Chemical evolution definition. The chemical evolution of the earth. Initial stages of biological evolution

Chemical evolution of living things. From hydrogen, nitrogen and carbon, in the presence of free energy on Earth, simple molecules should first have arisen: ammonia, methane and similar compounds. And in the future, these simple molecules in the primary ocean could enter into new bonds with each other and with other substances.

Apparently, the processes of growth of molecules proceeded with particular success in the presence of the –N=C=N– group. This group has great chemical capabilities to growth both by attaching an oxygen atom to the carbon atom, and by reacting with a nitrogenous base.

From a certain stage of chemical evolution, the participation of oxygen in this process became necessary. In the Earth's atmosphere, oxygen could accumulate as a result of the decomposition of water and water vapor. under the influence of the ultraviolet rays of the sun. It took at least 1–1.2 billion years for the transformation of the reduced atmosphere of the primary Earth into an oxidized one (Fig. 5.1). With the accumulation of oxygen in the atmosphere, the reduced compounds should have been oxidized, namely: NH 3 - to NO 3, CH 4 - to CO 2, H 2 S - to SO 3. In some cases, the oxidation of CH 4 could form methyl alcohol, formaldehyde, formic acid, etc., which, together with rainwater, fell into the primary ocean. These substances, reacting with ammonia and hydrogen cyanide, could give rise to amino acids and compounds such as adenine.

Rice. 5.1. Evolution of the Biosphere and Atmosphere (from Yu. Odum, 1975). Left side the curve should be continued, apparently, up to 2.5 billion years.

In the course of such and similar reactions, the waters of the primary ocean were saturated with various substances, forming a primary soup.

Possibility of synthesis of amino acids and other low-molecular organic compounds from inorganic elements and compounds is proved experimentally. Thus, by passing electric discharges or ultraviolet radiation through a mixture of methane and ammonia gases, in the presence of water vapor, it will be possible to obtain such relatively complex compounds as glycine, alanine, aspartic acid, γ-aminobutyric, succinic and lactic acids and other low molecular weight organic compounds of all four main classes: amino acids, nucleotides, sugars and fatty acids. The possibility of such a synthesis has been proven in numerous experiments using other ratios of initial gases and types of energy source.

Experiments in this direction turned out to be promising for elucidating the origin of other substances. Adenine, guanine, adenosine, adenosine monophosphate, adenosine diphosphate and adenosine triphosphate have been synthesized. More complex molecules, such as proteins, lipids, nucleic acids, and their derivatives, could be formed from simple molecules by the polymerization reaction.

Without dwelling on other features of the initial stages of chemical evolution, we note that one of its most important steps should be recognized as the combination of the ability for self-reproduction of polynucleotides with the catalytic activity of polypeptides. When life arose, the participation of both polynucleotides and polypeptides was necessary. The properties of each needed to be complemented by the properties of the other. The catalytic abilities of RNA molecules (A.S. Spirin), which probably played an important role in the course of prebiological evolution, were enhanced by the catalytic functions of protein molecules. In addition, the synthesis of proteins themselves by lengthening the peptide chain would not have been very successful without the transfer of stability by storing "information" about it in nucleic acids. In the course of prebiological selection, those complexes had the greatest chances for preservation, in which the ability for metabolism was combined with the ability for self-reproduction.

For this stage of prebiological evolution, a fraction of macromolecules of polynucleotides or polypeptides is distinguished as an elementary object of evolution, and a stable “collective” of macromolecules (connected by processes of synthesis, catalysis, etc.) is distinguished as an elementary evolving unit.

In the further complication of metabolism in such systems, catalysts (various organic and inorganic substances) and the space-time separation of the initial and final reaction products should have played a significant role. Probably, all this could not have arisen before the appearance of membranes. Education membrane structure considered one of the "difficult" stages of prebiological evolution. Although the possibility of self-assembly of the system was achieved to some extent by combining polynucleotides and polypeptides, however, the true being could not take shape before the appearance of the membrane structure and enzymes.

Rice. 5.2. Possible ways formations: A - membranes during the formation of coacervates in the primary broth (from M. Calvin, 1971); B - formation of mitochondria; B - formation of eukaryotic cells (according to E. Wolpe, 1981)

Biological membranes, as is known, are aggregates of proteins and lipids capable of separating substances from the environment and imparting strength to the packaging of molecules. The membranes could have arisen either during the formation of coacervates (Fig. 5.2), which are formed in water when two weakly interacting polymers come into contact, or during the adsorption of polymers on the surface of clays (see below).

As noted above, the main feature modern level analysis of the chemical form of matter is the transition from the third theoretical system - the doctrine of chemical processes - to the fourth, called evolutionary chemistry. The very emergence of evolutionary chemistry was the result of the previous path of development traversed by this science. It is prepared by studying and creating more and more complex substances and ever deeper penetration into the laws of their structure and mechanisms of change.

“The idea of ​​evolution, development in chemistry arose, did not crystallize immediately. Initially, it blurred, dissolved in general ideas about changes, transformations of substances. Until now, chemistry is often considered as the science of the composition, structure and properties of chemical compounds. "Chemistry can be defined as the science of substances - their structure, properties and reactions, as a result of which some substances turn into others," L. Polling and P. Polling believe. According to Yu.A. Zhdanov, at the present time" it can be called the science of the atomic and molecular history of natural and artificial bodies. This history includes the cosmic circulation of substances on the Earth and in its shells, on other planets, in the interstellar medium, where conditions allow the existence of molecular structures. But in endless cycles and cycles, we fix a very definite direction, which consists in the progressive evolution of the chemical form of motion.

