adp molecules. Structure of ATP
Judging by the above, a huge amount of ATP is required. In skeletal muscles, during their transition from a state of rest to contractile activity - 20 times (or even several hundred times) the rate of ATP splitting sharply increases simultaneously.
However, ATP stores in muscles are relatively insignificant (about 0.75% of its mass) and they can only last for 2-3 seconds of intense work.
Fig.15. Adenosine triphosphate (ATP, ATP). Molar mass 507.18g/mol
This is because ATP is a large, heavy molecule ( fig.15). ATP is a nucleotide formed by the nitrogenous base adenine, the five-carbon sugar ribose, and three phosphoric acid residues. Phosphate groups in the ATP molecule are interconnected by high-energy (macroergic) bonds. It has been calculated that if the body contained amount of ATP sufficient for use in within one day, then the weight of a person, even leading a sedentary lifestyle, would be on 75% more.
To sustain a sustained contraction, ATP molecules must be formed during metabolism at the same rate as they are broken down during contraction. Therefore, ATP is one of the most frequently updated substances, so in humans, the lifespan of one ATP molecule is less than 1 minute. During the day, one ATP molecule goes through an average of 2000-3000 resynthesis cycles (the human body synthesizes about 40 kg of ATP per day, but contains approximately 250 g at any given moment), that is, there is practically no ATP reserve in the body, and for normal life it is necessary to constantly synthesize new ATP molecules.
Thus, to maintain the activity of muscle tissue at a certain level, rapid resynthesis of ATP is required at the same rate as it is consumed. This occurs in the process of rephosphorylation, when ADP and phosphates are combined
ATP synthesis - ADP phosphorylation
In the body, ATP is formed from ADP and inorganic phosphate due to the energy released during the oxidation of organic substances and in the process of photosynthesis. This process is called phosphorylation. In this case, at least 40 kJ / mol of energy must be expended, which is accumulated in macroergic bonds:
ADP + H 3 PO 4 + energy→ ATP + H 2 O
Phosphorylation of ADP
Substrate phosphorylation of ATP Oxidative phosphorylation of ATP
Phosphorylation of ADP is possible in two ways: substrate phosphorylation and oxidative phosphorylation (using the energy of oxidizing substances). The bulk of ATP is formed on mitochondrial membranes during oxidative phosphorylation by H-dependent ATP synthase.
The reactions of ADP phosphorylation and the subsequent use of ATP as an energy source form a cyclic process that is the essence of energy metabolism.
There are three ways in which ATP is generated during muscle fiber contraction.
Three main pathways for ATP resynthesis:
1 - creatine phosphate (CP) system
2 - glycolysis
3 - oxidative phosphorylation
Creatine phosphate (CP) system -
Phosphorylation of ADP by transfer of a phosphate group from creatine phosphate
Anaerobic creatine phosphate resynthesis of ATP.
Fig.16. Creatine Phosphate ( CF) ATP resynthesis system in the body
To maintain the activity of muscle tissue at a certain level rapid resynthesis of ATP is required. This occurs in the process of rephosphorylation, when ADP and phosphates are combined. The most available substance that is used for ATP resynthesis is primarily creatine phosphate ( fig.16), easily transferring its phosphate group to ADP:
CrF + ADP → Creatine + ATP
CRF is a compound of the nitrogen-containing substance creatinine with phosphoric acid. Its concentration in muscles is approximately 2–3%, i.e., 3–4 times higher than that of ATP. A moderate (by 20–40%) decrease in the ATP content immediately leads to the use of CRF. However, at maximum work, creatine phosphate reserves are also quickly depleted. Through ADP phosphorylation creatine phosphate very rapid formation of ATP at the very beginning of the contraction is ensured.
During the rest period, the concentration of creatine phosphate in the muscle fiber rises to a level approximately five times higher than the content of ATP. At the beginning of the contraction, when the ATP concentration begins to decrease and the ADP concentration begins to increase due to the breakdown of ATP by the action of myosin ATPase, the reaction shifts towards the formation of ATP due to creatine phosphate. In this case, the energy transition occurs at such a high rate that at the beginning of the contraction, the concentration of ATP in the muscle fiber changes little, while the concentration of creatine phosphate falls rapidly.
Although ATP is formed from creatine phosphate very quickly, through a single enzymatic reaction (Fig. 16), the amount of ATP is limited by the initial concentration of creatine phosphate in the cell. In order for a muscle contraction to last longer than a few seconds, the other two sources of ATP formation mentioned above must be involved. After the onset of the contraction provided by the use of creatine phosphate, the slower, multi-enzymatic pathways of oxidative phosphorylation and glycolysis are activated, due to which the rate of ATP formation increases to a level corresponding to the rate of ATP splitting.
What is the fastest ATP synthesis system?
The CP (creatine phosphate) system is the fastest ATP resynthesis system in the body, as it involves only one enzymatic reaction. It carries out the transfer of high-energy phosphate directly from CP to ADP with the formation of ATP. However, the ability of this system to resynthesize ATP is limited, since the CP reserves in the cell are small. Since this system does not use oxygen to synthesize ATP, it is considered an anaerobic source of ATP.
How much CF is stored in the body?
The total reserves of CF and ATP in the body would be enough for less than 6 seconds of intense physical activity.
What is the advantage of anaerobic ATP production using CF?
The CF/ATP system is used during short-term intense exercise. It is located on the heads of myosin molecules, that is, directly at the place of energy consumption. The CF/ATF system is used when a person makes rapid movements, such as quickly climbing a mountain, performing high jumps, running a hundred meters, quickly getting out of bed, running away from a bee, or jumping away from a truck while crossing the street.
glycolysis
Phosphorylation of ADP in the cytoplasm
The breakdown of glycogen and glucose under anaerobic conditions to form lactic acid and ATP.
To restore ATP in order to continue intense muscle activity the process includes the following source of energy production - the enzymatic breakdown of carbohydrates in oxygen-free (anaerobic) conditions.
Fig.17. General scheme of glycolysis
The process of glycolysis is schematically represented as follows (p is.17).
The appearance of free phosphate groups during glycolysis makes possible the re-synthesis of ATP from ADP. However, in addition to ATP, two molecules of lactic acid are formed.
Process glycolysis is slower compared to creatine phosphate ATP resynthesis. The duration of muscle work in anaerobic (oxygen-free) conditions is limited due to the depletion of glycogen or glucose reserves and due to the accumulation of lactic acid.
Anaerobic energy production by glycolysis is produced uneconomical with high consumption of glycogen, since only part of the energy contained in it is used (lactic acid is not used in glycolysis, although contains a significant amount of energy).
Of course, already at this stage, part of the lactic acid is oxidized by some amount of oxygen to carbon dioxide and water:
С3Н6О3 + 3О2 = 3СО2 + 3Н2О 41
The resulting energy goes to the resynthesis of carbohydrate from other parts of lactic acid. However, the limited amount of oxygen during very intense physical activity is insufficient to support the reactions aimed at the conversion of lactic acid and the resynthesis of carbohydrates.
Where does ATP come from for physical activity lasting more than 6 seconds?
At glycolysis ATP is formed without the use of oxygen (anaerobically). Glycolysis occurs in the cytoplasm of the muscle cell. In the process of glycolysis, carbohydrates are oxidized to pyruvate or lactate and 2 ATP molecules are released (3 molecules if you start the calculation with glycogen). During glycolysis, ATP is synthesized quickly, but more slowly than in the CF system.
What is the end product of glycolysis - pyruvate or lactate?
When glycolysis proceeds slowly and mitochondria adequately accept reduced NADH, the end product of glycolysis is pyruvate. Pyruvate is converted to acetyl-CoA (a reaction requiring NAD) and undergoes complete oxidation in the Krebs and CPE cycle. When the mitochondria cannot provide adequate pyruvate oxidation or regeneration of electron acceptors (NAD or FADH), pyruvate is converted to lactate. The conversion of pyruvate to lactate reduces the concentration of pyruvate, which prevents the end products from inhibiting the reaction, and glycolysis continues.
When is lactate the main end product of glycolysis?
Lactate is formed when mitochondria cannot adequately oxidize pyruvate or regenerate enough electron acceptors. This occurs at low enzymatic activity of mitochondria, with insufficient oxygen supply, at a high rate of glycolysis. In general, lactate formation is increased during hypoxia, ischemia, bleeding, after carbohydrate intake, high muscle glycogen concentrations, and exercise-induced hyperthermia.
What other ways can pyruvate be metabolized?
