L ORIGEN DE LA VIDA THE ORIGIN OF LIFE

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1 L ORIGEN DE LA VIDA Xavier Hernández Alias 1 1 Estudiant de Bioquímica, Universitat de Barcelona xa.he.al@gmail.com Resum Alexander Oparin estableix en el seu llibre L'origen de la vida la base d'una nova concepció per entendre aquest procés. Explica de manera exhaustiva l'origen de la vida mitjançant l'ús dels coneixements i tecnologies disponibles en aquell moment. En el aquest treball, es descriu l'origen de la vida a través de la perspectiva d'oparin, des de l'aparició dels primers compostos orgànics fins a la creació de les primeres formes de vida. És interessant constatar que el pensament d'oparin era molt avançat en el seu temps, i la majoria dels seus raonaments segueixen sent vàlids avui. Avui en dia, el llegat d'oparin encara és viu, de manera que la seva teoria és generalment acceptat per la comunitat científica. Tot i això, s han desenvolupat nous experiments i descobriments en els últims anys, la qual cosa ha permès (i permetrà) una millor comprensió d'aquest procés complex. Paraules clau: Oparin, evolució, història. THE ORIGIN OF LIFE Xavier Hernández Alias 1 1 Biochemistry Student, University of Barcelona xa.he.al@gmail.com Abstract Alexander Oparin establishes in his book The Origin of Life the basis of a new conception of understanding this process. He explains exhaustively the origin of life by using the knowledge and technologies available at that moment. In the project presented, we describe the origin of life from the perspective of Oparin, since the apparition of the first organic compounds until the creation of first kinds of life. It is interesting to see that Oparin s thinking was extremely advanced at his time, and most of their ideas are still valid today. Nowadays, the legacy of Oparin is still alive, thus his theory is generally accepted by the scientific community. Nevertheless, new experiments and discoveries have taken place in the recent years, which has enabled (and will enable) a posterior perfection of that complex process.

2 Paraules clau: Oparin, evolution, history. 1 WHO WAS ALEXANDER OPARIN? Alexander Ivanovich Oparin (Uglich, 1894 Moscow, 1980) was a Soviet biochemist, pioneer in the development of a scientist theory to explain the origin of life. At that time, his ideas were not well considered, as he defended a revolutionary theory where religion and idealism couldn t be fitted in. Nowadays, they have been experimentally proved and accepted by the scientific community, especially after Oparin s hypothesis was tested by Miller and Urey in The Soviet biochemist s ideas are his book The Origin of Life (1936), which is based on a pamphlet he published in This book is an enormous contribution to our understanding of how life was formed from inanimate components. In it, Oparin argues that conditions on early Earth enabled the synthesis of amino acids and their chemical evolution ended up into the first organisms. 2 THE ORIGIN OF LIFE The transition from the inanimate components until the first life being consists on a long process of gradual transformation of material. In consequence, a chemical evolution is produced until the point where material suffers a qualitative change to a new form of existence: life. Therefore, the origin of life is actually nothing different than another step in the general evolution of material, which receives an especial name and consideration. 2.1 Origin of the first organic compounds All animals, plants and bacteria are composed of organic compounds, thus they are the basis of the origin of life. The question now is How were they formed?. What is common in all life beings is carbon, which takes part of those compounds with other elements. By using spectroscopic technologies, the composition of the atmospheres in different kinds of stars has been studied (Fig. 1): Type 0 and B (15000 to ºC): younger and heater stars. They contain carbon in gas state, without forming compounds. Type A (12000ºC): they contain some simple primordial compounds, hydrocarbons, which are a combination of carbon and hydrogen. Cooler stars: they contain other combination of carbon and various elements. In meteorites, hydrocarbons have also been found, among other compounds. In fact, the composition of these meteorites is very similar to the one in the centre of the Earth. This material is known as cogenita : a nickel, iron and cobalt carbide. This cogenita is still nowadays found in our planet, which reacts with water molecules to form hydrocarbons by an inorganic route. Furthermore, these first organic compounds would react with water or ammonia to generate more complex compounds (Fig. 2, alcohols, ketones, aldehydes, amines, amides, etc.).

3 Figure 1. Composition of the atmosphere of different stars. Some studies have shown that Earth and other planets were formed by condensation of gas material from the interstellar space, which contained hydrogen, methane, ammonia and water. When hydrosphere was created, these substances were dissolved in oceans and they reacted to form those first organic compounds. It was the basis for the posterior development of the more complex substances, such as proteins. Figure 2. Reactions that led to the formation of the first organic compounds. 2.2 Origin of proteins Nowadays, it has been proved that complex substances in life beings (sugars, lipids, pigments, aromas, alkaloids, vitamins ) could be synthetized from those first organic compounds. However, we have to take into account that Earth conditions in that moment were not the same ones we have now,

