BIO-ENERGETICS

From Big Medical Encyclopedia

BIO-ENERGETICS — set of processes of energy conversion in a live organism (biological systems): extraction of energy from the environment, its accumulation and use for life activity of an organism. Power processes in biol, systems submit to laws of physics and chemistry, and first of all laws thermodynamics (see). From the point of view of thermodynamics, organisms are open circuits which constancy of parameters is provided that organisms continuously receive energy from the environment in the quantity compensating its internal expenses. In biol, objects there are no considerable temperature drops or pressure, and they work by the principle of the «chemical cars» which are directly using chemical (electronic) energy for implementation of work. According to this efficiency of transformation of energy is defined by a ratio: efficiency = (μ1 - μ2)/μ1, where μ1 and μ2 energy (chemical) potentials of initial and final conditions of substance.

The central place in biopower transformations is taken by the principle of power interface, according to the Crimea the molecular transformations leading to increase of free energy of system (endergonic reactions) are interfaced in time and space to energy-releasing reactions — donors of energy who happen to considerable reduction of free energy. Therefore in an organism such reactions

which isolated course is impossible are implemented. ATP or other high-energy connections acts as the donor of energy (see. Vysokoergichesky connections ). In a similar way endergonichesky synthesis of ATP is accompanied by energy-releasing reactions of oxidation of various connections:

The elementary acts of transformation of energy which are made at molecular level are carried out by a set of the enzymes localized in specialized structures, and first of all in biological membranes. All biopower processes are thinly regulated at the molecular, membrane, cellular and organismal levels (see. Biological system , an autoregulyation in biological systems).

Almost only primary energy source for biological systems is the visible and passing infrared sunlight, energy to-rogo in process photosynthesis (see) turns into chemical energy. The solar energy reserved in products of photosynthesis is used then heterotrophic organisms — napr, herbivorous, and then carnivores. End products of photosynthesis are carbohydrates, amino acids (and consequently, and proteins), lipids and other organic compounds.

Photosynthesis is the complex multi-stage process which is carried out in specialized membrane organoids of cells of plants — chlorolayers. Photosynthetic pigments, and first of all a chlorophyll and and a chlorophyll of b are connected with membranes. At the same time the following sequence photochemical, photophysical takes place. and biochemical, acts, or events: energy of light —> energy of electronic excitement of a chlorophyll (and other pigments) —> oxidation-reduction energy of carriers of electrons —> chemical energy of ATP and NADF-N —> chemical energy of end products of photosynthesis (glucose and other connections).

All animals and the majority of microorganisms use energy of these connections arriving with food — organotrophic power exchange.

Energy of chemical bonds of organic molecules is released at their step oxidation. If a final oxidizer of organic molecules is oxygen, then speak about aerobic, or respiratory, type of power and if process happens without participation of oxygen — about anaerobic. However in both cases, as a rule, not direct interaction of carbon compounds with oxygen, and a degidrogenirovaniye takes place: the oxidation connected with removal of hydrogen atoms which are transferred to another, the substance which is recovered at the same time. In a kachestveprimer we will consider oxidation of glucose — process, on the final reaction the return to photosynthesis: With 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + 686 kcal/mol.

Basic feature biol, oxidations, or breath (see biological oxidation), is that it proceeds gradually, through numerous intermediate enzymatic stages (oxygen directly does not react with the oxidized molecules). The considerable part of energy of energy-releasing reactions is emitted not in the form of heat, and first of all ATP is used for synthesis of high-energy connections, and. Oxidation of glucose passes through four main stages. The first stage — glycolysis (see) — proceeds without participation of oxygen, it is localized in cytoplasm; at the same time one molecule of glucose turns into two molecules pyroracemic to - you. Free energy (ΔΡ) at the same time decreases by 50 kcal/mol, i.e. from glucose is released apprx. 7% of energy. A part of the released energy is spent for synthesis of two molecules ATP:

With 6 H 12 O 6 + 2ADF + 2H 3 PO 4 → 2CH 3 COCOOH + 2ATF + 2H 2 + 2H 2 O.

On the mechanism processes are close to glycolysis fermentations (see), carried out by yeast and other microorganisms. At the second stage — a stage oxidizing decarboxylation — Pyroracemic to - that is decarboxylized to acetyl which takes up with coenzyme A, forming acetyl coenzyme A. At the same time from a three-carbon molecule pyroracemic to - you are chipped off by CO 2 and two hydrogen atoms (the second hydrogen atom the sulphhydryl group of coenzyme A delivers) and are released apprx. 60 kcal/mol of energy (ΔF — 60 kcal/mol):

2CH 3 COCOOH + 2KOA-SH → 2CH 3 CO-SKoA + 2CO 2 + 2H 2 .

