0
Theory of biopoiesis
Based on the biochemical evolution hypothesis of Oparin-Haldane in 1947, the English researcher John Bernal formulated modern theory origin of life on earth, called theory of biopoiesis(gr. bios- life and poiesis- creation).
It included three stages:
- abiogenic occurrence of organic monomers;
- formation of biological polymers;
- the formation of membrane structures and primary organisms - probionts.
Abiogenic occurrence of organic monomers
Our planet arose about 4.6 billion years ago.
Education earth's crust accompanied by active volcanic activity. Gases accumulated in the primary atmosphere - products of reactions occurring in the bowels of the Earth: carbon dioxide (CO 2), carbon monoxide (CO), ammonia (NH 3), methane (CH 4), hydrogen sulfide (H 2 S) and many others. Such gases are currently emitted into the atmosphere during volcanic eruptions.
Water, constantly evaporating from the surface of the Earth, condensed in the upper layers of the atmosphere and again fell in the form of rain on the hot earth's surface. The gradual decrease in temperature led to the fact that downpours fell on the Earth, accompanied by continuous thunderstorms. Water bodies began to form on the earth's surface.
Atmospheric gases and those substances that were washed out of the earth's crust were dissolved in hot water. In the atmosphere, under the influence of frequent and strong electrical lightning discharges, powerful ultraviolet radiation coming from the Sun, and active volcanic activity, which was accompanied by emissions of radioactive compounds, the simplest organic substances (formaldehyde, glycerin, amino acids, urea, lactic acid) were formed.
Since there was no free oxygen in the atmosphere yet, these compounds, getting into the water ancient ocean, were not oxidized and could accumulate, becoming more complex in structure and forming a concentrated "primal broth" - a term introduced by A.I. Oparin. Organic matter, accumulating for millions of years in the water of the ancient ocean, formed a concentrated solution, or "primary soup".
Formation of biological polymers and coacervates
The first stage of biochemical evolution was confirmed by numerous experiments, but what happened at the next stage, scientists can only guess based on the knowledge of chemistry and molecular biology.
Apparently, the formed simplest organic substances interacted with each other and with inorganic compounds entering water bodies. Fatty acids, reacting with alcohols, formed lipids, which formed fatty films on the surface of water bodies. Amino acids combine with each other to form peptides. important event This stage was the emergence of nucleic acids - molecules capable of reduplication.
Modern biochemists believe that short chains of RNA were the first to form, which could be synthesized independently, without the participation of special enzymes. The formation of nucleic acids and their interaction with proteins has become a necessary prerequisite for the emergence of life, which is based on the reactions of matrix synthesis and metabolism.
A. I. Oparin believed that a vital role in the transformation of the inanimate into the living belonged to proteins. Due to the peculiarities of the structure, these molecules are able to form clots - colloidal complexes that attract water molecules to themselves. Such complexes, merging with each other, formed coacervates - structures isolated from the rest of the water mass. coacervates were able to exchange substances with environment and selectively accumulate various compounds. Absorption of metal ions by coacervates led to the formation of enzymes. Proteins in coacervates protected nucleic acids from the damaging effects of ultraviolet radiation. Systems of this kind already possessed some signs of life, but they lacked biological membranes to turn them into the first living organisms.
coacervatus(lat. coacervatio- gathering in a heap, accumulation) - clots with a higher concentration of colloid (solute) than in the rest of the solution of the same chemical composition.
Coacervates are formed in concentrated solutions of proteins and nucleic acids. They are able to adsorb various substances. From the solution inside the coacervate drops come chemical compounds, which are converted as a result of reactions taking place in coacervate drops and released into the environment.
The concept of "coacervate" is important in a number of hypotheses about the origin of life on Earth.
Formation of membrane structures and primary organisms (probionts)
How are membranes formed? early stages origin of life?
The surfaces of the reservoirs were covered with fatty films. The long non-polar hydrocarbon "tails" of the lipid molecules protruded outward, and the charged "heads" were turned into the water. Molecules of polypeptides and nucleic acids dissolved in water bodies could be adsorbed on the surface of the lipid film due to electrical attraction to charged “heads”. When the wind gusts, the surface film was bent, bubbles could break off from it. Such bubbles were lifted by the wind into the air, and when they fell to the surface of the reservoir, they were covered with a second lipid layer. This was due to hydrophobic interactions between the non-polar "tails" of lipids facing each other. Such a bilayer lipid shell surprisingly reminds us of a modern biological membrane and, possibly, could be its progenitor.
