Question 1. List the main provisions of the hypothesis of AI Oparin.

In modern conditions, the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only in the conditions of the 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 "primordial soup".

In the "primary soup" of biopolymers formed multimolecular complexes - coacervates. Metal ions, which acted as the first catalysts, entered the coacervate droplets from the external medium. 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 appearance of enzymes. Lipid molecules lined up on the border between coacervates and the external environment, which led to the formation of a primitive cell membrane.

At a certain stage, protein probionts included nucleic acids, creating single complexes, which led to the emergence of such living properties as self-reproduction, preservation of hereditary information and its transmission to subsequent generations.

Probionts, whose metabolism was combined with the ability to self-reproduce, can already be considered as primitive procells, the further development of which took place 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 presumably existed in the Earth's primary atmosphere 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 practically 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 is the difference between the hypothesis of A. I. Oparin and the hypothesis of J. Haldane?

J. Haldane also put forward the hypothesis of the abiogenic origin of life, but, unlike A.I. Oparin, he gave priority 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 the 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 did the qualitative leap from inanimate to living occur.

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 inanimate matter (abiogenically) as a result of complex biochemical reactions.

Regulations

To talk briefly about the hypothesis of the origin of life, it is necessary to highlight three stages in the development of life according to Oparin:

• the occurrence of organic compounds;
• the formation of polymeric 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, which resulted in the formation of complex substances. Their formation was influenced by the anoxic atmosphere of the Earth, ultraviolet, lightning discharges.

Biopolymers arose from organic substances, which formed into primitive life forms (probionts), gradually separated by a membrane from the external environment. The appearance of nucleic acids in probionts contributed to the transmission of hereditary information and complication of organization. As a result of long-term natural selection, only those organisms remained that were capable of successful reproduction.

Rice. 2. Probionts.

Probionts or procells have not yet been obtained experimentally. Therefore, it is not completely clear how a primitive accumulation of biopolymers could move from an inanimate stay 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.

TOP 2 articleswho read along with this

Year	Scientist	Main events
	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 drops or coacervates. These are organic substances gathered together, which are conditionally separated from the external environment and begin to maintain metabolism with it. The process of coacervation - separation of the solution with the formation of coacervates - is the previous stage of coagulation, i.e. clumping of small particles. It was as a result of these processes that amino acids appeared from the "primary broth" (Oparin's term) - the basis of living organisms.
	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 macromolecular substances capable of reproduction were formed instead of coacervates. Haldane believed that the first such substances were not proteins, but nucleic acids.
	American chemist Stanley Miller	As a student, he recreated an artificial environment for obtaining amino acids from inanimate matter (chemicals). 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 Earth's early atmosphere. In one part of the system there was constantly boiling water, the vapors of which were subjected to electrical discharges (imitation of lightning). Cooling, the steam accumulated in the form of condensate in the lower tube. After a week of continuous experiment, amino acids, sugars, lipids were found in the flask
	British biologist Richard Dawkins	In his book The Selfish Gene, he suggested that not coacervate droplets were formed in the primordial soup, 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 formed mixture of organic substances that form the basis of life.

What have we learned?

