The most popular among modern scientists is the Oparin-Haldane hypothesis about the origin of life on Earth. According to the hypothesis, life originated from nonliving matter (abiogenically) as a result of complex biochemical reactions.
Provisions
To briefly describe the hypothesis of the origin of life, we should highlight three stages of life formation according to Oparin:
- the appearance of organic compounds;
- formation of polymer compounds (proteins, lipids, polysaccharides);
- the emergence of primitive organisms capable of reproduction.
Rice. 1. Scheme of evolution according to Oparin.
Biogenic, i.e. biological evolution was preceded by chemical evolution, as a result of which complex substances were formed. Their formation was influenced by the oxygen-free atmosphere of the Earth, ultraviolet radiation, and lightning discharges.
Biopolymers arose from organic substances, which formed into primitive forms of life (probionts), gradually being separated by a membrane from external environment. The appearance of nucleic acids in probionts contributed to the transfer of hereditary information and the complication of organization. As a result of long natural selection Only those organisms that were capable of successful reproduction remained.
Rice. 2. Probionts.
Probionts or procells have not yet been obtained experimentally. Therefore, it is not completely clear how a primitive accumulation of biopolymers was able to move from lifeless existence in the broth to reproduction, nutrition and respiration.
Story
The Oparin-Haldane hypothesis has come a long way and has been criticized more than once. The history of the formation of the hypothesis is described in the table.
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Year |
Scientist |
Main events |
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Soviet biologist Alexander Ivanovich Oparin |
The main provisions of Oparin’s hypothesis were first formulated in his book “The Origin of Life”. Oparin suggested that biopolymers (high molecular weight compounds) dissolved in water under the influence of external factors can form coacervate droplets or coacervates. These are put together organic matter, which are conditionally separated from the external environment and begin to maintain metabolism with it. The process of coacervation - stratification of the solution with the formation of coacervates - is the previous stage of coagulation, i.e. sticking together of small particles. It was as a result of these processes that amino acids emerged from the “primary broth” (Oparin’s term) - the basis of living organisms |
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British biologist John Haldane |
Regardless of Oparin, he began to develop similar views on the problem of the origin of life. Unlike Oparin, Haldane assumed that instead of coacervates, macromolecular substances capable of reproduction were formed. Haldane believed that the first such substances were not proteins, but nucleic acids |
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American chemist Stanley Miller |
As a student, he recreated an artificial environment for obtaining amino acids from nonliving matter ( chemical substances). The Miller-Urey experiment simulated Earth conditions in interconnected flasks. The flasks were filled with a mixture of gases (ammonia, hydrogen, carbon monoxide), similar in composition to the early atmosphere of the Earth. In one part of the system there was constantly boiling water, the vapors of which were subjected to electrical discharges (simulating lightning). As it cooled, the steam accumulated in the form of condensate in the lower tube. After a week of continuous experiment, amino acids, sugars, lipids were discovered in the flask |
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British biologist Richard Dawkins |
In his book “The Selfish Gene,” he suggested that the primordial soup did not form coacervate drops, but molecules capable of reproduction. It was enough for one molecule to arise for its copies to fill the ocean |
Rice. 3. Miller's experiment.
Miller's experiment has been repeatedly criticized, and is not fully recognized as a practical confirmation of the Oparin-Haldane theory. The main problem is obtaining from the resulting mixture organic substances that form the basis of life.
What have we learned?
From the lesson we learned about the essence of the Oparin-Haldane hypothesis of the origin of life on Earth. According to the theory, high-molecular substances (proteins, fats, carbohydrates) arose from inanimate matter as a result of complex biochemical reactions under the influence of the external environment. The hypothesis was first tested by Stanley Miller, recreating the conditions of the Earth before the origin of life. As a result, amino acids and other complex substances were obtained. However, how these substances were reproduced remains unconfirmed.
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The hypothesis of the origin of life on Earth, proposed by the famous Russian biochemist Academician A. I. Oparin (1894-1980) and the English biochemist J. Haldane (1892-1964), received the greatest recognition and distribution in the 20th century. The essence of their hypothesis, formulated by them independently of each other in 1924-1928. and developed in subsequent times, boils down to the existence on Earth of a long period of abiogenic formation of a large number of organic compounds. These organic substances saturated the waters of the ancient oceans, forming (according to J. Haldane) the so-called “primary broth”. Subsequently, due to numerous processes of local shallowing and drying out of the oceans, the concentration of the “primary broth” could increase tens and hundreds of times. These processes occurred against the background of intense volcanic activity, frequent lightning discharges in the atmosphere and powerful cosmic radiation. Under these conditions, a gradual complication of molecules of organic substances could occur, the appearance of simple proteins, polysaccharides, lipids, and nucleic acids. Over many hundreds and thousands of years, they could form clumps of organic substances (coacervates). Under the conditions of the Earth's reducing atmosphere, coacervates were not destroyed, they gradually became more complex, and at a certain point in their development the first primitive organisms (probionts) could be formed from them. This hypothesis was accepted and further developed by many scientists different countries, and in 1947, the English scientist John Bernal formulated the hypothesis of biopoiesis. He identified three main stages in the formation of life: 1) abiogenic emergence of organic monomers; 2) formation of biological polymers; 3) development of membrane structures and the first organisms.
Let us briefly consider the processes and stages of biopoiesis.
The first stage of biopoiesis was a series of processes called chemical evolution, which led to the appearance of probionts - the first living beings. Its duration is estimated by different scientists from 100 to 1000 million years. This is the prehistory of life on our planet.
The Earth as a planet arose about 4.5 billion years ago (according to other sources - about 13 billion years ago, but they do not yet have strong evidence). The cooling of the Earth began about 4 billion years ago, and the age of the earth's crust is estimated at about 3.9 billion years. At this point, the ocean and the primary atmosphere of the Earth are also formed. The earth at this time was quite warm due to the release of heat during the solidification and crystallization of crustal components and active volcanic activity. Water for a long time was in a vaporous state, evaporating from the surface of the Earth, condensing in the upper layers of the atmosphere and falling again onto the hot surface. All this was accompanied by almost constant thunderstorms with powerful electrical discharges. Later, reservoirs and primary oceans begin to form. The ancient atmosphere of the Earth did not contain free oxygen and was saturated with volcanic gases, which included oxides of sulfur, nitrogen, ammonia, carbon oxides and dioxides, water vapor and a number of other components. Powerful cosmic radiation and solar radiation (there was no ozone layer in the atmosphere yet), frequent and strong electrical discharges, active volcanic activity, accompanied by the release of large masses of radioactive components, led to the formation of organic compounds such as formaldehyde, formic acid, urea, lactic acid, glycerin, glycine, some simple amino acids, etc. Since there was no free oxygen in the atmosphere, these compounds did not oxidize and could accumulate in warm and even boiling waters and gradually become more complex in structure, forming the so-called “primary broth.” The duration of these processes was many millions and tens of millions of years. This is how the first stage of biopoiesis was realized - the formation and accumulation of organic monomers.
Stage of polymerization of organic monomers
A significant part of the resulting monomers was destroyed under the influence of high temperatures and numerous chemical reactions that took place in the “primary broth.” Volatile compounds passed into the atmosphere and practically disappeared from water bodies. Periodic drying out of water bodies led to a manifold increase in the concentration of dissolved organic compounds. Against a high background chemical activity processes of complication of these compounds occurred in the environment, and they could enter into compounds with each other (condensation reactions, polymerization, etc.). Fatty acids, combining with alcohols, could form lipids and form fatty films on the surface of water bodies. Amino acids could combine with each other to form increasingly complex peptides. Other types of compounds could also be formed - nucleic acids, polysaccharides, etc. The first nucleic acids, as modern biochemists believe, were small RNA chains, since they, like oligopeptides, could be synthesized spontaneously in an environment with a high content of mineral components, without the participation of enzymes . Polymerization reactions could be noticeably activated with a significant increase in the concentration of the solution (drying out of the reservoir) and even in wet sand or when the reservoirs completely dried out (the possibility of such reactions occurring in a dry state was shown by the American biochemist S. Fox). Subsequent rains dissolved molecules synthesized on land and transported them with water currents into reservoirs. Such processes could be cyclic in nature, leading to even greater complexity of organic polymers.
