which are oxidized with the help of oxygen. Almost all carbohydrates, before reaching the cells of the body, are converted into glucose due to the work of the gastrointestinal tract and liver. Along with carbohydrates, proteins are also broken down - to amino acids and lipids - to fatty acids. In the cell, nutrients are oxidized under the action of oxygen and with the participation of enzymes that control the reactions of energy release and its utilization.
Almost all oxidative reactions occur in mitochondria, and the released energy is stored in the form of a macroergic compound - ATP. In the future, it is ATP, and not nutrients, that is used to provide energy for intracellular metabolic processes.
ATP molecule contains: (1) the nitrogenous base adenine; (2) pentose carbohydrate ribose, (3) three phosphoric acid residues. The last two phosphates are connected to each other and to the rest of the molecule by macroergic phosphate bonds, indicated by the symbol ~ in the ATP formula. Subject to the physical and chemical conditions characteristic of the body, the energy of each such bond is 12,000 calories per 1 mol of ATP, which is many times higher than the energy of an ordinary chemical bond, which is why phosphate bonds are called macroergic. Moreover, these bonds are easily destroyed, providing intracellular processes with energy as soon as the need arises.
When released ATP energy donates a phosphate group and is converted to adenosine diphosphate. The released energy is used for almost all cellular processes, for example, in biosynthesis reactions and during muscle contraction.
Scheme of the formation of adenosine triphosphate in the cell, showing the key role of mitochondria in this process.GI - glucose; FA - fatty acids; AA is an amino acid.
Replenishment of ATP reserves occurs by recombining ADP with a phosphoric acid residue at the expense of the energy of nutrients. This process is repeated over and over again. ATP is constantly consumed and accumulated, which is why it is called the energy currency of the cell. The turnover time of ATP is only a few minutes.
The role of mitochondria in chemical reactions ATP formation. When glucose enters the cell, under the action of cytoplasmic enzymes it turns into pyruvic acid (this process is called glycolysis). The energy released in this process is used to convert a small amount of ADP to ATP, less than 5% of the total energy reserves.
95% is carried out in mitochondria. Pyruvic acid, fatty acids and amino acids, formed respectively from carbohydrates, fats and proteins, are eventually converted in the mitochondrial matrix into a compound called acetyl-CoA. This compound, in turn, enters into a series of enzymatic reactions, collectively known as the tricarboxylic acid cycle or the Krebs cycle, to give up its energy.
In a cycle tricarboxylic acids acetyl-CoA splits into hydrogen atoms and carbon dioxide molecules. Carbon dioxide is removed from the mitochondria, then from the cell by diffusion and excreted from the body through the lungs.
hydrogen atoms are chemically very active and therefore immediately react with oxygen diffusing into the mitochondria. The large amount of energy released in this reaction is used to convert many ADP molecules into ATP. These reactions are quite complex and require the participation of a huge number of enzymes that make up the mitochondrial cristae. On initial stage an electron is split off from a hydrogen atom, and the atom becomes a hydrogen ion. The process ends with the addition of hydrogen ions to oxygen. As a result of this reaction, water and a large amount of energy are formed that are necessary for the operation of ATP synthetase, a large globular protein that acts as tubercles on the surface of mitochondrial cristae. Under the action of this enzyme, which uses the energy of hydrogen ions, ADP is converted into ATP. New ATP molecules are sent from the mitochondria to all parts of the cell, including the nucleus, where the energy of this compound is used to provide a variety of functions.
This process ATP synthesis generally called the chemiosmotic mechanism of ATP formation.
The use of mitochondrial adenosine triphosphate for the implementation of three important functions of the cell: membrane transport, protein synthesis and muscle contraction.
Any organism can exist as long as there is a supply of nutrients from external environment and while the products of its vital activity are excreted into this environment. Inside the cell there is a continuous very complex complex of chemical transformations, due to which the components of the cell body are formed from nutrients. The totality of the processes of transformation of matter in a living organism, accompanied by its constant renewal, is called metabolism.