The idea of ​​the transition of chemical knowledge to the evolutionary paradigm in its most abstract aspect is associated with the general philosophical concept of development as an endless ascent from the lowest to the highest, the growth of the richness of the content of objects and phenomena. This interpretation of the doctrine of development is based on a large ensemble of facts from all fields. scientific knowledge- physics, chemistry, biology, social sciences. The facts show, for example, that in the part of the Universe known to us, there is a pronounced tendency of material objects to become more complex, dominating over the tendencies of degradation and disintegration. According to the calculations of G. Kastler and L. Blumenfeld, in the case of an equal probability of the processes of simplification and complication of matter, the probability of the emergence of life from amino acids, pyrimidines, purines, polyphosphates, sugars, etc. in 2 times 10 to the 9th power of the Earth's evolution would be 10 to the minus 255th power, or even 10 to the minus 800th power, making this event essentially impossible. From the point of view of the level of quantum mechanical processes, the probability of the appearance of life turns out to be practically equal to zero. Thus, the direction of the process of development of matter as a whole from the lowest to the highest, from the simple to the complex, should be recognized as an objective regularity, the study of which becomes one of the main tasks of scientific knowledge at a fairly high level of its development. It is this stage that has now been reached by chemical science.

There are a number of approaches to unraveling the mechanisms by which a chemical develops. So, N.A. Budreiko argues that the sequence of qualitative and quantitative changes in the homologous series of organic compounds (saturated hydrocarbons, alcohols, acids, etc.) already expresses the process of development of substances of these classes. However, a more detailed consideration of the nature of these processes shows that the phenomena of homology cannot be taken as an accurate and representative model of chemical evolution. The quantitative addition of atoms in organic molecules is not, strictly speaking, a real development, since the progressive evolution of matter does not proceed, for example, from formic acid to melissa. “Individual substances of this class of homologues (for example, formic, acetic, propionic, etc. acids) undoubtedly represent an internal unity, but between them there is no genetic connection, connection of origin. Of course, it is possible, say, to obtain another from one acid, but these transitions are multiple, arbitrary and do not contain any internal line of development. The periodic law of D.I. Mendeleev. However, this evolutionary content is present in it in a latent, implicit form, since the periodicity in the repetition of the properties of the elements in itself is not yet a direct manifestation of progressive development (which is not at all directed in a primitive way from hydrogen to transuranium elements). In modern chemistry, other laws are also beginning to be formulated that more directly and directly describe the process of development - for example, the law of the increase in absolute catalytic activity in the theory of self-development of open catalytic systems by A.P. Rudenko, which will be discussed below.

A promising way to study the processes of chemical evolution is based on the analysis of the reactivity chemical substances as the most important manifestation of the nature of a chemical object.

Reactivity chemical elements(that is, their ability to react with other substances) includes two sides: quantitative and qualitative. The quantitative side of reactivity is the ease and speed of bond formation, as well as the number of atoms that a given element can integrate. The qualitative side is expressed in the variety of different chemical elements with which a given element can react, and the variety of compounds formed by them. The reactivity of one and the same element can be evaluated in different ways, depending on the point of view - qualitative or quantitative - we will approach it. So, from a quantitative point of view, fluorine has the greatest reactivity: it easily and quickly reacts with many substances, for example, it is the only element that oxidizes oxygen. Other halogens have almost the same activity, all of them are quantitatively much more active than organogenic elements. However, the compounds that form halogens, for the most part, turn out to be low molecular weight and have a weak reactivity, which limits the possibilities of further transformations. Organogenic elements, on the contrary, form a huge number of high-molecular and very active compounds. This is primarily due to the nature of carbon atoms, their unique ability to form complex branched chains, to have different degrees of oxidation within the same molecule. Because of this, they can create extremely complex organic substances. Consequently, from a qualitative point of view, carbon is superior in reactivity to all other chemical elements.

The qualitative side of reactivity is expressed not only in the directly obtained products, but also in the entire set of remote, final results of the reaction. In evaluating the reactivity of chemical substances, therefore, it is necessary to take into account the entire range of possibilities for further transformations that they have. Considered in this aspect, the reactivity acts as an indicator of the possibilities for further development associated with a particular chemical element (compound), as its evolutionary potential, or development potential. In terms of its evolutionary potential, the reactivity of organogenic elements far exceeds the reactivity of all other elements. Only carbon compounds, which have the greatest evolutionary potential, are able to take the chemical form of matter beyond its own limits and become the basis for the emergence of life. The main "rival" of carbon - silicon, which is sometimes credited with the hypothetical ability to create a chemical structure for "silicon life" in the Universe, cannot form a stable analogue of even the simplest acetic acid. The possibility of the emergence of silicon-based substances comparable in complexity to proteins and nucleic acids seems to be more fantastic than real in modern chemistry.

The concept of evolutionary potential serves as a concretization, a further deepening of the concept of reactivity from the point of view of development theory. The evolutionary potential of a chemical element or compound is the inner, deep side of its reactivity, which characterizes the fund of possibilities for further change and development. This concept is analogous to the concepts of evolutionary potential in physical, biological and social sciences. In the processes of change of any form of matter, the reduction of the evolutionary potential indicates that this direction of development is not the main, mainline, but a dead end. Thus, in chemistry, the damping of the evolutionary potential is observed in homological rows, the higher members of which (stearin, wax, paraffin) become extremely similar to each other in terms of chemical inertness. The homological series with its strict periodicity leads, according to Yu.A. Zhdanov, into the "chemical impasse". The most evolutionarily promising are not giant monotonic chains, but reactions of a different kind occurring in colloidal solutions and catalytic systems, to which we will return below.

In chemistry, one of the general patterns material world - the uneven distribution of the intensity of the process of development in space and time. The predominance of a progressive direction of development in living nature does not mean that all biological species in all epochs evolve with the same intensity. The idea of ​​social progress also does not imply that all human individuals and all social structures are constantly in a state of progressive development. Similarly, modern chemistry discovers two essentially different types of reactions in nature. The first of them does not directly include the processes of evolution of substances, the second, on the contrary, lays the foundation for evolutionary changes.

