Bioenergetics

BIOENERGETICS, biological energy, studies the mechanisms of energy conversion in the processes of vital activity of organisms. In other words, B. considers the phenomena of vital activity in their energetic. aspect. Methods and approaches to the studied phenomena used in B. are physico-chemical, objects and tasks are biological. Thus, B. stands at the junction of these sciences and is part of molecular biology, biophysics and biochemistry.

The beginning of B. can be considered the work of him. doctor J. R. Mayer, who discovered the law of conservation and transformation of energy (1841) based on the study of energy processes in the human body. A summary study of the processes that are sources of energy for living organisms (see Respiration, Fermentation), and energetics. the balance of the organism, its changes under various conditions (rest, work of different intensity, ambient temperature) has long been the main content of B. (see Basic metabolism, Heat transfer, Heat production). In the middle of the 20th century, in connection with the general direction of the development of biological. The research of the mechanism of energy conversion in living organisms took a central place in B.

All research in the field of B. is based on the only scientific. the point of view, according to which the laws of physics and chemistry are fully applicable to the phenomena of life, and to the transformations of energy in the body - the main. the beginnings of thermodynamics.

However, the complexity and specificity is biological. The structures and processes implemented in them cause a number of profound differences between B. and non-organic energy. the world, in particular technical. energy. The first fundamental feature of B. is that organisms are open systems that function only under conditions of constant exchange of matter and energy with the environment. The thermodynamics of such systems differs significantly from the classical one. Fundamental to the classic. in thermodynamics, the concept of equilibrium states is replaced by the idea of stationary states; the second principle of thermodynamics (the principle of increasing entropy) receives a different formulation in the form of Prigogine theorem. The second most important feature of B. is connected with the fact that processes in cells take place in the absence of temperature, pressure and volume changes; because of this, the transfer of heat into work in the body is impossible and heat release represents an irreversible loss of energy. Therefore, in the course of evolution, organisms have developed a number of specific features. mechanisms of direct conversion of one form of free energy into another, bypassing its transition into heat. In the body, only a small part of the released energy is converted into heat and lost. Most of it is converted into the form of free chemical energy of special compounds, in which it is extremely mobile, i.e. it can also transform into other forms at a constant rate, in particular, perform work or be used for biosynthesis with a very high efficiency, reaching, for example, 30% during muscle work.

One of the main results of the development of B. in recent decades is the establishment of uniformity of energy processes throughout the living world - from microorganisms to humans. The substances in which energy is accumulated in a mobile, biologically digestible form, and the processes by which such accumulation is carried out, turned out to be uniform for the entire plant and animal world. The same uniformity is established in the processes of using the energy accumulated in these substances. For example, the structure of proteins and the mechanism of the mechano-chemical effect (i.e., the transformation of chemical energy to work) are basically the same when the flagella in protozoa move, mimosa leaves are lowered, or when the most complex movements of birds, mammals and humans. Such uniformity is characteristic not only for the phenomena studied by B., but also for other functions inherent in all living things: storage and transmission of inheritances, information, the main pathways of biosynthesis, the mechanism of enzymatic reactions.

The substances through which the energy of organisms is realized are macroergic compounds characterized by the presence of phosphate groups. The role of these compounds in the processes of energy conversion in the body was first established by studying muscle contraction, sov. biochemist V. A. Engelhardt. In the future, the works of mn. researchers have shown that these compounds are involved in the accumulation and transformation of energy in all life processes. The energy released during the cleavage of phosphate groups can be used for the synthesis of biologically important substances with an increased supply of free energy and for life processes associated with the conversion of free chemical energy into work (mechanical, active transfer of substances, electrical, etc.). The most important of these compounds, the substance that plays the role of almost the only transformer and energy transmitter for the whole living world, is adenosine triphosphate k-ta - ATP (see Adenosine phosphoric acids), cleaved to adenosine diphosphoric acid (ADP) or adenosine monophosphoric acid (AMP). Hydrolysis of ATP, i.e. cleavage of the final phosphate group from it, proceeds according to the equation:

