Adenosine triphosphoric acid-ATP- an essential energy component of any living cell. ATP is also a nucleotide consisting of the nitrogenous base adenine, the sugar ribose and three phosphoric acid molecule residues. This is an unstable structure. In metabolic processes, phosphoric acid residues are sequentially split off from it by breaking the energy-rich but fragile bond between the second and third phosphoric acid residues. The detachment of one molecule of phosphoric acid is accompanied by the release of about 40 kJ of energy. In this case, ATP is converted into adenosine diphosphoric acid (ADP), and with further cleavage of the phosphoric acid residue from ADP, adenosine monophosphoric acid (AMP) is formed.
Scheme of the structure of ATP and its conversion to ADP ( T.A. Kozlova, V.S. Kuchmenko. Biology in tables. M., 2000 )
Consequently, ATP is a kind of energy accumulator in the cell, which is “discharged” when it is broken down. The breakdown of ATP occurs during the reactions of synthesis of proteins, fats, carbohydrates and any other vital functions of cells. These reactions occur with the absorption of energy, which is extracted during the breakdown of substances.
ATP is synthesized in mitochondria in several stages. The first one is preparatory - proceeds in stages, with the involvement of specific enzymes at each stage. In this case, complex organic compounds are broken down into monomers: proteins into amino acids, carbohydrates into glucose, nucleic acids into nucleotides, etc. The breaking of bonds in these substances is accompanied by the release of a small amount of energy. The resulting monomers, under the influence of other enzymes, can undergo further decomposition to form simpler substances, up to carbon dioxide and water.
Scheme ATP synthesis in cell mtochondria
EXPLANATIONS FOR THE DIAGRAM TRANSFORMATION OF SUBSTANCES AND ENERGY IN THE PROCESS OF DISSIMILIATION
Stage I - preparatory: complex organic substances, under the influence of digestive enzymes, break down into simple ones, and only thermal energy is released.
Proteins ->amino acids
Fats- >
glycerol and fatty acids
Starch ->glucose
Stage II - glycolysis (oxygen-free): carried out in the hyaloplasm, not associated with membranes; it involves enzymes; Glucose is broken down:
In yeast fungi, a glucose molecule without the participation of oxygen is converted into ethyl alcohol and carbon dioxide (alcoholic fermentation):
In other microorganisms, glycolysis can result in the formation of acetone, acetic acid, etc. In all cases, the breakdown of one glucose molecule is accompanied by the formation of two ATP molecules. During the oxygen-free breakdown of glucose in the form of a chemical bond in the ATP molecule, 40% of the anergy is retained, and the rest is dissipated as heat.
Stage III - hydrolysis (oxygen): carried out in mitochondria, associated with the mitochondrial matrix and the inner membrane, enzymes participate in it, lactic acid undergoes breakdown: C3H6O3 + 3H20 --> 3CO2+ 12H. CO2 (carbon dioxide) is released from mitochondria into the environment. The hydrogen atom is included in a chain of reactions, the final result of which is the synthesis of ATP. These reactions occur in the following sequence:
1. The hydrogen atom H, with the help of carrier enzymes, enters the inner membrane of mitochondria, forming cristae, where it is oxidized: H-e--> H+
2. Hydrogen proton H+(cation) is carried by carriers to the outer surface of the cristae membrane. This membrane is impermeable to protons, so they accumulate in the intermembrane space, forming a proton reservoir.
3. Hydrogen electrons e are transferred to the inner surface of the cristae membrane and immediately attach to oxygen using the enzyme oxidase, forming negatively charged active oxygen (anion): O2 + e--> O2-
4. Cations and anions on both sides of the membrane create an oppositely charged electric field, and when the potential difference reaches 200 mV, the proton channel begins to operate. It occurs in the molecules of ATP synthetase enzymes, which are embedded in the inner membrane that forms the cristae.