For the further evolution of life, those bubbles were important that contained coacervates with protein-nucleic acid complexes. Biological membranes provided protection and independent existence to coacervates, creating orderliness biochemical processes. In the future, only those structures that were capable of self-regulation and self-reproduction were preserved and turned into the simplest living organisms. So arose probionts (or protobionts : from Greek. protos- first and bios- life) - primitive heterotrophic organisms that fed on organic substances of the "primary broth". It happened 3.5-3.8 billion years ago. The chemical evolution has ended, the time has come for the biological evolution of living matter.
Probionts, or protobionts(gr. protos- first and bios- life), - precellular formations that have some properties of cells: the ability to metabolism, self-reproduction, etc.
Probionts were heterotrophic organisms that consumed organic matter from the "primordial soup". Obviously, they were anaerobic heterotrophs, since the ancient atmosphere, according to the researchers, did not contain oxygen.
These hypothetical primary organisms, which contained macromolecules of proteins and nucleic acids and acquired the ability to reproduce themselves, according to scientists, marked the beginning of all the modern diversity of life on Earth.
Question 1. What space factors in the early stages of the Earth's development were the prerequisites for the emergence of organic compounds?
In the early stages of the development of the Earth, organic compounds were formed from inorganic ones in an abiogenic way. The source of energy for these processes was the ultraviolet radiation of the Sun. There was no ozone or oxygen in the atmosphere, so the ultraviolet was not delayed by anything and reached the surface of the planet. Under its influence, as well as with the participation of electrical lightning discharges, the simplest organic substances were formed from water and gases: formaldehyde, glycerin, amino acids, urea, etc.
Question 2. Name the main stages of the origin of life according to the theory of biopoiesis.
According to the theory of biopoiesis, formulated in 1947 by English physicist and the historian of science John Bernal (1901-1971), there are three stages in the emergence of life:
1) abiogenic synthesis and accumulation of organic monomers (formation of "primary broth");
2) the formation of biological polymers and coacervates (from Latin coacervus - clot);
3) formation of membrane structures and primary organisms (probionts).
The main place of all these processes is the ancient ocean.
Question 3. How were coacervates formed, what properties did they have and in what direction did they evolve?
The formation of coacervates would be impossible without the interaction of organic substances with each other and with inorganic compounds. As a result of this interaction, lipids were formed from fatty acids and alcohols, peptides from amino acids, and nucleic acids from nucleotides. Lipids formed films on the surface of water bodies, while proteins formed polymeric complexes dissolved in water. Such complexes, merging with each other, formed coacervates - structures isolated from the rest of the water mass. Coacervates were able, exchanging with the environment, to concentrate various substances. Thus, the accumulation of metal ions and their interaction with proteins led to the formation of enzymes. Nucleic acids trapped in coacervates were more likely to retain their structure and not be destroyed. Coacervates had some signs of life, but they lacked biological membranes for their transformation into the first living organisms.
Question 4. Tell us how probionts arose.
Probiont membranes could be formed from lipid films on the surface of water bodies, to which coacervates floating in the water were attached. For the evolution of life, those coacervates were important, which contained not only protein, but also nucleic acids. Of their complexes with lipids, only those that proved capable of self-reproduction of nucleic acids can be considered living organisms. This is how probionts arose - primitive heterotrophs living at the expense of organic matter abiogenic origin ("primary broth"). At this stage, chemical evolution ended and biological evolution began.
Question 5. Describe how the complication could have happened. internal structure the first heterotrophs.
Gradually, the amount of organic substances of abiogenic origin began to decrease. This led to fierce competition between probionts, which accelerated the emergence of autotrophs that use energy to create organic matter. sunlight. The first autotrophs used an oxygen-free way of photosynthesis. Later, cyanobacteria appeared, capable of photosynthesis with the release of oxygen. The accumulation of oxygen in the atmosphere resulted, firstly, in the emergence of aerobic organisms, and secondly, in the formation of a protective ozone layer.
In parallel, there was a complication of the internal structure of cells, which eventually led to the emergence of eukaryotes. Some heterotrophs entered into symbiosis with aerobic bacteria, capturing them and using them as "energy stations" - future mitochondria. Such symbionts gave rise to animals and fungi. Other heterotrophs, in addition to aerobic bacteria, captured autotrophic cyanobacteria, which became chloroplasts. This is how the precursors of plants appeared.
Question 6. Why is the spontaneous generation of life impossible in modern conditions?
Spontaneous generation of life on Earth is currently impossible, because in the conditions of the modern oxygen-rich atmosphere organic compounds are quickly destroyed, do not accumulate and do not reach the proper degree of complexity. In addition, the appearance of coacervates and probionts does not occur due to the huge number of heterotrophs, which very quickly "eat" any accumulation of organic substances.