During exercise or a low-calorie diet, pyruvate is converted to the nonessential amino acid alanine. Synthesized in skeletal muscles, alanine enters the liver with blood flow, where it turns into pyruvate. Pyruvate is then converted to glucose, which enters the bloodstream. This process is similar to the Cori cycle and is called the alanine cycle.
19. Functions of cell mitochondria. ATP and its role in the cell.
The 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 influence 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 high-energy compound - ATP. In the future, it is ATP, and not nutrients, that is used to provide energy for intracellular metabolic processes.
The 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 energy is released, ATP donates a phosphate group and turns into adenosine diphosphate. The released energy is used for almost all cellular processes, for example, in biosynthesis reactions and during muscle contraction.
Replenishment of ATP reserves occurs by recombining ADP with the rest of phosphoric acid due to 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 the chemical reactions of 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.
ATP synthesis is 95% 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 the tricarboxylic acid cycle, acetyl-CoA is broken down 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. At the initial stage, an electron is split off from the hydrogen atom, and the atom turns into 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 of ATP synthesis is generally called the chemiosmotic mechanism of ATP formation.
Energy of muscle activity
As already mentioned, both phases of muscle activity - contraction and relaxation - proceed with the mandatory use of energy that is released during ATP hydrolysis.
However, the reserves of ATP in muscle cells are insignificant (at rest, the concentration of ATP in muscles is about 5 mmol / l), and they are sufficient for muscle work for 1-2 s. Therefore, to ensure longer muscle activity in the muscles, replenishment of ATP reserves must occur. The formation of ATP in muscle cells directly during physical work is called ATP resynthesis and comes with energy consumption.
Thus, during the functioning of the muscles, two processes simultaneously occur in them: ATP hydrolysis, which provides the necessary energy for contraction and relaxation, and ATP resynthesis, which replenishes the loss of this substance. If only the chemical energy of ATP is used to ensure muscle contraction and relaxation, then the chemical energy of a wide variety of compounds is suitable for ATP resynthesis: carbohydrates, fats, amino acids and creatine phosphate.
The structure and biological role of ATP
Adenosine triphosphate (ATP) is a nucleotide. The ATP (adenosine triphosphoric acid) molecule consists of the nitrogenous base of adenine, the five-carbon sugar of ribose, and three phosphoric acid residues interconnected by a macroergic bond. During its hydrolysis, a large amount of energy is released. ATP is the main macroerg of the cell, an energy accumulator in the form of the energy of high-energy chemical bonds.
Under physiological conditions, that is, under the conditions that exist in a living cell, the splitting of a mole of ATP (506 g) is accompanied by the release of 12 kcal, or 50 kJ of energy.
Ways of ATP formation
Aerobic oxidation (tissue respiration)
Synonyms: oxidative phosphorylation, respiratory phosphorylation, aerobic phosphorylation.
This pathway takes place in the mitochondria.
The tricarboxylic acid cycle was first discovered by the English biochemist G. Krebs (Fig. 4).
The first reaction is catalyzed by the enzyme citrate synthase, in which the acetyl group of acetyl-CoA condenses with oxaloacetate to form citric acid. Apparently, in this reaction, citryl-CoA bound to the enzyme is formed as an intermediate. Then the latter is spontaneously and irreversibly hydrolyzed to form citrate and HS-CoA.
As a result of the second reaction, the formed citric acid undergoes dehydration with the formation of cis-aconitic acid, which, by attaching a water molecule, passes into isocitric acid (isocitrate). These reversible reactions of hydration-dehydration are catalyzed by the enzyme aconitate hydratase (aconitase). As a result, there is a mutual displacement of H and OH in the citrate molecule.
Rice. 4. Tricarboxylic acid cycle (Krebs cycle)
The third reaction seems to limit the rate of the Krebs cycle. Isocitric acid is dehydrogenated in the presence of NAD-dependent isocitrate dehydrogenase. During the isocitrate dehydrogenase reaction, isocitric acid is simultaneously decarboxylated. NAD-dependent isocitrate dehydrogenase is an allosteric enzyme that requires ADP as a specific activator. In addition, the enzyme needs or ions to manifest its activity.
During the fourth reaction, α-ketoglutaric acid is oxidatively decarboxylated to form the high-energy compound succinyl-CoA. The mechanism of this reaction is similar to the reaction of oxidative decarboxylation of pyruvate to acetyl-CoA; The α-ketoglutarate dehydrogenase complex resembles the pyruvate dehydrogenase complex in its structure. Both in one and in the other case, 5 coenzymes take part in the reaction: TPP, lipoic acid amide, HS-CoA, FAD and NAD +.
The fifth reaction is catalyzed by the enzyme succinyl-CoA synthetase. During this reaction, succinyl-CoA, with the participation of GTP and inorganic phosphate, is converted into succinic acid (succinate). At the same time, the formation of a high-energy phosphate bond of GTP occurs due to the high-energy thioether bond of succinyl-CoA.
As a result of the sixth reaction, succinate is dehydrogenated to fumaric acid. The oxidation of succinate is catalyzed by succinate dehydrogenase,
in the molecule of which the coenzyme FAD is firmly (covalently) bound to the protein. In turn, succinate dehydrogenase is tightly bound to the inner mitochondrial membrane.
The seventh reaction is carried out under the influence of the enzyme fumarate hydratase (fumarase). The resulting fumaric acid is hydrated, the reaction product is malic acid (malate).
Finally, during the eighth reaction of the tricarboxylic acid cycle, L-malate is oxidized to oxaloacetate under the influence of mitochondrial NAD-dependent malate dehydrogenase.
During one turn of the cycle, during the oxidation of one molecule of acetyl-CoA in the Krebs cycle and the system of oxidative phosphorylation, 12 ATP molecules can be formed.
Anaerobic oxidation
Synonyms: substrate phosphorylation, anaerobic ATP synthesis. Goes in the cytoplasm, the split off hydrogen is attached to some other substance. Depending on the substrate, two pathways of anaerobic ATP resynthesis are distinguished: creatine phosphate (creatine kinase, alactate) and glycolytic (glycolysis, lactate). In the first case, the substrate is creatine phosphate, in the second - glucose.
These paths proceed without the participation of oxygen.
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- Introduction
- 1.1 Chemical properties of ATP
- 1.2 Physical properties of ATP
- 2.1
- 3.1 Role in the cage
- 3.2 Role in the work of enzymes
- 3.4 Other functions of ATP
- Conclusion
- Bibliographic list
List of symbols
ATP - adenosine triphosphate
ADP - adenosine diphosphate
AMP - adenosine monophosphate
RNA - ribonucleic acid
DNA - deoxyribonucleic acid
NAD - nicotinamide adenine dinucleotide
PVC - pyruvic acid
G-6-F - phosphoglucose isomerase
F-6-F - fructose-6-phosphate
TPP - thiamine pyrophosphate
FAD - phenyladenine dinucleotide
Fn - unlimited phosphate
G - entropy
RNR - ribonucleotide reductase
Introduction
The main source of energy for all living beings inhabiting our planet is the energy of sunlight, which is directly used only by the cells of green plants, algae, green and purple bacteria. In these cells, organic substances (carbohydrates, fats, proteins, nucleic acids, etc.) are formed from carbon dioxide and water during photosynthesis. By eating plants, animals receive organic matter in finished form. The energy stored in these substances passes with them into the cells of heterotrophic organisms.
In the cells of animal organisms, the energy of organic compounds during their oxidation is converted into the energy of ATP. (The carbon dioxide and water released at the same time are again used by autotrophic organisms for photosynthesis processes.) Due to the energy of ATP, all life processes are carried out: the biosynthesis of organic compounds, movement, growth, cell division, etc.
The topic of the formation and use of ATP in the body is not new for a long time, but rarely, where you will find a complete consideration of both in one source and even less often an analysis of both of these processes at once and in different organisms.
In this regard, the relevance of our work has become a thorough study of the formation and use of ATP in living organisms, because. this topic is not studied at the proper level in the popular science literature.
The aim of our work was:
· study of the mechanisms of formation and ways of using ATP in the body of animals and humans.
We were given the following tasks:
· To study the chemical nature and properties of ATP;
· Analyze the pathways of ATP formation in living organisms;
· Consider ways of using ATP in living organisms;
Consider the importance of ATP for humans and animals.
Chapter 1. Chemical nature and properties of ATP
1.1 Chemical properties of ATP
Adenosine triphosphate is a nucleotide that plays an extremely important role in the exchange of energy and substances in organisms; First of all, the compound is known as a universal source of energy for all biochemical processes occurring in living systems. ATP was discovered in 1929 by Karl Lohmann, and in 1941 Fritz Lipmann showed that ATP is the main energy carrier in the cell.
