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 general exchange, which consists in the absorption, assimilation of nutrients and the creation of structural components of the cell at their expense, 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. Each substance has a certain reserve 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 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 deprived of oxygen, or in aerobes with a lack of oxygen, dissimilation proceeds only in the first two stages with the formation of intermediate organic compounds that are 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 are embedded in the inner membrane of mitochondria, which have ion channel. 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.
In addition to proteins, fats and carbohydrates, a large number of other organic compounds are synthesized in the cell, which can be conditionally divided into intermediate and final. Most often, obtaining a certain substance is associated with the operation of a catalytic conveyor (a large number of enzymes), and is associated with the formation of intermediate reaction products, which are affected by the next enzyme. Final organic compounds perform independent functions in the cell or serve as monomers in the synthesis of polymers. The final substances are amino acids, glucose, nucleotides, ATP, hormones, vitamins.
Adenosine triphosphoric acid (ATP) is a universal source and main energy accumulator in living cells. ATP is found in all plant and animal cells. The amount of ATP fluctuates and averages 0.04% (per raw cell weight). The largest amount of ATP (0.2-0.5%) is found in skeletal muscles.
ATP is a nucleotide consisting of a nitrogenous base (adenine), a monosaccharide (ribose), and three phosphoric acid residues. Since ATP contains not one, but three residues of phosphoric acid, it belongs to ribonucleoside triphosphates.
For most types of work occurring in cells, the energy of ATP hydrolysis is used. At the same time, when the terminal residue of phosphoric acid is cleaved off, ATP passes into ADP ( adenosine diphosphate acid), with the elimination of the second residue of phosphoric acid - in AMP ( adenosine monophosphoric acid). The yield of free energy during the elimination of both the terminal and the second residues of phosphoric acid is 30.6 kJ each. Cleavage of the third phosphate group is accompanied by the release of only 13.8 kJ. The bonds between the terminal and the second, second and first residues of phosphoric acid are called macroergic (high-energy).
ATP reserves are constantly replenished. In the cells of all organisms, ATP synthesis occurs in the process of phosphorylation, i.e. addition of phosphoric acid to ADP. Phosphorylation occurs with different intensity in mitochondria, during glycolysis in the cytoplasm, during photosynthesis in chloroplasts. The ATP molecule is used in the cell in 1-2 minutes; in a person, ATP is formed and destroyed per day in an amount equal to the mass of his body.
final organic molecules, are also vitamins and hormones. Major role in life multicellular organisms play vitamins. Vitamins are those organic compounds that a given organism cannot synthesize (or synthesizes in insufficient quantities) and must receive them with food. Vitamins combine with proteins to form complex enzymes. With a lack of any vitamin in food, an enzyme cannot be formed and this or that vitamin deficiency develops. For example, a lack of vitamin C leads to scurvy, a lack of vitamin B 12 leads to anemia, a violation of the normal formation of red blood cells.
Hormones are regulators affecting the work of individual organs and the whole organism. They may be of a protein nature (hormones of the pituitary gland, pancreas), may be related to lipids (sex hormones), may be derivatives of amino acids (thyroxine). Hormones are produced by both animals and plants.
Ways to get energy in the cell
There are four main processes in the cell that ensure the release of energy from chemical bonds during the oxidation of substances and its storage:
1. Glycolysis (stage 2 of biological oxidation) - oxidation of a glucose molecule to two molecules of pyruvic acid, with the formation of 2 molecules ATP and NADH. Further, pyruvic acid is converted to acetyl-SCoA under aerobic conditions, and to lactic acid under anaerobic conditions.
2. β-Oxidation of fatty acids(stage 2 of biological oxidation) - oxidation of fatty acids to acetyl-SCoA, molecules are formed here NADH and FADN 2. ATP molecules "in pure form" do not appear.