5. Hydrogen protons pass through the proton channel H+ rush inside the mitochondria, creating a high level of energy, most of which goes to the synthesis of ATP from ADP and P (ADP+P-->ATP), and protons H+ interact with active oxygen, forming water and molecular 02:
(4Н++202- -->2Н20+02)
Thus, O2, which enters the mitochondria during the body’s respiration process, is necessary for the addition of hydrogen protons H. In its absence, the entire process in the mitochondria stops, since the electron transport chain ceases to function. General reaction of stage III:
(2C3NbOz + 6Oz + 36ADP + 36F ---> 6C02 + 36ATP + +42H20)
As a result of the breakdown of one glucose molecule, 38 ATP molecules are formed: at stage II - 2 ATP and at stage III - 36 ATP. The resulting ATP molecules go beyond the mitochondria and participate in all cellular processes where energy is needed. When splitting, ATP releases energy (one phosphate bond contains 40 kJ) and returns to the mitochondria in the form of ADP and P (phosphate).
Judging by everything stated above, a colossal amount of ATP is required. In skeletal muscles, during their transition from a state of rest to contractile activity, the rate of ATP breakdown increases sharply by 20 times (or even several hundred times).
However, ATP reserves in muscles are relatively insignificant (about 0.75% of its mass) and can only be enough for 2-3 seconds of intensive work.
Fig. 15. Adenosine triphosphate (ATP, ATP). Molar mass 507.18 g/mol
This happens 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. The phosphate groups in the ATP molecule are connected to each other by high-energy (macroergic) bonds. It is estimated 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 maintain long-term contraction, ATP molecules must be generated by metabolism at the same rate as they are broken down during contraction. Therefore, ATP is one of the most frequently renewed substances; 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 cycles of resynthesis (the human body synthesizes about 40 kg of ATP per day, but contains approximately 250 g at any given moment), that is, practically no ATP reserve is created 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 necessary at the same rate at which it is consumed. This occurs during the process of rephosphorylation, when ADP and phosphates combine
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 during photosynthesis. This process is called phosphorylation. In this case, at least 40 kJ/mol of energy must be expended, which is accumulated in high-energy 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. Substrate phosphorylation of ATP does not require the participation of membrane enzymes; it occurs during glycolysis or by transfer of a phosphate group from other high-energy compounds..
The reactions of phosphorylation of ADP 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 that ATP is produced 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 ( CP) ATP resynthesis system in the body
To maintain muscle tissue activity at a certain level rapid resynthesis of ATP is required. This occurs during the process of rephosphorylation, when ADP and phosphates combine. The most accessible substance that is used for ATP resynthesis is primarily creatine phosphate ( Fig.16), easily transferring its phosphate group to ADP:
CrP + ADP → Creatine + ATP
KrF is a combination of the nitrogen-containing substance creatinine with phosphoric acid. Its concentration in muscles is approximately 2–3%, i.e. 3–4 times more than ATP. A moderate (20–40%) decrease in ATP content immediately leads to the use of CrF. However, during maximum work, creatine phosphate reserves are also quickly depleted. Due to phosphorylation of ADP creatine phosphate very rapid formation of ATP is ensured at the very beginning of contraction.
During the resting period, the concentration of creatine phosphate in the muscle fiber increases to a level approximately five times higher than the ATP content. At the beginning of contraction, when the concentration of ATP decreases and the concentration of ADP increases 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 speed that at the beginning of contraction, the concentration of ATP in the muscle fiber changes little, while the concentration of creatine phosphate drops quickly.
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 muscle contraction to last longer than a few seconds, the participation of the other two sources of ATP formation mentioned above is necessary. Once the contraction achieved by creatine phosphate begins, the slower, multi-enzyme pathways of oxidative phosphorylation and glycolysis are activated to increase the rate of ATP production to match the rate of ATP breakdown.
Which ATP synthesis system is the fastest?
The CP (creatine phosphate) system is the fastest ATP resynthesis system in the body because it involves only one enzymatic reaction. It transfers high-energy phosphate directly from CP to ADP to form ATP. However, the ability of this system to resynthesize ATP is limited, since the reserves of CP 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 CP is stored in the body?
The total reserves of CP 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 CP?