The first group of reactions is characterized by a radical change in the nature of the reacting molecule, its transformation into a completely new state. Hegel called such processes a movement from "one" to "another" - the old quality is simply lost here, and not accumulated, not "removed". Such reactions are typical for not organic matter(acid and alkali turn into salt, oxygen and hydrogen form water), but they are also found in organic chemistry. At the same time, among organic compounds, processes are becoming more common, in which the molecule does not disappear completely, but is only modified, retaining some features of the original type. This occurs in reactions of substitution of one atom in a molecule for another, in tautomeric rearrangements, in the racemization of optically active compounds (racemization is the appearance of such a mixture of optically active isomers active substance, which loses optical activity). In fact, in these cases, a feature begins to form, which was fully developed later, in the biological form of matter - a stable individuality arises that is able to preserve itself in the course of chemical transformations. It is especially important that organic molecules under external influence, they may not change chemically at all, but only pass into another state as a result of redistribution of energy, excitation, rotations of individual groups, reversible migration of some atoms, formation of temporary interatomic bonds, etc.

Thus, the chemical individual acquires the ability to change his nature while preserving himself. At this stage of the development of matter, the dialectical process of negation of negation becomes clearly visible. Weak and ephemeral physical forces, manifesting themselves during the interaction of particles and only slightly modifying the molecule while maintaining its chemical structure, accumulate in macromolecules and their complexes. These forces form the specific structure of the living, including enzyme-substrate aggregates, intermolecular formations of nucleoproteins, glycolepids, complementary correspondences in the DNA double helix, interactions of DNA, RNA and proteins. All these weak physical interactions are determined by hydrogen bonds, polar, dipole-dipole and van der Waals forces, which precede the chemical process, prepare it, but do not yet exhaust it.

chemistry natural science evolutionary matter

According to most scientists (primarily astronomers and geologists), the Earth formed as a celestial body about 5 billion years ago. by condensation of particles of a gas and dust cloud rotating around the Sun.

Under the influence of compressive forces, the particles from which the Earth is formed release a huge amount of heat. Thermonuclear reactions begin in the bowels of the Earth. As a result, the Earth gets very hot. Thus, 5 billion years ago The Earth was a hot ball rushing through outer space, the surface temperature of which reached 4000-8000°C (Fig. 2.4.1.1).

Gradually, due to the radiation of thermal energy into outer space, the Earth begins to cool. About 4 billion years ago The earth cools so much that a hard crust forms on its surface; at the same time, light, gaseous substances escape from its bowels, rising up and forming the primary atmosphere. The composition of the primary atmosphere was significantly different from the modern one. Apparently, there was no free oxygen in the atmosphere of the ancient Earth, and its composition included substances in a reduced state, such as hydrogen (H 2), methane (CH 4), ammonia (NH 3), water vapor (H 2 O ), and possibly also nitrogen (N 2), carbon monoxide and carbon dioxide (CO and CO 2).

The reducing nature of the Earth's primary atmosphere is extremely important for the origin of life, since substances in a reduced state are highly reactive and, under certain conditions, are able to interact with each other, forming organic molecules. The absence of free oxygen in the atmosphere of the primary Earth (practically all of the Earth's oxygen was bound in the form of oxides) is also an important prerequisite for the emergence of life, since oxygen easily oxidizes and thereby destroys organic compounds. Therefore, in the presence of free oxygen in the atmosphere, the accumulation of a significant amount of organic matter on the ancient Earth would have been impossible.

About 5 billion years ago- the origin of the earth celestial body; surface temperature - 4000-8000°С

About 4 billion years ago - formation earth's crust and primary atmosphere

At 1000°C- synthesis of simple organic molecules begins in the primary atmosphere

The energy for synthesis is given by:

The temperature of the primary atmosphere is below 100 ° C - the formation of the primary ocean -

Synthesis of complex organic molecules - biopolymers from simple organic molecules:

simple organic molecules - monomers

complex organic molecules - biopolymers

Rice. 2.1. Main stages of chemical evolution

When the temperature of the primary atmosphere reaches 1000°C, the synthesis of simple organic molecules begins in it, such as amino acids, nucleotides, fatty acids, simple sugars, polyhydric alcohols, organic acids and others. Energy for synthesis is supplied by lightning discharges, volcanic activity, hard cosmic radiation, and, finally, ultraviolet radiation from the Sun, from which the Earth is not yet protected by an ozone screen, and scientists consider ultraviolet radiation to be the main source of energy for abiogenic (i.e., passing without the participation of living organisms) the synthesis of organic substances.

The recognition and wide dissemination of the theory of A.I. Oparin was greatly facilitated by the fact that the processes of abiogenic synthesis of organic molecules are easily reproduced in model experiments.

The possibility of synthesizing organic substances from inorganic substances has been known since the beginning of the 19th century. Already in 1828, the outstanding German chemist F. Wöhler synthesized an organic substance - urea from inorganic - ammonium cyanate. However, the possibility of abiogenic synthesis of organic substances under conditions close to those of the ancient Earth was first shown in the experiment of S. Miller.

In 1953, a young American researcher, a graduate student at the University of Chicago, Stanley Miller, reproduced in a glass flask with electrodes soldered into it the primary atmosphere of the Earth, which, according to scientists of that time, consisted of hydrogen, methane CH 4, ammonia NH, and water vapor H 2 0 (Fig. 2.4.1.2). Through this gas mixture, S. Miller passed electric discharges simulating thunderstorms for a week. At the end of the experiment, α-amino acids (glycine, alanine, asparagine, glutamine), organic acids (succinic, lactic, acetic, glycocolic), γ-hydroxybutyric acid and urea were found in the flask. When repeating the experiment, S. Miller managed to obtain individual nucleotides and short polynucleotide chains of five to six links.

