Modern ideas about the origin of life. The emergence of life on Earth (briefly)

If we analyze all the data that scientists have been able to obtain in the course of various studies, it becomes evident that life on Earth is a strikingly incredible fact. The chances for its appearance in our universe are negligible. All stages of the emergence of life contained the possibility of an alternative development of events, as a result of which the world would have remained a cold space abyss without a hint, not just that of the human mind, but even of the smallest microbe. Creationists explain such an incredible event by divine intervention. However, the existence of God can not be proved or disproved, and modern ideas about the origin of life, like all science as a whole, are based on experimental data and theoretical developments that can be questioned or confirmed.

Vitalism

Human knowledge is experiencing evolution, something similar to the main points with the process described by Darwin. Theories undergo a natural selection and the strongest survive, who have managed to withstand the onslaught of counterarguments or adapt, to adapt to them. Hypotheses of the origin of life also have passed a long way of becoming, the completion of which has not even emerged, as new facts are opened every day that force to correct already established views.

A major milestone on this road was vitalism - the theory of the constant spontaneous generation of life. According to her provisions, mice appeared in old rags, worms - in decaying remains of food. Vitalism dominated science until the experiments of Louis Pasteur in 1860, when he proved the impossibility of spontaneous generation of living organisms. The results sparked paradoxical events: they strengthened the belief in the divine beginning and forced scientists to seek evidence of what they had recently refuted. Science sought to explain that the independent origin of life took place, but for a long time and it took place in stages, taking millions of years.

Carbon Synthesis

The situation seemed hopeless until the moment when, in 1864, A.M. Butlerov did not make an important discovery. He managed to get organic matter (carbon) from inorganic (in his experiment it was formaldehyde). The data obtained destroyed an impressive wall, which separated the living organisms and the world of dead matter to this day. After a while, scientists were able to get other versions of organic from inorganic substances. From this moment, modern ideas about the origin of life began to be formed. They absorbed the data not only of biology, but also of cosmology and physics.

Consequences of the Big Bang

Theories of the origin of life cover a huge period: the first prerequisites for the future formation of organisms scientists are still in the early stages of the birth of the universe. Modern physics counts the existence of the world from the Big Bang, when practically everything came out of nothing. In the rapidly expanding and cooling universe, atoms and molecules were formed first, then they began to unite, forming the stars of the first generation. They became the place for the formation of most of the elements known today to science. New atoms filled the space after the explosions of stars and became the basis for the next generation of objects, including our Sun. Modern data suggest that the first organic compounds could appear in protoplanetary clouds surrounding new stars. Of these, soon formed and planets. It turns out that the first stages of the origin of life on Earth passed before it was formed.

Autocatalytic cycles

The processes that took place on the Blue Planet in its "childhood" were supported by substances that make up its subsoil and come from outer space as meteorites. Hypotheses of the emergence of life as one of the important foundations for the birth of organic matter on Earth are called catalysts of chemical reactions, trapped here with the fragments of these "newcomers". They led to the fact that the fastest processes began to play an overwhelming role in the formation of new substances on the planet.

The next stage is autocatalytic cycles. In such processes, substances that contribute to an increase in the reaction rate are formed, as well as renewing substrates, the elements that interact. The cycle thus closed: processes themselves accelerated and themselves "cooked food," that is, substances that reacted again, catalyzing themselves and re-forming the substrate, and so on.

Doubts

Contemporary ideas about the emergence of life for a long time contained conflicting opinions. The stumbling block is the problem of chicken and eggs. What arose first: proteins that carry out all processes in the cell, or DNA, which determines the structure of these proteins, storing all hereditary information. The first are necessary for the organism, since they contribute to the self-maintenance of the system, without which life is impossible. DNA contains a record of the structure of the cell, which also determines the viability. The opinions of the scientists were divided and the answer to the question was not until the moment when it became known that as a repository of hereditary information, the viruses are not DNA, but RNA, the third class of organic compounds, which was usually assigned to the theory of the emergence of life only a secondary role.

RNA world

Gradually began to accumulate facts and in the 80 years of the last century there were data that turned the notion of the initial stages of the formation of living matter. Ribozymes, RNA molecules, possessing the ability of proteins, in particular, catalyze the reaction have been found. The first forms of life, thus, could arise without the participation of proteins and DNA. In them, the function of storing information, as well as all internal work, was performed by RNA. Life on Earth now came from proto-organisms, which are autocatalytic cycles, consisting of self-replicating ribozymes. The theory was called "RNA-world."