Formation of coacervates
The next stage in the origin of life was the formation of coacervates, that is, large accumulations of complex organic polymers. The causes and mechanisms of this phenomenon are still largely unclear. Coacervates of this period were still a mechanical mixture of organic compounds, devoid of any signs of life. At some point in time, connections arose between RNA molecules and peptides, reminiscent of matrix protein synthesis reactions. However, it is still unclear how RNA came to encode the synthesis of peptides. Later, DNA molecules appeared, which, due to the presence of two helices and the possibility of more accurate (compared to RNA) self-copying (replication), became the main carriers of information about the synthesis of peptides, transferring this information to RNA. Such systems (coacervates) already resembled living organisms, but were not yet such, since they did not have an ordered internal structure, inherent in living organisms, and were not able to reproduce. After all, certain reactions of peptide synthesis can also occur in noncellular homogenates.
The emergence of biological membranes
Ordered biological structures are impossible without biological membranes. Therefore, the next stage in the formation of life was the formation of precisely these structures, isolating and protecting coacervates from environment, turning them into autonomous entities. The membranes could have formed from lipid films that appeared on the surface of water bodies. Peptides brought by rain flows into water bodies or formed in these water bodies could be attached to lipid molecules. When water bodies were agitated or precipitation fell on their surface, bubbles surrounded by membrane-like compounds could appear. For the emergence and evolution of life, those vesicles that surrounded coacervates with protein-nucleotide complexes were important. But such formations were not yet living organisms.
The emergence of probionts - the first self-reproducing organisms
Only those coacervates that were capable of self-regulation and self-reproduction could turn into living organisms. How these abilities arose is also still unclear. Biological membranes provided autonomy and protection to coacervates, which contributed to the emergence of significant orderliness in the biochemical reactions occurring in these bodies. The next step was the emergence of self-reproduction, when nucleic acids (DNA and/or RNA) began not only to ensure the synthesis of peptides, but also with its help to regulate the processes of self-reproduction and metabolism. This is how a cellular structure emerged with metabolism and the ability to reproduce itself. It was these forms that were able to be preserved through the process of natural selection. This is how coacervates turned into the first living organisms - probionts.
The stage of chemical evolution has ended, and the stage of biological evolution of living matter has begun. This happened 3.5-3.8 billion years ago. The appearance of a living cell is the first major aromorphosis in the evolution of the organic world.
The first living organisms were close in structure to prokaryotes, did not yet have a strong cell wall and any intracellular structures (they were covered biological membrane, the internal bends of which performed the functions of cellular structures). Perhaps the first probionts had hereditary material represented by RNA, and genomes with DNA appeared later in the process of evolution. There is an opinion that the further evolution of life came from a common ancestor, from which the first prokaryotes originated. This is what ensured the great similarity in the structure of all prokaryotes, and subsequently eukaryotes.
The impossibility of spontaneous generation of life in modern conditions
The question is often asked: why does the spontaneous generation of living beings not occur at the present time? After all, if living organisms do not appear now, then on what basis can we create hypotheses about the origin of life in the distant past? Where is the criterion for the likelihood of this hypothesis? The answers to these questions can be as follows: 1) the above hypothesis of biopoiesis is in many ways just a logical construction, it has not yet been proven, contains many contradictions and unclear points (although there is a lot of data, both paleontological and experimental, allowing us to assume precisely such a development of biopoiesis ); 2) this hypothesis, with all its incompleteness, nevertheless tries to explain the emergence of life based on specific earthly conditions, and this is precisely where its value lies; 3) self-education of new living beings on modern stage the development of life is impossible for the following reasons: a) organic compounds must exist for a long time in the form of clusters, gradually becoming more complex and transformed; in the conditions of the oxidizing atmosphere of the modern Earth this is impossible, they will be quickly destroyed; b) in modern conditions There are many organisms that can very quickly use even minor accumulations of organic matter for their nutrition.
4. Do your own work"Analysis and assessment of various hypotheses of the origin of life on Earth"
Enter the results in the table "Hypotheses of the origin of life on Earth."
The hypothesis of the abiogenic origin of life in the process of biochemical evolution with scientific point vision is the most developed. However, the unresolved question is when and where the abiogenic synthesis of organic compounds occurred and, most importantly, how the leap from nonliving to living occurred.
MAIN STAGES IN THE DEVELOPMENT OF LIFE ON EARTH.
1. Fill out the table " The main stages of the development of life on Earth from the standpoint of the theory of biopoiesis."
2. What hypotheses exist for the origin of eukaryotes?
Most scientists believe that eukaryotes arose from prokaryotic cells. There are two hypotheses for the origin of eukaryotes:
- The eukaryotic cell and its organelles were formed by invagination cell membrane;
- Symbiotic hypothesis according to which mitochondria, plastids, basal bodies of cilia and flagella were once free prokaryotes. They became organelles through a process of symbiosis.
3. What facts support the hypothesis of the symbiotic origin of the eukaryotic cell?
Answer: This hypothesis is supported by the presence of its own RNA and DNA in mitochondria and chloroplasts. In their structure, chloroplast RNA is similar to cyanobacterial RNA, mitochondrial RNA is similar to RNA of purple bacteria. INCREASING COMPLEXITY OF LIVING ORGANISMS ON EARTH DURING THE PROCESS OF EVOLUTION.
1. Give definitions of concepts.
- An era is a section of the geochronological scale, large on the Earth.
- A period is a section of the geochronological scale that divides an era into several parts.
2. What are the main reasons for the diversity of species of organisms on Earth?
Answer: The reasons for the diversity of species are the result of the interaction of the driving forces of evolution: hereditary variability, the struggle for existence, natural selection. There are different habitats on Earth. In this regard, each species has adapted to the living conditions of each in its own environment. Greater diversity of species in nature reduces the chances of extinction.
3. Fill out the table "Increasing complexity of living organisms on Earth."
Topic 4.2. Modern evolutionary teaching Topic 4.4. Human Origins
KSE Question 42
Hypotheses about the origin of life on earth
1.Creationism
2. Spontaneous (spontaneous) generation
3. Panspermia hypothesis
4.Hypothesis of biochemical evolution
5. Stationary state
1. Creationism. According to this concept, life and all species of living beings inhabiting the Earth are the result of a creative act of a supreme being at some specific time. The main principles of creationism are set out in the Bible, in the Book of Genesis. The process of divine creation of the world is conceived as having taken place only once and therefore inaccessible to observation. This is enough to take the whole concept of divine creation beyond scientific research. Science deals only with those phenomena that can be observed, and therefore it will never be able to either prove or disprove the concept.
2. Spontaneous (spontaneous) generation. The ideas of the origin of living beings from inanimate matter were widespread in Ancient China, Babylon, Egypt. The greatest philosopher Ancient Greece Aristotle suggested that certain “particles” of a substance contain a certain “active principle”, which, under suitable conditions, can create a living organism.
Van Helmont (1579-1644), a Dutch physician and natural philosopher, described an experiment in which he allegedly created mice in three weeks. All you needed was a dirty shirt, a dark closet and a handful of wheat. Van Helmont considered human sweat to be the active principle in the process of mouse generation. And until the appearance of the works of the founder of microbiology, Louis Pasteur, in the middle of the 10th century, this teaching continued to find adherents.