Systematic name of ATP:
9-in-D-ribofuranosyladenine-5"-triphosphate, or
9-in-D-ribofuranosyl-6-amino-purine-5"-triphosphate.
Chemically, ATP is the triphosphate ester of adenosine, which is a derivative of adenine and ribose.
The purine nitrogenous base - adenine - is connected by a n-N-glycosidic bond to the 1 "-carbon of ribose. Three molecules of phosphoric acid are sequentially attached to the 5"-carbon of ribose, denoted respectively by the letters: b, c and d.
In terms of structure, ATP is similar to the adenine nucleotide that is part of RNA, only instead of one phosphoric acid, ATP contains three phosphoric acid residues. Cells are not able to contain acids in noticeable quantities, but only their salts. Therefore, phosphoric acid enters ATP as a residue (instead of the OH group of the acid, there is a negatively charged oxygen atom).
Under the action of enzymes, the ATP molecule is easily hydrolyzed, that is, it attaches a water molecule and breaks down to form adenosine diphosphoric acid (ADP):
ATP + H2O ADP + H3PO4.
Cleavage of another phosphoric acid residue converts ADP to adenosine monophosphoric acid AMP:
ADP + H2O AMP + H3PO4.
These reactions are reversible, that is, AMP can be converted to ADP and then to ATP, accumulating energy. The destruction of a conventional peptide bond releases only 12 kJ/mol of energy. And the bonds that attach phosphoric acid residues are high-energy (they are also called macroergic): when each of them is destroyed, 40 kJ / mol of energy is released. Therefore, ATP plays a central role in cells as a universal biological energy accumulator. ATP molecules are synthesized in mitochondria and chloroplasts (only a small amount of them is synthesized in the cytoplasm), and then they enter the various organelles of the cell, providing energy for all life processes.
Due to the energy of ATP, cell division occurs, the active transfer of substances through cell membranes, the maintenance of the membrane electrical potential in the process of transmission of nerve impulses, as well as the biosynthesis of macromolecular compounds and physical work.
With an increased load (for example, in sprinting), the muscles work exclusively due to the supply of ATP. In muscle cells, this reserve is enough for several dozen contractions, and then the amount of ATP must be replenished. The synthesis of ATP from ADP and AMP occurs due to the energy released during the breakdown of carbohydrates, lipids and other substances. A large amount of ATP is also spent on the performance of mental work. For this reason, mental workers require an increased amount of glucose, the breakdown of which ensures the synthesis of ATP.
1.2 Physical properties of ATP
ATP is made up of adenosine and ribose - and three phosphate groups. ATP is highly soluble in water and fairly stable in solutions at pH 6.8-7.4, but rapidly hydrolyzes at extreme pH. Therefore, ATP is best stored in anhydrous salts.
ATP is an unstable molecule. In unbuffered water, it hydrolyses to ADP and phosphate. This is because the strength of the bonds between the phosphate groups in ATP is less than the strength of the hydrogen bonds (hydration bonds) between its products (ADP + phosphate) and water. Thus, if ATP and ADP are in chemical equilibrium in water, almost all of the ATP will eventually be converted to ADP. A system that is far from equilibrium contains Gibbs free energy and is capable of doing work. Living cells maintain the ratio of ATP to ADP at a point ten orders of magnitude from equilibrium, with an ATP concentration a thousand times higher than the ADP concentration. This shift from the equilibrium position means that ATP hydrolysis in the cell releases a large amount of free energy.
The two high-energy phosphate bonds (those that link adjacent phosphates) in an ATP molecule are responsible for the high energy content of that molecule. The energy stored in ATP can be released from hydrolysis. Located furthest from the ribose sugar, the z-phosphate group has a higher hydrolysis energy than either β- or β-phosphate. Bonds formed after hydrolysis or phosphorylation of an ATP residue are lower in energy than other ATP bonds. During enzyme-catalyzed ATP hydrolysis or ATP phosphorylation, available free energy can be used by living systems to do work.
Any unstable system of potentially reactive molecules can potentially serve as a way to store free energy if the cells have kept their concentration far from the equilibrium point of the reaction. However, as is the case with most polymeric biomolecules, the breakdown of RNA, DNA and ATP into simple monomers is due to both the release of energy and entropy, an increase in consideration, both in standard concentrations, and also in those concentrations in which it occurs in the cell.
The standard amount of energy released as a result of ATP hydrolysis can be calculated from changes in energy not related to natural (standard) conditions, then correcting the biological concentration. The net change in thermal energy (enthalpy) at standard temperature and pressure for the decomposition of ATP into ADP and inorganic phosphates is 20.5 kJ/mol, with a free energy change of 3.4 kJ/mol. Energy is released by splitting phosphate or pyrophosphate from ATP to the state standard 1 M are:
ATP + H 2 O > ADP + P I DG? = - 30.5 kJ/mol (-7.3 kcal/mol)
ATP + H 2 O > AMP + PP i DG? = - 45.6 kJ/mol (-10.9 kcal/mol)
These values can be used to calculate the change in energy under physiological conditions and cellular ATP/ADP. However, a more representative significance, called energy charge, often works. Values are given for the Gibbs free energy. These reactions depend on a number of factors, including overall ionic strength and the presence of alkaline earth metals such as Mg 2 + and Ca 2 + ions. Under normal conditions, DG is about -57 kJ/mol (-14 kcal/mol).
protein biological battery energy
Chapter 2
In the body, ATP is synthesized by phosphorylation of ADP:
ADP + H 3 PO 4 + energy> ATP + H 2 O.
Phosphorylation of ADP is possible in two ways: substrate phosphorylation and oxidative phosphorylation (using the energy of oxidizing substances). The bulk of ATP is formed on mitochondrial membranes during oxidative phosphorylation by H-dependent ATP synthase. Substrate phosphorylation of ATP does not require the participation of membrane enzymes; it occurs in the process of glycolysis or by transferring a phosphate group from other macroergic compounds.
The reactions of ADP phosphorylation and the subsequent use of ATP as an energy source form a cyclic process that is the essence of energy metabolism.
In the body, ATP is one of the most frequently updated substances. So in humans, the lifespan of one ATP molecule is less than 1 minute. During the day, one ATP molecule goes through an average of 2000-3000 resynthesis cycles (the human body synthesizes about 40 kg of ATP per day), that is, there is practically no ATP reserve in the body, and for normal life it is necessary to constantly synthesize new ATP molecules.
Oxidative phosphorylation -
However, most often carbohydrates are used as a substrate. So, brain cells are not able to use any other substrate for nutrition, except for carbohydrates.
Pre-complex carbohydrates are broken down to simple ones, up to the formation of glucose. Glucose is a universal substrate in the process of cellular respiration. Glucose oxidation is divided into 3 stages:
1. glycolysis;
2. oxidative decarboxylation and the Krebs cycle;
3. oxidative phosphorylation.
In this case, glycolysis is a common phase for aerobic and anaerobic respiration.
2 .1.1 ChikoLiz- an enzymatic process of sequential breakdown of glucose in cells, accompanied by the synthesis of ATP. Glycolysis under aerobic conditions leads to the formation of pyruvic acid (pyruvate), glycolysis under anaerobic conditions leads to the formation of lactic acid (lactate). Glycolysis is the main route of glucose catabolism in animals.
The glycolytic pathway consists of 10 consecutive reactions, each of which is catalyzed by a separate enzyme.
The process of glycolysis can be conditionally divided into two stages. The first stage, proceeding with the energy consumption of 2 ATP molecules, is the splitting of a glucose molecule into 2 molecules of glyceraldehyde-3-phosphate. At the second stage, NAD-dependent oxidation of glyceraldehyde-3-phosphate occurs, accompanied by ATP synthesis. By itself, glycolysis is a completely anaerobic process, that is, it does not require the presence of oxygen for the reactions to occur.
Glycolysis is one of the oldest metabolic processes known in almost all living organisms. Presumably, glycolysis appeared more than 3.5 billion years ago in primary prokaryotes.
The result of glycolysis is the conversion of one molecule of glucose into two molecules of pyruvic acid (PVA) and the formation of two reducing equivalents in the form of the coenzyme NAD H.
The complete equation for glycolysis is:
C 6 H 12 O 6 + 2NAD + + 2ADP + 2P n \u003d 2NAD H + 2PVC + 2ATP + 2H 2 O + 2H +.
