A proposal to solve one of the great mysteries of science - how did life originate on Earth
Prof. Doron Lantz. "We were looking for particles that could organize spontaneously in the environment of the 'primordial soup'," says Lantz, "and we locked on the idea that these were fat-like molecules called lipids"
The question of the "origin of life" has been preoccupying the best minds for thousands of years, and yet it remains open and intriguing. In contrast to the traditional creation stories, in religion and myth, where life is identified with the complete animals and man, modern science looks for the first sign of life in primitive microscopic entities such as the separated (molecule) H-NA or the living cell. Man is a collection of organic molecules organized in a masterly order, but our body systems are the product of the evolutionary refinement of those microscopic entities, which began 4-3.5 billion years ago.
"For the sake of it," suggests Prof. Doron Lantz from the Department of Molecular Genetics at the Weizmann Institute of Science, "a living entity is one that is able to reproduce itself and pass the information stored within it to its offspring. We hypothesize that before the evolution of living things, a chemical evolution took place on Earth, and it is this that led to the creation of the first molecules capable of replicating themselves."
A primordial soup, containing a random collection of materials (among other things organic matter), covered the surface of the earth at that time, and within it these molecules developed and the first living cells were formed.
The size of these bacteria-like cells did not exceed a thousandth of a millimeter, and within them existed a rich molecular world that included proteins, lipids, hereditary material and other components. "The ability to explain the transition from a collection of animals in the chaotic 'primordial soup' to the order known in the living cell is the key to solving the question of the origin of life," says Lantz, "and we believe that there is a scientific solution to the question."
The classical theory, developed starting in the 50s, divides the "origin of life" into two main stages. In the first stage chain molecules (hereditary material such as RNA or DNA) developed in the "ancestral soup", consisting of defined and replicable building blocks, and in the second stage the proteins joined. A fatty membrane formed around the hereditary material and the proteins, and in the created intracellular space the systems necessary for life took shape.
The theory is controversial, and research groups have not stopped looking for a more comprehensive and convincing answer. "It is very doubtful whether R-NA or D-NA fragments could have formed spontaneously in the primordial soup," says Lantz, "and even if they did, the transition from these fragments to the complete living cell is conditioned by the existence of quite complicated processes."
The theory of Prof. Lantz and his students assumes a direct transition from the primordial soup to a being that has more resemblance to an entire cell than to a single cell, and the developmental milestones they propose are different from those mentioned in most textbooks and articles dealing with the subject. "We researched and looked for particles that could organize spontaneously in the 'primordial soup' environment, and we came to the idea that these particles were fat-like molecules called lipids."
There is clear evidence that lipids inhabited the early Earth, and were able to survive in the conditions that prevailed there. Furthermore, the lipid molecules are made up of a water-loving part (hydrophilic) and a water-repelling part (hydrophobic), and in an aqueous environment they tend to organize spontaneously and form "micelles" (three-dimensional fat balls), reminiscent of the fat droplets we see in milk. "We hypothesize that even in the watery environment of the primordial soup, they arranged themselves in 'micelles', with the water-repellent tails facing inwards into the sphere's core and the water-loving heads facing outwards into the watery environment."
The question of the questions is how the "micelles" could replicate themselves, transmit information and form a basis for creating living cells. Already eighty years ago, Alexander Ofarin raised the possibility that lumps of white material, which organize spontaneously in water, may carry within them metabolic systems and even transfer their properties to lumps that split from them. But the theory was pushed aside after the discovery of DNA in the 50s. "We return to Oparin's theory, but with a certain change, when we attribute to lipids a central role in the process of the origin of life."
The "micelles" consist of thousands of types of lipids, in varying amounts, and Prof. Lantz and his team believe that they were capable of carrying information in an amount similar to that stored in DNA chains. In contrast to the coding of textual information based on the order of letters (as in human language, or in the modern genetic code), the coding of information in a "micelle" is based on the relative amount of each of the types of lipids that make it up.
The initial association of lipids into "micelles" occurred spontaneously, and in a random manner, in the primordial soup, and it has already been proven that the emerging "micelle" is able to bind more and more lipids, grow, and divide in a manner reminiscent of the division of living cells. "We hypothesize that the incorporation of the lipids into the 'micelle' was carried out according to the principle of the 'acceptance committee'," says Ran Kafri, a research student in the laboratory, "when the initial composition of the lipids in the emerging 'micelle' determines which types of lipids will be subsequently annexed and which will be rejected."
A network of chemical games was created between the lipids, and it is this that paved the way for a balanced multiplication of all the lipids that make up the "micelle", its division and the transfer of the same lipid composition to the daughter "micelles". It is important to emphasize that the replicating entity is the "micelle" as a whole, and not one of its components, and this is contrary to the classical theory that assumes the replication of a single chain molecule such as H-NA or H-NA.
The initial development of the model was done by Prof. Lanzet and his students, Daniel Segera, Yitzhak Falpel and Dafna Ben-Eli, and was published, among other things, in May 2000 in the journal. "Academy of Sciences Proceedings of the National" The main research tool for developing the model and testing it is simulations conducted with the help of supercomputers", says Barak Shanhav, a research student in the laboratory, "We feed the computer with data from 100 to 1,000 types of lipids, and the possible interactions between the molecules, and let the system run under conditions simulating the ancient Earth. The results are analyzed according to statistical principles. On the computer screen you see how the 'micelles' organize, grow and divide, and soon we will try to characterize the processes of rejection and fusion of 'micelles' with each other."
"In the next step," says Lantz, "we will try to understand the transition from a collection of 'micelles' to living cell-like entities, containing different functional areas. In fact, we already have a clue as to the development process of long RNA or protein-like chains inside the 'micelles'. We assume that DNA or H-DNA are the result of an evolutionary process on the way to the formation of life, and not its origin, when evolution is based on the ability of the 'micelles' to reproduce." Although the model is based on simple chemistry, the results begin to resemble complex behaviors of systems in living cells.
"Many attempts have been made to explain the origin of life on Earth," says Prof. Dan Cohen from the Hebrew University, "and Prof. Lantz's original ideas are the basis for a new approach to the subject and an opening for additional explanations. One of them, which I think is plausible, identifies the formation of life with the spontaneous organization of lipids into microscopic 'vesicles', and not necessarily into 'micelles'. The envelope of the vesicles, similar to the cell membranes we know today, contained two adjacent layers of lipids, with the water-loving part of the lipid layers facing the aqueous liquid outside and inside the vesicle and the water-repellent parts of the two layers facing each other and forming the inner part of the envelope. Even such vesicles, similar to the 'micelles' proposed by Prof. Lantz, will be able to multiply by selective absorption of lipids from the external soup and division of the vesicles."
Uri Nitzan. Country. The knowledge site was part of the IOL portal from the Haaretz group until the end of 2002