From the lesson we learned about the essence of the hypothesis of the origin of life on the Oparin-Haldane Earth. According to the theory, macromolecular 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, who recreated 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 remained 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 the subsequent time, is reduced 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 soup". Subsequently, due to numerous processes of local shallowing and drying up of the oceans, the concentration of the "primary soup" could increase by tens and hundreds of times. These processes took place against the background of intense volcanic activity, frequent lightning discharges in the atmosphere, and powerful cosmic radiation. Under these conditions, there could be a gradual complication of the molecules of organic substances, the appearance of simple proteins, polysaccharides, lipids, nucleic acids. Over many hundreds and thousands of years, they could form clots of organic matter (coacervates). Under the conditions of the reducing atmosphere of the Earth, the coacervates did not collapse, their gradual complication took place, and at a certain moment of development, the first primitive organisms (probionts) could form from them. This hypothesis was accepted and further developed by many scientists from 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) the abiogenic occurrence of organic monomers; 2) formation of biological polymers; 3) the 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 solid 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. By this time, the ocean and the Earth's primary atmosphere are also formed. The earth at that time was quite warm due to the release of heat during the solidification and crystallization of the components of the crust and active volcanic activity. Water was in a vapor state for a long time, evaporating from the Earth's surface, condensing in the upper atmosphere and falling again onto a 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, oxides and carbon dioxide, water vapor and a number of other components. Powerful cosmic radiation and radiation from the Sun (there was no ozone layer in the atmosphere yet), frequent and strong electrical discharges, active volcanic activity, accompanied by emissions 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 were not oxidized and could accumulate in warm and even boiling water bodies 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. Thus, 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 soup". Volatile compounds passed into the atmosphere and practically disappeared from water bodies. Periodic drying of water bodies led to a multiple increase in the concentration of dissolved organic compounds. Against the background of the high chemical activity of the medium, the processes of complication of these compounds took place, and they could enter into compounds with each other (reactions of condensation, 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, forming more and more 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 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 the molecules synthesized on land and moved them with water currents to water bodies. Such processes could be cyclical, leading to even greater complication 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 largely unclear. The coacervates of this period were still a mechanical mixture of organic compounds, devoid of any signs of life. In a certain period of time, bonds arose between RNA molecules and peptides, reminiscent of the reactions of matrix protein synthesis. However, it is still unclear how RNA came to encode peptide synthesis. 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 on peptide synthesis, transferring this information to RNA. Such systems (coacervates) already resembled living organisms, but they 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 non-cellular 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 that isolate and protect coacervates from the environment, turning them into autonomous formations. The membranes could be formed from lipid films that appeared on the surface of water bodies. Peptides brought by rain streams to water bodies or formed in these water bodies could be attached to lipid molecules. When water bodies were disturbed 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 the coacervates with protein-nucleide complexes were important. But even 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 not yet clear. Biological membranes provided autonomy and protection to coacervates, which contributed to the emergence of a significant orderliness of 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 to regulate the processes of self-reproduction and metabolism with its help. This is how a cellular structure appeared, which has a metabolism and the ability to reproduce itself. It is these forms that could be preserved in the process of natural selection. So coacervates turned into the first living organisms - probionts.

The stage of chemical evolution has ended, and the stage of biological evolution of already living matter has begun. It 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 similar in structure to prokaryotes, did not yet have a strong cell wall and some intracellular structures (they were covered with a 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 evolutionary process. There is an opinion that the further evolution of life went 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 is there no spontaneous generation of living beings 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 probability criterion for this hypothesis? The answers to these questions can be as follows: 1) the above hypothesis of biopoiesis is in many respects only a logical construction, it has not yet been proven, it contains many contradictions and unclear points (although there is a lot of data, both paleontological and experimental, suggesting just such a development of biopoiesis ); 2) this hypothesis, for all its incompleteness, nevertheless tries to explain the emergence of life, based on specific earthly conditions, and this is precisely its value; 3) self-formation of new living beings at the present stage of development of life is impossible for the following reasons: a) organic compounds must exist in the form of accumulations for a long time, gradually becoming more complex and transforming; 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 insignificant accumulations of organic matter for their nutrition.

4. Do your own work"Analysis and evaluation of various hypotheses of the origin of life on Earth"

Record the results in a tableHypotheses of the origin of life on Earth.

The hypothesis of the abiogenic origin of life in the process of biochemical evolution is the most developed from a scientific point of view. However, the unresolved question is when and where the abiogenic synthesis of organic compounds took place and, most importantly, how the jump from non-living to living occurred.

MAIN STAGES OF DEVELOPMENT OF LIFE ON EARTH.

1. Fill in 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 evolved from prokaryotic cells. There are two hypotheses for the origin of eukaryotes:

1. The eukaryotic cell and its organelles were formed by invagination of the cell membrane;
2. Symbiotic hypothesis that mitochondria, plastids, basal bodies of cilia and flagella were once free prokaryotes. They became organelles in the 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 cyanobacteria RNA, mitochondrial RNA is similar to purple bacteria RNA. COMPLICATION OF LIVING ORGANISMS ON EARTH IN THE PROCESS OF EVOLUTION.

1. Give definitions of concepts.

• An era is a section of the geochronological scale, a large 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 various habitats on Earth. In this regard, each species has adapted to the conditions of life, each in its own environment. A large variety of species in nature reduces the chances of extinction.

3. Complete the table "Complication of living organisms on Earth.

Topic 4.2. Modern evolutionary teaching Topic 4.4. Human Origins

CCE question 42

Hypotheses for 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 higher being at some specific time. The main provisions of creationism are set out in the Bible, in the Book of Genesis. The process of the 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 out of the scope of scientific research. Science deals only with observable phenomena and therefore will never be able to either prove or reject this concept.

2. Spontaneous (spontaneous) generation. The ideas of the origin of living beings from inanimate matter were widespread in Ancient China, Babylon, and Egypt. The largest philosopher of ancient Greece, Aristotle, suggested that certain “particles” of matter contain some kind of “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. For this, a dirty shirt, a dark closet and a handful of wheat were needed. Van Helmont considered human sweat to be the active principle in the process of the birth of a mouse. And until the appearance in the middle of the tenth century of the work of the founder of microbiology, Louis Pasteur, this doctrine continued to find adherents.

