The leading role of energy in the metabolic pathway depends on the process, the essence of which is oxidative phosphorylation. Nutrients are oxidized, thus forming energy, which the body stores in the mitochondria of cells as ATP. Each form of terrestrial life has its own favorite nutrients, but ATP is a universal compound, and the energy that oxidative phosphorylation produces is stored up to be used for metabolic processes.
Bacteria
More than three and a half billion years ago, the first living organisms appeared on our planet. Life originated on Earth due to the fact that the bacteria that appeared - prokaryotic organisms (without a nucleus) were divided into two types according to the principle of respiration and nutrition. By respiration - into aerobic and anaerobic, and by nutrition - into heterotrophic and autotrophic prokaryotes. This reminder is hardly redundant, because oxidative phosphorylation cannot be explained without basic concepts.
So, prokaryotes in relation to oxygen(physiological classification) are divided into aerobic microorganisms, which are indifferent to free oxygen, and aerobic, whose vital activity depends entirely on its presence. It is they who carry out oxidative phosphorylation, being in an environment saturated with free oxygen. It is the most widely used metabolic pathway with high energy efficiency compared to anaerobic fermentation.
Mitochondria
Another basic concept: what is a mitochondrion? This is the energy battery of the cell. Mitochondria are located in the cytoplasm and there are an incredible amount of them - in the muscles of a person or in his liver, for example, cells contain up to one and a half thousand mitochondria (just where the most intensive metabolism occurs). And when oxidative phosphorylation occurs in a cell, this is the work of mitochondria, they also store and distribute energy.
Even mitochondria do not depend on cell division, they are very mobile, move freely in the cytoplasm when they need it. They have their own DNA, and therefore they are born and die on their own. Nevertheless, the life of a cell depends entirely on them; without mitochondria, it does not function, that is, life is truly impossible. Fats, carbohydrates, proteins are oxidized, resulting in the formation of hydrogen atoms and electrons - reducing equivalents, which follow further along the respiratory chain. This is how oxidative phosphorylation occurs, its mechanism, it would seem, is simple.
Not so easy
The energy produced by mitochondria is converted into another, which is the energy of the electrochemical gradient purely for protons that are on the inner membrane of mitochondria. It is this energy that is needed for the synthesis of ATP. And that's exactly what oxidative phosphorylation is. Biochemistry is a rather young science, only in the middle of the nineteenth century were mitochondrial granules found in cells, and the process of obtaining energy was described much later. It has been observed how the trioses formed through glycolysis (and most importantly, pyruvic acid) produce further oxidation in the mitochondria.
Trioses use the energy of splitting, from which CO2 is released, oxygen is consumed and synthesizes a huge amount of ATP (adenosine triphosphoric acid, and what it is - people who are fond of bodybuilding know especially well). All of the above processes are closely related to oxidative cycles, as well as the respiratory chain that carries electrons. Thus, oxidative phosphorylation occurs in cells, synthesizing "fuel" for them - ATP molecules.
Oxidative cycles and the respiratory chain
In the oxidative cycle, tricarboxylic acids release electrons, which begin their journey along the electron transport chain: first to coenzyme molecules, here NAD is the main thing (nicotinamide adenine dinucleotide), and then electrons are transferred to the ETC (electric transport chain),until they combine with molecular oxygen and form a water molecule. Oxidative phosphorylation, the mechanism of which is briefly described above, is transferred to another site of action. This is the respiratory chain - protein complexes built into the inner membrane of mitochondria.
This is where the culmination occurs - the transformation of energy through a sequence of oxidation and reduction of elements. Of interest here are the three major points in the electrotransport chain where oxidative phosphorylation occurs. Biochemistry looks at this process very deeply and carefully. Perhaps someday a new cure for aging will be born from here. So, at three points of this chain, ATP is formed from phosphate and ADP (adenosine diphosphate is a nucleotide that consists of ribose, adenine and two portions of phosphoric acid). That is why the process got its name.
Cellular respiration
Cellular (in other words - tissue) respiration and oxidative phosphorylation are stages of the same process taken together. Air is used in every cell of tissues and organs, where cleavage products (fats, carbohydrates, proteins) are broken down, and this reaction produces energy stored in the form of macroergic compounds. Normal pulmonary respiration differs from tissue respiration in that oxygen enters the body and carbon dioxide is removed from it.
The body is always active, its energy is spent on movement and growth, on self-reproduction, on irritability and on many other processes. It is for this andoxidative phosphorylation occurs in mitochondria. Cellular respiration can be divided into three levels: the oxidative formation of ATP from pyruvic acid, as well as amino acids and fatty acids; acetyl residues are destroyed by tricarboxylic acids, after which two carbon dioxide molecules and four pairs of hydrogen atoms are released; electrons and protons are transferred to molecular oxygen.