The origin of life on Earth is a key and unresolved problem of natural science, often serving as a ground for a clash between science and religion. If the existence of the evolution of living matter in nature can be considered proven, since its mechanisms were discovered, archaeologists discovered ancient, more simply arranged organisms, then no hypothesis of the origin of life has such an extensive evidence base. We can observe evolution with our own eyes, at least in selection. No one has been able to create a living thing from an inanimate one.
Despite the large number of hypotheses about the origin of life, only one of them has an acceptable scientific explanation. It's a hypothesis abiogenesis- long chemical evolution, which proceeded in special conditions ancient earth and preceded biological evolution. At the same time, from inorganic substances at first, simple organic ones were synthesized, of which more complex ones, then biopolymers appeared, the next stages are more speculative and hardly proven. The hypothesis of abiogenesis has many unresolved problems, different views on certain stages of chemical evolution. However, some of its points were confirmed empirically.
Other hypotheses for the origin of life - panspermia(introduction of life from space), creationism(creation by the creator), spontaneous generation(living organisms suddenly appear in inanimate matter), steady state (life has always existed). The impossibility of spontaneous generation of life in the inanimate was proved by Louis Pasteur (XIX century) and a number of scientists before him, but not so categorically (F. Redi - XVII century). The panspermia hypothesis does not solve the problem of the origin of life, but transfers it from Earth to outer space or to other planets. However, it is difficult to refute this hypothesis, especially those of its representatives who claim that life was brought to Earth not by meteorites (in this case, living things could burn out in the layers of the atmosphere, undergo destructive action cosmic radiation etc.), but by rational beings. But how did they get to Earth? From the point of view of physics (the huge size of the Universe and the inability to overcome the speed of light), this is hardly possible.
For the first time, possible abiogenesis was substantiated by A.I. Oparin (1923-1924), later this hypothesis was developed by J. Haldane (1928). However, the idea that life on Earth could be preceded by the abiogenic formation of organic compounds was expressed by Darwin. The theory of abiogenesis has been finalized and is being finalized by other scientists to this day. Its main unresolved problem is the details of the transition from complex non-living systems to simple living organisms.
In 1947, J. Bernal, based on the developments of Oparin and Haldane, formulated the theory of biopoiesis, distinguishing three stages in abiogenesis: 1) the abiogenic occurrence of biological monomers; 2) formation of biopolymers; 3) the formation of membranes and the formation of primary organisms (protobionts).
Abiogenesis
The hypothetical scenario of the origin of life according to the theory of abiogenesis is described below in general terms.
The age of the Earth is about 4.5 billion years. Liquid water on the planet, so necessary for life, according to scientists, appeared no earlier than 4 billion years ago. At the same time, 3.5 billion years ago, life on Earth already existed, which is proved by the discovery of rocks of such ages with traces of the vital activity of microorganisms. Thus, the first simple organisms arose relatively quickly - in less than 500 million years.
When the Earth first formed, its temperature could reach 8000 °C. When the planet cooled, metals and carbon, as the heaviest elements, condensed and formed the earth's crust. At the same time, volcanic activity was taking place, the crust was moving and contracting, folds and ruptures formed on it. Gravitational forces led to the compaction of the crust, while energy was released in the form of heat.
Light gases (hydrogen, helium, nitrogen, oxygen, etc.) were not retained by the planet and escaped into space. But these elements remained in the composition of other substances. Until the temperature on Earth dropped below 100°C, all water was in a vapor state. After lowering the temperature, evaporation and condensation were repeated many times, heavy showers with thunderstorms. Hot lava and volcanic ash, once in the water, created different environmental conditions. In some, certain reactions could take place.
Thus, physical and chemical conditions on the early Earth were favorable for the formation of organic substances from their inorganic. The atmosphere was of a reducing type, there was no free oxygen and no ozone layer. Therefore, ultraviolet and cosmic radiation penetrated the Earth. Other sources of energy were the warmth of the earth's crust, which has not yet cooled down, erupting volcanoes, thunderstorms, radioactive decay.
Methane, carbon oxides, ammonia, hydrogen sulfide, cyanide compounds, and water vapor were present in the atmosphere. A number of the simplest organic substances were synthesized from them. Further, amino acids, sugars, nitrogenous bases, nucleotides and other more complex organic compounds could be formed. Many of them served as monomers for future biological polymers. The absence of free oxygen in the atmosphere favored the reactions.