In the absence or lack of oxygen in the cell, pyruvic acid undergoes reduction to lactic acid, then the general equation of glycolysis will be as follows:
C 6 H 12 O 6 + 2ADP + 2P n \u003d 2 lactate + 2ATP + 2H 2 O.
Thus, during the anaerobic breakdown of one glucose molecule, the total net ATP yield is two molecules obtained in the reactions of ADP substrate phosphorylation.
In aerobic organisms, the end products of glycolysis undergo further transformations in biochemical cycles related to cellular respiration. As a result, after the complete oxidation of all metabolites of one glucose molecule at the last stage of cellular respiration - oxidative phosphorylation occurring on the mitochondrial respiratory chain in the presence of oxygen - an additional 34 or 36 ATP molecules are additionally synthesized for each glucose molecule.
The first reaction of glycolysis is the phosphorylation of a glucose molecule, which occurs with the participation of the tissue-specific hexokinase enzyme with the energy consumption of 1 ATP molecule; the active form of glucose is formed - glucose-6-phosphate (G-6-F):
For the reaction to proceed, the presence of Mg 2+ ions in the medium is necessary, with which the ATP molecule complex binds. This reaction is irreversible and is the first key reaction glycolysis.
Phosphorylation of glucose has two goals: first, because the plasma membrane, which is permeable to a neutral glucose molecule, does not allow negatively charged G-6-P molecules to pass through, phosphorylated glucose is locked inside the cell. Secondly, during phosphorylation, glucose is converted into an active form that can participate in biochemical reactions and be included in metabolic cycles.
The hepatic isoenzyme of hexokinase - glucokinase - is important in the regulation of blood glucose levels.
In the next reaction ( 2 ) by the enzyme phosphoglucoisomerase G-6-P is converted into fructose-6-phosphate (F-6-F):
Energy is not required for this reaction, and the reaction is completely reversible. At this stage, fructose can also be included in the process of glycolysis by phosphorylation.
Then two reactions follow almost immediately one after another: irreversible phosphorylation of fructose-6-phosphate ( 3 ) and reversible aldol splitting of the resulting fructose-1,6-bisphosphate (F-1,6-bF) into two trioses ( 4 ).
Phosphorylation of F-6-F is carried out by phosphofructokinase with the expenditure of energy of another ATP molecule; this is the second key reaction glycolysis, its regulation determines the intensity of glycolysis as a whole.
Aldol cleavage F-1,6-bF occurs under the action of fructose-1,6-bisphosphate aldolase:
As a result of the fourth reaction, dihydroxyacetone phosphate And glyceraldehyde-3-phosphate, and the first one is almost immediately under the action phosphotriose isomerase goes to the second 5 ), which is involved in further transformations:
Each molecule of glyceraldehyde phosphate is oxidized by NAD+ in the presence of dehydrogenases glyceraldehyde phosphate before 1,3- disphosphoglyce- rata (6 ):
Coming from 1,3-diphosphoglycerate, containing a macroergic bond in 1 position, the phosphoglycerate kinase enzyme transfers a phosphoric acid residue to the ADP molecule (reaction 7 ) - an ATP molecule is formed:
This is the first reaction of substrate phosphorylation. From this moment, the process of glucose breakdown ceases to be unprofitable in terms of energy, since the energy costs of the first stage are compensated: 2 ATP molecules are synthesized (one for each 1,3-diphosphoglycerate) instead of the two spent in reactions 1 And 3 . For this reaction to occur, the presence of ADP in the cytosol is required, that is, with an excess of ATP in the cell (and a lack of ADP), its rate decreases. Since ATP, which is not metabolized, is not deposited in the cell, but is simply destroyed, this reaction is an important regulator of glycolysis.
Then sequentially: phosphoglycerol mutase forms 2-phospho- glycerate (8 ):
Enolase forms phosphoenolpyruvate (9 ):
And finally, the second reaction of substrate phosphorylation of ADP occurs with the formation of the enol form of pyruvate and ATP ( 10 ):
The reaction proceeds under the action of pyruvate kinase. This is the last key reaction of glycolysis. Isomerization of the enol form of pyruvate to pyruvate occurs non-enzymatically.
Since its inception F-1,6-bF only reactions proceed with the release of energy 7 And 10 , in which substrate phosphorylation of ADP occurs.
Regulation glycolysis
Distinguish between local and general regulation.
Local regulation is carried out by changing the activity of enzymes under the influence of various metabolites inside the cell.
The regulation of glycolysis as a whole, immediately for the whole organism, occurs under the action of hormones, which, influencing through molecules of secondary messengers, change intracellular metabolism.
Insulin plays an important role in stimulating glycolysis. Glucagon and adrenaline are the most significant hormonal inhibitors of glycolysis.
Insulin stimulates glycolysis through:
activation of the hexokinase reaction;
stimulation of phosphofructokinase;
stimulation of pyruvate kinase.
Other hormones also influence glycolysis. For example, somatotropin inhibits glycolysis enzymes, and thyroid hormones are stimulants.
Glycolysis is regulated through several key steps. Reactions catalyzed by hexokinase ( 1 ), phosphofructokinase ( 3 ) and pyruvate kinase ( 10 ) are characterized by a significant decrease in free energy and are practically irreversible, which allows them to be effective points for the regulation of glycolysis.
Glycolysis is a catabolic pathway of exceptional importance. It provides energy for cellular reactions, including protein synthesis. Intermediate products of glycolysis are used in the synthesis of fats. Pyruvate can also be used to synthesize alanine, aspartate, and other compounds. Thanks to glycolysis, mitochondrial performance and oxygen availability do not limit muscle power during short-term extreme loads.
2.1.2 Oxidative decarboxylation - the oxidation of pyruvate to acetyl-CoA occurs with the participation of a number of enzymes and coenzymes, structurally united in a multi-enzyme system, called the "pyruvate dehydrogenase complex".
At stage I of this process, pyruvate loses its carboxyl group as a result of interaction with thiamine pyrophosphate (TPP) as part of the active center of the pyruvate dehydrogenase enzyme (E 1). At stage II, the hydroxyethyl group of the E 1 -TPF-CHOH-CH 3 complex is oxidized to form an acetyl group, which is simultaneously transferred to the lipoic acid amide (coenzyme) associated with the enzyme dihydrolipoylacetyltransferase (E 2). This enzyme catalyzes stage III - the transfer of the acetyl group to the coenzyme CoA (HS-KoA) with the formation of the final product acetyl-CoA, which is a high-energy (macroergic) compound.
At stage IV, the oxidized form of lipoamide is regenerated from the reduced dihydrolipoamide-E 2 complex. With the participation of the enzyme dihydrolipoyl dehydrogenase (E 3), hydrogen atoms are transferred from the reduced sulfhydryl groups of dihydrolipoamide to FAD, which acts as a prosthetic group of this enzyme and is strongly associated with it. At stage V, the reduced FADH 2 dihydro-lipoyl dehydrogenase transfers hydrogen to the coenzyme NAD with the formation of NADH + H + .
The process of oxidative decarboxylation of pyruvate occurs in the mitochondrial matrix. It involves (as part of a complex multienzyme complex) 3 enzymes (pyruvate dehydrogenase, dihydrolipoylacetyltransferase, dihydrolipoyl dehydrogenase) and 5 coenzymes (TPF, lipoic acid amide, coenzyme A, FAD and NAD), of which three are relatively strongly associated with enzymes (TPF-E 1 , lipoamide-E 2 and FAD-E 3), and two are easily dissociated (HS-KoA and NAD).
Rice. 1 The mechanism of action of the pyruvate dehydrogenase complex
E 1 - pyruvate dehydrogenase; E 2 - di-hydrolipoylacetyltransfsraz; E 3 - dihydrolipoyl dehydrogenase; the numbers in the circles indicate the stages of the process.
All these enzymes, which have a subunit structure, and coenzymes are organized into a single complex. Therefore, intermediate products are able to quickly interact with each other. It has been shown that the polypeptide chains of dihydrolipoyl acetyltransferase subunits that make up the complex form, as it were, the core of the complex, around which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase are located. It is generally accepted that the native enzyme complex is formed by self-assembly.
The overall reaction catalyzed by the pyruvate dehydrogenase complex can be represented as follows:
Pyruvate + NAD + + HS-KoA -\u003e Acetyl-CoA + NADH + H + + CO 2.
The reaction is accompanied by a significant decrease in the standard free energy and is practically irreversible.