The CP/ATP system is used during short-term intense physical activity. It is located on the heads of myosin molecules, i.e. directly at the site of energy consumption. The CF/ATP system is used when a person makes rapid movements, such as quickly walking up a hill, performing high jumps, running a hundred meters, quickly getting out of bed, running away from a bee, or ducking out of the way of a truck while crossing the street.
Glycolysis
Phosphorylation of ADP in the cytoplasm
The breakdown of glycogen and glucose under anaerobic conditions produces lactic acid and ATP.
To restore ATP in order to continue intense muscle activity The process includes the following source of energy generation - 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 it possible to re-synthesize 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 under 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 glycogen consumption, since only part of the energy contained in it is used (lactic acid is not used during glycolysis, although contains significant energy reserves).
Of course, already at this stage, part of the lactic acid is oxidized by a certain amount of oxygen to carbon dioxide and water:
С3Н6О3 + 3О2 = 3СО2 + 3Н2О 41
The energy generated in this case is used for 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 reactions aimed at converting lactic acid and resynthesizing 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. During the process of glycolysis, carbohydrates are oxidized to pyruvate or lactate and 2 molecules of ATP are released (3 molecules if you start the calculation with glycogen). During glycolysis, ATP is synthesized quickly, but more slowly than in the CP 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 cycle and CPE. When mitochondria cannot adequately oxidize pyruvate or regenerate electron acceptors (NAD or FADH), pyruvate is converted to lactate. The conversion of pyruvate to lactate reduces the concentration of pyruvate, which prevents end products from inhibiting the reaction, and glycolysis continues.
In what cases is lactate the main end product of glycolysis?
Lactate is formed when mitochondria cannot adequately oxidize pyruvate or regenerate enough electron acceptors. This occurs with low enzymatic activity of mitochondria, with insufficient oxygen supply, and with a high rate of glycolysis. In general, lactate formation is enhanced during hypoxia, ischemia, bleeding, after carbohydrate consumption, high muscle glycogen concentrations, and exercise-induced hyperthermia.
What other ways can pyruvate be metabolized?
During exercise or when eating insufficient calories, pyruvate is converted into the non-essential amino acid alanine. Alanine synthesized in skeletal muscles travels through the bloodstream to the liver, where it is converted into pyruvate. Pyruvate is then converted into glucose, which enters the bloodstream. This process is similar to the Cori cycle and is called the alanine cycle.
What makes a person move? What is energy metabolism? Where does the body's energy come from? How long will it last? During what physical activity, what energy is consumed? As you can see, there are a lot of questions. But most of them appear when you start studying this topic. I will try to make life easier for the most curious and save time. Go…
Energy metabolism is a set of reactions of the breakdown of organic substances, accompanied by the release of energy.
To ensure movement (actin and myosin filaments in the muscle), the muscle requires Adenosine TriPhosphate (ATP). When chemical bonds between phosphates are broken, energy is released, which is used by the cell. In this case, ATP passes into a state with lower energy into Adenosine DiPhosphate (ADP) and inorganic Phosphorus (P)
If a muscle produces work, then ATP is constantly broken down into ADP and inorganic phosphorus, releasing Energy (about 40-60 kJ/mol). For long-term work, it is necessary to restore ATP at the rate at which this substance is used by the cell.
The energy sources used for short-term, short-term and long-term work are different. Energy can be produced both anaerobically (oxygen-free) and aerobically (oxidatively). What qualities does an athlete develop when training in the aerobic or anaerobic zone, I wrote in the article ““.
There are three energy systems that support human physical activity:
- Alactate or phosphagen (anaerobic). It is associated with the processes of ATP resynthesis mainly due to the high-energy phosphate compound – Creatine Phosphate (CrP).
- Glycolytic (anaerobic). Provides resynthesis of ATP and KrP due to the reactions of anaerobic breakdown of glycogen and/or glucose to lactic acid (lactate).
- Aerobic (oxidative). The ability to perform work due to the oxidation of carbohydrates, fats, proteins while simultaneously increasing the delivery and utilization of oxygen in working muscles.
Energy sources for short-term operation.
