Before life began on Earth, the environment probably contained a large number of chemicals that interacted with each other more or less by chance, and it is unclear how the complexity of cells could have resulted from such chemical chaos. A team led by Tony Z. Jia of the Tokyo Institute of Technology and Kuhan Chandru of the National University of Malaysia has now shown that simple α-hydroxy acids such as glycolic and lactic acid spontaneously polymerize and assemble into polyester microdroplets, if at all dried at moderate temperatures, followed by rehydration. This could have happened on primitive beaches and river banks or in dry puddles. These form a novel cellular compartment that can capture and concentrate biomolecules such as nucleic acids and proteins. These droplets, unlike most modern cells, are capable of easily fusing and reforming, and thus could harbor versatile early genetic and metabolic systems that may be critical to the emergence of life.
All life on earth consists of cells. Cells are made up of lipids, proteins, and nucleic acids, the lipid forming the cell membrane, a shell that holds the other components together and is in contact with the environment, exchanging food and waste. How molecular aggregates are as complex as originally formed cells remains a mystery.
Most origins of life research focus on how the molecules and structures of life were generated by the environment and then assembled into structures that led to the first cells. However, there were probably many other types of molecules that formed next to biomolecules on the early Earth, and it is possible that life began with a very simple chemistry that had nothing to do with modern biomolecules and then in ever more complex stages developed to bring about the structures in modern cells.
Previous work at ELSI has shown that the simple organic compounds (alpha-hydroxy acids) found in meteorites polymerize spontaneously to mixtures of long polyesters with moderate temperature drying and in many simulations of prebiological chemistry. Building on this work, Jia and colleagues studied these reactions under the microscope and found that these mixed polyester systems form a gel phase and spontaneously assemble into simple cell-like structures upon rewet.
The main challenge of this work was to develop new methods to characterize the properties and functions of droplets that no one had analyzed before. Jia noted that the team was fortunate to have such a variety of multidisciplinary skills, including chemists, biochemists, material scientists, and geologists. After determining their composition and their propensity for self-organization, the next question was whether these cell-like structures might be able to do anything chemically useful. Modern cell membranes perform many important functions that contribute to the maintenance of the cell, e.g. For example, maintaining macromolecules and metabolites in one place, as well as providing a constant internal environment that can be very different from those outside the cell. They first measured how stable these structures are, and found that they can persist for a long time, depending on environmental conditions, but can also fuse and fuse together.
They then tested the ability of these structures to segregate molecules from the environment and found that they remarkably accumulated large dye molecules. They then showed that these droplets can also take up RNA and protein molecules and still allow functional catalysis. In addition, the team was able to demonstrate that the droplets can contribute to the formation of a lipid layer on their surface, suggesting that they may have contributed to the formation of scaffold protocells.
Jia and colleagues are not sure if these structures are the direct ancestors of cells, but I think it is possible that such droplets might have enabled the construction of protocells on Earth. The new compartmentalization system that they have found is extremely simple, as they notice, and could easily form in primitive environments throughout the universe. Jia says, "This allows us to envision non-biological systems on the early Earth that may have been involved in the origins of life, suggesting that there may be many other non-biological systems, the target of future ones He believes that the development of these or similar model systems could allow better study of the evolution of various chemical systems representative of the complex chemical processes found on primitive planetary bodies.
"The early earth was chemically certainly a chaotic place." Jia explains, "and most of the origins of life studies often focus on modern biomolecules under relatively 'clean' conditions, perhaps it is important to take these 'chaotic' mixtures and see if there are interesting functions or structures that can spontaneously result from it. "The authors now believe that by systematically increasing the chemical complexity of such systems, they can observe how they evolve over time and possibly discover divergent and emergent properties ,
"We have this new experimental system we can play with now, so we can begin to study phenomena such as the evolution and developability of these droplets, and the possible combinations of structures or functions that these droplets can have are nearly complete If the physical rules governing the formation of droplets are inherently quite universal, we hope to investigate similar systems to find out if they can also form microdroplets with new properties, "adds Jia.
While the team is currently focusing on understanding the origins of life, they find that this basic research could have applications in other areas, such as drug delivery and personalized medicine. "This is just a wonderful example of the unexpected development of projects when a team of different scientists from all over the world come together to understand new and interesting phenomena," said team member Jim Cleaves, also from ELSI.
Study reveals simple chemical processes that may have led to the origin of life on Earth
Tony Z. Jia et al., Membrane-Free Polyester Microdroplets as Urcompartments at the Origin of Life, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1902336116
Scientists discover new chemistry that could help explain the origins of cellular life (2019, July 23)
retrieved on July 23, 2019
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