Part of the overall metabolism, which consists in the absorption, assimilation of nutrients and the creation at their expense structural components cells, is called assimilation - this is a constructive exchange. The second part of the general exchange is the processes of dissimilation, i.e. the processes of decomposition and oxidation of organic substances, as a result of which the cell receives energy, is an energy exchange. Constructive and energy exchange constitute a single whole.
In the process of constructive exchange, a cell synthesizes biopolymers of its body from a rather limited number of low molecular weight compounds. Biosynthetic reactions proceed with the participation of various enzymes and require energy.
Living organisms can only use chemically bound energy. Every substance has a certain amount of potential energy. Its main material carriers are chemical bonds, the breaking or transformation of which leads to the release of energy. The energy level of some bonds has a value of 8-10 kJ - these bonds are called normal. Other bonds contain much more energy - 25-40 kJ - these are the so-called macroergic bonds. Almost all known compounds with such bonds have phosphorus or sulfur atoms in their composition, in the place of which these bonds are localized in the molecule. Adenosine triphosphoric acid (ATP) is one of the compounds that play an important role in cell life.
Adenosine triphosphoric acid (ATP) consists of an organic adenine base (I), a ribose carbohydrate (II) and three phosphoric acid residues (III). The combination of adenine and ribose is called adenosine. Pyrophosphate groups have macroergic bonds, indicated by ~. The decomposition of one ATP molecule with the participation of water is accompanied by the elimination of one molecule of phosphoric acid and the release of free energy, which is 33-42 kJ / mol. All reactions involving ATP are regulated by enzyme systems.
Fig.1. Adenosine triphosphoric acid (ATP)
Energy metabolism in the cell. ATP synthesis
ATP synthesis occurs in mitochondrial membranes during respiration, therefore all enzymes and cofactors of the respiratory chain, all enzymes of oxidative phosphorylation are localized in these organelles.
ATP synthesis occurs in such a way that two H + ions are split off from ADP and phosphate (P) on the right side of the membrane, compensating for the loss of two H + during the reduction of substance B. One of the oxygen atoms of the phosphate is transferred to the other side of the membrane and, having attached two H ions + from the left compartment, forms H 2 O. The phosphoryl residue attaches to ADP, forming ATP.
Fig.2. Scheme of ATP oxidation and synthesis in mitochondrial membranes
In the cells of organisms, many biosynthetic reactions have been studied that use the energy contained in ATP, during which the processes of carboxylation and decarboxylation, the synthesis of amide bonds, the formation of macroergic compounds capable of transferring energy from ATP to anabolic reactions of synthesis of substances occur. These reactions play an important role in the metabolic processes of plant organisms.
With the participation of ATP and other high-energy nucleoside polyphosphates (GTP, CTP, UGF), monosaccharide molecules, amino acids, nitrogenous bases, acylglycerols can be activated by the synthesis of active intermediates that are derivatives of nucleotides. So, for example, in the process of starch synthesis with the participation of the enzyme ADP-glucose pyrophosphorylase, an activated form of glucose is formed - adenosine diphosphate glucose, which easily becomes a donor of glucose residues during the formation of the structure of the molecules of this polysaccharide.
ATP synthesis occurs in the cells of all organisms in the process of phosphorylation, i.e. addition of inorganic phosphate to ADP. The energy for ADP phosphorylation is generated during energy metabolism. Energy metabolism, or dissimilation, is a set of splitting reactions of organic substances, accompanied by the release of energy. Depending on the habitat, dissimilation can proceed in two or three stages.
In most living organisms - aerobes living in an oxygen environment - three stages are carried out during dissimilation: preparatory, oxygen-free and oxygen, during which organic substances decompose to inorganic compounds. In anaerobes living in an environment devoid of oxygen, or in aerobes with a lack of it, dissimilation occurs only in the first two stages with the formation of intermediate organic compounds still rich in energy.