The ATP molecule (Adenosine TriPhosphate) provides quickly accessible energy to the muscle. This energy is enough for 1-3 seconds. This source is used for instantaneous, maximum force operation.
ATP + H2O ⇒ ADP + P + Energy
In the body, ATP is one of the most frequently renewed substances; Thus, 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 cycles of resynthesis (the human body synthesizes about 40 kg of ATP per day, but contains approximately 250 g at any given moment), that is, practically no ATP reserve is created in the body, and for normal life it is necessary to constantly synthesize new ATP molecules.
ATP is replenished by CrP (Creatine Phosphate), this is the second molecule of phosphate, which has high energy in the muscle. CrP donates a Phosphate molecule to an ADP molecule to form ATP, thereby allowing the muscle to work for a certain time.
It looks like this:
ADP+ KrP ⇒ ATP + Kr
The KrF reserve lasts up to 9 seconds. work. In this case, the power peak occurs at 5-6 seconds. Professional sprinters try to increase this tank (KrF reserve) even further through training to 15 seconds.
Both in the first case and in the second, the process of ATP formation occurs in anaerobic mode, without the participation of oxygen. Resynthesis of ATP due to CrP occurs almost instantly. This system has the greatest power compared to the glycolytic and aerobic ones and provides “explosive” work with maximum strength and speed of muscle contractions. This is what energy metabolism looks like during short-term work; in other words, this is how the alactic energy supply system of the body works.
Energy sources for short-term work.
Where does the body get energy during short-term work? In this case, the source is animal carbohydrate, which is found in the muscles and liver of humans - glycogen. The process by which glycogen promotes ATP resynthesis and energy release is called Anaerobic glycolysis(Glycolytic energy supply system).
Glycolysis is a process of glucose oxidation in which two molecules of pyruvic acid (Pyruvate) are formed from one molecule of glucose. Further metabolism of pyruvic acid is possible in two ways - aerobic and anaerobic.
During aerobic work pyruvic acid (Pyruvate) is involved in metabolism and many biochemical reactions in the body. It is converted into Acetyl-coenzyme A, which participates in the Krebs Cycle ensuring respiration in the cell. In eukaryotes (cells of living organisms that contain a nucleus, that is, in human and animal cells), the Krebs cycle occurs inside the mitochondria (MC, this is the energy station of the cell).
Krebs cycle(tricarboxylic acid cycle) is a key stage in the respiration of all cells that use oxygen, it is the center of intersection of many metabolic pathways in the body. In addition to its energetic role, the Krebs Cycle has a significant plastic function. By participating in biochemical processes, it helps synthesize such important cellular compounds as amino acids, carbohydrates, fatty acids, etc.
If there is not enough oxygen, that is, the work is carried out in anaerobic mode, then pyruvic acid in the body undergoes anaerobic breakdown with the formation of lactic acid (lactate)
The glycolytic anaerobic system is characterized by high power. This process begins almost from the very beginning of work and reaches power after 15-20 seconds. work of maximum intensity, and this power cannot be maintained for more than 3 to 6 minutes. For beginners who are just starting to play sports, the power is barely enough for 1 minute.
Carbohydrates – glycogen and glucose – serve as energy substrates for providing muscles with energy. In total, the glycogen reserve in the human body is enough for 1-1.5 hours of work.
As mentioned above, as a result of the high power and duration of glycolytic anaerobic work, a significant amount of lactate (lactic acid) is formed in the muscles.
Glycogen ⇒ ATP + Lactic acid
Lactate from muscles enters the blood and binds to blood buffer systems to preserve the internal environment of the body. If the level of lactate in the blood increases, then the buffer systems at some point may not cope, which will cause a shift in the acid-base balance to the acidic side. When acidified, the blood becomes thick and the body cells cannot receive the necessary oxygen and nutrition. As a result, this causes inhibition of key enzymes of anaerobic glycolysis, up to complete inhibition of their activity. The rate of glycolysis itself, the alactic anaerobic process, and the power of work decreases.
The duration of work in anaerobic mode depends on the level of lactate concentration in the blood and the degree of resistance of muscles and blood to acid shifts.