Chemical experiments (for the first time in 1953 by S. Miller and G. Urey), simulating the conditions of the ancient Earth, proved the possibility of abiogenic synthesis of organic substances from inorganic ones. When electrical discharges are passed through gas mixture, imitating the primitive atmosphere, in the presence of water vapor, amino acids were obtained, organic acids, nitrogenous bases, ATP, etc.
It should be noted that in the ancient atmosphere of the Earth, the simplest organic substances could be formed not only abiogenically. They were also brought from space, contained in volcanic dust. Moreover, it could be quite large amounts of organic matter.
Low molecular weight organic compounds accumulated in the ocean, creating the so-called primordial soup. Substances were adsorbed on the surface of clay deposits, which increased their concentration.
Under certain conditions of the ancient Earth (for example, on clay, the slopes of cooling volcanoes), polymerization of monomers could occur. This is how proteins and nucleic acids were formed - biopolymers, which later became the chemical basis of life. In an aqueous environment, polymerization is unlikely, since depolymerization usually occurs in water. Experience has proven the possibility of synthesizing a polypeptide from amino acids in contact with pieces of hot lava.
The next important step towards the origin of life is the formation of coacervate drops in water ( coacervates) from polypeptides, polynucleotides, other organic compounds. Such complexes could have a layer on the outside that imitated a membrane and preserved their stability. Coacervates were obtained experimentally in colloidal solutions.
Protein molecules are amphoteric. They attract water molecules to themselves so that a shell forms around them. Colloidal hydrophilic complexes are obtained, isolated from the water mass. As a result, an emulsion is formed in water. Further, the colloids merge with each other and form coacervates (the process is called coacervation). The colloidal composition of the coacervate depended on the composition of the medium in which it was formed. In different reservoirs of the ancient Earth, coacervates of different chemical composition were formed. Some of them were more stable and could, to a certain extent, carry out selective metabolism with the environment. There was a kind of biochemical natural selection.
Coacervates are able to selectively absorb certain substances from the environment and release into it some products of chemical reactions occurring in them. It's like metabolism. As the substances accumulated, the coacervates grew, and when they reached a critical size, they broke up into parts, each of which retained the features of the original organization.
In the coacervates themselves could occur chemical reactions. During the absorption of metal ions by coacervates, enzymes could be formed.
In the process of evolution, only such systems remained that were capable of self-regulation and self-reproduction. This marked the onset of the next stage in the origin of life - the emergence protobionts(according to some sources, this is the same as coacervates) - bodies that have a complex chemical composition and a number of properties of living beings. Protobionts can be considered as the most stable and successful coacervates.
The membrane could be formed in the following way. Fatty acids combine with alcohols to form lipids. Lipids formed films on the surface of water bodies. Their charged heads face into the water, while the non-polar ends face out. Protein molecules floating in water were attracted to the heads of lipids, resulting in the formation of double lipoprotein films. From the wind, such a film could bend, and bubbles formed. Coacervates may have been accidentally trapped in these vesicles. When such complexes again appeared on the surface of the water, they were already covered with a second lipoprotein layer (due to hydrophobic interactions of non-polar ends of lipids facing each other). General scheme The membrane of today's living organisms has two layers of lipids inside and two layers of proteins located at the edges. But over millions of years of evolution, the membrane became more complex due to the inclusion of proteins immersed in the lipid layer and penetrating it, protrusion and protrusion of individual sections of the membrane, etc.
Coacervates (or protobionts) could get already existing nucleic acid molecules capable of self-reproduction. Further, in some protobionts, such a rearrangement could occur that the nucleic acid began to encode the protein.
The evolution of protobionts is no longer chemical, but prebiological evolution. It led to an improvement in the catalytic function of proteins (they began to play the role of enzymes), membranes and their selective permeability (which makes the protobiont a stable set of polymers), the emergence of matrix synthesis (transfer of information from nucleic acid to nucleic acid and from nucleic acid to protein).
| Evolution | results | |
|---|---|---|
| 1 | Chemical evolution - synthesis of compounds |
|
| 2 | Prebiological evolution - chemical selection: the most stable, self-reproducing protobionts remain |
|
| 3 | biological evolution- biological selection: the struggle for existence, the survival of the most adapted to environmental conditions |
|
One of the biggest mysteries about the origin of life is how RNA came to code for the amino acid sequence of proteins. The question refers to RNA, not DNA, since it is believed that at first ribonucleic acid played not only a role in the implementation of hereditary information, but was also responsible for its storage. DNA replaced it later, emerging from RNA by reverse transcription. DNA is better at storing information and is more stable (less prone to reactions). Therefore, in the process of evolution, it was she who was left as the custodian of information.