The development of the idea of spontaneous generation essentially dates back to the era when public consciousness Religious ideas prevailed. Those philosophers and naturalists who did not want to accept the church teaching about the “creation of life,” at the then level of knowledge, easily came to the idea of its spontaneous generation. To the extent that, in contrast to the belief in creation, the idea of the natural origin of organisms was emphasized, the idea of spontaneous generation had at a certain stage a progressive meaning. Therefore, the Church and theologians often opposed this idea.
3. Panspermia hypothesis. According to this hypothesis, proposed in 1865. by the German scientist G. Richter and finally formulated by the Swedish scientist Arrhenius in 1895, life could have been brought to Earth from space. Living organisms of extraterrestrial origin are most likely to enter with meteorites and cosmic dust. This assumption is based on data on the high resistance of some organisms and their spores to radiation, high vacuum, low temperatures and other influences. However, there are still no reliable facts confirming the extraterrestrial origin of microorganisms found in meteorites. But even if they got to Earth and gave rise to life on our planet, the question of the original origin of life would remain unanswered.
4. Biochemical evolution hypothesis. In 1924, the biochemist A.I. Oparin, and later the English scientist J. Haldane (1929), formulated a hypothesis that considered life as the result of a long evolution of carbon compounds.
Currently, the process of life formation is conventionally divided into four stages:
1. Synthesis of low molecular weight organic compounds (biological monomers) from gases of the primary atmosphere.
2. Formation of biological polymers.
3. Formation of phase-separated systems of organic substances, separated from the external environment by membranes (protobionts).
4. The emergence of the simplest cells with the properties of living things, including a reproductive apparatus that ensures the transfer of the properties of parent cells to daughter cells.
"PRIMARY BROTH" (optional)
In 1923, Russian scientist Alexander Ivanovich Oparin suggested that under the conditions of the primitive Earth, organic substances arose from the simplest compounds - ammonia, methane, hydrogen and water. The energy required for such transformations could be obtained either from ultraviolet radiation or from frequent thunderstorm electrical discharges - lightning. Perhaps these organic substances gradually accumulated in the Ancient Ocean, forming the primordial broth in which life originated.
According to the hypothesis of A.I.
Oparin, in the primordial broth, long thread-like protein molecules could curl into balls, “stick together” with each other, becoming larger. Thanks to this, they became resistant to the destructive effects of surf and ultraviolet radiation. Something similar happened to what can be observed by pouring mercury from a broken thermometer onto a saucer: the mercury, scattered into many small droplets, gradually gathers into slightly larger drops, and then into one large ball. The protein “balls” in the “primary broth” attracted and bound water and fat molecules. Fats settled on the surface of protein bodies, enveloping them in a layer whose structure vaguely resembled a cell membrane. Oparin called this process coacervation (from the Latin coacervus - “clump”), and the resulting bodies - coacervate drops, or simply coacervates. Over time, the coacervates absorbed more and more new portions of the substance from the solution surrounding them, their structure became more complex until they turned into very primitive, but already living cells.
5. Stationary state
According to the steady state theory, the Earth never came into being, but existed forever; it was always capable of supporting life, and if it changed, it was very little. According to this version, species also never arose, they always existed, and each species has only two possibilities - either a change in numbers or extinction.
The problem of the origin and evolution of life is one of the most interesting and at the same time least explored issues related to philosophy and religion. Throughout almost the entire history of the development of scientific thought, it was believed that life is a spontaneously generated phenomenon.
Main theories:
1) life was created by the Creator at a certain time - creationism (from lat. creatio - creation);
2) life arose spontaneously from nonliving matter;
3) life has always existed;
4) life was brought to Earth from Space;
5) life arose as a result of biochemical evolution.
According to theory creationism , the origin of life refers to a specific event in the past that can be calculated. The organisms that inhabit the Earth today are descended from the individually created basic types of living beings. The created species were from the very beginning superbly organized and endowed with the capacity for some variability within certain boundaries (microevolution).
Theory of spontaneous origin of life existed in Babylon, Egypt and China as an alternative to creationism. It goes back to Empedocles and Aristotle: certain “particles” of a substance contain a certain “active principle”, which, under certain conditions, can create a living organism. Aristotle believed that the active principle is in a fertilized egg, sunlight, and rotting meat. For Democritus, the beginning of life was in mud, for Thales - in water, for Anaxagoras - in the air.
With the spread of Christianity, the ideas of spontaneous generation were declared heretical, and for a long time they were not remembered. But Helmont came up with a recipe for producing mice from wheat and dirty laundry. Bacon believed that decay is the germ of a new birth. The ideas of spontaneous generation of life were supported by Copernicus, Galileo, Descartes, Harvey, Hegel, Lamarck, Goethe, and Schelling.
L. Pasteur finally showed in 1860 that bacteria can appear in organic solutions only if they were introduced there earlier. And to get rid of microorganisms, sterilization is necessary, called pasteurization . Hence, the idea was strengthened that a new organism can only come from a living one.
Supporters theories of eternal existence of life they think it will last forever existing Earth some species were forced to become extinct or dramatically change in number in certain places due to changes external conditions. A clear concept on this path has not been developed, since there are some gaps and ambiguities in the fossil record of the Earth.
The hypothesis about the emergence of life on Earth as a result of the transfer of certain embryos of life from other planets is called panspermia (from Greek pan- all, every and sperma- seed). The panspermia theory does not offer a mechanism to explain the primary origin of life and shifts the problem to another place in the Universe. Having originated in space, life remained for a long time in suspended animation at almost T= O K and was brought to Earth by meteorites. At the beginning of the 20th century. Arrhenius came up with the idea of radiopanspermia. He described how particles of matter, grains of dust and living spores of microorganisms escape from inhabited planets into outer space. They, while maintaining vitality, fly in the Universe due to light pressure and, arriving on a planet with suitable conditions, begin a new life.
In the last century, when studying the substances of meteorites and comets, many “precursors of living things” were discovered - organic compounds, water, formaldehyde, cyanogens. Modern adherents of the concept of panspermia believe that life was brought to Earth either accidentally or intentionally by space aliens. The panspermia hypothesis is supported by the point of view of astronomers Ch.
Wickramasingha (Sri Lanka) and F. Hoyle (Great Britain). They believe that microorganisms are present in large numbers in outer space, mainly in gas and dust clouds, where, according to scientists, they are formed. Next, these microorganisms are captured by comets, which then, passing near the planets, “sow the germs of life.”
The first scientific theory regarding the origin of living organisms on Earth was created by the Soviet biochemist A.I. Oparin. In 1924, he published works in which he outlined ideas about how life on Earth could have arisen. According to this theory, life arose in the specific conditions of the ancient Earth, and is considered as a natural result of the chemical evolution of carbon compounds in the Universe. According to this theory, the process that led to the emergence of life on Earth can be divided into three stages:
1) The emergence of organic substances.
2) Formation of biopolymers (proteins, nucleic acids, polysaccharides, lipids, etc.) from simpler organic substances.
3) The emergence of primitive self-reproducing organisms.
In ideas about the origin of life as a result of biochemical evolution important role the evolution of the planet itself plays a role. The earth has existed for almost 4.5 billion years, and organic life for about 3.5 billion years. The young Earth was a hot planet with a temperature of 5...8103 K. As it cooled, refractory metals and carbon condensed, forming the earth's crust. The atmosphere of the primordial Earth was very different from the modern one. Light gases - hydrogen, helium, nitrogen, oxygen, argon, etc. - were not yet retained by the insufficiently dense planet, but heavier compounds remained (water, ammonia, carbon dioxide, methane).
When the Earth's temperature dropped below 100ºC, water vapor began to condense, forming the World Ocean. At this time, abiogenic synthesis took place, that is, in the primary earth’s oceans, saturated with various simple chemical compounds, “in the primary broth” under the influence of volcanic heat, lightning discharges, intense ultraviolet radiation and other environmental factors, the synthesis of more complex organic compounds began, and then biopolymers. The formation of organic substances was facilitated by the absence of living organisms - consumers of organic matter - and the main oxidizing agent - oxygen. Complex amino acid molecules randomly combined into peptides, which in turn created the original proteins. From these proteins, primary living beings of microscopic size were synthesized.