Additional mechanisms
Respiration at the cellular level ensures the formation and replenishment of ADP directly in the cells. Although the body can be replenished with adenosine triphosphoric acid in another way. For this, additional mechanisms exist and, if necessary, are included, although they are not so effective.
These are systems in which oxygen-free breakdown of carbohydrates occurs - glycogenolysis and glycolysis. This is no longer oxidative phosphorylation, the reactions are somewhat different. But cellular respiration cannot stop, because in its process very necessary molecules of the most important compounds are formed, which are used for a variety of biosynthesis.
Forms of Energy
When electrons are transferred in the mitochondrial membrane, where oxidative phosphorylation occurs, the respiratory chain from each of its complexes directs the released energy to move protons through the membrane, that is, from the matrix to the space between the membranes. Then a potential difference is formed. Protons are positively charged and located in the intermembrane space, and negativelycharged act from the mitochondrial matrix.
When a certain potential difference is reached, the protein complex returns protons back to the matrix, turning the received energy into a completely different one, where oxidative processes are coupled with synthetic - ADP phosphorylation. Throughout the oxidation of substrates and the pumping of protons through the mitochondrial membrane, ATP synthesis does not stop, that is, oxidative phosphorylation.
Two kinds
Oxidative and substrate phosphorylation are fundamentally different from each other. According to modern ideas, the most ancient forms of life were able to use only the reactions of substrate phosphorylation. For this, organic compounds existing in the external environment were used through two channels - as a source of energy and as a source of carbon. However, such compounds in the environment gradually dried up, and the organisms that had already appeared began to adapt, look for new sources of energy and new sources of carbon.
So they learned to use the energy of light and carbon dioxide. But until this happened, organisms released energy from oxidative fermentation processes and also stored it in ATP molecules. This is called substrate phosphorylation when the method of catalysis by soluble enzymes is used. The fermented substrate forms a reducing agent that transfers electrons to the desired endogenous acceptor - acetone, acetalhyd, pyruvate and the like, or H2 - gaseous hydrogen is released.
Comparative characteristics
Compared to fermentation, oxidative phosphorylation has a much higher energy yield. Glycolysis gives a total ATP yield of two molecules, and in the course of the process, thirty to thirty-six are synthesized. There is a movement of electrons to acceptor compounds from donor compounds through oxidative and reduction reactions, forming energy stored as ATP.
Eukaryotes carry out these reactions with protein complexes that are localized inside the mitochondrial cell membrane, and prokaryotes work outside - in its intermembrane space. It is this complex of linked proteins that makes up the ETC (electron transport chain). Eukaryotes have only five protein complexes in their composition, while prokaryotes have many, and they all work with a wide variety of electron donors and their acceptors.
Connections and disconnections
The process of oxidation creates an electrochemical potential, and with the process of phosphorylation this potential is used. This means that conjugation is provided, otherwise, the binding of the processes of phosphorylation and oxidation. Hence the name, oxidative phosphorylation. The electrochemical potential required for conjugation is created by three complexes of the respiratory chain - the first, third and fourth, which are called conjugation points.
If the inner membrane of the mitochondria is damaged or its permeability increased from the activity of uncouplers, this will certainly cause the disappearance or decrease in the electrochemical potential, andnext comes the uncoupling of the processes of phosphorylation and oxidation, that is, the cessation of ATP synthesis. It is the phenomenon when the electrochemical potential disappears that is called the uncoupling of phosphorylation and respiration.
Disconnectors
The state where the oxidation of substrates continues and phosphorylation does not occur (that is, ATP is not formed from P and ADP) is the uncoupling of phosphorylation and oxidation. This happens when uncouplers interfere with the process. What are they and what results do they strive for? Suppose ATP synthesis is greatly reduced, that is, it is synthesized in a smaller amount, while the respiratory chain functions. What happens to energy? It exudes like warmth. Everyone feels this when they are sick with a fever.
Do you have a temperature? So the breakers have worked. For example, antibiotics. These are weak acids that dissolve in fats. Penetrating into the intermembrane space of the cell, they diffuse into the matrix, dragging bound protons with them. Uncoupling action, for example, have hormones secreted by the thyroid gland, which contain iodine (triiodothyronine and thyroxine). If the thyroid gland is hyperfunctioning, the condition of patients is terrible: they lack the energy of ATP, they consume a lot of food, because the body requires a lot of substrates for oxidation, but they lose weight, since the main part of the energy received is lost in the form of heat.