In 1982, T. Chek discovered the catalytic activity of RNA. In addition, RNA can be synthesized under certain conditions even in the absence of enzymes, and also form copies of themselves. Therefore, it can be assumed that RNAs were the first biopolymers (the RNA world hypothesis). Some sections of RNA could accidentally encode peptides useful for the protobiont, while other sections of RNA became excised introns in the course of evolution.
In protobionts arose Feedback- RNA encodes enzyme proteins, enzyme proteins increase the amount of nucleic acids.
Beginning of biological evolution
Chemical evolution and the evolution of protobionts lasted more than 1 billion years. Life arose, and its biological evolution began.
Some protobionts gave rise to primitive cells, which include the totality of the properties of living things that we observe today. They implemented the storage and transmission of hereditary information, its use to create structures and metabolism. Energy for life processes was provided ATP molecules, membranes typical of cells appeared.
The first organisms were anaerobic heterotrophs. They obtained the energy stored in ATP through fermentation. An example is glycolysis - the oxygen-free breakdown of sugars. These organisms ate at the expense of organic substances of the primary broth.
But stocks organic molecules were gradually depleted, as the conditions on the Earth changed, and the new organic matter was almost no longer synthesized abiogenically. Under conditions of competition for food resources, the evolution of heterotrophs accelerated.
The advantage was gained by bacteria, which turned out to be able to fix carbon dioxide with the formation of organic substances. Autotrophic synthesis of nutrients is more complex than heterotrophic nutrition, so it could not have arisen in early life forms. From some substances, under the influence of the energy of solar radiation, compounds necessary for the cell were formed.
The first photosynthetic organisms did not produce oxygen. Photosynthesis with its release most likely appeared later in organisms similar to the current blue-green algae.
The accumulation of oxygen in the atmosphere, the appearance of an ozone screen, and a decrease in the amount of ultraviolet radiation led to the almost impossibility of the abiogenic synthesis of complex organic substances. On the other hand, emerging life forms have become more resilient under such conditions.
Spread across the earth oxygen respiration. Anaerobic organisms have survived only in a few places (for example, there are anaerobic bacteria living in hot underground springs).
| Abiogenic synthesis of organic molecules. Modern views to the emergence of life. Is life possible on Earth now?? | The date: Lesson 47 Class 9 |
|||
| Expected Lesson Outcomes | ||||
| Lesson Objectives | educational Formation of conscious ideas about evolution as a historical development organic world on the ground. Consider different theories of the origin of life on Earth, analyze the arguments "for" and "against" Educational Development of thinking, the ability to apply it in cognitive and communicative practice Development of the ability to build logical reasoning, inference and draw conclusions; analyze and highlight the main thing from the proposed material. Educational Formation of scientific outlook. Education of a tolerant attitude towards dissidents - supporters of other points of view that differ from generally accepted ones; |
|||
| Lesson type | combined |
|||
| Type of lesson | study |
|||
| Work form | Group individual |
|||
| Equipment | Handouts, whatman paper, felt-tip pens |
|||
| "Oh, solve for me the riddle of life, painful ancient riddle over which so much has already beaten heads, heads in hats painted with hieroglyphs, heads in turbans and black berets, heads in wigs and thousands of other poor human heads ... " G. Heine. |
||||
| time | Stage / activity | resources |
||
| Org moment. 3 min Knowledge update | Dear friends, I think all of you, without exception, have asked yourself the question: “How did life originate on our planet?” Today we will try to solve this age-old "mystery of life", over which, as can be seen from the epigraph of our lesson, a lot of smart heads thought about it. To do this, we will pose problematic questions. Lesson topic Determination of goals How did life originate on Earth? What are the modern views and hypotheses of the origin of life on Earth? Which of them are the most persuasive? WHAT IS LIFE Friedrich Engels: “Life is a mode of existence of protein bodies, the essential point of which is the constant exchange of substances with the external nature surrounding them, and with the cessation of this metabolism, life also ceases, which leads to the decomposition of the protein.” | |||