The development of the idea of ​​spontaneous generation refers, in essence, to the era when religious ideas dominated the public consciousness. Those philosophers and naturalists who did not want to accept the Church's teaching on the "creation of life", with 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 was at a certain stage of progressive significance. Therefore, this idea was often opposed by the Church and theologians.

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 be brought to Earth from space. The most likely hit of living organisms of extraterrestrial origin 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. Hypothesis of biochemical evolution. In 1924, the biochemist A. I. Oparin, and later the English scientist J. Haldane (1929), formulated a hypothesis that considers life as the result of a long evolution of carbon compounds.

Currently, in the process of the formation of life, four stages are conventionally distinguished:

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 that have the properties of a living thing, including the reproductive apparatus, which ensures the transfer of the properties of parental cells to daughter cells.

"PRIMARY SOFT" (optional)

In 1923, the 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 necessary for such transformations could be obtained either from ultraviolet radiation, or from frequent lightning electrical discharges - lightning. Perhaps these organic substances gradually accumulated in the ancient ocean, forming the primordial soup in which life originated.

According to the hypothesis of A.I.

Oparin, in the primary broth, long filamentous protein molecules could fold into balls, “stick together” with each other, becoming larger. Thanks to this, they became resistant to the destructive action of the surf and ultraviolet radiation. Something similar happened to what can be observed by pouring mercury from a broken thermometer onto a saucer: the mercury, crumbling into many small droplets, gradually collects into slightly larger drops, and then into one large ball. Protein "balls" in the "primary broth" attracted to themselves, bound water molecules, as well as fats. Fats settled on the surface of protein bodies, enveloping them with a layer, the structure of which remotely resembled a cell membrane. Oparin called this process coacervation (from Latin coacervus - “clot”), and the resulting bodies were called coacervate drops, or simply coacervates. Over time, coacervates absorbed more and more portions of the substance from the solution surrounding them, their structure became more complicated 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 has always been capable of sustaining life, and if it has changed, it has changed 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 the least studied issues related to philosophy and religion. Almost throughout almost the entire history of the development of scientific thought, it was believed that life is a self-generating phenomenon.

Main theories:

1) life was created by the Creator at a certain time - creationism (from lat. creation - creation);

2) life arose spontaneously from inanimate 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 the 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 separately created basic types of living beings. The created species were from the very beginning excellently 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 matter contain some kind of “active principle”, which, under certain conditions, can create a living organism. Aristotle believed that the active principle is in a fertilized egg, sunlight, rotting meat. For Democritus, the beginning of life was in silt, for Thales, in water, for Anaxagoras, in 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 getting 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, Schelling.

L. Pasteur in 1860 finally showed that bacteria can appear in organic solutions only if they were brought there earlier. And to get rid of microorganisms, sterilization is necessary, called pasteurization . Hence, the idea was strengthened that a new organism can only be from a living one.

Supporters theories of the eternal existence of life believe that on the ever-existing Earth, some species were forced to become extinct or dramatically change their numbers in certain places due to changes in external conditions. A clear concept on this path has not been developed, since there are some gaps and ambiguities in the paleontological record of the Earth.

The hypothesis about the appearance of life on Earth as a result of the transfer of certain germs of life from other planets was called panspermia (from Greek. pan- all, everyone and sperma- seed). The panspermia theory offers no mechanism for explaining the origin of life and moves the problem elsewhere in the universe. Having originated in space, life was preserved for a long time in anabiosis almost at T= O K and was brought to Earth by meteorites. At the beginning of the XX century. Arrhenius came up with the idea of ​​radiopanspermia. He described how particles of matter, dust particles and living spores of microorganisms leave the inhabited planets into the world space. They, while maintaining their viability, fly in the Universe due to light pressure and, when they land on a planet with suitable conditions, begin a new life.

In the last century, in the study of the substance of meteorites and comets, many "precursors of the living" were discovered - organic compounds, water, formaldehyde, cyanogens. Modern adherents of the concept of panspermia believe that life on Earth was brought by accident or intentionally by space aliens. The panspermia hypothesis is adjoined by the point of view of astronomers Ch.

Vikramasingha (Sri Lanka) and F. Hoyle (Great Britain). They believe that in outer space, mainly in gas and dust clouds, microorganisms are present in large numbers, where, according to scientists, they are formed. Further, 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 could have arisen on Earth. 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) The 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 the evolution of the planet itself plays an important 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 ... 8 103 K. As it cooled, refractory metals and carbon condensed, forming the earth's crust. The atmosphere of the primitive 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, while heavier compounds remained (water, ammonia, carbon dioxide, methane).