Rice. 2.2. Installation by S. Miller

In further experiments on abiogenic synthesis conducted by various researchers, not only electrical discharges were used, but also other types of energy characteristic of the ancient Earth - cosmic, ultraviolet and radioactive radiation, high temperatures inherent in volcanic activity, as well as a variety of gas mixtures that mimic the primary atmosphere. As a result, almost the entire spectrum of organic molecules characteristic of living things was obtained: amino acids, nucleotides, fat-like substances, simple sugars, organic acids.

Moreover, abiogenic synthesis of organic molecules can also occur on Earth at the present time (for example, in the course of volcanic activity). At the same time, not only hydrocyanic acid HCN, which is a precursor of amino acids and nucleotides, but also individual amino acids, nucleotides, and even such complex organic substances as porphyrins can be found in volcanic emissions. Abiogenic synthesis of organic substances is possible not only on Earth, but also in outer space. The simplest amino acids are found in meteorites and comets.

When the temperature of the primary atmosphere dropped below 100 ° C, hot rains fell on the Earth and the primary ocean appeared. With streams of rain, abiogenically synthesized organic substances entered the primary ocean, which turned it, but in the figurative expression of the English biochemist John Haldane, into a dilute "primary soup". Apparently, it is in the primary ocean that the processes of formation from simple organic molecules - monomers of complex organic molecules - biopolymers begin (see Fig. 2.4.1.1).

However, the processes of polymerization of individual nucleoside, amino acids and sugars are condensation reactions, they proceed with the elimination of water, therefore, the aqueous medium does not contribute to polymerization, but, on the contrary, to the hydrolysis of biopolymers (i.e., their destruction with the addition of water).

The formation of biopolymers (in particular, proteins from amino acids) could take place in the atmosphere at a temperature of about 180°C, from where they were washed into the primary ocean with atmospheric precipitation. In addition, it is possible that on the ancient Earth, amino acids were concentrated in drying up reservoirs and polymerized in a dry form under the influence of ultraviolet light and the heat of lava flows.

Despite the fact that water promotes the hydrolysis of biopolymers, the synthesis of biopolymers in a living cell occurs precisely in an aqueous medium. This process is catalyzed by special catalytic proteins - enzymes, and the energy necessary for synthesis is released during the breakdown of adenosine triphosphoric acid - ATP. It is possible that the synthesis of biopolymers in the aquatic environment of the primary ocean was catalyzed by the surface of certain minerals. It has been experimentally shown that a solution of the amino acid alanine can polymerize in an aqueous medium in the presence of a special type of alumina. In this case, the peptide polyalanine is formed. The polymerization reaction of alanine is accompanied by the breakdown of ATP.

The polymerization of nucleotides is easier than the polymerization of amino acids. It has been shown that in solutions with a high salt concentration, individual nucleotides spontaneously polymerize, turning into nucleic acids.

The life of all modern living beings is a process of continuous interaction of the most important biopolymers of a living cell - proteins and nucleic acids.

Proteins are the “working molecules”, “engineer molecules” of a living cell. Describing their role in metabolism, biochemists often use such figurative expressions as "the protein works", "the enzyme leads the reaction." The most important function of proteins is catalytic. As you know, catalysts are substances that accelerate chemical reactions, but they do not enter into the final products of the reaction. Tanks-catalysts are called enzymes. Enzymes in bend and thousands of times accelerate metabolic reactions. Metabolism, and hence life without them, is impossible.

Nucleic acids- these are "molecules-computers", molecules - keepers hereditary information. Nucleic acids do not store information about all the substances of a living cell, but only about proteins. It is enough to reproduce in the daughter cell the proteins characteristic of the mother cell so that they accurately recreate all the chemical and structural features mother cell, as well as its inherent nature and rate of metabolism. Nucleic acids themselves are also reproduced due to the catalytic activity of proteins.

Thus, the mystery of the origin of life is the mystery of the emergence of the mechanism of interaction between proteins and nucleic acids. What information does modern science have about this process? What molecules were the primary basis of life - proteins or nucleic acids?

Scholars believe that despite key role proteins in the metabolism of modern living organisms, the first "living" molecules were not proteins, but nucleic acids, namely ribonucleic acids (RNA).

In 1982, American biochemist Thomas Check discovered the autocatalytic properties of RNA. He experimentally showed that in a medium containing a high concentration of mineral salts, ribonucleotides spontaneously (spontaneously) polymerize, forming polynucleotides - RNA molecules. On the initial polynucleotide chains of RNA, as on a template, RNA copies are formed by pairing of complementary nitrogenous bases. The RNA template copying reaction is catalyzed by the original RNA molecule and does not require the participation of enzymes or other proteins.

What happened next is fairly well explained by what might be called "natural selection" at the molecular level. During self-copying (self-assembly) of RNA molecules, inaccuracies and errors inevitably arise. The erroneous RNA copies are copied again. When copying again, errors may occur again. As a result, the population of RNA molecules in a certain part of the primary ocean will be heterogeneous.

Since RNA decay processes are also taking place in parallel with the synthesis processes, molecules with either greater stability or better autocatalytic properties will accumulate in the reaction medium (i.e., molecules that copy themselves faster, “multiply” faster).

On some RNA molecules, as on a matrix, self-assembly of small protein fragments - peptides can occur. A protein "sheath" is formed around the RNA molecule.