The third and fourth stages are localized in vocational intracellular educations — mitochondrions. At the third stage which received the name of a cycle lemon to - you, or a tricarbonic acid cycle, acetyl coenzyme A connects with oxalacetic to - that to emergence six-carbon lemon to - you and regeneration of coenzyme A. Then an enzymatic way lemon to - that undergoes a number of the transformations leading to regeneration oxalacetic to - you (see. Tricarboxylic acids cycle ). Features of this stage — use for oxidation of carbon not of oxygen of air, and oxygen of water and acetic to - you, release of almost all energy in the form of «high-energy» electrons (hydrogen atoms) and synthesis of two molecules of vysokoergichesky connection — a guanozintrifosfat (GTF).

The hydrogen atoms which are emitted at all stages of destruction of glucose are entered into a uniform chain of oxidation-reduction enzymes (respiratory chain), on a cut an electron, losing energy, goes down to oxygen (see. Respiratory enzymes ).

During such process 52,6 kcal/mol of energy are released. Oxygen of air reacts only with the latest component of a respiratory chain — cytochrome oxydase with formation of a water molecule:

2e - + 2H + 0,5O 2 → H 2 O.

Other oxidations considered above a stage proceed without participation of oxygen. Passing of each couple of electrons on a respiratory chain is followed by synthesis of three molecules ATP. This process received the name of oxidizing phosphorylations (see). The mechanism of power transmission from carriers of a respiratory chain to system of synthesis of ATP (power interface between oxidation and phosphorylation) is finally not found out. It is supposed that at the same time intermediate storage of energy in the form of an electrochemical gradient of protons across an inner membrane of mitochondrions (the hemiosmotichesky mechanism of interface) takes place. It is obviously possible that at certain stages of this process energy can collect in the form of intense structure of proteins of a membrane (a conformational hypothesis).

In organisms of plants and animals there is also other way of aerobic oxidation of glucose — the so-called pentozofosfatny shunt. It originates from a product of the first stage of glycolysis — glyukozo-6-phosphate and through a difficult chain of specific transformations leads to disintegration of one of six molecules of glyukozo-6-phosphate, and five other molecules during anaerobic chemical transformations are regenerated:

6th glyukozo-6-phosphate + 12NADF + 7H 2 O → 5th glyukozo-6-phosphate + 6CO 2 + H 3 PO 4 + 12NADFN-N + .

Got into condition at the same time nikotinamidadenin dinucleotide (NADF-N) can be exposed further to oxidation in a respiratory chain or be used in various processes of synthesis of organic compounds.

The enzymatic system of a tricarbonic acid cycle and a respiratory chain are used for oxidation not only glucose, but also other substances consumed with food and containing stocks of chemical energy (carbohydrates, fats, proteins). Previously huge number of various complicated organic molecules of food is exposed to unification and turns into a small number of carboxylic acids which then are consistently utilized by the same cyclic set of enzymes.

Thus, the universal energy source for implementation of various vital processes — ATP — is created during endergonic reaction:

ADF + H 3 PO 4 → ATP,

using energy of oxidation or fragments of molecules of organic matters (substrate phosphorylation), or carriers of a respiratory chain (oxidizing phosphorylation and photosynthetic phosphorylation).

At disintegration of ATP energy is emitted: free energy of reaction

of ATP + H 2 O → ADF + H 3 PO 4

in solution makes apprx. 10 kcal/mol; in cells taking into account real concentration of reagents free energy can reach 12 — 14 kcal/mol.

Except ATP, in wildlife a significant amount of other high-energy connections is presented: guanine riboside - inosine - and uridinetriphosphates; creatine - arginine - and atsetilfosfata; acetyl coenzyme A, etc. They perform functions of deposition of energy owing to easy exchange of phosphatic groups with ADF (I); predecessors of ATP in the course of biosynthesis (II); intermediaries in power transmission of ATP to substrates consumers (III).

At all variety of the vital signs connected with consumption of energy three types of transformation of energy are their cornerstone: 1) chemical energy of labile chemical communication in molecule ATP — chemical energy stable biol, connections; 2) energy of ATP — mechanical work; 3) energy of ATP — osmotic work. The first type of use of energy makes a basis of endergonichesky sintez of various chemical connections, including and biopolymers — nucleic acids, proteins and polysaccharides (an anabolic branch of metabolism). Their power supply is reached by interface of piece - and the endergonic reactions proceeding on one enzyme («energy from hand to hand»). At the same time margins of energy in one of participants of reaction increase due to disintegration of makroergichesky connections with decrease in margins of energy of system in general. E.g., energy level of reagent raises by accession of the ATP final phosphate to it (phosphorylation):

In + ATP → V-F + ADF

or two trailer phosphates (pyrophosphorylation):

In + ATP → V-F-F + AMF

or AMF (adenilirovany):

In + ATP → V-AMF + FF.

