What Stanley Miller's experiment proved. Miller experience

Kuramshin A.I.

("HiZh", 2017, No. 7)

The "Holy Grail" of chemists and biologists is the mystery of the origin of life on Earth. There are many hypotheses on this subject, but the hypothesis of abiogenesis is still considered the most harmonious, according to which the “substances of life” were formed as a result of a complex cascade of chemical reactions of relatively simple substances under the conditions of the young Earth. A weighty argument in its favor was the famous Miller-Urey experiment, in which the amino acids that make up proteins were obtained from the alleged components of the prebiotic Earth's atmosphere. 65 years later, researchers from the Czech Republic showed that nitrogenous bases of RNA could also be formed under similar conditions (Proceedings of the National Academy of Sciences USA, 2017, 114, 17, 4306-4311, doi: 10.1073/pnas.1700010114 ).
In 1952, chemists Stanley Miller and Harold Urey conducted what has become a classic experiment - they simulated the processes that could take place in the atmosphere of the ancient Earth to test the possibility of abiogenesis. A heated gaseous mixture of water, methane, ammonia, carbon monoxide and hydrogen, isolated in a glass flask, was subjected to electrical discharges, from time to time supplying fresh portions of water vapor. In this mode, the reaction was carried out for about a week.
Analyzing the resulting solution, Miller and Urey unambiguously identified the amino acids glycine, α-alanine, and β-alanine in it, and also obtained evidence for the formation of other amino acids that make up modern proteins. Decades later, when more powerful instruments appeared in the tools of analytical chemistry, 18 out of 20 proteinogenic amino acids were found in that very solution (fortunately, it had been kept in a sealed ampoule in Yuuri’s desk all this time, and after his death, in the possession of his student). The remaining two, cysteine ​​and methionine, failed simply because there was no source of sulfur in Miller and Urey's original experiments.
Although these results have always been considered a strong argument in favor of the concept of abiogenesis, there have been criticisms. The main claims of critics: when simulating the atmosphere of the early Earth, the researchers took a gas mixture with too significant reducing abilities, moreover, amino acids for the emergence of life
not enough, we need more nucleotides.
Since then, many experiments have been carried out in which it was possible to obtain both nitrogenous bases and nucleotides from relatively simple molecules (for more details, see. ). Employees of the Institute of Physical Chemistry of the Academy of Sciences of the Czech Republic, working under the guidance of Svätopluk Civish, decided to reproduce the good old experiment, slightly changing its conditions. A lot of things in the new version remained the same - the reducing gas mixture from NH 3 , CO and H 2 Oh, electrical impulses. However, the researchers added irradiation of the system with a powerful laser - in their opinion, this was supposed to simulate plasma discharges in the Earth's atmosphere, which arose due to shock waves caused by large meteorites regularly falling to Earth. As a result, they managed to obtain not only amino acids, but also all the nitrogenous bases of ribonucleic acids.
The reactions proceeding in the experiment were described by the authors as follows. Formamide HC(O)NH 2 and hydrogen cyanide HCN, which then, interacting, give the nitrogenous base guanine. Other canonical nitrogenous bases - uracil, cytosine and adenine - were formed in amounts more modest than guanine, but their presence was also confirmed. The reaction products also contained urea and amino acids.
The researchers emphasize that their experiment did not seek to refute alternative hypotheses of abiogenesis, but to show that RNA components could be formed in various ways.

Molecules necessary for life may have originated from chemical reactions at the dawn of the Earth's development.

4.5 billion years ago, when the Earth arose, it was a hot, lifeless ball. Today, different life forms are found in abundance on it. In this regard, the question arises: what changes have occurred on our planet from the moment of its formation to the present day, and most importantly, how did the molecules that form living organisms arise on the lifeless Earth? In 1953, an experiment was performed at the University of Chicago that today has become a classic. He showed scientists the way to answer this fundamental question.