The first stage - preparatory - consists in the enzymatic splitting of complex organic compounds into simpler ones (proteins - into amino acids, fats - into glycerol and fatty acids, polysaccharides - into monosaccharides, nucleic acids - into nucleotides). The breakdown of organic food substrates is carried out at different levels of the gastrointestinal tract of multicellular organisms. Intracellular cleavage of organic substances occurs under the action of hydrolytic enzymes of lysosomes. The energy released in this case is dissipated in the form of heat, and the resulting small organic molecules can undergo further splitting or be used by the cell as a “building material” for the synthesis of its own organic compounds.
The second stage - incomplete oxidation (oxygen-free) - is carried out directly in the cytoplasm of the cell, it does not need the presence of oxygen and consists in further splitting of organic substrates. The main source of energy in the cell is glucose. Anoxic, incomplete breakdown of glucose is called glycolysis.
Glycolysis is a multi-stage enzymatic process of converting six-carbon glucose into two three-carbon molecules of pyruvic acid (pyruvate, PVA) C3H4O3. During the reactions of glycolysis, a large amount of energy is released - 200 kJ / mol. Part of this energy (60%) is dissipated as heat, the rest (40%) is used for ATP synthesis.
As a result of glycolysis of one glucose molecule, two molecules of PVC, ATP and water are formed, as well as hydrogen atoms, which are stored by the cell in the form of NADH, i.e. as part of a specific carrier - nicotinamide adenine dinucleotide. The further fate of glycolysis products - pyruvate and hydrogen in the form of NAD H - can develop in different ways. In yeast or in plant cells, with a lack of oxygen, alcoholic fermentation occurs - PVC is reduced to ethyl alcohol:
In animal cells experiencing a temporary lack of oxygen, for example, in human muscle cells during excessive exercise, as well as in some bacteria, lactic acid fermentation occurs, in which pyruvate is reduced to lactic acid. In the presence of oxygen in the environment, the products of glycolysis undergo further splitting to final products.
The third stage - complete oxidation (respiration) - proceeds with the obligatory participation of oxygen. Aerobic respiration is a chain of reactions controlled by enzymes of the inner membrane and mitochondrial matrix. Once in the mitochondria, PVC interacts with matrix enzymes and forms: carbon dioxide, which is excreted from the cell; hydrogen atoms, which, as part of the carriers, are sent to the inner membrane; acetyl coenzyme A (acetyl-CoA), which is involved in the tricarboxylic acid cycle (Krebs cycle). The Krebs cycle is a chain of successive reactions during which two CO2 molecules, an ATP molecule and four pairs of hydrogen atoms are formed from one acetyl-CoA molecule, transferred to carrier molecules - NAD and FAD (flavin adenine dinucleotide). The overall reaction of glycolysis and the Krebs cycle can be represented as follows:
So, as a result of the oxygen-free stage of dissimilation and the Krebs cycle, the glucose molecule is broken down to inorganic carbon dioxide (CO2), and the energy released in this process is partially spent on ATP synthesis, but is mainly saved in the electron-loaded carriers NAD H2 and FAD H2. Carrier proteins transport hydrogen atoms to the inner mitochondrial membrane, where they are passed along a chain of proteins built into the membrane. The transport of particles along the transport chain is carried out in such a way that protons remain on the outer side of the membrane and accumulate in the intermembrane space, turning it into an H+ reservoir, while electrons are transferred to the inner surface of the inner mitochondrial membrane, where they eventually combine with oxygen.
As a result of the activity of the electron transport chain enzymes, the inner mitochondrial membrane is negatively charged from the inside, and positively charged from the outside (due to H), so that a potential difference is created between its surfaces. It is known that molecules of the enzyme ATP synthetase with an ion channel are embedded in the inner membrane of mitochondria. When the potential difference across the membrane reaches a critical level (200 mV), the positively charged H+ particles begin to push through the ATPase channel by the force of the electric field and, once on the inner surface of the membrane, interact with oxygen, forming water.