| Checking d.z 5 minutes | Test " evolutionary doctrine» 1. Evolution is called: a) individual development of organisms b) change of individuals c) historical irreversible development of the organic world d) changes in plant and animal life 2 , Main driving force evolution is: a) variability b) heredity c) struggle for existence d) natural selection 3. The struggle for existence is: a) competition between organisms for environmental conditions b) the destruction of individuals of one species by individuals of another species c) symbiotic relationships of some species with others d) dispersal of the species to a new territory 4. Sexual selection is: a) natural selection occurring between individuals of the same sex during the breeding season b) natural selection, due to: competition of individuals of different sexes of the same species for food c) a form of artificial selection aimed at the destruction of males (for example, in chickens, ducks) 5. Not examples of natural action selection: a) the pedigree of the Spanish Great Dane. b) industrial melanism of insects c) bacterial resistance to antibiotics d) resistance of houseflies to pesticides 6. Mimicry is: a) the similarity of a defenseless and edible species with one or more unrelated species that are well protected and have a warning color b) similarity in shape and color of individuals of two related species. c) the presence of special means of protection in individuals of the species 7. Aromorphosis is one of the following evolutionary events: a) the emergence of a class of birds b) the emergence of a large number of families of a number of predatory mammals | |||
| Learning new material 7 minutes | Tasks: 1 make a cluster 2. draw conclusions Compilation of clusters by groups. Group 1 Abiogenic synthesis of organic substances Group 2 Modern views on the origin of life Group 3 Development of ideas about the origin of life | |||
| Primary fastening 5 minutes | Algorithm for writing a discussion essay: Discussed topic (problem). My position. Brief rationale. Possible objections that others may raise. The reason why this position is still correct. Conclusion | |||
| Reflection | open mic | |||
| 3 min House. exercise | Formulate a new hypothesis for the origin of life on Earth Geologists, biologists and all paleontologists Geneticists and chemists Breaking their heads Or maybe one of you Create your own hypothesis How, why, when and where Did life originate on Earth? | |||
I. Abiogenic synthesis of organic substances - formation of organic substances from inorganic
1. Occurred 3.5 billion years ago
2. Carried out in two stages in the primary ocean:
The first stage is the formation of low molecular weight organic compounds
- hydrocarbons (CH4) of the primary atmosphere reacted with water vapor, NH3, H2, CO2, CO, N2 with the formation of intermediate organic compounds: alcohols, aldehydes, ketones, organic acids, which rained into the ocean
- intermediate compounds in the primary ocean turned into monosaccharides, amino acids, nucleotides, phosphates - ATP (energy sources for synthesis could be electric lightning discharges, ultraviolet radiation, thermal energy, shock waves, energy from erupting volcanoes, tidal energy, etc.)
- the possibility of such a synthesis was experimentally proven in 1953 by S. Miller (amer) in a sealed apparatus with boiling water and a refrigerator, simulating the conditions that existed on Earth 4 billion years ago, in which a mixture of CH4, NH4 and H2 gases was placed while passing through it, low molecular weight organic compounds were obtained - urea, alcohols, aldehydes, organic acids, monosaccharides, fatty acids, various amino acids (in the case of using ionizing UV radiation or heat up to 600 instead of electric discharges, other amino acids, fatty acids, sugars were obtained - ribose, deoxyribose, nitrogenous bases - nucleotides)
- the possibility of abiogenic synthesis of organic compounds is confirmed by the fact that they are found in space (formaldehydes, formic acid, ethanol, and etc.)
The second stage is the synthesis of high-molecular organic substances from simple organic compounds - biopolymers: proteins, lipids, polysaccharides, nucleic acids (RNA)
1 Occurred In The Primordial Ocean
2. Carried out as a result of polycondensation reactions (polymerization); the required energy was achieved by a temperature of about 100 C or by ionizing radiation with the removal of free water (S. Fox, Amer., 1997)
3. The concentration of low molecular weight substances necessary to start the reaction was achieved as a result of their adsorption in bottom clay sediments or porous volcanic tuffs.
(experimentally shown that an aqueous solution of amino acids in the presence of alumina and ATP can give polymer chains - polypeptides)
4. The water of the seas and oceans was saturated with biopolymers of abiogenic origin, forming the so-called. "primal broth"
Modern views on the origin of life
Hypothesis of A. I. Oparin. The most significant feature of AI Oparin's hypothesis is the gradual complication of the chemical structure and morphological appearance of the precursors of life (probionts) on the way to living organisms.
A large amount of data suggests that the coastal regions of the seas and oceans could be the environment for the origin of life. Here, at the junction of the sea, land and air, favorable conditions were created for the formation of complex organic compounds. For example, solutions of certain organic substances (sugars, alcohols) are highly stable and can exist indefinitely. In concentrated solutions of proteins, nucleic acids, clots can form, similar to gelatin clots in aqueous solutions. Such clots are called coacervate drops or coacervates (Fig. 70). Coacervates are able to adsorb various substances. From the solution, chemical compounds enter them, which are transformed as a result of reactions occurring in coacervate drops, and are released into the environment.