The acetyl-CoA formed in the process of oxidative decarboxylation undergoes further oxidation with the formation of CO 2 and H 2 O. Complete oxidation of acetyl-CoA occurs in the tricarboxylic acid cycle (Krebs cycle). This process, like the oxidative decarboxylation of pyruvate, occurs in the mitochondria of cells.
2 .1.3 CycletricarbonsourT (cycle Crebsa, zithertny cycle) is the central part of the general path of catabolism, a cyclic biochemical aerobic process, during which the transformation of two- and three-carbon compounds, which are formed as intermediate products in living organisms during the breakdown of carbohydrates, fats and proteins, to CO 2 takes place. In this case, the released hydrogen is sent to the tissue respiration chain, where it is further oxidized to water, taking a direct part in the synthesis of the universal energy source - ATP.
The Krebs cycle is a key step in the respiration of all cells that use oxygen, the crossroads of many metabolic pathways in the body. In addition to a significant energy role, the cycle is also assigned a significant plastic function, that is, it is an important source of precursor molecules, from which, in the course of other biochemical transformations, such important compounds for cell life as amino acids, carbohydrates, fatty acids, etc. are synthesized.
The cycle of transformation lemonacids in living cells was discovered and studied by the German biochemist Sir Hans Krebs, for this work he (together with F. Lipman) was awarded the Nobel Prize (1953).
In eukaryotes, all reactions of the Krebs cycle occur inside mitochondria, and the enzymes that catalyze them, except for one, are in a free state in the mitochondrial matrix, with the exception of succinate dehydrogenase, which is localized on the inner mitochondrial membrane, integrating into the lipid bilayer. In prokaryotes, the reactions of the cycle take place in the cytoplasm.
The general equation for one revolution of the Krebs cycle is:
Acetyl-CoA > 2CO 2 + CoA + 8e?
Regulation cycleA:
The Krebs cycle is regulated "according to the negative feedback mechanism", in the presence of a large number of substrates (acetyl-CoA, oxaloacetate), the cycle actively works, and with an excess of reaction products (NAD, ATP) it is inhibited. Regulation is also carried out with the help of hormones, the main source of acetyl-CoA is glucose, therefore hormones that promote the aerobic breakdown of glucose contribute to the Krebs cycle. These hormones are:
Insulin
adrenaline.
Glucagon stimulates glucose synthesis and inhibits the reactions of the Krebs cycle.
As a rule, the work of the Krebs cycle is not interrupted due to anaplerotic reactions that replenish the cycle with substrates:
Pyruvate + CO 2 + ATP = Oxaloacetate (substrate of the Krebs Cycle) + ADP + Fn.
Job ATP synthase
The process of oxidative phosphorylation is carried out by the fifth complex of the mitochondrial respiratory chain - Proton ATP synthase, consisting of 9 subunits of 5 types:
3 subunits (d,e,f) contribute to the integrity of ATP synthase
· The subunit is the basic functional unit. It has 3 conformations:
L-conformation - attaches ADP and Phosphate (they enter the mitochondria from the cytoplasm using special carriers)
T-conformation - phosphate is attached to ADP and ATP is formed
O-conformation - ATP splits off from the b-subunit and passes to the b-subunit.
In order for a subunit to change conformation, a hydrogen proton is needed, since the conformation changes 3 times, 3 hydrogen protons are needed. Protons are pumped from the intermembrane space of the mitochondria under the action of an electrochemical potential.
· b-subunit transports ATP to the membrane carrier, which "throws out" ATP into the cytoplasm. In return, the same carrier transports ADP from the cytoplasm. On the inner membrane of mitochondria there is also a Phosphate carrier from the cytoplasm to the mitochondrion, but its operation requires a hydrogen proton. Such carriers are called translocases.
Total exit
For the synthesis of 1 ATP molecule, 3 protons are needed.
Inhibitors oxidative phosphorylation
Inhibitors block the V complex:
Oligomycin - block the proton channels of ATP synthase.
Atractyloside, cyclophyllin - block translocases.
Uncouplers oxidative phosphorylation
Uncouplers- lipophilic substances that are able to accept protons and transport them through the inner membrane of mitochondria, bypassing the V complex (its proton channel). Disconnectors:
· Natural- products of lipid peroxidation, long chain fatty acids; large doses of thyroid hormones.
· artificial- dinitrophenol, ether, vitamin K derivatives, anesthetics.
2.2 Substrate phosphorylation
Substr A otherphosphoryl And ing ( biochemical), the synthesis of energy-rich phosphorus compounds due to the energy of redox reactions of glycolysis (catalyzed by phosphoglyceraldehyde dehydrogenase and enolase) and during the oxidation of a-ketoglutaric acid in the tricarboxylic acid cycle (under the action of a-ketoglutarate dehydrogenase and succinatethiokinase). For bacteria cases of S. are described f. during the oxidation of pyruvic acid.S. f., in contrast to phosphorylation in the electron transport chain, is not inhibited by "uncoupling" poisons (for example, dinitrophenol) and is not associated with the fixation of enzymes in mitochondrial membranes. The contribution of S. f. to the cellular pool of ATP under aerobic conditions is much less than the contribution of phosphorylation to the electron transport chain.
Chapter 3
3.1 Role in the cage
The main role of ATP in the body is associated with providing energy for numerous biochemical reactions. Being the carrier of two high-energy bonds, ATP serves as a direct source of energy for many energy-consuming biochemical and physiological processes. All these are reactions of the synthesis of complex substances in the body: the implementation of the active transfer of molecules through biological membranes, including for the creation of a transmembrane electrical potential; implementation of muscle contraction.
As you know, in the bioenergetics of living organisms, two main points are important:
a) chemical energy is stored through the formation of ATP, coupled with exergonic catabolic reactions of oxidation of organic substrates;
b) chemical energy is utilized by splitting ATP, associated with endergonic reactions of anabolism and other processes that require energy expenditure.
The question arises why the ATP molecule corresponds to its central role in bioenergetics. To resolve it, consider the structure of ATP Structure ATP - (at pH 7,0 tetracharge anion) .
ATP is a thermodynamically unstable compound. The instability of ATP is determined, firstly, by electrostatic repulsion in the region of a cluster of negative charges of the same name, which leads to a voltage of the entire molecule, but the strongest bond is P - O - P, and secondly, by a specific resonance. In accordance with the latter factor, there is competition between phosphorus atoms for the lone mobile electrons of the oxygen atom located between them, since each phosphorus atom has a partial positive charge due to the significant electron acceptor effect of the P=O and P - O- groups. Thus, the possibility of the existence of ATP is determined by the presence of a sufficient amount of chemical energy in the molecule, which makes it possible to compensate for these physicochemical stresses. The ATP molecule has two phosphoanhydride (pyrophosphate) bonds, the hydrolysis of which is accompanied by a significant decrease in free energy (at pH 7.0 and 37 o C).
ATP + H 2 O \u003d ADP + H 3 RO 4 G0I \u003d - 31.0 kJ / mol.
ADP + H 2 O \u003d AMP + H 3 RO 4 G0I \u003d - 31.9 kJ / mol.
One of the central problems of bioenergetics is the biosynthesis of ATP, which in wildlife occurs by ADP phosphorylation.
Phosphorylation of ADP is an endergonic process and requires an energy source. As noted earlier, two such sources of energy predominate in nature - solar energy and the chemical energy of reduced organic compounds. Green plants and some microorganisms are able to transform the energy of absorbed light quanta into chemical energy, which is spent on ADP phosphorylation in the light stage of photosynthesis. This process of ATP regeneration is called photosynthetic phosphorylation. The transformation of the energy of oxidation of organic compounds into macroenergetic bonds of ATP under aerobic conditions occurs mainly through oxidative phosphorylation. The free energy required for the formation of ATP is generated in the respiratory oxidative chain of mitochodria.
Another type of ATP synthesis is known, called substrate phosphorylation. In contrast to oxidative phosphorylation associated with electron transfer, the donor of the activated phosphoryl group (-PO3 H2), necessary for ATP regeneration, are the intermediates of the processes of glycolysis and the tricarboxylic acid cycle. In all these cases, oxidative processes lead to the formation of high-energy compounds: 1,3 - diphosphoglycerate (glycolysis), succinyl - CoA (tricarboxylic acid cycle), which, with the participation of appropriate enzymes, are able to folirate ADP and form ATP. Energy transformation at the substrate level is the only way for ATP synthesis in anaerobic organisms. This process of ATP synthesis allows you to maintain intensive work of skeletal muscles during periods of oxygen starvation. It should be remembered that it is the only way of ATP synthesis in mature erythrocytes without mitochondria.