Most complex problem V modern theory evolution is the transformation of complex organic substances into simple living organisms. Oparin believed that the decisive role in the transformation of non-living things into living things belongs to proteins. Apparently, protein molecules, attracting water molecules, formed colloidal hydrophilic complexes. Further fusion of such complexes with each other led to the separation of colloids from the aqueous medium (coacervation). At the border between the coacervate (from lat. coacervus- clot, heap) and the environment formed lipid molecules - a primitive cell membrane. It is assumed that colloids could exchange molecules with the environment (a prototype of heterotrophic nutrition) and accumulate certain substances.
The first organisms on earth were single-celled - prokaryotes. After several billion years, eukaryotes formed, and with their appearance, a choice of plant or animal lifestyles emerged, the difference between which lies in the method of nutrition and is associated with the process of photosynthesis. It is accompanied by the entry of oxygen into the atmosphere; the current oxygen content in the atmosphere of 21% was achieved 25 million years ago as a result of the intensive development of plants.
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1. What is life?
Answer. Life is a way of being for entities (living organisms) endowed with internal activity, the process of development of bodies of organic structure with a stable predominance of synthesis processes over decay processes, a special state of matter achieved through the following properties. Life is a way of existence of protein bodies and nucleic acids, the essential point of which is the constant exchange of substances with the environment, and with the cessation of this exchange, life also ceases.
2. What hypotheses of the origin of life do you know?
Answer. Various ideas about the origin of life can be combined into five hypotheses:
1) creationism - Divine creation of living things;
2) spontaneous generation - living organisms arise spontaneously from nonliving matter;
3) steady state hypothesis - life has always existed;
4) panspermia hypothesis - life was brought to our planet from the outside;
5) the hypothesis of biochemical evolution - life arose as a result of processes that obey chemical and physical laws. Currently, most scientists support the idea of the abiogenic origin of life in the process of biochemical evolution.
3. What is the basic principle scientific method?
Answer. The scientific method is a set of techniques and operations used to build a system scientific knowledge. The basic principle of the scientific method is to take nothing for granted. Any statement or refutation of something should be verified.
Questions after § 89
1. Why can the idea of the divine origin of life be neither confirmed nor refuted?
Answer. The process of the Divine creation of the world is conceived as having taken place only once and therefore inaccessible to research. Science deals only with those phenomena that are amenable to observation and experimental research. Consequently, from a scientific point of view, the hypothesis of the Divine origin of living things can neither be proven nor disproved. The main principle of the scientific method is “take nothing for granted.” Consequently, logically there can be no contradiction between the scientific and religious explanation of the origin of life, since these two spheres of thinking are mutually exclusive.
2. What are the main provisions of the Oparin–Haldane hypothesis?
Answer. In modern conditions, the emergence of living beings from inanimate nature impossible. Abiogenic (i.e., without the participation of living organisms) emergence of living matter was possible only under conditions of an ancient atmosphere and the absence of living organisms. The ancient atmosphere included methane, ammonia, carbon dioxide, hydrogen, water vapor and other inorganic compounds. Under the influence of powerful electrical discharges, ultraviolet radiation and high radiation, organic compounds could arise from these substances, which accumulated in the ocean, forming a “primary broth”. In the “primary broth” of biopolymers, multimolecular complexes - coacervates - were formed. Metal ions, which acted as the first catalysts, entered the coacervate droplets from the external environment. From the huge number of chemical compounds present in the “primordial soup”, the most catalytically effective combinations of molecules were selected, which ultimately led to the emergence of enzymes. At the interface between the coacervates and the external environment, lipid molecules lined up, which led to the formation of a primitive cell membrane. At a certain stage, protein probionts incorporated nucleic acids, creating unified complexes, which led to the emergence of such properties of living things as self-reproduction, preservation of hereditary information and its transmission to subsequent generations. Probionts, whose metabolism was combined with the ability to reproduce themselves, can already be considered as primitive procells, the further development of which occurred according to the laws of the evolution of living matter.
3. What experimental evidence can be given in favor of this hypothesis?
Answer. In 1953, this hypothesis of A.I. Oparin was experimentally confirmed by the experiments of the American scientist S. Miller. In the installation he created, the conditions that supposedly existed in the primary atmosphere of the Earth were simulated. As a result of the experiments, amino acids were obtained. Similar experiments were repeated many times in various laboratories and made it possible to prove the fundamental possibility of synthesizing almost all monomers of the main biopolymers under such conditions. Subsequently, it was found that, under certain conditions, it is possible to synthesize more complex organic biopolymers from monomers: polypeptides, polynucleotides, polysaccharides and lipids.
4. What are the differences between A.I. Oparin’s hypothesis and J. Haldane’s hypothesis?
Answer. J. Haldane also put forward the hypothesis of the abiogenic origin of life, but, unlike A.I. Oparin, he gave primacy not to proteins - coacervate systems capable of metabolism, but to nucleic acids, that is, macromolecular systems capable of self-reproduction.
5. What arguments do opponents give when criticizing the Oparin–Haldane hypothesis?
Answer. The Oparin–Haldane hypothesis also has a weak side, which its opponents point out. Within the framework of this hypothesis, it is not possible to explain the main problem: how the qualitative leap from inanimate to living occurred. After all, for the self-reproduction of nucleic acids, enzyme proteins are needed, and for the synthesis of proteins, nucleic acids are needed.
Give possible arguments for and against the panspermia hypothesis.
Answer. Arguments for:
Life at the prokaryotic level appeared on Earth almost immediately after its formation, although the distance (in the sense of the difference in the level of complexity of organization) between prokaryotes and mammals is comparable to the distance from the primordial soup to pokaryotes;
In the event of the emergence of life on any planet of our galaxy, it, as shown, for example, by the estimates of A.D. Panov, can “infect” the entire galaxy over a period of just a few hundred million years;
Findings of artifacts in some meteorites that can be interpreted as the result of the activity of microorganisms (even before the meteorite hit Earth).
The hypothesis of panspermia (life brought to our planet from the outside) does not answer the main question of how life arose, but transfers this problem to some other place in the Universe;
Complete radio silence of the Universe;
Since it turned out that our entire Universe is only 13 billion years old (i.e., our entire Universe is only 3 times older (!) than planet Earth), then there is very little time left for the origin of life somewhere in the distance... The distance to the nearest star to us is a-centauri - 4 light years. of the year. A modern fighter (4 speeds of sound) will fly to this star ~ 800,000 years.
Charles Darwin wrote in 1871: “But if now... in some warm body of water containing all the necessary salts of ammonium and phosphorus and accessible to the influence of light, heat, electricity, etc., a protein was chemically formed, capable of further , increasingly complex transformations, then this substance would immediately be destroyed or absorbed, which was impossible in the period before the emergence of living beings.”
Confirm or refute this statement by Charles Darwin.
Answer. The process of the emergence of living organisms from simple organic compounds was extremely long. For life to arise on Earth, it took an evolutionary process that lasted many millions of years, during which complex molecular structures, primarily nucleic acids and proteins, were selected for stability, for the ability to reproduce their own kind.
If today on Earth, somewhere in areas of intense volcanic activity, quite complex organic compounds can arise, then the likelihood of these compounds existing for any length of time is negligible. The possibility of life re-emerging on Earth is excluded. Now living beings appear only through reproduction.
Question 1. List the main provisions of A.I. Oparin’s hypothesis.
In modern conditions, the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) emergence of living matter was possible only under the conditions of an ancient atmosphere and the absence of living organisms. The composition of the ancient atmosphere included methane, ammonia, carbon dioxide, hydrogen, water vapor and other inorganic compounds. Under the influence of powerful electrical discharges, ultraviolet radiation and high radiation, organic compounds could arise from these substances, which accumulated in the ocean, forming a “primary broth”.