3. Tricarboxylic acid cycle(TsTK, stage 3 of biological oxidation) - oxidation of the acetyl group (as part of acetyl-SCoA) or other keto acids to carbon dioxide. Reactions full cycle accompanied by the formation of 1 molecule GTP(which is equivalent to one ATP), 3 molecules NADH and 1 molecule FADN 2.
4. Oxidative phosphorylation(stage 3 of biological oxidation) - NADH and FADH 2 are oxidized, obtained in the reactions of catabolism of glucose, amino acids and fatty acids. At the same time, the enzymes of the respiratory chain on the inner membrane of mitochondria provide the formation greater parts of the cell ATP.
Two ways to synthesize ATP
All nucleosides are constantly used in the cell three phosphates (ATP, GTP, CTP, UTP, TTP) as an energy donor. At the same time, ATP is universal macroerg, participating in almost all aspects of metabolism and cell activity. And it is precisely due to ATP that the phosphorylation of the nucleotides of GDP, CDP, UDP, TDP to the nucleoside is ensured. three phosphates.
In others, the nucleoside three phosphates, there is a certain specialization. So, UTP is involved in the metabolism of carbohydrates, in particular in the synthesis of glycogen. GTP is involved in ribosomes, participates in the formation of peptide bonds in proteins. CTP is used in the synthesis of phospholipids.
The main way to obtain ATP in the cell is oxidative phosphorylation, which occurs in the structures of the inner membrane of mitochondria. At the same time, the energy of hydrogen atoms of NADH and FADH 2 molecules formed in glycolysis, TCA, and fatty acid oxidation is converted into the energy of ATP bonds.
However, there is also another way of phosphorylation of ADP to ATP - substrate phosphorylation. This method is associated with the transfer of macroergic phosphate or the energy of a macroergic bond of a substance (substrate) to ADP. These substances include metabolites of glycolysis ( 1,3-diphosphoglyceric acid, phosphoenolpyruvate), tricarboxylic acid cycle ( succinyl-SCoA) and reserve macroerg creatine phosphate. The energy of hydrolysis of their macroergic bond is higher than 7.3 kcal/mol in ATP, and the role of these substances is reduced to the use of this energy for phosphorylation of the ADP molecule to ATP.
Classification of macroergs
Macroergic compounds are classified according to type of connection, carrying additional energy:
1. Phosphoanhydride connection. All nucleotides have such a bond: nucleoside triphosphates (ATP, GTP, CTP, UTP, TTP) and nucleoside diphosphates (ADP, GDP, CDP, UDP, TDP).
2. Thioether connection. An example is the acyl derivatives of coenzyme A: acetyl-SCoA, succinyl-SCoA, and other compounds of any fatty acid and HS-CoA.
3. Guanidine phosphate connection - present in creatine phosphate, a reserve macroerg of muscle and nervous tissue.
4. Acyl phosphate connection. These macroergs include the glycolysis metabolite 1,3-diphosphoglyceric acid (1,3-diphosphoglycerate). It provides the synthesis of ATP in the reaction of substrate phosphorylation.
5. Enolphosphate connection. The representative is phosphoenolpyruvate, a metabolite of glycolysis. It also provides the synthesis of ATP in the reaction of substrate phosphorylation in glycolysis.
The figure shows two ways ATP structure images. Adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) belong to a class of compounds called nucleoside. A nucleotide molecule consists of a five-carbon sugar, a nitrogenous base, and phosphoric acid. In the AMP molecule, the sugar is represented by ribose, and the base is represented by adenine. ADP has two phosphate groups, while ATP has three.
ATP value
When ATP is broken down into ADP and inorganic phosphate (Fn) energy is released:
The reaction proceeds with the absorption of water, i.e., it is hydrolysis (in our article we have met many times with this very common type of biochemical reactions). The third phosphate group split off from ATP remains in the cell in the form of inorganic phosphate (Pn). The free energy yield in this reaction is 30.6 kJ per 1 mole of ATP.