Along with autocatalytic functions, Thomas Check discovered the phenomenon of self-splicing in RNA molecules. As a result of self-splicing, RNA regions that are not protected by peptides are spontaneously removed from RNA (they are, as it were, “cut out” and “ejected”), and the remaining RNA regions encoding protein fragments “grow together”, i.e. spontaneously combine into a single molecule. This new RNA molecule will already code for a large complex protein (Figure 2.4.1.3).

Apparently, initially protein sheaths performed primarily a protective function, protecting RNA from destruction and thereby increasing its stability in solution (this is the function of protein sheaths in the simplest modern viruses).

Obviously, at a certain stage of biochemical evolution, RNA molecules, which encode not only protective proteins, but also catalytic proteins (enzymes), sharply accelerating the rate of RNA copying, gained an advantage. Apparently, this is how the process of interaction between proteins and nucleic acids, which we now call life, arose.

In the process of further development, due to the appearance of a protein with the functions of an enzyme - reverse transcriptase, on single-stranded RNA molecules, molecules of deoxyribonucleic acid (DNA) consisting of two strands began to be synthesized. The absence of an OH group in the 2" position of deoxyribose makes DNA molecules more stable with respect to hydrolytic cleavage in slightly alkaline solutions, namely, the reaction of the medium in primary reservoirs was slightly alkaline (this reaction of the medium was also preserved in the cytoplasm of modern cells).

Where did development take place? complex process interactions between proteins and nucleic acids? According to the theory of A.I. Oparin, the so-called coacervate drops became the birthplace of life.

Rice. 2.3. Hypothesis of the occurrence of the interaction of proteins and nucleic acids:

a) in the process of self-copying of RNA, errors accumulate (1 - nucleotides corresponding to the original RNA; 2 - nucleotides that do not correspond to the original RNA - errors in copying); b) due to its physicochemical properties, amino acids “stick” to a part of the RNA molecule (3 - RNA molecule; 4 - amino acids), which, interacting with each other, turn into short protein molecules - peptides.

As a result of self-splicing inherent in RNA molecules, the parts of the RNA molecule that are not protected by peptides are destroyed, and the remaining ones "grow" into a single molecule encoding a large protein.

The result is an RNA molecule covered with a protein sheath (the most primitive modern viruses, for example, the tobacco mosaic virus, have a similar structure)

The phenomenon of coacervation consists in the fact that under certain conditions (for example, in the presence of electrolytes), macromolecular substances are separated from the solution, but not in the form of a precipitate, but in the form of a more concentrated solution - coacervate. When shaken, the coacervate breaks up into separate small droplets. In water, such drops are covered with a hydration shell that stabilizes them (a shell of water molecules) - fig. 2.4.1.4.

Coacervate drops have some semblance of metabolism: under the influence of purely physical and chemical forces, they can selectively absorb certain substances from the solution and release their decay products into the environment. Due to the selective concentration of substances from the environment, they can grow, but when they reach a certain size, they begin to "multiply", budding small droplets, which, in turn, can grow and "bud".

The coacervate droplets formed as a result of the concentration of protein solutions during mixing under the action of waves and wind can be covered with a shell of lipids: a single shell resembling soap micelles (with a single detachment of a droplet from the water surface covered with a lipid layer), or a double shell resembling cell membrane(when a drop covered with a single-layer lipid membrane falls again onto a lipid film covering the surface of a reservoir - Fig. 2.4.1.4).

The processes of the emergence of coacervate droplets, their growth and "budding", as well as "clothing" them with a membrane from a double lipid layer are easily modeled in the laboratory.

For coacervate droplets, there is also a process of "natural selection" in which the most stable droplets remain in solution.

Despite the outward resemblance of coacervate drops to living cells, coacervate drops lack the main sign of a living thing - the ability for accurate self-reproduction, self-copying. Obviously, the precursors of living cells were such coacervate drops, which included complexes of replicator molecules (RNA or DNA) and the proteins they encode. It is possible that RNA-protein complexes existed for a long time outside coacervate droplets in the form of the so-called “free-living gene”, or it is possible that their formation took place directly inside some coacervate droplets.

Figure 2.4. Possible way of transition from coacervate drops to primitive flares:

a) the formation of a coat; 6) stabilization of coacervate drops in aqueous solution; c) - formation of a double lipid layer around the drop, similar to a cell membrane: 1 - coacervate drop; 2 - monomolecular layer of lipid on the surface of the reservoir; 3 - formation of a single lipid layer around the drop; 4 - formation of a double lipid layer around the drop, similar to a cell membrane; d) - a coacervate drop surrounded by a double lipid layer, with a protein-nucleotide complex included in its composition - a prototype of the first living cell

Extremely complex, not fully understood modern science From a historical point of view, the process of the emergence of life on Earth was extremely fast. For 3.5 billion years, the so-called. chemical evolution ended with the appearance of the first living cells and began biological evolution.

Chemical evolution is a process of irreversible changes leading to the emergence of new chemical compounds - products that are more complex and highly organized compared to the original substances. These processes began to be actively and purposefully investigated in the 1970s. in connection with the study of the problem of ever-complicating chemical processes to a level that contributed to the emergence of living matter on Earth. Interest in these processes goes back to long-standing attempts to understand how organic, and then life, arises from inorganic matter. The first to realize the high orderliness and efficiency of chemical processes in living organisms was the founder of organic chemistry Y.Ya. Berzelius (late XVIII - early XIX in.). He established that the basis of the laboratories of a living organism is biocatalysis. Great importance catalytic experience of wildlife was given in the XX century. So, Academician N.N. Semenov considered the chemical processes occurring in the tissues of plants and animals as a kind of " chemical production» Wildlife.