In 1953, Harold Urey was already a Nobel laureate, and Stanley Miller was just his graduate student. The idea of ​​Miller's experiment was simple: in a semi-basement laboratory, he reproduced the atmosphere of the most ancient Earth, as it was, according to scientists, and from the side watched what was happening. With Yuri's support, he assembled a simple apparatus from a glass spherical flask and tubes, in which the evaporated substances circulated in a closed circuit, cooled, and returned to the flask. Miller filled the flask with gases that Urey and the Russian biochemist Alexander Oparin (1894–1980) believed were present in the atmosphere at the dawn of the Earth's formation—water vapor, hydrogen, methane, and ammonia. To simulate solar heat, Miller heated the flask on a Bunsen burner, and to get an analog of lightning flashes, he inserted two electrodes into a glass tube. According to his plan, the material, evaporating from the flask, had to enter the tube and be exposed to an electric spark discharge. After that, the material had to be cooled and returned to the flask, where the whole cycle began again.

After two weeks of system operation, the liquid in the flask began to acquire a dark red-brown hue. Miller analyzed this liquid and found amino acids in it - the basic structural units of proteins. So scientists have the opportunity to study the origin of life in terms of basic chemical processes. Beginning in 1953, sophisticated versions of the Miller-Urey experiment, as it has since come to be known, have generated all sorts of biological molecules—including the complex proteins needed for cell metabolism and the fat molecules called lipids that make up cell membranes. Apparently, the same result could also be obtained by using other sources of energy instead of electric discharges - for example, heat and ultraviolet radiation. So there is almost no doubt that all the components necessary for the assembly of the cell could be obtained in chemical reactions that took place on Earth in ancient times.

The value of the Miller-Urey experiment lies in the fact that it showed that lightning flashes in the atmosphere of the ancient Earth over several hundred million years could cause the formation of organic molecules that fell with rain into the "primordial soup" ( see also Evolution theory). The chemical reactions that have not yet been established in this "broth" could lead to the formation of the first living cells. In recent years, serious questions have arisen about how these events developed, in particular, the presence of ammonia in the atmosphere of the most ancient Earth is questioned. In addition, several alternative scenarios have been proposed that could lead to the formation of the first cell, ranging from the enzymatic activity of a biochemical RNA molecule to simple chemical processes in the ocean depths. Some scientists even suggest that the origin of life is related to the new science of complex adaptive systems and that it is possible that life is an unexpected property of matter that appears abruptly at a certain moment and is absent from its constituent parts. Nowadays, this field of knowledge is undergoing a period of rapid development, various hypotheses appear and are being tested in it. From this maelstrom of hypotheses, a theory of how our most distant ancestors arose should emerge.

See also:

Stanley Lloyd Miller, b. 1930

American chemist. Born in Oakland, California, he was educated at the University of California at Berkeley and the University of Chicago. Beginning in 1960, Miller's professional activities were mainly associated with the University of California at San Diego, where he held the position of professor of chemistry. For his work on the Miller-Urey experiment, he was awarded the title of Research Fellow at the California Institute of Technology.

Harold Clayton Urey, 1893-1981

American chemist. Born in Walkerton, Indiana, the son of a priest. He studied zoology at the University of Montana and received his PhD in chemistry from the University of California, Berkeley. He pioneered the use of physical methods in chemistry and was awarded the Nobel Prize in Chemistry in 1934 for the discovery of deuterium, the heavy isotope of hydrogen. Later, his work was mainly associated with the study of differences in the rate of chemical reactions when using different isotopes.

"Biochemical evolution of Oparin" - 2) Formation in the primary reservoirs of the Earth from the accumulated organic compounds of biopolymers, lipids, hydrocarbons. 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. 1) Synthesis of initial organic compounds from inorganic substances in the conditions of the primary atmosphere of the primitive Earth. Oparin's theory. 1894-1980.