From ADP and phosphate, ATP can be synthesized again, but this requires 30.6 kJ of energy per 1 mol of newly formed ATP.
In this reaction, called the condensation reaction, water is released. The addition of phosphate to ADP is called a phosphorylation reaction. Both of the above equations can be combined:
This reversible reaction is catalyzed by an enzyme called ATPase.
All cells, as already mentioned, need energy to perform their work, and for all cells of any organism, the source of this energy serves as ATP. Therefore, ATP is called the "universal energy carrier" or "energy currency" of cells. Electric batteries are a good analogy. Remember why we don't use them. With their help we can receive light in one case, sound in another, sometimes mechanical movement, and sometimes we need their own electrical energy. The convenience of batteries is that we can use the same source of energy - a battery - for a variety of purposes, depending on where we put it. ATP plays the same role in cells. It provides energy for various processes such as muscle contraction, transmission of nerve impulses, active transport of substances or protein synthesis, and for all other types of cellular activity. To do this, it must simply be “connected” to the appropriate part of the cell apparatus.
The analogy can be continued. Batteries must first be made, and some of them (rechargeable) can be recharged just like. In the manufacture of batteries at the factory, they must contain (and thereby expend by the factory) a certain amount of energy. ATP synthesis also requires energy; its source is the oxidation of organic substances in the process of respiration. Because energy is released to phosphorylate ADP during oxidation, this phosphorylation is called oxidative phosphorylation. In photosynthesis, ATP is produced using light energy. This process is called photophosphorylation (see section 7.6.2). There are also "factories" in the cell that produce most of the ATP. These are mitochondria; they house the chemical "assembly lines" that form ATP during aerobic respiration. Finally, the discharged “accumulators” are also recharged in the cell: after ATP, having released the energy contained in it, turns into ADP and Phn, it can be quickly synthesized again from ADP and Phn due to the energy received in the process of respiration from the oxidation of new portions of organic matter.
ATP amount in a cage at any this moment very small. Therefore, in ATP one should see only the carrier of energy, and not its depot. For long-term energy storage, substances such as fats or glycogen are used. Cells are very sensitive to the level of ATP. As soon as the rate of its use increases, the rate of the breathing process that maintains this level also increases.
Role of ATP as a link between cellular respiration and processes that go with energy consumption, is visible from the figure. This scheme looks simple, but it illustrates a very important pattern.
It can thus be said that, on the whole, the function of respiration is to produce ATP.
Let's summarize the above.
1. The synthesis of ATP from ADP and inorganic phosphate requires 30.6 kJ of energy per 1 mole of ATP.
2. ATP is present in all living cells and is, therefore, a universal energy carrier. Other energy carriers are not used. This simplifies the matter - the necessary cellular apparatus can be simpler and work more efficiently and economically.
3. ATP easily delivers energy to any part of the cell to any process that needs energy.
4. ATP quickly releases energy. This requires only one reaction - hydrolysis.
5. The rate of reproduction of ATP from ADP and inorganic phosphate (the rate of the respiration process) is easily adjusted according to needs.
6. ATP is synthesized during respiration due to the chemical energy released during the oxidation of organic substances such as glucose, and during photosynthesis - due to solar energy. The formation of ATP from ADP and inorganic phosphate is called the phosphorylation reaction. If energy for phosphorylation is supplied by oxidation, then they speak of oxidative phosphorylation (this process occurs during respiration), but if light energy is used for phosphorylation, then the process is called photophosphorylation (this takes place during photosynthesis).
The most important substance in the cells of living organisms is adenosine triphosphate or adenosine triphosphate. If we enter the abbreviation of this name, we get ATP (eng. ATP). This substance belongs to the group of nucleoside triphosphates and plays a leading role in the metabolic processes in living cells, being an indispensable source of energy for them.