4 which enabled those reactions. Moreover, although there exist a great amount of different organic compounds, all of them could be formed by a combination of three basic types of reactions: Condensation/Rupture: forming or breaking bonds between carbon atoms. Polymerization/Hydrolysis: forming or breaking an oxygen or nitrogen bond between two organic molecules. Oxidation/Reduction: redox reactions. Depending on the kind of reaction that takes place and the moment when it happens, it generates all types of complex organic compounds. In the primitive oceans, those reactions were produced in a chaotic and disordered way, forming new molecules and compounds (Fig. 3). Figure 3. First proteins and other compounds (alcohol, vitamin C, etc.) that could have been produced. One of the most important kinds of organic substances are proteins, which are the basis of life. They are formed by amino acids joined by peptic bonds. In these molecules, it is important the composition of amino acids, but also their order, which can determine the structure and function of the protein. In this sense, it is very difficult to synthesise specific proteins in laboratories. Nevertheless, it is known how they were produced in those primitive conditions. In 1953, some amino acids were synthetized in the laboratory by reproducing the conditions of the primitive atmosphere. These amino acids could be then bonded (the mechanism is not absolutely known, as peptic bonds require a great amount of energy) to form large chains of proteins. These proteins contained enormous chemical possibilities to posterior development of life. 2.3 Origin of the first colloids Life beings are not only determined by their composition, but also their organization. This basis of organisms is called protoplasm (viscose mass made of proteins and other substances), which presents certain order and regulation on chemical-physical processes. In the primitive oceans, they contained a great variety of organic compounds, but it was needed a certain organization to form the first organisms. When substances with a high molecular weight are mixed, they form colloids, which present a specific structure and relation among molecules. This phenomenon also occurs with proteins, which form an accumulation of molecules called coacervate

5 (Fig. 4). In consequence, the composition of primitive oceans was not homogeny, but there were regions with an accumulation of material (coacervates) and other with almost no substance. In a first step, the structure of coacervates was relatively simple. However, their molecules could interact with the external medium or even with other internal substances, which could provoke an alteration of their stability: they could react and disintegrate or generate new molecules by increasing their size, order and stability. For this reason, each coacervate was different depending on their chemical-physical structure. The formation of these coacervates was essential to understand the origin of first organisms, as it explains how the individuality of life beings and their interaction with the environment was created. Notwithstanding, we couldn t consider these coacervates as a life being yet. Figure 4. Images of two types of coacervates. 2.4 Origin of the life protoplasm Before continuing with the evolution to the origin of life, we must know the organization of cell protoplasm. Protoplasm is a liquid mass, like a coacervate, that contains enormous proteins or groups of proteins and other substances in a certain order. There are also some clots of material known as morphologic elements, visible at microscope: nucleus, mitochondria, etc. In fact, the most important part of protoplasm is not its spatial organization, which is relatively simple, but its established temporal order of the chemical processes, whose harmonious combination enables the conservation of the vital system. As a result, protoplasm is static, so it is constantly interacting with the surroundings. Therefore, when a chemical substance enters, it is modified and transformed by chemical reactions and, finally, it can be assimilated or disassimilated. For this reason, protoplasm is a dynamic system where new substances are assimilated and others are disintegrated, remaining a constant composition.

6 In this harmonious state, it is essential the temporal order of the reactions that take place, so the chemical transformations consist of large chains of different chemical reactions. Thanks to this rigorous order, there exist proteins with a specific sequence of amino acids. How is this order regulated? When a molecule enters in the protoplasm, a lot of reactions can be produced, but most of them at a very slow velocity. There actually exist biological catalysts called ferments, which are extremely efficient and absolutely specific. In consequence, these ferments can accelerate only those reactions that are needed in a certain moment, even though the latent possibilities of the reactive molecule. At the same time, the activity of these ferments depends on a great number of factors: temperature, acidity, oxidative potential, etc. In consequence, it exist a cycle of phenomena that regulates the protoplasm (Fig. 5). The rigorous order of the chemical reactions produces determined substances, these substances modify the chemical-physical properties of the system, and these changes modify the velocity and direction of the reactions throughout ferments, which in their turn determine the order of the reactions. This cycle lays life beings to an ultimate finality: the self-preservation of the system in interaction with the environment. The question now is: how did coacervates develop to generate this harmony of life beings? Figure 5. Diagram that shows the cycle that led to the formation of the life protoplasm. 2.5 Origin of the first organisms First of all, in the primitive oceans there existed a great diversity of coacervates, which had different chemical-physical properties (concentration of substances, simple catalysts, organization, etc.). These differences influenced on the chemical transformations that were produced. Secondly, the chemical processes that took place on those coacervates conditioned their stability. While some modifications

7 were useful and enabled the existence of the coacervate, other ones were negative and provoked its destruction. Coacervates were surrounded by other organic and inorganic molecules, so when they absorbed new substances these molecules were integrated. At the same time, there exist in the coacervates other processes of degradation. The velocity of both processes was determined by the environment conditions (temperature, concentration, pressure ) and the internal structure of the coacervates. For this reason, only those coacervates whose velocity of synthesis processes was higher than velocity of degradation ones could remain in the oceans. If not, the coacervate would disappear and its components would be re-dissolved in the oceans. In consequence, the complexity and size of coacervates would increase, and large ones would divide into smaller ones with a similar stability. Therefore, coacervates would have improved their chemical organization and, as a result, their self-preservation. Furthermore, this chemical selection would give advantage to those coacervates whose chemical dynamism was quicker. It provoked a gradual transformation of inorganic catalysts into other combinations with an organic part. Those changes that increased their efficiency and specificity would have been benefitted, since it meant a higher organization of the coacervate. Then appeared the first ferments. At the same time coacervates gained a certain order, specific proteins with a determined sequence of amino acids could be synthesized. It involved a greater stability of coacervates, which were able to carry out their vital functions. It was the origin of the first life beings. During the posterior centuries and millennia, organisms were perfected, with a higher organization of protoplasm. When organic molecules started to be in short supply, there appeared the first photosynthetic organisms, which produced their own nutrients from CO2 and solar energy. Furthermore, unicellular organisms associated one another to form multicellular structures, which have been developed along the different eras until today. REFERENCES [1] Oparin, A. (1936). The Origin of Life. [2] Solomon, E. P. (2008). Biologia. McGraw-Hill Interamericana de España S.L. [3] (15/01/2015)