The normal course of metabolic reactions at the molecular level is due to the harmonious combination of the processes of catabolism and anabolism. When catabolic processes are disturbed, first of all, energy difficulties arise, ATP regeneration is disrupted, as well as the supply of the initial anabolism substrates necessary for biosynthetic processes. In turn, damage to anabolic processes that is primary or associated with changes in catabolism processes leads to a disruption in the reproduction of functionally important compounds - enzymes, hormones, etc.
Violation of various links of metabolic chains is unequal in its consequences. The most significant, profound pathological changes in catabolism occur when the biological oxidation system is damaged due to blockade of tissue respiration enzymes, hypoxia, etc., or damage to the mechanisms of conjugation of tissue respiration and oxidative phosphorylation (for example, uncoupling of tissue respiration and oxidative phosphorylation in thyrotoxicosis). In these cases, the cells are deprived of the main source of energy, almost all oxidative reactions of catabolism are blocked or lose the ability to accumulate the released energy in ATP molecules. By inhibiting the reactions of the tricarboxylic acid cycle, energy production from catabolism is reduced by about two-thirds.
Millions of biochemical reactions take place in any cell of our body. They are catalyzed by a variety of enzymes that often require energy. Where does the cell take it? This question can be answered if we consider the structure of the ATP molecule - one of the main sources of energy.
ATP is a universal source of energy
ATP stands for adenosine triphosphate, or adenosine triphosphate. Matter is one of the two most important sources of energy in any cell. The structure of ATP and the biological role are closely related. Most biochemical reactions can only take place with the participation of molecules of a substance, especially this applies. However, ATP is rarely directly involved in the reaction: for any process to take place, energy is needed that is contained precisely in adenosine triphosphate.
The structure of the molecules of the substance is such that the bonds formed between the phosphate groups carry a huge amount of energy. Therefore, such bonds are also called macroergic, or macroenergetic (macro=many, large number). The term was first introduced by the scientist F. Lipman, and he also suggested using the icon ̴ to designate them.
It is very important for the cell to maintain a constant level of adenosine triphosphate. This is especially true for muscle cells and nerve fibers, because they are the most energy-dependent and need a high content of adenosine triphosphate to perform their functions.
The structure of the ATP molecule
Adenosine triphosphate is made up of three elements: ribose, adenine, and
Ribose- a carbohydrate that belongs to the group of pentoses. This means that ribose contains 5 carbon atoms, which are enclosed in a cycle. Ribose is connected to adenine by a β-N-glycosidic bond on the 1st carbon atom. Also, phosphoric acid residues on the 5th carbon atom are attached to the pentose.
Adenine is a nitrogenous base. Depending on which nitrogenous base is attached to the ribose, GTP (guanosine triphosphate), TTP (thymidine triphosphate), CTP (cytidine triphosphate) and UTP (uridine triphosphate) are also isolated. All these substances are similar in structure to adenosine triphosphate and perform approximately the same functions, but they are much less common in the cell.
Residues of phosphoric acid. A maximum of three phosphoric acid residues can be attached to a ribose. If there are two or only one of them, then, respectively, the substance is called ADP (diphosphate) or AMP (monophosphate). It is between the phosphorus residues that macroenergetic bonds are concluded, after the rupture of which from 40 to 60 kJ of energy is released. If two bonds are broken, 80, less often - 120 kJ of energy is released. When the bond between the ribose and the phosphorus residue is broken, only 13.8 kJ is released, therefore, there are only two high-energy bonds in the triphosphate molecule (P ̴ P ̴ P), and one in the ADP molecule (P ̴ P).
What are the structural features of ATP. Due to the fact that a macroenergetic bond is formed between phosphoric acid residues, the structure and functions of ATP are interconnected.