"The Oparin Hypothesis" - Biography. The hypothesis of spontaneous origin of life. The hypothesis of biochemical evolution. Hypothesis of the origin of life on Earth AI Oparina. Clots called coacervate drops. Biography of A.I. Oparin. English biologist. Alexander Ivanovich Oparin. Concept. Living cell. theory of the origin of life on earth. Installation by Stanley Miller. Formation of the Earth's atmosphere. Stages of the origin of life on Earth.

"Theories of biogenesis and abiogenesis" - Absence of living organisms. Theory of spontaneous generation. The heyday of the classical doctrine of spontaneous generation. Theory of spontaneous generation. Worms. Stages of the origin of life on Earth. Amino acids. Theory of biochemical evolution. Proponents of the theory of panspermia. Creationism. Theories of biogenesis and abiogenesis about the origin of living matter. Democritus. English biochemist and geneticist John Haldane. Describe the biochemical stage of chemical evolution.

"Chemical Evolution" - The Panspermia Hypothesis. Extraterrestrial origin of microorganisms. The hypothesis of spontaneous generation. Geochronology. About 8 million chemical compounds are known. The geological history of the Earth is inseparable from its biological evolution. Chemical evolution and biogenesis. Geological scale. Protostar - Sun. The sun warmed the interior. Radioactivity. Russian chemist A.P. Rudenko. As the atomic number increases, the prevalence of elements decreases.

"Theory of biochemical evolution" - Life was created by a supernatural being. The formation of a membrane structure. The hypothesis of biochemical evolution. A hypothesis that considers life as the result of a long evolution. The third stage was characterized by isolation. The concentration of substances in coacervate drops. Molecules of many substances. simple molecules. The first primitive living organisms. Long filamentous molecules. "Primary broth". One of the main features of living things is the ability to replicate.

"Hypothesis of biochemical evolution" - The process that led to the emergence of life on Earth. Origin of life on earth. Primary broth. Miller, Stanley Lloyd. Oparin-Haldane theory. Miller-Urey experiment. Various aspects. conditions for the origin of life. Hypothesis of A. I. Oparin. Coacervate drops.

Main article: Miller-Urey experiment

One of the most famous hypotheses of evolution was published in the twenties of the XX century by the Russian researcher A. I. Oparin and the British researcher J. Haldane. The theory stated that conditions on Earth at that time favored chemical reactions. From inorganic compounds in the atmosphere and the sea, complex organic compounds were to be synthesized. The necessary energy was supplied by very intense ultraviolet irradiation, which could freely penetrate the atmosphere due to the low content of O 2 and O 3 in it.

In 1953, this theory was substantiated by chemists Stanley Miller and Harold C. Urey with very good results from the primordial soup experiment. They proved experimentally that in an environment similar to an environment with supposedly prebiotic conditions, through the influx of energy from the outside (lightning), from inorganic compounds (water, methane, ammonia and hydrogen), amino acids and simpler carboxylic and fatty acids can arise - some of the most important building blocks of biomolecules (moreover, modern studies of the surviving contents of Miller's flasks showed that they contained more amino acids than Miller could detect).

In later, in most cases, more complex experiments with primordial broth, experimenters were able to obtain both all the most important building blocks of living beings - amino acids, fats, sugars, nucleotides - and more complex organic compounds - porphins and isoprenoids [ source not specified 1264 days] .

According to biochemist Robert Shapiro, the amino acids synthesized by Miller and Urey are much less complex molecules than nucleotides. The simplest of those 20 amino acids that are part of natural proteins has only two carbon atoms, and 17 amino acids from the same set have six or more. Amino acids and other molecules synthesized by Miller and Urey contained no more than three carbon atoms. And nucleotides in the process of such experiments were only obtained in 2009.

Although this showed the possibility of the natural formation of organic molecules, these results are sometimes criticized today. In the primordial soup experiment, it was assumed that the atmosphere at that time had an alkaline character, which corresponded to the scientific ideas of that time. Today, however, it is assumed that the atmosphere is weakly alkaline or even neutral, although the issue has not yet been finally resolved and local chemical deviations of atmospheric conditions are also discussed, for example, in the vicinity of volcanoes. Later experiments proved the possibility of the appearance of organic molecules even under these conditions, even those that did not turn out in the first experiments, but in much smaller quantities. This often argues that the origin of organic molecules in a different way played at least an additional role. Theories of the origin of organics in the vicinity of hydrothermal vents of mid-ocean ridges are also presented.