In contact with
Classmates
The discoverers of ATP were the biochemists of the Harvard School of Tropical Medicine - Yellapragada Subbarao, Karl Loman and Cyrus Fiske. The discovery occurred in 1929 and became a major milestone in the biology of living systems. Later, in 1941, the German biochemist Fritz Lipmann found that ATP in cells is the main energy carrier.
The structure of ATP
This molecule has a systematic name, which is written as follows: 9-β-D-ribofuranosyladenine-5'-triphosphate, or 9-β-D-ribofuranosyl-6-amino-purine-5'-triphosphate. What compounds are in ATP? Chemically, it is the triphosphate ester of adenosine - derivative of adenine and ribose. This substance is formed by the connection of adenine, which is a purine nitrogenous base, with the 1'-carbon of ribose using a β-N-glycosidic bond. The α-, β-, and γ-molecules of phosphoric acid are then sequentially attached to the 5'-carbon of the ribose.
Thus, the ATP molecule contains compounds such as adenine, ribose, and three phosphoric acid residues. ATP is a special compound containing bonds that release a large amount of energy. Such bonds and substances are called macroergic. During the hydrolysis of these bonds of the ATP molecule, an amount of energy from 40 to 60 kJ / mol is released, while this process is accompanied by the elimination of one or two phosphoric acid residues.
This is how these chemical reactions are written:
- one). ATP + water → ADP + phosphoric acid + energy;
- 2). ADP + water → AMP + phosphoric acid + energy.
The energy released during these reactions is used in further biochemical processes that require certain energy inputs.
The role of ATP in a living organism. Its functions
What is the function of ATP? First of all, energy. As mentioned above, the main role of adenosine triphosphate is the energy supply of biochemical processes in a living organism. This role is due to the fact that, due to the presence of two high-energy bonds, ATP acts as an energy source for many physiological and biochemical processes that require large energy costs. Such processes are all synthesis reactions complex substances in the body. This is, first of all, the active transfer of molecules through cell membranes, including participation in the creation of an intermembrane electrical potential, and the implementation of muscle contraction.
In addition to the above, we list a few more, no less important functions of ATP, such as:
How is ATP formed in the body?
Synthesis of adenosine triphosphoric acid is ongoing, because the body always needs energy for normal life. At any given moment, there is very little of this substance - about 250 grams, which are an "emergency reserve" for a "rainy day". During illness, there is an intensive synthesis of this acid, because a lot of energy is required for the functioning of the immune and excretory systems, as well as the body's thermoregulation system, which is necessary to effectively combat the onset of the disease.
Which cell has the most ATP? These are cells of muscle and nervous tissues, since energy exchange processes are most intensive in them. And this is obvious, because the muscles are involved in the movement, which requires the contraction of muscle fibers, and neurons transmit electrical impulses, without which the work of all body systems is impossible. Therefore, it is so important for the cell to maintain an unchanged and high level adenosine triphosphate.
How can adenosine triphosphate molecules be formed in the body? They are formed by the so-called phosphorylation of ADP (adenosine diphosphate). This chemical reaction as follows:
ADP + phosphoric acid + energy→ATP + water.
Phosphorylation of ADP occurs with the participation of such catalysts as enzymes and light, and is carried out in one of three ways:
Both oxidative and substrate phosphorylation use the energy of substances oxidized in the course of such synthesis.
Conclusion
Adenosine triphosphoric acid is the most frequently updated substance in the body. How long does an adenosine triphosphate molecule live on average? In the human body, for example, its life span is less than one minute, so one molecule of such a substance is born and decays up to 3000 times per day. Amazingly, during the day the human body synthesizes about 40 kg of this substance! So great is the need for this "internal energy" for us!
The whole cycle of synthesis and further use of ATP as an energy fuel for metabolic processes in the organism of a living being is the very essence of energy metabolism in this organism. Thus, adenosine triphosphate is a kind of "battery" that ensures the normal functioning of all cells of a living organism.