Adenyl nucleotide plays a particularly important role in cell bioenergetics, to which two phosphoric acid residues are attached. This substance is called adenosine triphosphate (ATP). In the chemical bonds between the residues of phosphoric acid of the ATP molecule, energy is stored, which is released when the organic phosphorite is split off:
ATP \u003d ADP + P + E,
where F is an enzyme, E is a liberating energy. In this reaction, adenosine phosphoric acid (ADP) is formed - the remainder of the ATP molecule and organic phosphate. All cells use the energy of ATP for the processes of biosynthesis, movement, production of heat, nerve impulses, luminescence (for example, luminescent bacteria), that is, for all life processes.
ATP is a universal biological energy accumulator. The light energy contained in the food consumed is stored in ATP molecules.
The supply of ATP in the cell is small. So, in a muscle, the ATP reserve is enough for 20-30 contractions. With increased, but short-term work, the muscles work solely due to the splitting of the ATP contained in them. After finishing work, a person breathes heavily - during this period, the breakdown of carbohydrates and other substances occurs (energy is accumulated) and the supply of ATP in the cells is restored.
Also known is the role of ATP as a neurotransmitter in synapses.
3.2 Role in the work of enzymes
A living cell is a chemical system far from equilibrium: after all, the approach of a living system to equilibrium means its decay and death. The product of each enzyme is usually used up quickly as it is used as a substrate by another enzyme in the metabolic pathway. More importantly, a large number of enzymatic reactions are associated with the breakdown of ATP into ADP and inorganic phosphate. For this to be possible, the pool of ATP, in turn, must be maintained at a level far from equilibrium, so that the ratio of the concentration of ATP to the concentration of its hydrolysis products is high. Thus, the ATP pool plays the role of a "accumulator" that maintains a constant transfer of energy and atoms in the cell along the metabolic pathways determined by the presence of enzymes.
So, let's consider the process of ATP hydrolysis and its effect on the work of enzymes. Imagine a typical biosynthetic process, in which two monomers - A and B - must combine with each other in a dehydration reaction (it is also called condensation), accompanied by the release of water:
A - H + B - OH - AB + H2O
The reverse reaction, which is called hydrolysis, in which a water molecule breaks down a covalently bonded A-B compound, will almost always be energetically favorable. This occurs, for example, during the hydrolytic cleavage of proteins, nucleic acids and polysaccharides into subunits.
The general strategy by which the cell A-B is formed with A-N and B-OH includes a multi-stage sequence of reactions, as a result of which there is an energetically unfavorable synthesis of the desired compounds with a balanced favorable reaction.
Does ATP hydrolysis correspond to a large negative value? G, therefore, ATP hydrolysis often plays the role of an energetically favorable reaction, due to which intracellular biosynthesis reactions are carried out.
On the way from A - H and B - OH-A - B associated with ATP hydrolysis, the energy of hydrolysis first converts B - OH into a high-energy intermediate, which then directly reacts with A - H, forming A - B. a simple mechanism for this process includes the transfer of phosphate from ATP to B - OH with the formation of B - ORO 3, or B - O - R, and in this case the total reaction occurs in only two stages:
1) B - OH + ATP - B - C - R + ADP
2) A - N + B - O - R - A - B + R
Since the intermediate compound B - O - P, formed during the reaction, is destroyed again, the overall reactions can be described using the following equations:
3) A-N + B - OH - A - B and ATP - ADP + P
The first, energetically unfavorable reaction, is possible because it is associated with the second, energetically favorable reaction (ATP hydrolysis). An example of related biosynthetic reactions of this type can be the synthesis of the amino acid glutamine.
The G value of ATP hydrolysis to ADP and inorganic phosphate depends on the concentration of all reactants and usually for cell conditions lies in the range from - 11 to - 13 kcal / mol. The ATP hydrolysis reaction can finally be used to carry out a thermodynamically unfavorable reaction with a G value of approximately +10 kcal/mol, of course in the presence of an appropriate reaction sequence. However, for many biosynthetic reactions, even ? G = - 13 kcal/mol. In these and other cases, the path of ATP hydrolysis changes in such a way that AMP and PP (pyrophosphate) are first formed. In the next step, the pyrophosphate also undergoes hydrolysis; the total free energy change of the entire process is approximately - 26 kcal/mol.
How is the energy of pyrophosphate hydrolysis used in biosynthetic reactions? One of the ways can be demonstrated by the example of the above synthesis of compounds A - B with A - H and B - OH. With the help of the appropriate enzyme, B - OH can react with ATP and turn into a high-energy compound B - O - R - R. Now the reaction consists of three stages:
1) B - OH + ATP - B - C - R - R + AMP
2) A - N + B - O - R - R - A - B + PP
3) PP + H2O - 2P
The overall reaction can be represented as follows:
A - H + B - OH - A - B and ATP + H2O - AMP + 2P
Since the enzyme always accelerates the reaction catalyzed by it both in the forward and in the reverse direction, the compound A - B can decompose by reacting with pyrophosphate (reverse reaction of stage 2). However, the energetically favorable pyrophosphate hydrolysis reaction (step 3) contributes to maintaining the stability of compound A-B by keeping the pyrophosphate concentration very low (this prevents the reverse reaction to step 2). Thus, the energy of pyrophosphate hydrolysis ensures that the reaction proceeds in the forward direction. An example of an important biosynthetic reaction of this type is the synthesis of polynucleotides.
3.3 Role in the synthesis of DNA and RNA and proteins
In all known organisms, the deoxyribonucleotides that make up DNA are synthesized by the action of ribonucleotide reductase (RNR) enzymes on the corresponding ribonucleotides. These enzymes reduce the sugar residue from ribose to deoxyribose by removing oxygen from the 2" hydroxyl groups, substrates of ribonucleoside diphosphates, and products of deoxyribonucleoside diphosphates. All reductase enzymes use a common sulfhydryl radical mechanism dependent on reactive cysteine residues, which are oxidized to form disulfide bonds during the course of the reaction. The PHP enzyme is processed by reaction with thioredoxin or glutaredoxin.
Regulation of PHP and related enzymes maintains a balance in relation to each other. A very low concentration inhibits DNA synthesis and DNA repair and is lethal to the cell, while an abnormal ratio is mutagenic due to an increase in the likelihood of DNA polymerase incorporation during DNA synthesis.
In the synthesis of RNA nucleic acids, adenosine derived from ATP is one of four nucleotides incorporated directly into RNA molecules by RNA polymerase. Energy, this polymerization occurs with the elimination of pyrophosphate (two phosphate groups). This process is similar in DNA biosynthesis, except that ATP is reduced to the deoxyribonucleotide dATP before being incorporated into DNA.
IN synthesis squirrel. Aminoacyl-tRNA synthetases use ATP enzymes as a source of energy to attach a tRNA molecule to its specific amino acid, forming an aminoacyl-tRNA ready for translation into ribosomes. Energy becomes available as a result of ATP hydrolysis of adenosine monophosphate (AMP) to remove two phosphate groups.
ATP is used for many cellular functions, including the transport job of moving substances across cell membranes. It is also used for mechanical work, supplying the energy needed for muscle contraction. It supplies energy not only to the heart muscle (for blood circulation) and skeletal muscles (for example, for the gross movement of the body), but also to the chromosomes and flagella so that they can perform their many functions. The great role of ATP is in chemical work, providing the necessary energy for the synthesis of the several thousand types of macromolecules that a cell needs to exist.
ATP is also used as an on-off switch both to control chemical reactions and to send information. The shape of the protein chains that produce the building blocks and other structures used in life is determined mainly by weak chemical bonds that easily break down and restructure. These circuits can shorten, lengthen, and change shape in response to energy input or output. Changes in the chains change the shape of the protein and may also change its function or cause it to become active or inactive.
ATP molecules can bind to one part of a protein molecule, causing another part of the same molecule to slide or move slightly which causes it to change its conformation, inactivating the molecules. Once the ATP is removed it causes the protein to return to its original form and thus it is functional again.
The cycle can be repeated as long as the molecule returns, effectively acting as both switch and switch. Both the addition of phosphorus (phosphorylation) and the removal of phosphorus from a protein (dephosphorylation) can serve as either an on or off switch.
3.4 Other functions of ATP
Role V metabolism, synthesis And active transport
Thus, ATP transfers energy between spatially separated metabolic reactions. ATP is the main source of energy for most cellular functions. This includes the synthesis of macromolecules, including DNA and RNA, and proteins. ATP also plays an important role in the transport of macromolecules across cell membranes, such as exocytosis and endocytosis.