Let us briefly consider the stages of chemical evolution. Probably, it should be recognized that it began with the appearance of the simplest carrier - the atom. According to the concept big bang, existing now, the chemical elements arose in the process of the evolution of the Universe from a superdense and superhot state to modern world stars and galaxies. It is assumed that the simplest atoms (or rather, their nuclei) of hydrogen were the first to form. Approximately 1 s after the Big Bang, the density of matter decreased to 1 t/cm 3 , the temperature to 100 billion K, and the diameter increased to 1500 billion km. The substance was in the state of a fully ionized plasma, consisting of nucleons (protons and neutrons) and electrons. After another 10 s, when the temperature dropped to 10 billion K, conditions appeared for the flow nuclear reaction the formation of deuterons - nuclei of deuterium (heavy hydrogen).

However, at this temperature, the equilibrium of this reaction is strongly shifted to the left (it shifts to the right only at a temperature of 1 billion K - approximately 100 s after the Big Bang), and deuterons could not accumulate, since under these conditions they turn into helium nuclei (this scheme is quite satisfactory explains the amount of helium in our universe). At the prestellar stage of the development of matter, the nuclei of other chemical elements are not formed, since the density and temperature of the expanding Universe are rapidly falling. In this case, the process of formation of 4 He (the figure at the top left is the relative atomic mass, i.e. the mass of the atom, expressed in atomic mass units, which is 1/12 of the mass of the carbon isotope with a mass number of 12-1.6605655 (86) 10 "27 kg), starting approximately 2 minutes after the Big Bang, stops by the end of the 4th minute.When the Universe cools down to a temperature of 3500 K (after about 1 million years), helium nuclei and the remaining hydrogen nuclei recombine with electrons: atoms are formed helium and hydrogen - the source material for interstellar gas and star systems.

Further synthesis of chemical elements continues in the interiors of stars as the temperature rises. In the process of condensation of interstellar gas consisting of hydrogen and helium into a protostar, as a result of gravitational compression, the temperature rises and the reaction of formation of helium from hydrogen again becomes possible. This stage is characterized by temperatures not exceeding 20 106 K.

After helium nuclei, 12 C and 16 O nuclei are the most stable. The thermonuclear epoch of the formation of such nuclei (T< 100 млн К) наступает после того, как на первом этапе истощается, «выгорает» водород. В эту эпоху в плотных выгоревших ядрах звезд-гигантов возможно непосредственное образование углерода и кислорода (не атомов, а ядер). Дальнейшее слияние ядер гелия приводит к образованию 20 Ne, 24 Mg и т.п. Более поздняя ядерная эпоха, когда обеспечивается температура до 1 млрд. К, характеризуется «горением» углерода. При этом образуются ядра вплоть до 27 А1 и 28 Si. Выше 30 млрд. К в реакцию вступают более тяжелые ядра, начиная с кремния 32 Si. В условиях складывающегося при этом термодинамического равновесия синтезируются элементы вплоть до железа и атомы близких ему элементов, ядра которых являются самыми стабильными ядрами. При этом достигается минимум энергии всей системы, и более тяжелые ядра не синтезируются. Получение элементов с большими атомными номерами осуществляется по другому механизму - последовательный захват ядрами нейтронов и последующий 3-распад. В подобных процессах в качестве самого тяжелого может получиться нуклид l81 Bi. Ядра, более тяжелые, чем 181 Bi, синтезируются во время взрывов новых и сверхновых звезд в условиях огромной плотности нейтронных потоков, когда возможен захват ядрами нейтронов не по одному, а группами.

It can be assumed with a high degree of probability that several stages of nuclear fusion have changed in the solar system. Comparison of the chemical composition of the Sun and the chemical composition of stellar matter allows us to conclude that all the processes of nuclear synthesis described above took place in the Solar System, and the initial mass of the star formed in our section of the Galaxy exceeded the critical one (equal to 1.44 solar masses), and it turned out to be unstable. Under the influence of gravitational attraction, the protostar contracted, its temperature increased, providing the first stages of nuclear fusion. The energy released in this case turned out to be too great, as a result of which, after a while, an explosion occurred and the nuclei of the heaviest elements were formed. The mass of the star decreased due to the ejection of matter. This process was repeated several times until the mass of the central massive star was below the critical limit. Such a mechanism provides a time interval sufficient for chemical, geological-geographical and biological evolution.

Currently, many researchers believe that the planets solar system formed from solar matter ejected from the sun when it went supernova. The cooling of the disc-shaped gaseous nebula that formed around the Sun made it possible to combine atoms into molecules, i.e. chemical evolution began.

Molecules could not form at stellar temperatures, when most atoms exist in the form of multiply charged ions (for example, in the solar corona at 1 million K, iron atoms are Fe 13+ ions). Diatomic molecules have been found in the spectra of only the coldest stars with a surface temperature of 2000-3000 K (oxides of Al, Mg, Ti, Zr, C, Si and some other diatomic molecules with the strongest chemical bond). At the same time, in interstellar space there is a large number of molecules, including quite complex ones. It is assumed that the composition of these molecules corresponds to the composition of the first molecules formed as a result of the cooling of stellar matter. Other molecules have also been found, but in much smaller quantities.

When the temperature of the protoplanetary nebula dropped to 1000-1800 K, they began to condense, i.e. become liquid and solid, the most refractory substances, in particular, droplets of iron were formed, and subsequently silicates (salts of silicic acids).

At temperatures of 400–1000 K, other metals and their compounds with sulfur and oxygen condensed. The frozen drops of silicate material in the form of chondrules (small spherical bodies) formed, apparently, during subsequent condensation, many asteroids - the primary bodies of chondrite meteorites. It can be assumed that as a result of the differentiation of the primary gas under the influence of the solar wind (outflow of the plasma of the solar corona into interplanetary space) and the temperature gradient, the atoms of the lightest elements were thrown to the periphery of the solar system and planets located closer to the Sun earth type arose by thickening the highest-temperature fraction with a high iron content.