In the “primary broth” of biopolymers, multimolecular complexes—coacervates—were formed. Metal ions, which acted as the first catalysts, entered the coacervate droplets from the external environment. From the huge number of chemical compounds present in the “primary broth”, the most catalytically effective combinations of molecules were selected, which ultimately led to the appearance of enzymes. Lipid molecules lined up at the boundary between the coacervates and the external environment, which led to the formation of a primitive cell membrane.
At a certain stage, protein probionts incorporated nucleic acids, creating unified complexes, which led to the emergence of such properties of living things as self-reproduction, preservation of hereditary information and its transmission to subsequent generations.
Probionts, whose metabolism was combined with the ability to reproduce themselves, can already be considered as primitive procells, the further development of which occurred according to the laws of the evolution of living matter.
Question 2. What experimental evidence can be given in favor of this hypothesis?
In 1953, this hypothesis of A.I. Oparin was experimentally confirmed by the experiments of the American scientist S. Miller. In the installation he created, the conditions that supposedly existed in the primary atmosphere of the Earth were simulated. As a result of the experiments, amino acids were obtained. Similar experiments were repeated many times in various laboratories and made it possible to prove the fundamental possibility of synthesizing almost all monomers of the main biopolymers under such conditions. Subsequently, it was found that, under certain conditions, it is possible to synthesize more complex organic biopolymers from monomers: polypeptides, polynucleotides, polysaccharides and lipids.
Question 3. What are the differences between A.I. Oparin’s hypothesis and J. Haldane’s hypothesis?Material from the site
J. Haldane also put forward the hypothesis of the abiogenic origin of life, but, unlike A.I. Oparin, he gave primacy not to proteins - coacervate systems capable of metabolism, but to nucleic acids, i.e. macromolecular systems capable of self-reproduction.
Question 4. What arguments do opponents give when criticizing the hypothesis of A.I. Oparin?
Unfortunately, within the framework of the hypothesis of A.I. Oparin (and J. Haldane too) it is not possible to explain the main problem: how the qualitative leap from inanimate to living occurred.
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Topic: A. I. Oparin’s hypothesis about the origin of life on Earth
Performed:
1. Introduction
2. Main part
2.1 A. I. Oparin's hypothesis about the origin of life on Earth
2.2 Strong and weak sides concepts
3. Conclusion
4. Literature used
Introduction
Life is so understandable and at the same time so mysterious for everyone thinking man word. It would seem that the meaning of this word should be clear and unambiguous for all times and all peoples. However, we know that over many centuries views on the problem of the origin of life have changed, and it has been expressed a large number of a wide variety of hypotheses and concepts. Some of them became widespread and dominated in certain periods of the development of natural science.
One of the main obstacles that stood at the beginning of the 20th century. On the way to solving the problem of the origin of life, there was a prevailing belief in science and based on everyday experience that there was no relationship between organic and inorganic compounds. Until the middle of the 20th century. many scientists believed that organic compounds can only arise in a living organism, biogenically. That is why they were called organic compounds, as opposed to inanimate substances - minerals, which were called inorganic compounds. It was believed that the nature of inorganic substances was completely different, and therefore the emergence of even the simplest organisms from inorganic substances was fundamentally impossible. However, after the usual chemical elements the first organic compound was synthesized, the idea of two different entities of organic and inorganic substances turned out to be untenable. As a result of this discovery arose organic chemistry and biochemistry, the study of chemical processes in living organisms.
In addition, this scientific discovery made it possible to create the concept of biochemical evolution, according to which life on Earth arose as a result of physical and chemical processes. The initial basis for this hypothesis was data on the similarity of substances that make up plants and animals, as well as on the possibility of synthesizing organic substances that make up protein in laboratory conditions.
These discoveries formed the basis of the concept of A.I. Oparin, published in 1924 in the book “The Origin of Life,” which outlined a fundamentally new hypothesis of the origin of life.
Main part
2.1. A. I. Oparin's hypothesis about the origin of life on Earth
In 1924, the Russian scientist Alexander Ivanovich Oparin first formulated the basic principles of the concept of prebiological evolution.
He viewed the emergence of life as a single natural process, which consisted of the initial chemical evolution that took place under the conditions of the early Earth, which gradually moved to a qualitatively new level - biochemical evolution. The essence of the hypothesis was as follows: the origin of life on Earth is a long evolutionary process of the formation of living matter in the depths of nonliving matter. And this happened through chemical evolution, as a result of which the simplest organic substances were formed from inorganic ones under the influence of strong physicochemical factors.
Considering the problem of the emergence of life through biochemical evolution, Oparin identifies three stages of transition from inanimate to living matter:
1) the stage of synthesis of initial organic compounds from inorganic substances under the conditions of the primary atmosphere of the early Earth;
2) the stage of formation of biopolymers, lipids, hydrocarbons from accumulated organic compounds in the primary reservoirs of the Earth;
3) the stage of self-organization of complex organic compounds, the emergence on their basis and evolutionary improvement of the processes of metabolism and reproduction of organic structures, culminating in the formation of the simplest cell.
On first stage, about 4 billion years ago, when the Earth was lifeless, abiotic synthesis of carbon compounds and their subsequent prebiological evolution took place on it. This period of the Earth's evolution was characterized by numerous volcanic eruptions with the release of huge amounts of hot lava. As the planet cooled, water vapor in the atmosphere condensed and rained down on the Earth, forming huge expanses of water. Since the Earth's surface remained hot, the water evaporated and then, cooling in the upper layers of the atmosphere, fell back onto the surface of the planet. These processes continued for many millions of years. Thus, various salts were dissolved in the waters of the primary ocean. In addition, it also contained organic compounds: sugars, amino acids, nitrogenous bases, organic acids, etc., which were continuously formed in the atmosphere under the influence of ultraviolet radiation, high temperature and active volcanic activity.
The primordial ocean probably contained in dissolved form various organic and inorganic molecules that entered it from the atmosphere and surface layers of the Earth. The concentration of organic compounds constantly increased, and, in the end, the ocean waters became a “broth” of protein-like substances - peptides.
On second stage, As conditions on Earth softened, under the influence of electrical discharges, thermal energy and ultraviolet rays on the chemical mixtures of the primary ocean, it became possible to form complex organic compounds - biopolymers and nucleotides, which, gradually combining and becoming more complex, turned into protobionts (precellular ancestors of living organisms). The result of the evolution of complex organic substances was the appearance of coacervates, or coacervate drops.
Coacervates are complexes of colloidal particles, the solution of which is divided into two layers: a layer rich in colloidal particles and a liquid almost free of them. Coacervates had the ability to absorb various substances, dissolved in the waters of the primary ocean. As a result internal structure coacervates changed, which led either to their disintegration or to the accumulation of substances, i.e. to growth and changes in chemical composition, increasing their stability in constantly changing conditions. The theory of biochemical evolution considers coacervates as prebiological systems, which are groups of molecules surrounded by a water shell. Coacervates turned out to be able to absorb various organic substances from the external environment, which provided the possibility of primary metabolism with the environment.
On third stage, as Oparin assumed, natural selection began to act. In the mass of coacervate droplets, the selection of coacervates that were most resistant to given environmental conditions occurred. The selection process took place over many millions of years, resulting in only a small fraction of coacervates being preserved. However, the preserved coacervate droplets had the ability to undergo primary metabolism. And metabolism is the primary property of life. At the same time, having reached a certain size, the mother drop could break up into daughter drops, which retained the features of the mother structure. Thus, we can talk about the acquisition by coacervates of the property of self-reproduction - one of the most important signs of life. In fact, at this stage, coacervates turned into the simplest living organisms.