When the Earth's temperature dropped below 100ºC, water vapor began to condense, forming the oceans. At this time, abiogenic synthesis took place, that is, in the primary terrestrial oceans saturated with various simple chemical compounds, “in the primary soup”, 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 organics - and the main oxidizing agent - oxygen. Complex amino acid molecules randomly combined into peptides, which in turn created the original proteins. From these proteins, the primary living creatures of microscopic size were synthesized.

The most difficult problem in the modern theory of evolution is the transformation of complex organic substances into simple living organisms. Oparin believed that the decisive role in the transformation of the inanimate into the living belongs to proteins. Apparently, protein molecules, attracting water molecules, formed colloidal hydrophilic complexes. Further merging of such complexes with each other led to the separation of colloids from the aqueous medium (coacervation). On the border between the coacervate (from lat. coacervus- clot, heap) and the environment lined up 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 were formed, and with their appearance there was a choice of a plant or animal way of life, 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 reached 25 million years ago as a result of the intensive development of plants.

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Topic: A. I. Oparin's hypothesis about the origin of life on Earth

Performed:

1. Introduction

2. Main body

2.1 Hypothesis of A. I. Oparin about the origin of life on Earth

2.2 Strengths and weaknesses of the concept

3. Conclusion

4. Literature used

Introduction

Life is such an understandable and at the same time such a mysterious word for every thinking person. 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 the course of many centuries, views on the problem of the origin of life have changed, and a large number of the most diverse hypotheses and concepts have been expressed. 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 XX century. on the way to solving the problem of the origin of life, there was a conviction that prevailed in science and based on everyday experience that there is no relationship between organic and inorganic compounds. Until the middle of the XX century. many scientists believed that organic compounds can only occur 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 is completely different, and therefore the emergence of even the simplest organisms from inorganic substances is fundamentally impossible. However, after the first organic compound was synthesized from ordinary chemical elements, the concept of two different essences of organic and inorganic substances turned out to be untenable. As a result of this discovery, organic chemistry and biochemistry arose, studying the 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 of this hypothesis was data on the similarity of the substances that make up plants and animals, as well as on the possibility of synthesizing organic substances that make up protein under laboratory conditions.

These discoveries formed the basis of A. I. Oparin's concept, published in 1924 in the book "The Origin of Life", where a fundamentally new hypothesis of the origin of life was presented.

Main part

2.1. Hypothesis of A. I. Oparin about the origin of life on Earth

In 1924, the Russian scientist Alexander Ivanovich Oparin for the first time formulated the main provisions of the concept of prebiological evolution.

He considered the emergence of life as a single natural process, which consisted of the initial chemical evolution taking place under the conditions of the early Earth, which gradually moved to a qualitatively new level - biochemical evolution. The essence of the hypothesis boiled down to the following: the origin of life on Earth is a long evolutionary process of the formation of living matter in the depths of inanimate 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 potent physical and chemical factors.

Considering the problem of the emergence of life through biochemical evolution, Oparin distinguishes three stages of the transition from inanimate to living matter:

1) the stage of synthesis of initial organic compounds from inorganic substances in the conditions of the primary atmosphere of the early Earth;

2) the stage of formation in the primary reservoirs of the Earth from the accumulated organic compounds of biopolymers, lipids, hydrocarbons;

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 a simple cell.

On the 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 a huge amount of red-hot lava. As the planet cooled, the water vapor in the atmosphere condensed and fell on the Earth in showers, forming huge expanses of water. Since the surface of the Earth remained still hot, the water evaporated, and then, cooling in the upper layers of the atmosphere, again fell to 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, organic compounds also got into it: sugars, amino acids, nitrogenous bases, organic acids, etc., continuously formed in the atmosphere under the influence of ultraviolet radiation, high temperature and active volcanic activity.

The primary ocean probably contained in dissolved form various organic and inorganic molecules that got into it from the atmosphere and the surface layers of the Earth. The concentration of organic compounds was constantly increasing, and, in the end, the ocean waters became a "broth" of protein-like substances - peptides.

On the second stage, as the conditions on Earth softened, under the influence of electric 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 (pre-cellular 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, the internal structure of the coacervates changed, which led either to their disintegration or to the accumulation of substances, i.e. to the growth and change of the chemical composition, increasing their resistance 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 made it possible for the primary exchange of substances with the environment.