Role V structure cells And movement
ATP is involved in maintaining the cellular structure by facilitating the assembly and disassembly of cytoskeletal elements. Due to this process, ATP is required for the contraction of actin filaments and myosin is required for muscle contraction. This last process is one of the basic energy requirements of animals and is essential for movement and respiration.
Role V signal systems
Inextracellularsignalsystems
ATP is also a signaling molecule. ATP, ADP, or adenosine are recognized as purinergic receptors. Purinoreceptors may be the most abundant receptors in mammalian tissues.
In humans this signaling role is important in both the central and peripheral nervous systems. Activity depends on the release of ATP from synapses, axons and glia purinergic activates membrane receptors
Inintracellularsignalsystems
ATP is critical in signal transduction processes. It is used by kinases as a source of phosphate groups in their phosphate transfer reactions. Kinases on substrates such as proteins or membrane lipids are a common signal shape. Phosphorylation of a protein by a kinase can activate this cascade, such as the mitogen-activated protein kinase cascade.
ATP is also used by adenylate cyclase and is converted into a second messenger molecule AMP, which is involved in triggering calcium signals to release calcium from intracellular depots. [38] This waveform is particularly important in brain function, although it is involved in the regulation of numerous other cellular processes.
Conclusion
1. Adenosine triphosphate - a nucleotide that plays an extremely important role in the metabolism of energy and substances in organisms; First of all, the compound is known as a universal source of energy for all biochemical processes occurring in living systems. Chemically, ATP is the triphosphate ester of adenosine, which is a derivative of adenine and ribose. In terms of structure, ATP is similar to the adenine nucleotide that is part of RNA, only instead of one phosphoric acid, ATP contains three phosphoric acid residues. Cells are not able to contain acids in noticeable quantities, but only their salts. Therefore, phosphoric acid enters ATP as a residue (instead of the OH group of the acid, there is a negatively charged oxygen atom).
2. In the body, ATP is synthesized by ADP phosphorylation:
ADP + H 3 PO 4 + energy> ATP + H 2 O.
Phosphorylation of ADP is possible in two ways: substrate phosphorylation and oxidative phosphorylation (using the energy of oxidizing substances).
Oxidative phosphorylation - one of the most important components of cellular respiration, leading to the production of energy in the form of ATP. The substrates of oxidative phosphorylation are the breakdown products of organic compounds - proteins, fats and carbohydrates. The process of oxidative phosphorylation takes place on the cristae of mitochondria.
Substr A otherphosphoryl And ing ( biochemical), the synthesis of energy-rich phosphorus compounds due to the energy of redox reactions of glycolysis and during the oxidation of a-ketoglutaric acid in the tricarboxylic acid cycle.
3. The main role of ATP in the body is associated with providing energy for numerous biochemical reactions. Being the carrier of two high-energy bonds, ATP serves as a direct source of energy for many energy-consuming biochemical and physiological processes. In the bioenergetics of living organisms, the following are important: chemical energy is stored through the formation of ATP, coupled with exergonic catabolic reactions of oxidation of organic substrates; chemical energy is utilized by splitting ATP, associated with endergonic reactions of anabolism and other processes that require energy expenditure.
4. With an increased load (for example, in sprinting), the muscles work solely due to the supply of ATP. In muscle cells, this reserve is enough for several dozen contractions, and then the amount of ATP must be replenished. The synthesis of ATP from ADP and AMP occurs due to the energy released during the breakdown of carbohydrates, lipids and other substances. A large amount of ATP is also spent on the performance of mental work. For this reason, mental workers require an increased amount of glucose, the breakdown of which ensures the synthesis of ATP.
In addition to energy ATP, it performs a number of other equally important functions in the body:
· Together with other nucleoside triphosphates, ATP is the starting product in the synthesis of nucleic acids.
In addition, ATP plays an important role in the regulation of many biochemical processes. Being an allosteric effector of a number of enzymes, ATP, by joining their regulatory centers, enhances or suppresses their activity.
· ATP is also a direct precursor to the synthesis of cyclic adenosine monophosphate, a secondary messenger for the transmission of a hormonal signal into the cell.
The role of ATP as a mediator in synapses is also known.
Bibliographic list
1. Lemeza, N.A. Biology manual for applicants to universities / L.V. Kamlyuk N.D. Lisov. - Minsk: Unipress, 2011 - 624 p.
2. Lodish, H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J. Molecular Cell Biology, 5th ed. - New York: W.H. Freeman, 2004.
3. Romanovsky, Yu.M. Molecular energy converters of a living cell. Proton ATP synthase - a rotating molecular motor / Yu.M. Romanovsky A.N. Tikhonov // UFN. - 2010. - T.180. - S.931 - 956.
4 Voet D, Voet JG. Biochemistry Vol 1 3rd ed. Wiley: Hoboken, NJ. - N-Y: W. H. Freeman and Company, 2002. - 487 rubles.
5. General chemistry. Biophysical chemistry. Chemistry of biogenic elements. M.: Higher school, 1993
6. Vershubsky, A.V. Biophysics. / A.V. Vershubsky, V.I. Priklonsky, A.N. Tikhonov. - M: 471-481.
7. Alberts B. Molecular biology of the cell in 3 volumes. / Alberts B., Bray D., Lewis J. et al. M.: Mir, 1994.1558 p.
8. Nikolaev A.Ya. Biological chemistry - M .: LLC "Medical Information Agency", 1998.
9. Berg, J. M. Biochemistry, international edition. / Berg, J. M, Tymoczko, J. L, Stryer, L. - New York: W.H. Freeman, 2011; p 287.
10. Knorre D.G. Biological chemistry: Proc. for chemical, biol. And honey. specialist. universities. - 3rd ed., Rev. / Knorre D.G., Mysina S.D. - M.: Higher. school, 2000. - 479 p.: ill.
11. Eliot, V. Biochemistry and molecular biology / V. Eliot, D. Eliot. - M.: Publishing House of the Research Institute of Biomedical Chemistry of the Russian Academy of Medical Sciences, OOO "Materik-alpha", 1999, - 372 p.
12. Shina CL, K., 7 Areieh, W. On the Energetics of ATP Hydrolysis in Solution. Journal of Physical Chemistry B,113 (47), (2009).
13. Berg, J. M. Biochemistry / J. M. Berg: J. L. Tymoczko, L. Stryer. - N-Y: W. H. Freeman and Company, 2002. - 1514 p.
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There are about 70 trillion cells in the human body. For healthy growth, each of them needs helpers - vitamins. Vitamin molecules are small, but their deficiency is always noticeable. If it is difficult to adapt to the dark, you need vitamins A and B2, dandruff has appeared - there is not enough B12, B6, P, bruises do not heal for a long time - vitamin C deficiency. In this lesson, you will learn how and where the strategic a supply of vitamins, how vitamins activate the body, and you will also learn about ATP - the main source of energy in the cell.
Topic: Fundamentals of Cytology
Lesson: The structure and functions of ATP
As you remember, nucleic acidsmade up of nucleotides. It turned out that nucleotides in a cell can be in a bound state or in a free state. In the free state, they perform a number of important functions for the life of the body.
To such free nucleotides applies ATP molecule or adenosine triphosphoric acid(adenosine triphosphate). Like all nucleotides, ATP is made up of a five-carbon sugar. ribose, nitrogenous base - adenine, and, unlike DNA and RNA nucleotides, three residues of phosphoric acid(Fig. 1).
Rice. 1. Three schematic representations of ATP
The most important ATP function is that it is a universal custodian and carrier energy in a cage.
All biochemical reactions in the cell that require energy expenditure use ATP as its source.
When separating one residue of phosphoric acid, ATP goes into ADP (adenosine diphosphate). If another phosphoric acid residue separates (which happens in special cases), ADP goes into AMF(adenosine monophosphate) (Fig. 2).
Rice. 2. Hydrolysis of ATP and its transformation into ADP
When separating the second and third residues of phosphoric acid, a large amount of energy is released, up to 40 kJ. That is why the bond between these phosphoric acid residues is called macroergic and is denoted by the corresponding symbol.
During the hydrolysis of an ordinary bond, a small amount of energy is released (or absorbed), and during the hydrolysis of a macroergic bond, much more energy (40 kJ) is released. The bond between ribose and the first residue of phosphoric acid is not macroergic; its hydrolysis releases only 14 kJ of energy.