Such fosforilirovanny or adenilirovanny connections can enter synthetic reactions as power loss at connection of molecular fragments is offset by allocation of energy at dephosphorylation (deadenilirovaniye) of fragments. E.g., endergonichesky synthesis of sucrose comes from glucose and fructose as follows:

1) ATP + glucose → ADF + glyukozo-1-phosphate (phosphorylation);

2) glyukozo-1-phosphate + fructose → sucrose + phosphate.

Overall reaction:

ATP + glucose + fructose → sucrose + phosphate + ADF.

Ekzergonichesky semi-reaction:

ATP → ADF + phosphate (ΔF = - 8000 kcal/mol).

Endergonichesky semi-reaction: glucose + fructose → sucrose (ΔF' = + 5500 kcal / lyul). ΔF> ΔF'; the efficiency of reaction makes apprx. 70%.

In certain cases a direct donor of energy is not ATP, and other nukleozidtrifosfata: e.g., functioning of ribosomes is ensured by energy of a guanozintrifosfat (GTF), and synthesis of phosphatides — cytidinetriphosphate (TsTF).

Use of energy of ATP for implementation of mechanical work is the cornerstone of various forms of a physical activity of organisms and cells: reductions of muscles at animals, the movements of leaves and flowers at plants, works of flagellums and cilia at protozoa, etc. the Efficiency of transformation of energy in a muscle makes movements of the nuclear device at cell fission apprx. 40%.

A crucial role in such mechano-chemical processes (see) play the sokratitelny proteins of an aktomiozinovy complex capable to reconstruct the structure and interposition that finds the external manifestation in macroscopic effect — reduction of a muscle.

The third type of use of energy of ATP — osmotic work. Generation and maintenance of concentration differences (gradients) of various substances, and first of all ions of sodium and potassium in systems is its cornerstone: a cell — the environment or cellular organoids — cytoplasm. The transfer of substances connected with an expense of high-energy connections received the name of active transport. Thanks to active transport in cells necessary constancy of ionic structure and ionic polarization of membranes excitable (nervous, muscular) cells — the membrane potential, or rest potential is maintained. It is the main premises for emergence and distribution of nervous impulse — action potential (see. Bioelectric phenomena).

At last, energy of ATP can be transformed with high performance to light energy. It takes place in the phenomenon of a bioluminescence (see. Biokhemilyuminestsention ).

Considerably a smaller role in B. is played by processes of purely physical transfer of energy. Migration of energy has the greatest functional value in the course of photosynthesis: with its help transfer of energy of the light quantums absorbed by various pigments to reactive centers by means of which energy of electronic excitement is transformed to chemical energy of products of photosynthesis is carried out.

Knowledge of biopower processes is of great importance for medicine. The majority of pathological processes is anyway connected with disturbances in energy balance. E.g., at B1 avitaminosis oxidation pyroracemic to - you is blocked, at a hyperthyroidism free oxidation against the background of weakening of interface to phosphorylation of ADF amplifies, at malignant regeneration of cells the glycoclastic way of disintegration of carbohydrates over a mitochondrial tricarbonic acid cycle and oxidizing phosphorylation begins to prevail. Deaths at myocardial infarctions and many intoxications (a poisoning with carbon monoxide, potassium cyanide etc.) are observed at blockade of the power generating systems at molecular level. On the effects for an organism the most considerable disturbance of biopower processes is decrease in efficiency of oxidizing phosphorylation in mitochondrions. It can occur owing to:

1) blockings of electron transfer on any site of a chain of mitochondrions, inhibition ATF-sintetazy or systems of transport of ATP, ADF and phosphate;

2) dissociation of processes of oxidation and phosphorylation, normal strongly interfaced. In the latter case the effect is explained by increase in permeability of membranes of mitochondrions for protons or cations (e.g., K + , Na + ). At increase in permeability of membranes of mitochondrions for cations the swelling of mitochondrions leading to secondary increase in permeability for ions is observed.