With the formation of the Earth as a planet, the evolution of the Earth began to influence the chemical evolution. This influence was expressed (and is currently expressed) in changing the concentration distribution of chemical elements in the body of the Earth and in its shells (in the atmosphere, hydrosphere, crust, mantle, core), as well as in creating conditions (temperature, pressure) for the formation of new substances .

Of course, the opposite effect also took place. The formation of new substances and the emergence of opportunities for new chemical processes caused the formation of new geological formations, such as sedimentary rocks. Thus, geological and chemical evolution proceed to a large extent jointly, mutually influencing each other. Chemical evolution has led to the emergence of life. This happened due to the development not of substances, but of chemical systems and processes occurring in them.

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Chemical evolution

Also, these terms denote the theory of the emergence and development of those molecules that are of fundamental importance for the emergence and development of living matter.

Everything that is known about the chemistry of matter makes it possible to limit the problem of chemical evolution to the framework of the so-called "water-carbon chauvinism", postulating that life in our Universe is presented in the only possible way: as a "mode of existence of protein bodies", feasible due to a unique combination of polymerization the properties of carbon and the depolarizing properties of the liquid-phase aqueous medium, as both necessary and/or sufficient (?) conditions for the emergence and development of all life forms known to us. This implies that, at least within one formed biosphere, there can be only one code of heredity common to all living beings of a given biota, but so far there remains open question whether there are other biospheres outside the Earth and whether other variants of the genetic apparatus are possible.

It is also unknown when and where chemical evolution began. Any dates are possible after the end of the second cycle of star formation, which occurred after the condensation of the products of explosions of primary supernovae, supplying heavy elements (with atomic mass over 26). The second generation of stars, already with planetary systems enriched heavy elements, which are necessary for the implementation of chemical evolution appeared 0.5-1.2 billion years after the Big Bang. Under certain quite probable conditions, almost any environment can be suitable for launching chemical evolution: the depths of the oceans, the bowels of planets, their surfaces, protoplanetary formations and even clouds of interstellar gas, which is confirmed by the widespread detection in space by astrophysics methods of many types of organic substances - aldehydes, alcohols, sugars, and even the amino acid glycine, which together can serve as the starting material for chemical evolution, which has as its end result the emergence of life.

Methodology for the study of chemical evolution (theory)

The study of chemical evolution is complicated by the fact that at present knowledge about the geochemical conditions of the ancient Earth is not sufficiently complete.

Therefore, in addition to geological data, astronomical data are also involved. Thus, the conditions on Venus and Mars are considered as close to those on the Earth at various stages of its evolution.

The main data on chemical evolution were obtained as a result of model experiments, during which it was possible to obtain complex organic molecules by simulating various chemical compositions atmosphere, hydrosphere and lithosphere and climatic conditions.

Based on the available data, a number of hypotheses have been put forward about the specific mechanisms and direct driving forces of chemical evolution.

Abiogenesis

Abiogenesis - the formation of organic compounds common in wildlife, outside the body without the participation of enzymes.

In a broad sense, abiogenesis is the emergence of living things from non-living things, that is, the initial hypothesis modern theory origin of life

There is also a theory of hypercycles; according to which the first manifestations of life were, respectively, in the form of hypercycles - a complex of complex catalytic reactions, the output products of which are catalysts for subsequent reactions.

In 2008, American biologists took an important step towards understanding initial stages the origin of life. They managed to create a "protocell" with a shell of simple lipids and fatty acids, capable of drawing in activated nucleotides from the environment - the "building blocks" necessary for DNA synthesis. In 2011, Japanese scientists reported that they had succeeded in creating a synthetic cell with a shell and DNA elements inside, capable of reproducing when the "primordial soup" was heated to 94 degrees Celsius.

Evolution

Biological evolution is a natural process of development of living nature, accompanied by a change in the genetic composition of populations, the formation of adaptations, speciation and extinction of species, the transformation of ecosystems and the biosphere as a whole.

There are several evolutionary theories explaining the mechanisms underlying evolutionary processes. AT this moment generally accepted is the synthetic theory of evolution (STE), which is a development of Darwin's theory. STE makes it possible to explain the relationship between the substrate of evolution (genes) and the mechanism of evolution (natural selection). Within the framework of STE, evolution is a process of changing hereditary traits in populations of organisms over a period of time exceeding the life span of one generation.

Charles Darwin was the first to formulate the theory of evolution by natural selection. Evolution by natural selection is a process that follows from three facts about populations: 1) more offspring are born than can survive; 2) different organisms have different traits, which leads to differences in survival and the likelihood of having offspring; 3) these traits are inherited. Thus, in the next generation, the number of such individuals will increase, the features of which contribute to survival and reproduction in this environment. Natural selection- the only known cause of adaptations, but not the only reason evolution. Non-adaptive causes include genetic drift, gene flow, and mutations.

Despite the ambiguous perception in society, the fact of evolution is one of the most proven in biology. Discoveries in evolutionary biology have had a huge impact not only on the traditional fields of biology, but also on other academic disciplines such as anthropology and psychology.

Introduction

Evolution occurs over a period of time exceeding the lifetime of one generation and consists in changing the inherited traits of an organism. The first step in this process is to change the allele frequencies of genes in a population. In an ideal population, in which there is no environmental influence, drift and gene flow, according to the Hardy-Weinberg law, the allele frequency will be unchanged from generation to generation. Mutations increase variability in a population due to the emergence of new allelic variants of genes - mutational variability. In addition to mutational, there is also combinative variability due to recombination, but it does not lead to changes in allele frequencies, but to their new combinations. Another factor leading to changes in allele frequencies is gene flow.