As an argument against the origin of organic molecules from the primordial broth, the fact is sometimes cited that during the experiment a racemate is obtained, that is, an equal mixture of the L and D forms of amino acids. Accordingly, there must have been a natural process in which a certain variant of chiral molecules was preferred. Some space biologists argue that it is easier to prove the origin of organic compounds in space, since, in their opinion, photochemical processes with circularly polarized radiation, such as from pulsars, are only able to destroy molecules of a certain rotation. Indeed, chiral organic molecules found in meteorites were dominated by 9% left-handed. However, in 2001 Alan Saghatelian showed that self-replicating peptide systems are also able to efficiently select molecules of a certain rotation in a racemic mixture, which makes possible the terrestrial origin of polymers from certain optical isomers.

Molecules necessary for life may have originated from chemical reactions at the dawn of the Earth's development.

4.5 billion years ago, when the Earth arose, it was a hot, lifeless ball. Today, different life forms are found in abundance on it. In this regard, the question arises: what changes have occurred on our planet from the moment of its formation to the present day, and most importantly, how did the molecules that form living organisms arise on the lifeless Earth? In 1953, an experiment was performed at the University of Chicago that today has become a classic. He showed scientists the way to answer this fundamental question.

In 1953, Harold Urey was already a Nobel laureate, and Stanley Miller was just his graduate student. The idea of ​​Miller's experiment was simple: in a semi-basement laboratory, he reproduced the atmosphere of the most ancient Earth, as it was, according to scientists, and from the side watched what was happening. With Yuri's support, he assembled a simple apparatus from a glass spherical flask and tubes, in which the evaporated substances circulated in a closed circuit, cooled, and returned to the flask. Miller filled the flask with gases that Urey and the Russian biochemist Alexander Oparin (1894–1980) believed were present in the atmosphere at the dawn of the Earth's formation—water vapor, hydrogen, methane, and ammonia. To simulate solar heat, Miller heated the flask on a Bunsen burner, and to get an analog of lightning flashes, he inserted two electrodes into a glass tube. According to his plan, the material, evaporating from the flask, had to enter the tube and be exposed to an electric spark discharge. After that, the material had to be cooled and returned to the flask, where the whole cycle began again.

After two weeks of system operation, the liquid in the flask began to acquire a dark red-brown hue. Miller analyzed this liquid and found amino acids in it - the basic structural units of proteins. So scientists have the opportunity to study the origin of life in terms of basic chemical processes. Beginning in 1953, sophisticated versions of the Miller-Urey experiment, as it has since come to be known, have generated all sorts of biological molecules—including the complex proteins needed for cell metabolism and the fat molecules called lipids that make up cell membranes. Apparently, the same result could also be obtained by using other sources of energy instead of electric discharges - for example, heat and ultraviolet radiation. So there is almost no doubt that all the components necessary for the assembly of the cell could be obtained in chemical reactions that took place on Earth in ancient times.

The value of the Miller-Urey experiment lies in the fact that it showed that lightning flashes in the atmosphere of the ancient Earth over several hundred million years could cause the formation of organic molecules that fell with rain into the "primordial soup" (see also Theory of Evolution). The chemical reactions that have not yet been established in this "broth" could lead to the formation of the first living cells. In recent years, serious questions have arisen about how these events developed, in particular, the presence of ammonia in the atmosphere of the most ancient Earth is questioned. In addition, several alternative scenarios have been proposed that could lead to the formation of the first cell, ranging from the enzymatic activity of a biochemical RNA molecule to simple chemical processes in the ocean depths. Some scientists even suggest that the origin of life is related to the new science of