Blood buffering capacity is the ability of blood to neutralize lactate. The more trained a person is, the greater his buffer capacity.
Energy sources for long-term operation.
Sources of energy for the human body during prolonged aerobic work, necessary for the formation of ATP, are muscle glycogen, blood glucose, fatty acids, and intramuscular fat. This process is triggered by prolonged aerobic work. For example, fat burning (fat oxidation) in beginning runners begins after 40 minutes of running in the 2nd pulse zone (PZ). For athletes, the oxidation process starts within 15-20 minutes of running. There is enough fat in the human body for 10-12 hours of continuous aerobic work.
When exposed to oxygen, molecules of glycogen, glucose, and fat are broken down, synthesizing ATP with the release of carbon dioxide and water. Most reactions occur in the mitochondria of the cell.
Glycogen + Oxygen ⇒ ATP + Carbon dioxide + Water
The formation of ATP using this mechanism occurs more slowly than with the help of energy sources used for short-term and short-term work. It takes 2 to 4 minutes before the cell's need for ATP is completely satisfied by the aerobic process discussed. This delay is caused by the time it takes for the heart to begin increasing its supply of oxygenated blood to the muscles at the rate necessary to meet the muscles' ATP needs.
Fat + Oxygen ⇒ ATP + Carbon dioxide + Water
The fat oxidation factory in the body is the most energy-intensive. Since during the oxidation of carbohydrates, 38 molecules of ATP are produced from 1 molecule of glucose. And when 1 molecule of fat is oxidized, it produces 130 molecules of ATP. But this happens much more slowly. In addition, the production of ATP through fat oxidation requires more oxygen than the oxidation of carbohydrates. Another feature of the oxidative, aerobic factory is that it gains momentum gradually, as oxygen delivery increases and the concentration of fatty acids released from adipose tissue in the blood increases.
You can find more useful information and articles.
If you imagine all the energy-producing systems (energy metabolism) in the body in the form of fuel tanks, then they will look like this:
- The smallest tank is Creatine Phosphate (it's like 98 gasoline). It is located closer to the muscle and starts working quickly. This “gasoline” lasts for 9 seconds. work.
- Middle tank – Glycogen (92 petrol). This tank is located a little further in the body and fuel comes from it with 15-30 seconds of physical work. This fuel is enough for 1-1.5 hours of operation.
- Large tank - Fat (diesel fuel). This tank is located far away and it will take 3-6 minutes before fuel starts flowing from it. The reserve of fat in the human body for 10-12 hours of intense, aerobic work.
I didn’t come up with all this myself, but took extracts from books, literature, and Internet resources and tried to convey it to you succinctly. If you have any questions, write.
The phosphorylation process is the reaction of transfer of a phosphoryl group from one compound to another with the participation of the kinase enzyme. ATP is synthesized by oxidative and substrate phosphorylation. Oxidative phosphorylation is the synthesis of ATP by adding inorganic phosphate to ADP using the energy released during the oxidation of bioorganic substances.
ADP + ~P → ATP
Substrate phosphorylation is the direct transfer of a phosphoryl group with a high-energy ADP bond for the synthesis of ATP.
Examples of substrate phosphorylation:
1. An intermediate product of carbohydrate metabolism is phosphoenolpyruvic acid, which transfers the ADP phosphoryl group with a high-energy bond:
Interaction of the intermediate product of the Krebs cycle - high-energy succinyl-Co-A - with ADP to form one molecule of ATP.
Let's look at the three main stages of energy release and ATP synthesis in the body.
The first stage (preparatory) includes digestion and absorption. At this stage, 0.1% of the energy of food compounds is released.
Second phase. After transportation, monomers (decomposition products of bioorganic compounds) enter cells, where they undergo oxidation. As a result of the oxidation of fuel molecules (amino acids, glucose, fats), the compound acetyl-Co-A is formed. During this stage, about 30% of the energy of food substances is released.