Further evolution of these prebiological structures was possible only with the complication of metabolic and energy processes inside the coacervate. Stronger insulation internal environment Only a membrane could provide protection from external influences. Around the coacervates, rich in organic compounds, layers of lipids appeared, separating the coacervate from the surrounding aqueous environment. During the process of evolution, lipids were transformed into the outer membrane, which significantly increased the viability and stability of organisms.
In protocells like coacervates or microspheres, nucleotide polymerization reactions occurred until a protogen was formed from them - a primary gene capable of catalyzing the emergence of a certain amino acid sequence - the first protein. Probably the first such protein was a precursor to an enzyme that catalyzes the synthesis of DNA or RNA. Those protocells in which the primitive mechanism of heredity and protein synthesis arose divided faster and took into themselves all the organic substances of the primary ocean. At this stage, natural selection was already underway for the speed of reproduction; any improvement in biosynthesis was picked up, and new protocells replaced all previous ones.
Schematic representation of the path of the origin of life according to the protein-coacervate theory of A.I. Oparina
Oparin's theory was warmly supported by Cambridge professor Haldane. He opened the debate on the origin of life in an article published in the Rationalist Annual in 1929. In it, Halden hypothesized that huge quantities of organic compounds accumulated on the primitive Earth, forming what he called a hot dilute soup; the name later became primeval soup.
The modern dual concept of the primordial soup and the spontaneous generation of life comes from the Oparin-Haldane theory of the origin of life.
The greatest success of the Oparin-Haldane theory was a widely publicized experiment conducted in 1953 by American graduate student Stanley Miller.
Miller's experiment
Charles Darwin believed that inanimate matter could be transformed into living matter with the help of electricity - after all, his grandfather, Erasmus Darwin, was greatly impressed by Frankenstein, written by Mary Shelley. The idea that pyrotechnic exercises with electricity could give rise to life had enormous appeal; so it is not surprising that there was great interest in Stanley Miller's experiment, the results of which were published in 1953.
The hypothesis of the origin of life through biochemical evolution, or the “Oparin-Haldane hypothesis,” should be recognized as the most fully developed, reasoned and widely accepted.
A. I. Oparin, Russian biochemist, academician, back in. published his first book on this problem. J. Haldane, English geneticist and biochemist, p. developed ideas consonant with the ideas of A.I. Oparin.
It postulates that life arose on Earth precisely from inanimate matter, under conditions that existed on the planet billions of years ago. These conditions included the presence of energy sources, a certain temperature regime, water and other inorganic substances - precursors of organic compounds. The atmosphere then was oxygen-free (the source of oxygen today is plants, but then there were none).
Within the framework of this theory, we can distinguish five main stages on the path to the emergence of life, which are given in Table. 1.
Table 1
Stages of development of life on Earth according to hypothesisOparin-Haldane
|
Cooling of the planet (below the temperature of +100 °C on its surface); condensation of water vapor; formation of the primary ocean; dissolution of gases and minerals in its water; powerful thunderstorms Synthesis of simple organic compounds - amino acids, sugars, nitrogenous bases - as a result of the action of powerful electrical discharges (lightning) and ultraviolet radiation |
||
|
Formation of the simplest proteins, nucleic acids, polysaccharides, fats; coacervates |
||
|
3 billion years ago |
Formation of protobionts capable of self-reproduction and regulated metabolism as a result of the emergence of membranes with selective permeability and interactions of nucleic acids and proteins |
|
|
3 billion years ago |
The emergence of organisms with a cellular structure (primary prokaryotes-bacteria) |
Ideas about the formation and composition of the Earth's primary atmosphere are based on objective data from various sciences, on the study of the gaseous envelopes of other planets solar system. Very convincing evidence of the possibility of implementing the 2nd and 3rd stages of life development was obtained as a result of numerous experiments on the artificial synthesis of biological monomers. So, for the first time in... S. Miller (USA) created a fairly simple installation in which he managed to synthesize a number of amino acids and other organic compounds from a mixture of gases and water vapor under the influence of ultraviolet irradiation and electrical discharges (Fig. 1).
Rice. 1. Stanley Miller's facility in which he synthesized amino acids from gases, creating conditions believed to have existed in the atmosphere of the primitive Earth. Gases and water vapor circulating in the installation under high pressure were subjected to high voltage for a week. After this, the substances collected in the “trap” were examined by paper chromatography. A total of 15 amino acids were isolated, including glycine, alanine and aspartic acid.
In S. Miller's experiment, his installation reproduced the conditions that existed on Earth at the supposed time. The device contained a mixture of gases: hydrogen, ammonia, methane and water vapor. Electrodes were inserted into one of the chambers to produce discharges that simulated lightning, as a possible source of energy for chemical reactions. Water was poured into another chamber, and this chamber was heated (to saturate the gas mixture with water vapor). Another chamber was cooled, and here the water condensed (“rainfall”). Within a week, various organic substances were found in the condensate.
In subsequent decades, many laboratories around the world carried out the artificial synthesis of various amino acids, nucleotides, simple sugars, and then more complex organic compounds. All this confirms the possibility of the formation of organic substances on Earth in distant times without the participation of living organisms.
In the absence of free oxygen (which would destroy them) and living organisms (which could use them as food), these substances accumulated in the primordial ocean in high concentrations.
At the next stage, more complex compounds were formed - protein-like substances (chains of amino acids) and short polynucleotide molecules. The likelihood of this has been confirmed many times: today something similar is obtained experimentally. When a certain concentration of organic substances was reached in the primary ocean, complex aggregates of various compounds could arise - coacervates, small spherical formations.
The study of artificially created coacervates (very widely studied by A.I. Oparin and his colleagues) showed that they exhibit some properties of living systems. Having a compacted outer layer, a kind of cell membrane, coacervates are able to selectively absorb various substances from the environment that participate in chemical reactions inside the coacervate droplets, and some of the products of these reactions are released back into the environment. By accumulating substances, coacervates “grow” and, having increased in size, can break up into several parts - “multiply”.
Coacervates, different in their composition, are characterized to varying degrees sustainability. The more stable ones are preserved, others disappear and are destroyed.
These observations gave reason to A.I. Oparin to suggest the possibility of the action of natural selection (see below) already at this stage of the formation of living things.
Nevertheless, coacervates, with all the complexity of their organization, cannot be considered living beings, primarily because they do not have stable self-reproduction.
At the next stage, interconnections of nucleic acids and proteins were formed in the coacervates. The synthesis of proteins of a certain composition began to be carried out on the basis of information contained in nucleic acids.
The ability of nucleic acids to self-reproduce arises with the participation of specific proteins - enzymes. That is, we can already talk about the emergence of protobionts - primary forms of life that do not yet have a cellular organization, but are capable of self-reproduction and metabolism.
The further development of protobionts and the complication of their organization led to the emergence of organisms with a cellular structure - primary prokaryotes and bacteria. From this moment biological evolution begins. Apparently, heterotrophic organisms initially existed (since the primordial ocean contained many different organic substances). As their number increased, food resources decreased and competition between them increased. This led to the emergence of autotrophs - organisms that synthesize the organic substances they need from inorganic ones.
First, organisms appeared that used the energy obtained as a result of the oxidation of minerals. This process is known as chemosynthesis, and the organisms are called chemosynthetics. Then, during subsequent evolutionary transformations, autotrophic organisms arose that use the energy of sunlight - these are photosynthetic organisms (photosynthetics). Further biological evolution determined the formation of the diverse world of living nature that we see today.
Species diversity as a result of biological evolutiontions. Evolutionary doctrine (theory of evolution) is a biological discipline that studies the causes and driving forces, patterns and mechanisms of development of living organisms.
Under biological evolution understand the irreversible and natural process of the historical development of living things from simple to more complex, starting from the moment the first living organisms appeared on Earth.
In the course of evolution, some species were replaced by others, the complexity and organization of living organisms increased, their diversity increased, and man appeared.
