Before life began on Earth, the environment probably contained a massive amount of chemicals that reacted with each other more or less randomly, and it is not clear how the complexity of the cells could have arisen from that chemical chaos. Now, a team led by Tony Z. Jia at the Tokyo Institute of Technology and Kuhan Chandru of the National University of Malaysia has shown that simple α-hydroxy acids, such as glycolic and lactic acid, spontaneously polymerize and self-assemble into microdroplets of polyester when dried at moderate temperatures followed by rehydration. This could be what happened along primitive beaches and river banks, or in drying puddles. These form a new type of compartment similar to a cell that can trap and concentrate biomolecules such as nucleic acids and proteins. These droplets, unlike most modern cells, are capable of easily fusing and reforming, so they could have housed early and versatile genetic and metabolic systems potentially critical to the origins of life.
All life on Earth is made up of cells. The cells are composed of lipids, proteins and nucleic acids, with the lipid that forms the cell membrane, an enclosure that holds the other components together and interacts with the environment, exchanging food and waste. How molecular assemblies as complex as originally formed cells remain a mystery.
Most of the origins of life research focus on how the molecules and structures of life were produced by the environment and then assembled into structures that led to the first cells. However, it is likely that there are many other types of molecules that formed along with the biomolecules on the early Earth, and it is possible that life began using a very simple chemistry unrelated to modern biomolecules, then evolved through stages increasingly complex to give rise to the structures found in modern cells. .
Previous work done in ELSI showed that moderate temperature drying of simple organic compounds known as alpha-hydroxy acids, found in meteorites and in many prebiological chemistry simulations, spontaneously polymerizes them in mixtures of long polyesters. Based on this work, Jia and his colleagues took the next step and examined these reactions under the microscope, and found that these mixed polyester systems form a gel phase and spontaneously self-assemble when they are rehabbed to form simple cell-type structures. .
The most challenging aspect of this work was to devise new methods to characterize the properties and functions of the droplets, since no one had analyzed such systems before. Jia said the team was fortunate to have a diversity of multidisciplinary experts, including chemists, biochemists, materials scientists and geologists. After determining their composition and showing their propensity to assemble themselves, the next question was whether these cell-type structures could do something chemically useful. Modern cell membranes perform many crucial functions that help keep the cell, for example, by retaining macromolecules and metabolites in one place, in addition to providing a constant internal environment, which can be very different from what is outside the cell. First they measured how stable these structures were and discovered that they could persist for long periods of time depending on environmental conditions, but they could also merge and merge.
They then tested the ability of these structures to sequester molecules from the environment and discovered that they accumulated large dye molecules to a remarkable degree. They then demonstrated that these droplets could also house RNA molecules and proteins and still allow them to be functionally catalytic. In addition, the team showed that the droplets could help in the formation of a lipid layer on its surface, suggesting that they could have helped the formation of proto-cells in the scaffolds.
Jia and her colleagues are not sure that these structures are the direct ancestors of the cells, but they believe that it is possible that these drops have allowed the assembly of the proto-cells on Earth. The new compartmentalization system they have found is extremely simple, they point out, and could easily be formed in primitive environments throughout the universe. Jia says: "This allows us to imagine non-biological systems on primitive Earth that could still have had a hand in the origins of life. This suggests that there may be many other non-biological systems that should be targets of future research of this kind. "He believes that the development of these model systems or a similar one could allow a better study of the evolution of various chemical systems representative of the chemical complexes that are likely to be found in the primitive planetary bodies.
"The primitive Earth was undoubtedly a chemically messy place," Jia explains, "and often, most of the origins of life studies focus on modern biomolecules in relatively" clean "conditions. Perhaps it is important to take these "messy" mixes and see if they are interesting functions or structures that can arise spontaneously ". The authors now think that by systematically increasing the chemical complexity of such systems, they will be able to observe how they evolve over time and possibly discover divergent and emerging properties.
"We have this new experimental system with which we can now play, so we can begin to study phenomena such as the evolution and the evolution capacity of these drops. The possible combinations of structures or functions that these drops could have are almost infinite. Yes the physical rules that govern "The formation of drops is quite universal by nature, so we hope to study similar systems to discover if they can also form microdroplets with novel properties," adds Jia.
Finally, although the team is currently focused on understanding the origins of life, they point out that this basic research could have applications in other areas, for example, medication administration and personalized medicine. "This is just a wonderful example of the unexpected ways in which projects can be developed when a team of diverse scientists from around the world gather to try to understand new and interesting phenomena," said team member Jim Cleaves, also of ELSI .
A study reveals a simple chemical process that may have led to the origin of life on Earth
Tony Z. Jia and others, membrane-free polyester microdroplets as primary compartments in the origins of life, procedures of the National Academy of Sciences (2019). DOI: 10.1073 / pnas. 1902336116
Scientists discover a new chemistry that can help explain the origins of cell life (2019, July 23)
retrieved on July 23, 2019
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