The third stage - the Krebs cycle - is a closed system of biochemical redox reactions. The cycle is named after the English biochemist Hans Krebs, who postulated and experimentally confirmed the basic reactions of aerobic oxidation. For his research, Krebs received the Nobel Prize (1953). The cycle has two more names:
The tricarboxylic acid cycle, since it includes reactions of transformation of tricarboxylic acids (acids containing three carboxyl groups);
Citric acid cycle, since the first reaction of the cycle is the formation of citric acid.
The Krebs cycle includes 10 reactions, four of which are redox. During the reactions, 70% of the energy is released.
The biological role of this cycle is extremely important, since it is the common end point of the oxidative breakdown of all major foods. This is the main mechanism of oxidation in the cell; it is figuratively called the metabolic “cauldron”. During the oxidation of fuel molecules (carbohydrates, amino acids, fatty acids), the body is provided with energy in the form of ATP. Fuel molecules enter the Krebs cycle after being converted into acetyl-Co-A.
In addition, the tricarboxylic acid cycle supplies intermediate products for biosynthetic processes. This cycle occurs in the mitochondrial matrix.
Consider the reactions of the Krebs cycle:
The cycle begins with the condensation of the four-carbon component oxaloacetate and the two-carbon component acetyl-Co-A. The reaction is catalyzed by citrate synthase and involves aldol condensation followed by hydrolysis. The intermediate is citril-Co-A, which is hydrolyzed into citrate and CoA:
IV. This is the first redox reaction.
The reaction is catalyzed by an α-oxoglutarate dehydrogenase complex consisting of three enzymes:
 |
VII.
Succinyl contains a bond that is rich in energy. Cleavage of the thioester bond of succinyl-CoA is associated with phosphorylation of guanosine diphosphate (GDP):
Succinyl-CoA + ~ F +GDP Succinate + GTP +CoA
The phosphoryl group of GTP is easily transferred to ADP to form ATP:
GTP + ADP ATP + GDP
This is the only reaction in the cycle that is a substrate phosphorylation reaction.
VIII. This is the third redox reaction:
The Krebs cycle produces carbon dioxide, protons, and electrons. The four reactions of the cycle are redox, catalyzed by enzymes - dehydrogenases containing the coenzymes NAD and FAD. Coenzymes capture the resulting H + and ē and transfer them to the respiratory chain (biological oxidation chain). Elements of the respiratory chain are located on the inner membrane of mitochondria.
The respiratory chain is a system of redox reactions, during which there is a gradual transfer of H + and ē to O 2, which enters the body as a result of respiration. ATP is formed in the respiratory chain. The main carriers ē in the chain are iron- and copper-containing proteins (cytochromes), coenzyme Q (ubiquinone). There are 5 cytochromes in the chain (b 1, c 1, c, a, a 3).
The prosthetic group of cytochromes b 1, c 1, c is iron-containing heme. The mechanism of action of these cytochromes is that they contain an iron atom with variable valence, which can be in both an oxidized and reduced state as a result of the transfer of ē and H +.
Undoubtedly, the most important molecule in our body in terms of energy production is ATP (adenosine triphosphate: an adenyl nucleotide containing three phosphoric acid residues and produced in mitochondria).
In fact, every cell in our body stores and uses energy for biochemical reactions through ATP, thus ATP can be considered the universal currency of biological energy. All living beings require a continuous supply of energy to support protein and DNA synthesis, metabolism and transport of various ions and molecules, and maintain the vital functions of the body. Muscle fibers during strength training also require readily available energy. As already mentioned, ATP supplies the energy for all these processes. However, in order to form ATP, our cells require raw materials. Humans obtain these raw materials through calories through the oxidation of food consumed. To obtain energy, this food must first be processed into an easily used molecule - ATP.
The ATP molecule must go through several phases before being used.
First, a special coenzyme separates one of the three phosphates (each containing ten calories of energy), releasing large amounts of energy and forming the reaction product adenosine diphosphate (ADP). If more energy is required, the next phosphate group is separated, forming adenosine monophosphate (AMP).