The structure of ATP and the biological role of the molecule. Additional functions of adenosine triphosphate
In addition to energy, ATP can perform many other functions in the cell. Along with other nucleotide triphosphates, triphosphate is involved in the construction nucleic acid. In this case, ATP, GTP, TTP, CTP and UTP are the suppliers of nitrogenous bases. This property is used in processes and transcription.
ATP is also required for the operation of ion channels. For example, the Na-K channel pumps 3 molecules of sodium out of the cell and pumps 2 molecules of potassium into the cell. Such an ion current is needed to maintain positive charge on the outer surface of the membrane, and only with the help of adenosine triphosphate can the channel function. The same applies to proton and calcium channels.
ATP is a precursor of the second messenger cAMP (cyclic adenosine monophosphate) - cAMP not only transmits the signal received by the cell membrane receptors, but is also an allosteric effector. Allosteric effectors are substances that speed up or slow down enzymatic reactions. So, cyclic adenosine triphosphate inhibits the synthesis of an enzyme that catalyzes the breakdown of lactose in bacterial cells.
The adenosine triphosphate molecule itself can also be an allosteric effector. Moreover, in such processes, ADP acts as an ATP antagonist: if triphosphate accelerates the reaction, then diphosphate slows down, and vice versa. These are the functions and structure of ATP.
How is ATP formed in the cell
The functions and structure of ATP are such that the molecules of the substance are quickly used and destroyed. Therefore, the synthesis of triphosphate is an important process in the formation of energy in the cell.
There are three most important ways to synthesize adenosine triphosphate:
1. Substrate phosphorylation.
2. Oxidative phosphorylation.
3. Photophosphorylation.
Substrate phosphorylation is based on multiple reactions occurring in the cytoplasm of the cell. These reactions are called glycolysis - the anaerobic stage. As a result of 1 glycolysis cycle, two molecules are synthesized from 1 glucose molecule, which are further used for energy production, and two ATP are also synthesized.
- C 6 H 12 O 6 + 2ADP + 2Fn --> 2C 3 H 4 O 3 + 2ATP + 4H.
Cell respiration
Oxidative phosphorylation is the formation of adenosine triphosphate by the transfer of electrons along the electron transport chain of the membrane. As a result of this transfer, a proton gradient is formed on one of the sides of the membrane, and with the help of the protein integral set of ATP synthase, molecules are built. The process takes place on the mitochondrial membrane.
The sequence of steps of glycolysis and oxidative phosphorylation in mitochondria makes up the overall process called respiration. After full cycle 36 ATP molecules are formed from 1 glucose molecule in a cell.
Photophosphorylation
The process of photophosphorylation is the same oxidative phosphorylation with only one difference: photophosphorylation reactions occur in the chloroplasts of the cell under the action of light. ATP is produced during the light stage of photosynthesis, the main energy-producing process in green plants, algae, and some bacteria.
In the process of photosynthesis, electrons pass through the same electron transport chain, resulting in the formation of a proton gradient. The concentration of protons on one side of the membrane is the source of ATP synthesis. The assembly of molecules is carried out by the enzyme ATP synthase.
The average cell contains 0.04% adenosine triphosphate of the total mass. However, the most great importance observed in muscle cells: 0.2-0.5%.
There are about 1 billion ATP molecules in a cell.
Each molecule lives no more than 1 minute.
One molecule of adenosine triphosphate is renewed 2000-3000 times a day.
In total, the human body synthesizes 40 kg of adenosine triphosphate per day, and at each time point the supply of ATP is 250 g.
Conclusion
The structure of ATP and the biological role of its molecules are closely related. The substance plays a key role in life processes, because the macroergic bonds between phosphate residues contain a huge amount of energy. Adenosine triphosphate performs many functions in the cell, and therefore it is important to maintain a constant concentration of the substance. Decay and synthesis proceed at a high speed, since the energy of bonds is constantly used in biochemical reactions. It is an indispensable substance of any cell of the body. That, perhaps, is all that can be said about the structure of ATP.