Great ideological significance evolutionary doctrine: it affirms the idea of the unity of origin of all living things, explains the reasons for the diversity of species living on Earth, the expediency of the organization of living beings (i.e., the correspondence of the structure and functioning of all their systems and organs to the conditions of existence), the simultaneous presence in nature of both simple and highly organized organisms .
The doctrine of evolution serves as the theoretical basis of modern biology, combining and generalizing the results obtained by numerous special biological sciences.
Its importance for humans in solving problems of interaction with the biosphere is obvious.
Finally, knowledge of the laws and mechanisms of evolution is the basis for the development of selection - a science that develops methods for creating and improving varieties of cultivated plants and breeds of domestic animals.
The history of the development of ideas about the natural origin of life and the evolution of organisms can be divided into three stages: pre-Darwinian, Darwinian and post-Darwinian (modern).
Krasnodembsky E. G. "General biology: A manual for high school students and applicants to universities"
Introduction.
Life is one of the most complex phenomena of nature. Since ancient times, it has seemed mysterious and unknowable to people. Adherents of religious idealistic views considered life to be a spiritual, immaterial principle that arose as a result of divine creation. In the Middle Ages, life was associated with the presence in organisms of a certain “vital force” that was inaccessible to knowledge by means of science and practice.
The problem of the origin of life on Earth has long haunted many scientists. Many years have passed since man began to wonder where all living things came from, and during all this time many hypotheses and assumptions about the origin of life have been considered. Religious theory, theory of spontaneous generation, theory of panspermia, theory of the eternal existence of life... Humanity still cannot fully solve this riddle. I have always been interested in questions, the answers to which are definitely unknown and exist only in the form of assumptions and theories. One such problem is the origin of life. WITH summary We were introduced to these theories back in school, now I have the opportunity to consider one of them, the closest to me, the most probable, in more detail and in depth, to understand its provisions and the evidence provided.
In the development of doctrines about the origin of life, a significant place is occupied by the theory that claims that all living things come only from living things - the theory of biogenesis. In the mid-nineteenth century, this theory was contrasted with unscientific ideas about the spontaneous generation of organisms (worms, flies, etc.). However, as a theory of the origin of life, biogenesis is untenable, since it fundamentally contrasts the living with the inanimate, and affirms the idea of the eternity of life, rejected by science.
The theory proposed by A.I. Oparin in the first half of the twentieth century is based on the assumption of chemical evolution, which gradually moves to biochemical and then to biological evolution. The formation of a cell was a very complex phenomenon. But it marked the beginning of the development of life and all its diversity. Abiogenesis - the idea of the origin of living things from non-living things - is the initial hypothesis of the modern theory of the origin of life. This led to the revival of the theory of spontaneous generation. The new version was called the theory of chemical evolution.
Alexander Ivanovich Oparin was born on March 2, 1894 in the city of Uglich. In 1912 Graduated from the Second Moscow Gymnasium.
1912–1917 – student of the natural sciences department of the Faculty of Physics and Mathematics of Moscow University.
1915 – chemist at the pharmaceutical plant of the All-Russian Union of Cities.
1917 – graduated from the natural sciences department of the Faculty of Physics and Mathematics of Moscow University and was left at the Department of Plant Physiology to prepare for the professorship.
Alexander Ivanovich Oparin is the creator of the internationally recognized theory of the origin of life, the provisions of which have brilliantly stood the test of time for more than half a century; one of the largest Soviet biochemists, who laid the foundation for research in the field of evolutionary and comparative biochemistry, enzymology, plant biochemistry and subcellular structures, the founder of Soviet technical biochemistry; an outstanding teacher, organizer of science, public figure and brilliant popularizer of scientific knowledge.
Works of A.I. Oparin are devoted to the study of the biochemical foundations of the processing of plant raw materials, issues of the action of enzymes in a living organism and the problem of the origin of life on Earth. His work laid the foundations of technical biochemistry in the USSR. Studying the actions of enzymes in various plants, A.I. Oparin came to the conclusion that the technology of a number of industries dealing with raw materials of plant origin is based on biological catalysis.
Developing theoretical basis biology, A.I.
Oparin put forward a theory of the origin of life on Earth. Based on factual materials from the field of astronomy, chemistry, geology and biology A.I. Oparin proposed a hypothesis of the development of matter that explains the emergence of life on Earth. He considered the problem of the origin of life from a materialistic position and explained the emergence of life as a definite and natural qualitative stage in historical development matter.
Already A.I. Oparin’s early studies in the field of comparative biochemistry of redox processes in the simplest algae led him to study the evolutionary development of life and develop the basic principles of the problem of the origin of life on Earth. In those years (at the beginning of the 20th century), among natural scientists the problem of the origin of life was considered a problem that did not allow an experimental approach and could not be solved by methods natural sciences. The greatest scientific achievement of A.I. Oparin is that he convincingly demonstrated the possibility of a scientific experimental approach to studying the problem of the origin of life. He outlined his ideas in the book "The Origin of Life", published in the Soviet Union in 1924 and translated into English language in 1938. The peak of research by A.I. Oparin and his co-authors was in the 50-60s, although his book “The Origin of Life” was published earlier.
The emergence of life A.I. Oparin considered it as a single natural process, which consisted of the initial chemical evolution that took place under the conditions of the early Earth, which gradually moved to a qualitatively new level - biochemical evolution.
1. The primitive Earth had a rarefied (that is, oxygen-deprived) atmosphere. When this atmosphere began to be affected by various natural sources of energy - for example, thunderstorms and volcanic eruptions - then the main chemical compounds essential for organic life.
From the very beginning this process was associated with geological evolution. It is currently believed that the age of our planet is approximately 4.3 billion years. In the distant past, the Earth was very hot (4000-8000 °C). As it cooled, the earth's crust was formed, and an atmosphere was formed from water, ammonia, carbon dioxide and methane. This atmosphere is called “reducing” because it does not contain free oxygen. When the temperature on the Earth's surface dropped below 1000C, primary reservoirs formed. Under the influence of electrical discharges, thermal energy, and ultraviolet rays on gas mixtures, organic substances-monomers were synthesized, which locally accumulated and combined with each other, forming polymers. It can be assumed that at the same time, simultaneously with polymerization, the formation of supramolecular membrane complexes took place.
2. Over time, organic molecules accumulated in the oceans until they reached the consistency of a hot, dilute soup. However, in some areas the concentration of molecules necessary for the origin of life was particularly high, and nucleic acids and proteins were formed there.
According to the same rules, polymers of all types were synthesized in the “primary broth” of the Earth’s hydrosphere: amino acids, polysaccharides, fatty acids, nucleic acids, resins, essential oils, etc. This assumption was tested experimentally in 1953 at Stanley Miller’s installation.
Miller's experiment, which became a turning point in this field, was extremely simple. The apparatus consisted of two glass flasks connected in closed circuit. A device that simulates lightning effects is placed in one of the flasks - two electrodes, between which a discharge occurs at a voltage of about 60 thousand volts; In another flask, water is constantly boiling. The apparatus is then filled with the atmosphere believed to have existed on ancient Earth: methane, hydrogen and ammonia. The apparatus worked for a week, after which the reaction products were examined. Basically it turned out to be a viscous mess of random compounds; a certain amount of organic substances was also found in the solution, including the simplest amino acids - glycine and alanine.
Primary cells supposedly arose with the help of fat molecules (lipids).
Water molecules, wetting only the hydrophilic ends of fat molecules, placed them, as it were, “on their heads,” with their hydrophobic ends up. In this way, a complex of ordered fat molecules was created, which, by adding new molecules to them, gradually demarcated a certain space from the entire environment, which became the primary cell, or coacervate - spatially isolated whole system. Coacervates turned out to be able to absorb various organic substances from the external environment, which provided the possibility of primary metabolism with the environment.
3. The first cells were heterotrophs; they could not reproduce their components on their own and received them from the broth. But over time, many compounds began to disappear from the broth, and the cells were forced to reproduce them on their own. So the cells developed their own metabolism for independent reproduction.