On the third stage, as Oparin suggested, natural selection began to act. In the mass of coacervate drops, the selection of coacervates, the most resistant to given environmental conditions, took place. The selection process has been going on for many millions of years, as a result of which only a small part of the coacervates has been preserved. However, the preserved coacervate drops were capable of primary metabolism. And metabolism is the first property of life. At the same time, having reached a certain size, the parent drop could break up into daughter ones, which retained the features of the parent 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 have become the simplest living organisms.

Further evolution of these prebiological structures was possible only with the complication of metabolic and energy processes inside the coacervate. Only a membrane could provide a stronger isolation of the internal environment from external influences. Around the coacervates, rich in organic compounds, layers of lipids arose, separating the coacervates from the surrounding aquatic environment. In the process of evolution, lipids were transformed into the outer membrane, which significantly increased the viability and resistance of organisms.

In protocells like coacervates or microspheres, nucleotide polymerization reactions took place until they formed a protogen - a primary gene that can catalyze the emergence of a certain amino acid sequence - the first protein. Probably the first such protein was the precursor of an enzyme catalyzing the synthesis of DNA or RNA. Those protocells, in which a primitive mechanism of heredity and protein synthesis arose, divided more quickly and took into themselves all the organic substances of the primary ocean. At this stage, there was already natural selection for the speed of reproduction; any improvement in biosynthesis was picked up, and new protocells replaced all previous ones.

Schematic representation of the origin of life according to the protein-coacervate theory of A.I. Oparina

Oparin's theory was warmly supported by the Cambridge professor Haldane. He opened the origin of life controversy in an article published in the Rationalist Annual in 1929. In it, Halden hypothesized that vast amounts of organic compounds accumulated on the primitive Earth, forming what he called hot dilute soup (later called primeval soup or proto-broth).

The modern dual concept of the primordial broth 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 experiment

Charles Darwin believed that inanimate matter could be transformed into living matter with the help of electricity - after all, even his grandfather, Erasmus Darwin, was impressed by Mary Shelley's Frankenstein. The idea that pyrotechnic exercises with electricity could give birth to life had great appeal; so it is not surprising that Stanley Miller's experiment, the results of which were published in 1953, was of great interest.

The hypothesis of the origin of life through biochemical evolution, or the Oparin-Haldane hypothesis, should be recognized as the most fully developed, argued and widely recognized.

A. I. Oparin, Russian biochemist, academician, still in. published his first book on the subject. 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 took place 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. At that time, the atmosphere was anoxic (plants are now the source of oxygen, but they did not exist then).

Within the framework of this theory, five main stages can be distinguished on the way to the emergence of life, which are given in Table. one.

Table 1

Stages of development of life on Earth according to the hypothesisOparina-Haldane

	Cooling of the planet (below the temperature of +100 °C on its surface); water vapor condensation; the formation of a 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 prokaryotic 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 gaseous shells of other planets in the solar system. Very convincing evidence of the possibility of implementing the 2nd and 3rd stages of the development of life has been 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, on which he managed to synthesize a number of amino acids and other organic compounds from a mixture of gases and water vapor under the action of ultraviolet irradiation and electric discharges (Fig. 1).

Rice. one. Stanley Miller's installation, in which he synthesized amino acids from gases, creating conditions that supposedly existed in the atmosphere of the primitive Earth. The gases and water vapor circulating in the high pressure plant were subjected to high voltage for a week. After that, the substances collected in the "trap" were examined by paper chromatography. A total of 15 amino acids have been isolated, including glycine, alanine, and aspartic acid.

In the experiment of S. Miller, the conditions that existed on Earth at the assumed time were reproduced in his installation. The device contained a mixture of gases: hydrogen, ammonia, methane, and water vapor. Electrodes were introduced 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 subjected to cooling, and here the water condensed ("rainfall"). A week later, various organic substances were found in the condensate.

In the following decades, artificial synthesis of various amino acids, nucleotides, simple sugars, and then more complex organic compounds was carried out in many laboratories around the world. All this confirms the possibility of the formation of organic substances on Earth in remote 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 probability of this has been repeatedly confirmed: today this is obtained experimentally. Upon reaching a certain concentration of organic substances in the primary ocean, complex aggregates of various compounds could arise - coacervates, small spherical formations.

The study of artificially created coacervates (very extensively studied by A. I. Oparin and his collaborators) 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 are involved in chemical reactions inside the coacervate drops, and some of the products of these reactions are released back into the environment. Accumulating substances, coacervates "grow" and, having increased in size, can break up into several parts - "multiply".

Coacervates, different in composition, are characterized by varying degrees of stability. The more stable ones are preserved, the others disappear and are destroyed.

These observations gave AI Oparin reason to assume the possibility 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 coacervates. The synthesis of proteins of a certain composition began to be carried out on the basis of information contained in nucleic acids.