ATP + H 2 O → ADP + H 3 PO 4 + energy
ATP + H 2 O → AMP + H 4 P 2 O 7 + energy
When rapid energy production is not required, the reverse reaction occurs - with the help of ADP, phosphagen and glycogen, the phosphate group is reattached to the molecule, resulting in the formation of ATP. This process involves the transfer of free phosphates to other substances contained in the muscles, which include and. At the same time, glucose is taken from glycogen reserves and broken down.
The energy obtained from this glucose helps convert the glucose back into its original form, after which the free phosphates can again be attached to ADP to form new ATP. Once the cycle is complete, the newly created ATP is ready for the next use.
In essence, ATP works like a molecular battery, storing energy when it is not needed and releasing it when it is needed. Indeed, ATP is like a fully rechargeable battery.
ATP structure
The ATP molecule consists of three components:
- Ribose (the same five-carbon sugar that forms the backbone of DNA)
- Adenine (connected carbon and nitrogen atoms)
- Triphosphate
The ribose molecule is located in the center of the ATP molecule, the edge of which serves as a base for adenosine.
A chain of three phosphates is located on the other side of the ribose molecule. ATP saturates the long, thin fibers containing the protein myosin, which forms the basis of our muscle cells.
ATP retention
The average adult's body uses about 200-300 moles of ATP daily (a mole is the chemical term for the amount of substance in a system that contains as many elementary particles as there are carbon atoms in 0.012 kg of the isotope carbon-12). The total amount of ATP in the body at any given moment is 0.1 mole. This means that ATP must be reused 2000-3000 times throughout the day. ATP cannot be stored, so the level of its synthesis almost matches the level of consumption.
ATP systems
Because ATP is important from an energy standpoint, and because of its widespread use, the body has different ways of producing ATP. These are three different biochemical systems. Let's look at them in order:
When the muscles have a short but intense period of activity (about 8-10 seconds), the phosphagen system is used - ATP combines with creatine phosphate. The phosphagen system ensures that small amounts of ATP are constantly circulating in our muscle cells.
Muscle cells also contain a high-energy phosphate, creatine phosphate, which is used to restore ATP levels after short-term, high-intensity activity. The enzyme creatine kinase takes the phosphate group from creatine phosphate and quickly transfers it to ADP to form ATP. So, the muscle cell converts ATP to ADP, and phosphagen quickly reduces ADP to ATP. Creatine phosphate levels begin to decline after just 10 seconds of high-intensity activity, and energy levels drop. An example of how the phosphagen system works is, for example, the 100-meter sprint.
The glycogen-lactic acid system supplies energy to the body at a slower pace than the phosphagen system, although it works relatively quickly and provides enough ATP for about 90 seconds of high-intensity activity. In this system, lactic acid is produced from glucose in muscle cells through anaerobic metabolism.
Given the fact that in the anaerobic state the body does not use oxygen, this system provides short-term energy without activating the cardiorespiratory system in the same way as the aerobic system, but with time savings. Moreover, when in anaerobic mode the muscles work quickly, contract powerfully, they block the supply of oxygen, since the vessels are compressed.
This system is also sometimes called anaerobic respiration, and a good example in this case is the 400-meter sprint.
If physical activity lasts more than a few minutes, the aerobic system comes into play, and the muscles receive ATP first from, then from fats and finally from amino acids (). Protein is used for energy mainly in conditions of famine (dieting in some cases).
Aerobic respiration produces the slowest amount of ATP, but produces enough energy to sustain physical activity for several hours. This occurs because during aerobic respiration, glucose is broken down into carbon dioxide and water without being counteracted by lactic acid in the glycogen-lactic acid system. Glycogen (the stored form of glucose) during aerobic respiration is supplied from three sources:
- Absorption of glucose from food in the gastrointestinal tract, which enters the muscles through the circulatory system.
- Glucose residues in muscles
- The breakdown of liver glycogen into glucose, which enters the muscles through the circulatory system.
Conclusion
If you've ever wondered where we get the energy to perform different activities under different conditions, the answer is mostly ATP. This complex molecule assists in converting various food components into easily usable energy.
Without ATP, our body simply would not be able to function. Thus, the role of ATP in energy production is multifaceted, but at the same time simple.