In experiments it is shown that one inorganic and organic compounds have an inhibiting effect on system of oxidizing phosphorylation, and others (them it is much bigger) — separating. E.g., cyanides, nitrites and carbon monoxide inhibit cytochrome oxydase; ions of zinc block electron transfer on the site between tsitokhroma in — c1, barbiturates — on the site OVER · H — FAD; rtutnoorganichesky connections inhibit preferential transfer of phosphate; Dicumarinum and other antagonists of phthiocol, and also dinitrophenol are razobshchitel. Possibly, as effect of many bacterial toxins can be mediated via similar mechanisms. Disturbance of oxidizing phosphorylation in fabrics arises not only owing to inhibition, but also as a result of a lack of coenzymes of a respiratory chain at avitaminosis (e.g., OVER · H — at deficit nicotinic to - you, FAD — at deficit of Riboflavinum, coenzymes — at a vitamin deficiency of the E and K groups). A number of substances of an endogenous origin has properties of inhibitors or razobshchitel. It is possible to carry some hormones to them, napr, thyroxine (razobshchitel), steroid hormones (inhibitors of electron transfer).

However disturbances of the phosphorylating ability of mitochondrions, probably, mostly are mediated through changes of structure and properties of lipids of membranes of mitochondrions. Two main mechanisms of modification of membrane lipids are known: peroxide oxidation of unsaturated fatty acids and splitting of phospholipids mitochondrial phospholipase And.

Products of peroxide oxidation of unsaturated fatty acids of lipids increase ion permeability of membranes of mitochondrions, being, thus, razobshchitel. Besides, peroxide oxidation is resulted by the inhibition of a respiratory chain of mitochondrions connected with oxidation of sulphhydryl groups of proteins — carriers of electrons. In fiziol, conditions process of peroxide oxidation is controlled by a cell and proceeds with a small speed. However at some morbid conditions peroxide oxidation can proceed very intensively (e.g., at action of a penetrating radiation and ultraviolet radiation, at a hyperoxia and intoxication ozone, at avitaminosis of E, a hypervitaminosis of D and at a lack of a microelement of selenium). It is supposed that activation of peroxide oxidation arises also after a temporary hypoxia of bodies.

Essentially other is the mechanism of regulation of efficiency of oxidizing phosphorylation with participation of a mitochondrial phospholipase And. End products in this case are lizofosfatida and free fatty acids. Lizofosfatida are capable to inhibit transport of electrons on a respiratory chain on sites OVER · H — ubikhinon and ubikhinon-cytochrome s1. Free unsaturated fatty acids increase ion permeability of membranes, i.e. are razobshchitel and, besides probably inhibit transport of adeninenucleotides.

The mitochondrial phospholipase And is activated by calcium ions and free fatty acids; an antagonist of a lipolysis is ATP, edges shifts reaction towards synthesis of phospholipids. The effect of activation of a phospholipase And is most accurately shown at an anoxia when concentration of ATP in a cell sharply decreases and increases the maintenance of Ca2 + in cytoplasm. It is very probable that the same mechanism is shown also at cold adaptation, and at influence of a number of hormones, napr, at indirect effect of thyroxine. There is a possibility that in above-mentioned cases a part is played by cyclic AMF.

Except disturbances of oxidizing phosphorylation of mitochondrions, in pathological conditions other changes of energy balance, napr, glycolysis can be observed. So, at an anoxia and a hypoxia there is a compensatory activation of glycoclastic process. In cells of malignant tumors even at the normal oxygen content activation of glycolysis is observed (in particular, at the expense of an exit of cofactors of glycolysis in cytoplasm from mitochondrions of a cancer cell), however in general the nature of this phenomenon is insufficiently clear.

The research of the biopower status, in particular oxidizing phosphorylation of fabrics and cells in spite of the fact that in a crust, time it is based on use of indirect methods, has essential value for diagnosis, forecasting and therapy of various diseases.

See also Metabolism and energy .


Bibliography: Vladimirov Yu. A. and Archakov A. I. Peroxide oxidation of lipids in biological membranes, M., 1972; Konev S. V. and Bolotovsky I. D. Introduction to molecular photobiology, Minsk, 1971, bibliogr.; Leniidzher A. Mitokhondriya, the lane with English, M., 1966, bibliogr.; P e to e r E. Biopower mechanisms, the lane with English, M., 1967, bibliogr.; Skulachev B. P. Accumulation of energy in a cell, M., 1969; it, Transformation of energy in biomembranes, M., 1972, bibliogr.; Yasaytis A. A. Molecular bio-energetics, p.1, M., 1973, bibliogr.; Current topics in bioenergetics, ed. by D. R. Sanadi, v. 1—5, N. Y. — L., 1966 — 1973; Lehninger A. L. Bio-energetics, California, 1971, bibliogr.

S. V. Konev; V. I. Sorokova (medical value).

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