There is the ability of nucleic acids to self-reproduce with the participation of specific proteins - enzymes. That is, we can already talk about the appearance of protobionts - primary life forms that do not yet have a cellular organization, but are capable of self-reproduction and metabolism.

Further development of protobionts, the complication of their organization led to the emergence of organisms with a cellular structure - primary prokaryotes, bacteria. From this point on, biological evolution begins. Apparently, heterotrophic organisms originally existed (since the primary ocean contained many different organic substances). As their number increased, there was a decrease in food resources and competition between them increased. This led to the emergence of autotrophs - organisms that synthesize the organic substances they need from inorganic ones.

At first, organisms appeared that used the energy obtained as a result of the oxidation of mineral substances. This process is known as chemosynthesis, and organisms are called chemosynthetics. Then, in the course of subsequent evolutionary transformations, autotrophic organisms arose that use the energy of sunlight - these are photosynthetic organisms (photosynthetics). Further biological evolution led to the formation of the diverse world of wildlife that we see today.

Species diversity as a result of biological evolutiontions. Evolutionary doctrine (the 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, there was a complication and an increase in the organization of living organisms, their diversity increased, and man appeared.

The ideological significance of evolutionary doctrine is great: it affirms the idea of ​​the unity of the origin of all living things, explains the reasons for the diversity of species living on Earth, the expediency of organizing 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 and simple and highly organized organisms.

The evolutionary doctrine serves as the theoretical basis of modern biology, combining and generalizing the results obtained by numerous particular biological sciences.

Its importance is also obvious for a person in solving problems of interaction with the biosphere.

Finally, knowledge of the laws and mechanisms of evolution is the basis for the development of breeding - 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 university applicants"

Introduction.

Life is one of the most complex natural phenomena. Since ancient times, it has seemed mysterious and unknowable to people. Adherents of religious idealistic views considered life to be a spiritual, non-material beginning that arose as a result of divine creation. In the Middle Ages, life was associated with the presence in organisms of a certain "life 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, the theory of spontaneous generation, the theory of panspermia, the theory of the eternal existence of life ... Mankind still cannot fully solve this riddle. I have always been interested in questions, the answers to which are not exactly known and exist only in the form of assumptions, theories. One such problem is the origin of life. We were introduced to the summary of these theories at school, now I have the opportunity to consider one of them, the closest to me, the most probable, in more detail and deeper, to understand its provisions, the evidence given.

In the development of the teachings on the origin of life, an important place is occupied by the theory that all living things come only from living things - the theory of biogenesis. In the middle of the 19th century, this theory was opposed to 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 opposes the living to the inanimate, and affirms the idea of ​​the eternity of life rejected by science.

The theory proposed by AI Oparin in the first half of the 20th century is based on the assumption of chemical evolution, which gradually passes to biochemical and then to biological evolution. Cell formation was the most complex phenomenon. But it laid the foundation for 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 a 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 department of the Faculty of Physics and Mathematics of Moscow University.

1915 - Chemist of the pharmaceutical plant of the All-Russian Union of Cities.

1917 - graduated from the natural department of the Faculty of Physics and Mathematics of Moscow University and was left at the Department of Plant Physiology to prepare for a 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; outstanding teacher, organizer of science, public figure and brilliant popularizer of scientific knowledge.

Proceedings of A.I. Oparin are devoted to the study of the biochemical foundations of the processing of plant materials, the action of enzymes in a living organism and the problem of the emergence of life on Earth. His work laid the foundations for technical biochemistry in the USSR. Investigating 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 the theoretical foundations of biology, A.I.

Oparin put forward the theory of the origin of life on Earth. Based on actual materials from the field of astronomy, chemistry, geology and biology, A.I. Oparin proposed a hypothesis of the development of matter, explaining the origin of life on Earth. He considered the problem of the origin of life from a materialistic position and explained the origin of life as a definite and regular qualitative stage in the historical development of matter.

Already early studies of A.I. Oparin in the field of comparative biochemistry of redox processes in protozoan algae led him to study the evolutionary development of life and develop the main provisions 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 the methods of natural sciences. AI Oparin's greatest scientific contribution is that he convincingly demonstrated the possibility of a scientific experimental approach to the study of the problem of the origin of life. He outlined his ideas in The Origin of Life, published in the Soviet Union in 1924 and translated into English in 1938. The peak of research by AI Oparin and his co-authors fell on 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 taking 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, devoid of oxygen) atmosphere. When this atmosphere began to be affected by various natural sources of energy - for example, thunderstorms and volcanic eruptions - then the basic chemical compounds necessary for organic life began to spontaneously form.