Coacervates are not yet living beings. They show only an outward resemblance to such signs of living organisms as growth and metabolism with the environment. Therefore, the emergence of coacervates is considered as a stage in the development of pre-life.
Coacervates have undergone a very long selection for the stability of the structure. Stability was achieved due to the creation of enzymes that control the synthesis of certain compounds. The most important stage in the origin of life was the emergence of a mechanism for reproducing one's own kind and inheriting the properties of previous generations. This became possible due to the formation of complex complexes of nucleic acids and proteins. Nucleic acids capable of self-replication began to control the synthesis of proteins, determining the order of amino acids in them. And enzyme proteins carried out the process of creating new copies of nucleic acids. This is how the main property characteristic of life arose - the ability to reproduce molecules similar to itself.
Living beings are so-called open systems, i.e. systems into which energy comes from outside. Without energy, life cannot exist. As you know, according to the methods of energy consumption (see Chapter III), organisms are divided into two large groups: autotrophic and heterotrophic. Autotrophic organisms directly use solar energy in the process of photosynthesis (green plants), heterotrophic organisms use energy that is released during the decay of organic substances.
Obviously, the first organisms were heterotrophs, obtaining energy by the oxygen-free splitting of organic compounds. At the dawn of life, there was no free oxygen in the Earth's atmosphere. The emergence of an atmosphere of modern chemical composition is closely connected with the development of life. The emergence of organisms capable of photosynthesis led to the release of oxygen into the atmosphere and water. In its presence, oxygen splitting of organic substances became possible, in which many times more energy is obtained than with anoxic.
From the moment of its origin, life forms a single biological system - the biosphere (see Chapter XVI). In other words, life arose not in the form of separate isolated organisms, but immediately in the form of communities. The evolution of the biosphere as a whole is characterized by constant complication, i.e., the emergence of more and more complex structures.
Is life possible on Earth now? From what we know about the origin of life on Earth, it is clear that the process of the emergence of living organisms from simple organic compounds was extremely long. In order for life to originate on Earth, it took an evolutionary process that lasted for 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 now on Earth somewhere in areas of intense volcanic activity quite complex organic compounds can arise, then the probability of any prolonged existence of these compounds is negligible. They will immediately be oxidized or used by heterotrophic organisms. Charles Darwin understood this very well. In 1871, he wrote: “But now ... in some warm reservoir containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, etc., a protein 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.
Life originated on Earth in an abiogenic way. At present, the living comes only from the living (biogenic origin). The possibility of the re-emergence of life on Earth is excluded.
Development of ideas about the origin of life
theory of the origin of life on earth. From ancient times to our time, countless hypotheses have been put forward about the origin of life on Earth. All their diversity comes down to two mutually exclusive points of view.
Proponents of the theory of biogenesis (from the Greek "bios" - life and "genesis" - origin) believed that all living things come only from living things. Their opponents defended the theory of abiogenesis ("a" - Latin, negative prefix); they considered possible the origin of the living from the non-living.
Many scientists of the Middle Ages admitted the possibility of spontaneous generation of life. According to them, fish could be born from silt, worms from soil, mice from mud, flies from meat, etc.
Against the theory of spontaneous generation in the 17th century. the Florentine doctor Francesco Redi spoke. Putting the meat in a covered pot, Redi showed that blowfly larvae do not spontaneously reproduce in rotten meat. Supporters of the theory of spontaneous generation did not give up, they argued that spontaneous generation of larvae did not occur for the sole reason that air did not enter the closed pot. Then Redi placed the pieces of meat in several deep vessels. He left some of them open, and covered some with muslin. After some time, in the open vessels, the meat swarmed with fly larvae, while in the vessels covered with muslin, there were no larvae in the rotten meat.
The microscope opened the microworld to people. Observations showed that in a tightly closed flask with meat broth or hay infusion, microorganisms are detected after a while. But as soon as the meat broth was boiled for an hour and the neck was sealed, nothing appeared in the sealed flask. Vitalists suggested that prolonged boiling kills the "life force" that cannot penetrate the sealed flask.
Disputes between supporters of abiogenesis and biogenesis continued into the 19th century. Even Lamarck in 1809 wrote about the possibility of spontaneous generation of fungi.
Pasteur experiment. With the advent of Darwin's book "The Origin of Species", the question arose again of how life on Earth nevertheless arose. The French Academy of Sciences in 1859 appointed a special prize for an attempt to elucidate in a new way the question of spontaneous generation. This award was received in 1862 by the famous French scientist Louis Pasteur.