Macroergic compounds can also be formed on the basis of other nucleotides, for example GTP(guanosine triphosphate) is used as an energy source in protein biosynthesis, takes part in signal transduction reactions, is a substrate for RNA synthesis during transcription, but it is ATP that is the most common and universal source of energy in the cell.
ATP contained as in the cytoplasm, and in the nucleus, mitochondria and chloroplasts.
Thus, we remembered what ATP is, what its functions are, and what a macroergic bond is.
Vitamins are biologically active organic compounds that are necessary in small quantities to maintain vital processes in the cell.
They are not structural components of living matter and are not used as an energy source.
Most vitamins are not synthesized in the human and animal body, but enter it with food, some are synthesized in small amounts by the intestinal microflora and tissues (vitamin D is synthesized by the skin).
The need for vitamins in humans and animals is not the same and depends on factors such as gender, age, physiological state and environmental conditions. Some vitamins are not needed by all animals.
For example, ascorbic acid, or vitamin C, is essential for humans and other primates. At the same time, it is synthesized in the body of reptiles (sailors took turtles on voyages to combat scurvy - vitamin C deficiency).
Vitamins were discovered at the end of the 19th century thanks to the work of Russian scientists N. I. Lunina And V. Pashutina, which showed that for good nutrition, it is necessary not only to have proteins, fats and carbohydrates, but also some other, at that time unknown, substances.
In 1912, a Polish scientist K. Funk(Fig. 3), studying the components of rice husk, which protects against Beri-Beri disease (avitaminosis of vitamin B), suggested that these substances must necessarily include amine groups. It was he who proposed to call these substances vitamins, that is, the amines of life.
Later it was found that many of these substances do not contain amino groups, but the term vitamins has taken root well in the language of science and practice.
As individual vitamins were discovered, they were designated in Latin letters and named depending on their functions. For example, vitamin E was called tocopherol (from ancient Greek τόκος - "childbirth", and φέρειν - "bring").
Today, vitamins are divided according to their ability to dissolve in water or in fats.
For water soluble vitamins include vitamins H, C, P, IN.
to fat-soluble vitamins refer A, D, E, K(can be remembered as a word: keda) .
As already noted, the need for vitamins depends on age, gender, physiological state of the organism and habitat. At a young age, there is a clear need for vitamins. A weakened body also requires large doses of these substances. With age, the ability to absorb vitamins decreases.
The need for vitamins is also determined by the body's ability to utilize them.
In 1912, a Polish scientist Casimir Funk received partially purified vitamin B1 - thiamine from rice husks. It took another 15 years to obtain this substance in a crystalline state.
Crystalline vitamin B1 is colorless, has a bitter taste and is readily soluble in water. Thiamine is found in both plant and microbial cells. Especially a lot of it in grain crops and yeast (Fig. 4).
Rice. 4. Thiamine Tablets and Foods
Heat treatment of foods and various additives destroy thiamine. With beriberi, pathologies of the nervous, cardiovascular and digestive systems are observed. Avitaminosis leads to disruption of water metabolism and hematopoiesis function. One of the clearest examples of thiamine deficiency is the development of Beri-Beri disease (Fig. 5).
Rice. 5. A person suffering from thiamine deficiency - beriberi disease
Vitamin B1 is widely used in medical practice for the treatment of various nervous diseases, cardiovascular disorders.
In baking, thiamine, along with other vitamins - riboflavin and nicotinic acid, is used to fortify bakery products.
In 1922 G. Evans And A. Bisho discovered a fat-soluble vitamin, which they called tocopherol or vitamin E (literally: “promoting childbirth”).
Vitamin E in its purest form is an oily liquid. It is widely distributed in cereals, such as wheat. It is abundant in vegetable and animal fats (Fig. 6).
Rice. 6. Tocopherol and products that contain it
A lot of vitamin E in carrots, eggs and milk. Vitamin E is antioxidant, that is, it protects cells from pathological oxidation, which leads them to aging and death. It is the "vitamin of youth". The importance of the vitamin for the reproductive system is enormous, so it is often called the reproduction vitamin.
As a result, vitamin E deficiency, first of all, leads to disruption of embryogenesis and reproductive organs.
The production of vitamin E is based on its isolation from wheat germ - by the method of alcohol extraction and distillation of solvents at low temperatures.
In medical practice, both natural and synthetic preparations are used - tocopherol acetate in vegetable oil, enclosed in a capsule (the famous "fish oil").
Vitamin E preparations are used as antioxidants for irradiation and other pathological conditions associated with an increased content of ionized particles and reactive oxygen species in the body.
In addition, vitamin E is prescribed for pregnant women, and is also used in complex therapy for the treatment of infertility, with muscular dystrophy and some liver diseases.
Vitamin A (Fig. 7) was discovered N. Drummond in 1916.
This discovery was preceded by observations of the presence of a fat-soluble factor in food, which is necessary for the full development of farm animals.
Vitamin A is right at the top of the vitamin alphabet. It is involved in almost all life processes. This vitamin is essential for restoring and maintaining good vision.
It also helps develop immunity to many diseases, including colds.
Without vitamin A, a healthy state of the skin epithelium is impossible. If you have goosebumps, which most often appears on the elbows, thighs, knees, shins, if dry skin on the hands appears, or other similar phenomena occur, this means that you are deficient in vitamin A.
Vitamin A, like vitamin E, is necessary for the normal functioning of the sex glands (gonads). With hypovitaminosis of vitamin A, damage to the reproductive system and respiratory organs was noted.
One of the specific consequences of a lack of vitamin A is a violation of the process of vision, in particular, a decrease in the ability of the eyes to dark adaptation - night blindness. Avitaminosis leads to the occurrence of xerophthalmia and the destruction of the cornea. The latter process is irreversible, and is characterized by complete loss of vision. Hypervitaminosis leads to eye inflammation and hair loss, loss of appetite and complete exhaustion of the body.
Rice. 7. Vitamin A and foods that contain it
Group A vitamins are primarily found in animal products: in the liver, in fish oil, in oil, in eggs (Fig. 8).
Rice. 8. The content of vitamin A in products of plant and animal origin
Vegetable products contain carotenoids, which in the human body are converted into vitamin A by the action of the enzyme carotenoses.
Thus, today you got acquainted with the structure and functions of ATP, and also remembered the importance of vitamins and found out how some of them are involved in life processes.
With insufficient intake of vitamins in the body, primary vitamin deficiency develops. Different foods contain different amounts of vitamins.
For example, carrots contain a lot of provitamin A (carotene), cabbage contains vitamin C, etc. Hence the need for a balanced diet that includes a variety of plant and animal products.
Avitaminosis under normal nutritional conditions is very rare, much more common hypovitaminosis, which are associated with inadequate intake of vitamins with food.
Hypovitaminosis can occur not only as a result of an unbalanced diet, but also as a result of various pathologies of the gastrointestinal tract or liver, or as a result of various endocrine or infectious diseases that lead to malabsorption of vitamins in the body.
Some vitamins are produced by the intestinal microflora (gut microbiota). Suppression of biosynthetic processes as a result of action antibiotics may also lead to the development hypovitaminosis, as a consequence dysbacteriosis.
Excessive consumption of food vitamin supplements, as well as medicines containing vitamins, leads to the occurrence of a pathological condition - hypervitaminosis. This is especially true for fat-soluble vitamins, such as A, D, E, K.
Homework
1. What substances are called biologically active?
2. What is ATP? What is the structure of the ATP molecule? What types of chemical bonds exist in this complex molecule?
3. What are the functions of ATP in the cells of living organisms?
4. Where does ATP synthesis take place? Where does ATP hydrolysis take place?
5. What are vitamins? What are their functions in the body?
6. How are vitamins different from hormones?
7. What classifications of vitamins do you know?
8. What is avitaminosis, hypovitaminosis and hypervitaminosis? Give examples of these phenomena.
9. What diseases can be the result of insufficient or excessive intake of vitamins in the body?
10. Discuss your menu with friends and relatives, calculate, using additional information about the content of vitamins in different foods, whether you are getting enough vitamins.
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Bibliography
1. Kamensky A. A., Kriksunov E. A., Pasechnik V. V. General biology 10-11 class Bustard, 2005.
2. Belyaev D.K. Biology grade 10-11. General biology. A basic level of. - 11th ed., stereotype. - M.: Education, 2012. - 304 p.
3. Agafonova I. B., Zakharova E. T., Sivoglazov V. I. Biology 10-11 class. General biology. A basic level of. - 6th ed., add. - Bustard, 2010. - 384 p.