ATP + H2O -> ADP + Phosphate

and is accompanied by a decrease in free energy by the value of delta F. If this reaction proceeds at a concentration of all reagents and products of 1.0 mol at 25 ° C and pH 7.0, then the free energy of ADP is less than the free energy of ATP by 29.3 kj. (7000 kal). In the cell, this change in free energy is greater: delta F = 50 kj/mol (12,000 cal/mol). The DR values for the ATP->ADP reaction are higher than for most hydrolysis reactions. The bonds of the third (final) and second phosphate groups in the ATP molecule and similar bonds in other macroergic compounds are also called macroergic. These bonds are denoted by the sign ~ (tilde); for example, the ATP formula can be written as follows: adenine - ribose -phosphate ~ phosphate ~ phosphate. Speaking about the energy of macroergic bonds, in B. they do not mean the actual energy of the covalent bond between phosphorus and oxygen (or nitrogen) atoms, as is customary in physics. chemistry, but only the difference between the values of the free energy (delta F) of the initial reagents and the products of ATP hydrolysis reactions, etc. similar reactions. "Binding energy" in this sense, strictly speaking, is not localized in this connection, but characterizes the reaction as a whole.

The energy of macroergic ATP bonds is a universal form of storing free energy for the whole living world: all energy transformations in the processes of vital activity are carried out through the accumulation of energy in these bonds and its use when they break. The delta F value for these reactions is like a "biological quantum" of energy, since all energy transformations in organisms occur in portions approximately equal to delta F. During enzymatic hydrolysis of ATP in the cell, the cleavable phosphate group is always transferred to the substrate, the energy reserve in the k-rom turns out to be greater as a result than in the initial compound.

The metabolism in the cell consists of the continuous decomposition of complex substances to simpler ones (catabolic processes) and the synthesis of more complex substances (anabolic processes). Catabolic processes are exergonic, i.e. they proceed with a decrease in free energy (delta F<0); anabolic processes are endergonic, they proceed with an increase in free energy (delta F>0). According to the general laws of thermodynamics, exergonic processes can proceed spontaneously, spontaneously, but endergonic processes require an influx of free energy from the outside. In the cell, this is done through the coupling of both processes: some use the energy released during the flow of others. This coupling, which underlies the entire metabolism and vital activity of the cell, is carried out through the ATP -ADP system, which creates intermediate, energy-enriched compounds.

For example, the synthesis of sucrose from glucose and fructose occurs due to the energy released during the reaction of ATP hydrolysis by the formation of an intermediate activated compound - glu-cozo-1-phosphate: 1) ATP + glucose -> -> ADP + glucose-1-phosphate; 2) glucose-1-phosphate + fructose -> sucrose + phosphate. Total reaction: ATP + glucose + fructose -> ADP + sucrose + phosphate.

Energetich. process balance:

ATP->ADP + phosphate - 29.3 kj/mol (-7000 kal/mol) (decrease in free energy); glucose + fructose -> sucrose + 23 kj/mol (+ 5500 kal/mol) (increase in free energy). The loss of energy for heat is 6.3 kj/mol (1500 kal/mol), i.e. the efficiency of the process is 79%.

The same type of coupling of reactions is carried out in the synthesis of other complex compounds (lipids, polysaccharides, proteins and nucleic k-t). In these processes, in addition to ATP, some similar compounds take part, which, instead of adenine, include other nitrogenous bases (guanine-, cytosine-, uridine-, thymidine triphosphates or creatine phosphates). During the synthesis of proteins and nucleic acids, not one terminal phosphate group is split off from ATP, but the last two (pyrophosphate). Thus, all the processes of accumulation (accumulation) of energy in organisms should be reduced to the processes of formation of ATP, i.e. phosphorylation (inclusion of phosphate groups in ADP or AMP).

The energetics of the metabolic processes in which energy retains the form of chemical is clear in basic terms, but this cannot be said about the processes in which energy passes from chemical. forms in mechanical. work or some other type of energy (e.g. electric). So, it is known, for example, that the work performed by the contracting muscle is produced by the energy released during the hydrolysis of ATP, but the mechanism of this energy conversion is not yet clear. Elucidation of intimate mechanisms of mechanochemical effect and other chemical transformations. energy is an important and urgent task of B., the successful solution of which can open the way to the direct conversion of chemical energy into mechanical and electrical without an intermediate "ruinous" transformation of it into heat.