LOUIS PASTEUR (1822-1895) - French microbiologist and chemist. Founder of microbiology. Discovered anaerobic bacteria. Showed the energy value of fermentation. Investigated the problem of the possibility of the origin of life. He proposed vaccinations against rabies, anthrax, as well as pasteurization (heating to 70 ° C) as a way to destroy live bacteria (but not their spores) to preserve food.
L. Pasteur conducted an experiment that rivaled Redi's famous experiment in simplicity. He boiled various nutrient media in a flask in which microorganisms could develop. Prolonged boiling in the flask killed not only microorganisms, but also their spores. Mindful of the vitalists' contention that the mythical "life force" could not penetrate a sealed flask, Pasteur attached an S-shaped tube with a free end to it (Fig. 68). Spores of microorganisms settled on the surface of a thin curved tube and could not penetrate into the nutrient medium. Well boiled culture medium remained sterile, no spontaneous generation of microorganisms was observed in it, although air access (and with it the notorious “life force”) was provided.
Rice. 68. Scheme of the experiment of L. Pasteur in flasks with an S-shaped neck.
A - in a flask with an S-shaped neck, the nutrient medium after boiling remains sterile for a long time; B - if you remove the S-shaped throat, then microorganisms quickly develop in the medium
Pasteur, by his experiments, proved the impossibility of the spontaneous generation of life. The concept of "life force" - vitalism was dealt a crushing blow.
Abiogenic synthesis of organic substances. Pasteur's experiment demonstrated the impossibility of spontaneous generation of life at the present time. The question of the origin of life on our planet has long remained open.
In 1924, the famous biochemist A.I. Oparin suggested that with powerful electric discharges in earth's atmosphere, which 4-4.5 billion years ago consisted of ammonia, methane, carbon dioxide and water vapor, the simplest organic compounds necessary for the emergence of life could arise. Academician Oparin's prediction was confirmed. In 1955, the American researcher S. Miller, passing electric discharges up to 60,000 V through a mixture of CH 4, NH 3, H 2 and H 2 0 vapors under a pressure of several pascals at a temperature of 80 ° C, obtained the simplest fatty acids, urea , acetic and formic acids and several amino acids, including glycine and alanine (Fig. 69).
Rice. 69. Scheme of the device S. Miller, in which amino acids are synthesized
As we already know, amino acids are the building blocks from which protein molecules are built. Therefore, experimental proof of the possibility of the formation of amino acids from inorganic compounds is an extremely important indication that the first step towards the emergence of life on Earth was the abiogenic (non-biological) synthesis of organic substances (see the front flyleaf).
For people who want to constantly improve, learn something and constantly learn something new, we have specially made this category. It contains exclusively educational, useful content that you will definitely enjoy. A large number of videos, perhaps, can even compete with the education that we are given at school, college or university. The biggest advantage of instructional videos is that they try to provide the latest, most up-to-date information. The world around us in the era of technology is constantly changing, and printed educational publications simply do not have time to give out fresh information.
Among the videos you can also find educational videos for children. preschool age. There your child will be taught letters, numbers, counting, reading, etc. Agree, a very good alternative to cartoons. For students primary school you can also find tutorials English language, assistance in studying school subjects. For older students, training videos have been created that will help prepare for tests, exams, or simply deepen their knowledge in a particular subject. The acquired knowledge can qualitatively affect their mental potential, as well as please you with excellent grades.
For young people who are out of school, in university or not, there are plenty of entertaining educational videos available. They can help them deepen their knowledge of the profession for which they are studying. Or get a profession, such as a programmer, web designer, SEO optimizer, and so on. Universities do not teach such a profession yet, so you can become a specialist in this advanced and relevant area only by doing self-education, which is what we try to help by collecting the most useful videos.
For adults, this topic is also relevant, since it often happens that after working in the profession for years, it comes to the understanding that this is not yours and you want to learn something more suitable for yourself and at the same time profitable. Also among this category of people there are often videos on the type of self-improvement, saving time and money, optimizing their lives, in which they find ways to live much better and happier. Even for adults, the topic of creating and developing your own business is very well suited.
Also among the educational videos there are videos with a general focus, which are suitable for almost any age, in which you can learn about how life originated, what theories of evolution exist, facts from history, etc. They perfectly expand the horizons of a person, make him a much more erudite and pleasant intellectual interlocutor. It is really useful to watch such informative videos for everyone without exception, since knowledge is power. We wish you a pleasant and useful viewing!
In our time, it is simply necessary to be what is called "on the wave." This refers not only to news, but also to the development of one's own mind. If you want to develop, explore the world, be in demand in society and interesting, then this section is for you.