Coacervates

Today it is difficult to imagine the life of that period, since it did not have one important feature - the shell or the border. In fact, it was a solution containing autocatalytic cycles from RNA. The problem of the lack of boundaries necessary for the proper flow of processes, was solved in improvised ways. Proto-organisms found shelter near the minerals of zeolites, which had a lattice lattice structure. Their surface was able to catalyze the formation of RNA chains and give them a certain configuration.

Further - more: on the scene appear coacervates or water-lipid drops. Hypotheses of the origin of life, both recently and in modern times, largely rely on AI's theory. Oparin, who studied the properties of such formations. Coacervates are drops of solution encased in fat from lipids. Their membranes are characterized by selective permeability and the ability to metabolize. Some of them, apparently, were combined with chains of self-reproducing RNA, including those that catalyzed the synthesis of lipids themselves. Thus, new forms of life arose that had overcome the path from the preorganizational level to the proper organismal level. The possibility of such formations was confirmed quite recently: scientists have experimentally confirmed the ability of RNA in combination with calcium ions to attach to lipid membranes and regulate their permeability.

Skillful assistants

The origin of life at the next stage was the process of improving the functions of the organisms formed. RNA has acquired the ability to catalyze the synthesis of amino acid polymers, initially quite simple. The crowning of the adjustment of the new mechanism has become the ability to synthesize proteins. Appeared formations were several times more effective in coping with biological processes than ribozymes.

Initially, the synthesis of peptides was not ordered. The process took place "as horrible", leaving the occasion to guide the sequence of amino acids in the new chains. In due course the exact copying was fixed, because it helped to increase the stability of the whole system. So there was a genetic code that allows you to synthesize certain proteins with the necessary functions.

Improvement

The sharpening of the ability to synthesize the necessary proteins passed gradually. The first stage was the appearance of a special type of RNA that could combine amino acids. The next phase was accompanied by the construction of the process of formation of peptide molecules using bases built in a certain order. The sequence was set by the RNA template. By matching the "instructions" of informative RNA and elements of the future proteins, a new type of RNA, called transport, has been taken up. Like information, it is still important parts of the synthesis of peptides.

DNA

The complication of organisms further went along the way of improving the ways of storing information. It is assumed that initially DNA was one of the phases of the life cycle of the RNA colonies. It had a more stable structure. Its degree of protection of information was an order of magnitude higher, therefore, after some quite long time, DNA became the main repository of the genetic code.

One of the properties of the new education, at one time not allowed to put DNA at the head of the theory of the origin of life, is the inability to act actively. It became a kind of payment for the advanced functions of the information store. All the "work" was left to the proteins and RNA.

Symbiosis

Modern ideas about the origin of life do not infer as an ancestor a closed and fenced off from the rest of the body. Scientists are more inclined to support the assumption that in the first stages there were communities of microscopic similarities of cells performing different functions. Such a symbiosis is not difficult to meet in nature today. The simplest example is cyano-bacterial mats, which are simultaneously a commonwealth of microorganisms and a single whole living being.

The emergence of life on Earth biology at the present stage of its development sees a process characterized not by constant struggle and competition, but rather by the ever-growing cohesion of certain diverse structures that eventually led to the emergence of a living cell, as we imagine it today.

Generalization

Summarizing, it is possible to briefly list all the stages of life formation that appear in the framework of modern theories as the most probable version of the emergence and development of organisms on Earth:

1. Formation of primary organic compounds in protoplanetary clouds.

2. The gradual emergence of reactions that have the ability to self-accelerate, and autocatalytic cycles.

3. The appearance of autocatalytic cycles consisting of RNA.

4. Union of RNA and lipid membranes.

5. Acquisition of RNA ability to synthesize protein.

6. The emergence of DNA and its approval as the main repository of information.

7. Formation of the first unicellular organisms on the basis of symbiosis.

Understanding the processes that led to the emergence of life is still imperfect. The scientists have a lot of questions. It is not known exactly how RNA originated, many intermediate phases remain only theoretical. However, every day new experiments are put, facts and hypotheses are checked. It is safe to say that our century will give the world many more discoveries related to the prehistoric era.