From the very beginning, this process has been associated with geological evolution. It is currently accepted 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 the atmosphere was formed from water, ammonia, carbon dioxide and methane. Such an atmosphere is called "reducing" because it does not contain free oxygen. When the temperature on the Earth's surface dropped below 1000C, primary reservoirs were formed. Under the action of electric discharges, thermal energy, 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 broth. However, in some areas, the concentration of molecules necessary for the origin of life was especially high, and nucleic acids and proteins were formed there.

According to the same type of rules, polymers of all types were synthesized in the "primary soup" 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 area, was extremely simple. The apparatus consisted of two glass flasks connected in a closed circuit. One of the flasks contains a device that simulates lightning effects - two electrodes, between which a discharge occurs at a voltage of about 60,000 volts; water is constantly boiling in another flask. Then the apparatus is filled with the atmosphere that supposedly existed on the 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 connections; a certain amount of organic substances was also found in the solution, including the simplest amino acids - glycine and alanine.

Primary cells presumably arose with the help of fat molecules (lipids).

Water molecules, wetting only the hydrophilic ends of the fat molecules, put 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 delimited a certain space from the entire environment, which became the primary cell, or coacervate - a spatially isolated integral system. Coacervates turned out to be able to absorb various organic substances from the external environment, which ensured 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 self-reproduction.

Thus, the primary cellular structure, according to Oparin, was an open chemical microstructure that 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 course 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 disparate parts that determine the organization of the whole, but the whole, continuing to evolve, 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 selection of such coacervate drops, which had the advantage of better use of the matter and energy of the environment. Selection as the main reason for the improvement of coacervates to primary living beings is the central position in Oparin's hypothesis.

Oparin's theory of the origin of life on Earth

At present, the hypothesis about the origin of life on Earth, developed by the Soviet scientist Academician A.I. Oparin, has received the widest recognition. 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 formed from a gas-dust cloud about 4.5 billion years ago. In the early stages of its formation, the Earth had a high temperature. As the planet cooled, heavy elements moved towards its center, while lighter elements remained on the surface. The atmosphere consisted of free hydrogen and its compounds (H2O, CH4, NH3, HCN) and therefore had a reducing character. This circumstance served as an important prerequisite for the emergence of organic molecules in a non-biological way. Compounds that are reducing agents easily enter into chemical reactions, donating hydrogen, and at the same time oxidize themselves. The components of the atmosphere were exposed to various sources of energy: hard, close to X-ray, short-wave radiation of 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 influences, 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 arose.

Scientists have been able to reproduce some of these reactions in the laboratory. In 1935, the American scientist L.S. Miller, by passing an electrical 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 make up biological polymers - proteins, nucleic acids and polysaccharides - can be synthesized abiogenically in the absence of oxygen. In an aquatic environment, under certain conditions, amino acids can arise from hydrocyanic acid, ammonia, and some other compounds. Adenosine monophosphate (AMP) is formed from nitrogenous bases in the presence of inorganic phosphorus compounds, as well as adenosine diphosphate (ADP) and adenosine triphosphate (ATP), sugars, and amino acids.

The possibility of abiogenic synthesis of organic compounds is proved 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, 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 at that time was not yet trapped by the ozone screen.

As the Earth cooled, the water vapor contained in the atmosphere condensed, rains 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 medium can bind to each other (condense) to form polymers. This releases water. Two amino acids can be linked by a peptide bond, and two nucleotides by 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 in the absence of protein-enzymes are very slow. Among randomly formed polypeptides, there are those that have catalytic activity and could accelerate the processes of template synthesis of polynucleotides. Therefore, the next important step in prebiological evolution was the unification of the ability of nucleotides to reproduce themselves with the ability of polypeptides to catalytic activity. Stability, stability of "successful" combinations of amino acids - polypeptides is provided only by the preservation of information about them in nucleic acids. In turn, polypeptides or proteins synthesized on the basis of information embedded in RNA molecules can facilitate the reduplication of these molecules. Thus, through selection, a genetic code, or "dictionary" arose, establishing a correspondence between nucleotide triplets and amino acids.

Further complication of metabolism could occur only under conditions of spatial proximity of the genetic code and the proteins encoded by it, as well as isolation of the reacting components from the external environment. Indeed, the selection of RNA molecules according to the quality of the protein it encodes is carried out only if the protein does not diffuse in any direction, but is stored 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 the physicochemical properties of the molecules. Organic molecules are also surrounded by an aqueous shell, the thickness of which depends on the charge of the molecule, the concentration of salts in the solution, temperature, and so on.