Two other evolutionary factors, natural selection and genetic drift, "sort out" the variability created by mutations and gene flow, leading to the establishment of a new allele frequency in the population. Genetic drift is a probabilistic process of changing gene frequencies and is most pronounced in relatively small populations. Drift can lead to the complete disappearance of certain alleles from the population. Natural selection is the main creative factor in evolution. Under its influence, individuals with a certain phenotype (and a certain set of hereditary traits) will be more successful than others, that is, they will have a higher probability of surviving and leaving offspring. Thus, the proportion of such organisms in the population that have hereditary traits with a selective advantage will increase. The mutual influence of drift and natural selection is difficult to unambiguously assess, but in general it probably depends on the size of the population and the intensity of selection. In addition to the above factors, horizontal gene transfer can also be important, which can lead to the appearance of completely new genes for a given organism.

Natural selection increases the fitness of organisms, leading to the formation of adaptations. Evolutionary processes proceeding for a long time can lead both to the formation of new species and their further divergence, and to the extinction of entire species.

Heredity

Heredity is the property of organisms to repeat in a number of generations similar types of metabolism and individual development in general. The evolution of organisms occurs through changes in the hereditary characteristics of the organism. An example of a hereditary trait in a person is the brown color of the eyes, inherited from one of the parents. Hereditary traits are controlled by genes. The totality of all the genes of an organism forms its genotype.

Heritability can also occur on a larger scale. For example, ecological inheritance through niche construction. Thus, the descendants inherit not only genes, but also the ecological features of the habitat created by the activity from the ancestors. Other examples of inheritance not under the control of genes are the inheritance of cultural traits and symbiogenesis.

Variability

The phenotype of an organism is determined by its genotype and environmental influences. A significant part of the phenotype variations in populations is caused by differences in their genotypes. In STE, evolution is defined as the change over time in the genetic structure of populations. The frequency of one of the alleles changes, becoming more or less common among other forms of this gene. The operating forces of evolution lead to changes in the frequency of the allele in one direction or the other. The change disappears when new allele reaches the fixation point - completely replaces the ancestral allele or disappears from the population.

Variation is made up of mutations, gene flow, and recombination of genetic material. Variation is also increased by gene exchanges between different types such as horizontal gene transfer in bacteria, hybridization in plants. Despite the constant increase in variability due to these processes, most of the genome is identical in all representatives of this species. However, even comparatively slight changes in the genotype can cause huge differences in the phenotype, for example, the genomes of chimpanzees and humans differ by only 5%.

Mutations

Random mutations constantly occur in the genomes of all organisms. These mutations create genetic variation. Mutations are changes in the DNA sequence. They are caused by radiation, viruses, transposons, mutagens, and errors that occur during DNA replication or meiosis. Mutations may have no effect, may change the gene product, or interfere with its function. Studies done on Drosophila have shown that if a mutation changes a protein produced by a gene, then in about 70% of cases this will have harmful effects, and in other cases, neutral or weakly positive effects. To reduce the negative effect of mutations in cells, there are DNA repair mechanisms. The optimal mutation rate is a balance between high level harmful mutations and the cost of maintaining the repair system. RNA viruses have a high level of mutability, which seems to be an advantage in helping to avoid defensive responses of the immune system.

Mutations can involve large sections of chromosomes. For example, with duplication, which causes the appearance of additional copies of a gene in the genome. These copies become the basic material for the emergence of new genes. This is important process, as new genes develop within a gene family from a common ancestor.

Recombination

In asexual organisms, genes during reproduction cannot mix with the genes of other individuals. In contrast, in sexually reproducing organisms, offspring receive random mixtures of chromosomes from their parents. This is due to the process of homologous recombination, during which there is an exchange of sections of two homologous chromosomes. During recombination, there is no change in the frequency of alleles, but the formation of their new combinations occurs. Thus, sexual reproduction usually increases hereditary variability and can accelerate the rate of evolution of the organism. However, asexual reproduction is often advantageous and may develop in animals with sexual reproduction. This may allow the two sets of alleles in the genome to diverge to acquire new functions.

Recombination allows even alleles that are close to each other in DNA to be inherited independently. However, the level of recombination is low - about two recombinations per chromosome per generation.

gene flow

Gene flow is the transfer of alleles of genes between populations. The flow of genes can be carried out by the migration of individuals between populations in the case of mobile organisms, or, for example, by the transfer of pollen or seeds in the case of plants. The rate of gene flow is highly dependent on the mobility of organisms.

The extent to which gene flow influences variability in populations is not entirely clear. There are two points of view, one of them is that gene flow can have a significant impact on large population systems, homogenizing them and, accordingly, acting against the processes of speciation; second, that the rate of gene flow is only sufficient to affect local populations.

Mechanisms of evolution

Natural selection

Evolution by natural selection is the process by which mutations are fixed that increase the fitness of organisms. Natural selection is often referred to as a "self-evident" mechanism because it follows from facts such as:

1. Hereditary changes exist in populations of organisms;
2. Organisms produce more offspring than can survive;
3. These offspring differ in that they have different survival rates and ability to reproduce.

Such conditions create competition between organisms for survival and reproduction. Thus, organisms with inherited traits that give them a competitive advantage are more likely to pass them on to their offspring than organisms with inherited traits that do not.

The central concept of the concept of natural selection is the fitness of organisms. Fitness is defined as the ability of an organism to survive and reproduce, which determines the size of its genetic contribution to the next generation. However, the main thing in determining fitness is not total number offspring, but the number of offspring with a given genotype (relative fitness). Natural selection for traits that can vary over a range of values ​​(such as the size of an organism) can be divided into three types:

Description of work

Chemical evolution or prebiotic evolution is the first stage in the evolution of life, during which organic, prebiotic substances arose from inorganic molecules under the influence of external energy and selection factors and due to the deployment of self-organization processes inherent in all relatively complex systems, which are undoubtedly all carbon-containing molecules. .