Thus, the primary cellular structure, according to Oparin, was an open chemical microstructure, which was endowed with the ability for primary metabolism, but did not yet have a system for transmitting genetic information based on nucleic acids. Such systems, drawing substances and energy from the environment, can resist the increase in entropy and contribute to its decrease in the process of their growth and development, which is a characteristic feature of all living systems. A single molecule, even a very complex one, cannot be alive. This means that it is not the isolated parts that determine the organization of the whole, but the whole, continuing to evolve, that determines the expediency of the structure of the parts.
Natural selection preserved those systems in which the metabolic function and the adaptability of the organism as a whole to existence in given environmental conditions were more perfect. The gradual complication of protobionts was carried out by the selection of such coacervate drops, which had the advantage of better utilization of the matter and energy of the environment. Selection as the main reason for the improvement of coacervates to primary living beings is a central position in Oparin's hypothesis.
Oparin's theory about the origin of life on Earth
Currently, the most widely accepted hypothesis about the origin of life on Earth, developed by the Soviet scientist academician A.I. Oparin. This hypothesis is based on the assumption of the gradual emergence of life on Earth from inorganic substances through long-term abiogenic (non-biological) molecular evolution.
It is believed that the Earth and other planets of the solar system were formed from a gas and dust cloud about 4.5 billion years ago. In the first stages of its formation, the Earth had a high temperature. As the planet cooled, heavy elements moved to its center, while lighter elements remained on the surface. The atmosphere consisted of free hydrogen and its compounds (H2O, CH4, NH3, HCN) and therefore was of a reducing nature. This circumstance served as an important prerequisite for the emergence of organic molecules by non-biological means. Compounds that are reducing agents easily enter into chemical reactions, giving up hydrogen, and at the same time oxidize themselves. The components of the atmosphere were exposed to various energy sources: hard, close to X-ray, short-wave radiation from the Sun, lightning discharges, high temperatures in the area of lightning discharges and in areas of active volcanic activity, etc. As a result of these impacts, the chemically simple components of the atmosphere interacted, changing and becoming more complex. Molecules of sugars, amino acids, nitrogenous bases, organic acids (acetic, formic, lactic, etc.) and other simple organic compounds appeared.
Scientists have been able to reproduce some of these reactions in the laboratory. In 1935, American scientist L.S. Miller, by passing an electric discharge through a mixture of H2, H2O, CH4 and NH3, obtained a mixture of several amino acids and organic acids. Later it turned out that many simple organic compounds that are part of biological polymers - proteins, nucleic acids and polysaccharides - can be synthesized abiogenically in the absence of oxygen. In an aqueous environment, under certain conditions, amino acids can arise from hydrocyanic acid, ammonia and some other compounds. From nitrogenous bases in the presence of inorganic phosphorus compounds, adenosine monophosphate (AMP), as well as adenosine diphosphate (ADP) and adenosine triphosphate (ATP), sugars, and amino acids are formed.
The possibility of abiogenic synthesis of organic compounds is proven by the fact that they are found in outer space. Hydrogen cyanide, formaldehyde, formic acid, methyl and ethyl alcohols and other substances have been found in space. Some meteorites contain fatty acids, sugars, and amino acids. All this indicates that organic compounds could have arisen purely chemically under the conditions that existed on Earth about 4 billion years ago.
Thus, the conditions for the abiogenic occurrence of organic compounds can be considered the reducing nature of the Earth’s atmosphere, high temperature, lightning discharges and powerful ultraviolet radiation from the Sun, which was not yet blocked by the ozone screen.
As the Earth cooled, the water vapor contained in the atmosphere condensed, and rain fell on the Earth's surface, forming large expanses of water on it. Ammonia, carbon dioxide, hydrocyanic acid, methane and more complex organic compounds formed in the atmosphere were dissolved in the water. Organic molecules, such as amino acids or nucleotides, in an aqueous environment can bind to each other (condense) to form polymers. This releases water. Two amino acids can combine peptide bond, and two nucleotides are a phosphodiester bond. It should be noted that the synthesis of simple compounds requires more stringent conditions than the formation of complex ones. For example, the synthesis of amino acids occurs at a temperature of about 1000 C, and their condensation into polypeptides occurs at a temperature of 160 C.
However, these reactions proceed very slowly in the absence of enzyme proteins. Among the randomly formed polypeptides, there are those that have catalytic activity and could accelerate the processes of matrix synthesis of polynucleotides. Consequently, the next important step in prebiological evolution was the combination of the ability of nucleotides to reproduce themselves with the ability of polypeptides to be catalytic. The stability and stability of “successful” combinations of amino acids - polypeptides is ensured only by the preservation of information about them in nucleic acids. In turn, polypeptides or proteins synthesized based on information contained in RNA molecules can facilitate the reduplication of these molecules. Thus, through selection, a genetic code or “dictionary” arose, establishing a correspondence between triplets of nucleotides and amino acids.
Further complication of metabolism could occur only in conditions of spatial proximity genetic code and the proteins it encodes, as well as isolation of the reacting components from the external environment. Indeed, the selection of RNA molecules based on the quality of the protein it encodes is carried out only if the protein does not diffuse in any direction, but remains in some isolated space, where it participates in metabolic processes. The possibility of separating the protein synthesizing system from the external environment is inherent in physical and chemical properties molecules. Organic molecules are also surrounded by a water shell, the thickness of which depends on the charge of the molecule, the concentration of salts in the solution, temperature, etc.
Under certain conditions, the aqueous shell acquires clear boundaries and separates from the surrounding solution. Molecules surrounded by an aqueous shell can combine to form multimolecular complexes - coacervates. In the primordial ocean, coacervates, or coacervate drops, had the ability to absorb various substances. As a result of this, the internal composition of the coacervate underwent changes, which led to either disintegration or accumulation of substances, i.e. to growth and to changes in the chemical composition, which increases the stability of the coacervate droplet. The fate of the drop was determined by the predominance of one of these processes. Academician A.I. Oparin noted that in the mass of coacervate droplets there had to be a selection of the most stable ones under these specific conditions. Having reached a certain size, the mother coacervate droplet could break up into daughter droplets. The daughter coacervates, the structure of which differed little from the parent, continued to grow, and the sharply different droplets disintegrated. Only those coacervate drops continued to exist which, entering into some elementary forms of exchange with the environment, retained the relative constancy of their composition. Subsequently, they acquired the ability to absorb not all substances from the environment, but only those that provided them with stability, as well as the ability to excrete metabolic products. The differences between chemical composition drops and the environment. In the process of long-term selection (it is called chemical evolution), only those drops were preserved that, when disintegrating into daughter ones, did not lose the features of their structure, i.e. acquired the property of self-reproduction. The evolution of coacervates culminated in the formation of a membrane separating them from the environment and consisting of phospholipids. Such artificial membranes, bordering bubbles ranging in size from 1 to 10 microns, are now easily created under experimental conditions. The formation of the outer membrane predetermined the direction of further chemical evolution along the path of development of increasingly more advanced self-regulating systems until the emergence of the first primitive cells. Finding themselves in a closed space surrounded by a membrane, RNA molecules evolved, and the feature by which selection occurred was not the RNA’s own structure, but mainly the properties of the proteins they encode.
Thus, the RNA nucleotide sequence began to manifest itself in the properties of the cell as a whole. The key event in the emergence of the cell was the combination of the matrix function of RNA and the catalytic function of peptides. At some later stage in evolution, DNA replaced RNA as the substance of heredity.
The appearance of the first cellular organisms marked the beginning of biological evolution. This happened 3 - 3.5 billion years ago. The first living organisms had the ability to reproduce themselves and other basic characteristics of life, existed in a reducing environment and had an anaerobic type of metabolism. In their structure they resembled modern bacteria.