Under certain conditions, the water 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, the internal composition of the coacervate underwent changes, which led either to decay or accumulation of substances, i.e. to growth and to a change in the chemical composition, which increases the stability of the coacervate drop. 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 drops, the most stable under given specific conditions should have been selected. Having reached a certain size, the parent coacervate drop could break up into daughter ones. Daughter coacervates, the structure of which differed little from the parent, continued to grow, and sharply different drops disintegrated. Only those coacervate drops continued to exist, which, entering into some elementary forms of exchange with the medium, retained a relative constancy of their composition. Subsequently, they acquired the ability to absorb from the environment not all substances, but only those that provided them with stability, as well as the ability to excrete metabolic products. The differences between the chemical composition of the drop and the environment gradually increased. In the process of long-term selection (it is called chemical evolution), only those drops were preserved that did not lose the features of their structure during the decay into daughter ones, i.e. acquired the property of self-reproduction. The evolution of coacervates ended with the formation of a membrane that separates them from the environment and consists of phospholipids. Such artificial membranes, bordering bubbles ranging in size from 1 to 10 μm, 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 more and more perfect self-regulating systems up to the appearance of the first primitive cells. Once in a closed space surrounded by a membrane, the RNA molecules evolved, and the feature by which the selection took place was not the RNA's own structure, but mainly the properties of the proteins they encode.

Thus, the nucleotide sequence of RNA began to manifest itself in the properties of the cell as a whole. The key event in the emergence of the cell was the unification of the template 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 possessed the ability to self-reproduce and other basic features of the living, existed in a reducing environment and had an anaerobic type of metabolism. In their structure, they resembled modern bacteria.

"Introduction to General Biology and Ecology. Grade 9". A.A. Kamensky (gdz)

Oparin-Haldane hypothesis. Experimental evidence of the abiogenic origin of life

Question 1. The main provisions of the Oparin-Haldane hypothesis
According to the theory of the origin of life on Earth, created by A.I. Oparin and J. Haldane in 1924-1927, living bodies arose from inorganic substances in three stages:
1. At the first stage, the formation of organic substances from inorganic substances took place. In modern conditions, the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only in the conditions of the 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 “primordial soup”.
2. At the second stage - the formation of proteins, fats, carbohydrates and nucleic acids from simple organic compounds in the waters of the primary ocean. In the "primary broth" of biopolymers formed multimolecular complexes - coacervates. Metal ions, which acted as the first catalysts, entered the coacervate droplets from the external medium. 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 appearance of enzymes. Lipid molecules lined up on the border between coacervates and the external environment, which led to the formation of a primitive cell membrane.
3. The third stage is the stage of development of life. At this stage, coacervates (lat. coacervo - I collect, accumulate), that is, colloidal drops, in which the concentration of substances was higher than in the surrounding solution, began to grow larger and interact with each other and with other substances. As a result of the interaction of coacervates with nucleic acids, self-reproducing protobionts(protein particles that included nucleic acids), which led to the emergence of self-reproduction, the preservation of hereditary information and its transmission to subsequent generations; from that moment began the period of organic evolution. It should be emphasized that living organisms are open systems capable of self-reproduction, in which energy comes from outside. In this regard, it is obvious that the first living organisms were heterotrophs that received energy due to the anaerobic breakdown of organic compounds. The emergence of the modern atmosphere is directly related to the emergence and development of autotrophic organisms and photosynthesis. From the moment of the emergence of life, a connection has also appeared between biological, geological and geochemical processes, which are studied by the academician V.I. Vernadsky Science "biogeochemistry".

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 (he was awarded the Nobel Prize in Chemistry for the experimental production of amino acids). In the installation he created, the conditions that presumably existed in the Earth's primary atmosphere 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 practically 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. Oparin was the first to conduct a study of chemical reactions that could cause the formation of carbohydrates, fats and amino acids without the participation of living organisms, was carried out by Oparin and continued by Calvin et al. urea in 1828, Kolbe synthesized acetic acid in 1845, Berthelot synthesized fat in 1854, Butlerov obtained a sugary substance in 1861), but none of these scientists conducted experiments under conditions analogous to those that existed in historical times on Earth (atmosphere without O2, strong ultraviolet radiation, giant electrical discharges).

Question 3. What is the difference between the hypothesis of A. I. Oparin and the hypothesis of J. Haldane?
J. Haldane also put forward the hypothesis of the abiogenic origin of life, but, unlike A.I. Oparin, he gave priority 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 the opponents give when criticizing the hypothesis of A. I. Oparin?
The hypothesis of A. I. Oparin, in its essence, does not explain the mechanism of a qualitative leap from inanimate to living.