Before life began on Earth, the environment probably contained a massive number of chemicals that reacted with each other more or less randomly, and it is unclear how complexity of cells might have emerged from such 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, like glycolic and lactic acid, spontaneously polymerize and self-assemble into polyester microdroplets 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 cell-like compartment that can trap and concentrate biomolecules like nucleic acids and proteins. These droplets, unlike most modern cells, are able to merge and reform easily, and thus could have hosted versatile early genetic and metabolic systems potentially critical to the origins of life.
All life on Earth is made up of cells. Cells are composed of lipids, proteins and nucleic acids, with the cell membrane lipid, an enclosure that keeps the other components together and interfaces with the environment, exchanging food and waste. How molecular molecules as complex as cells originally formed remains a mystery
Most origins of life research focus on how molecules and structures of life were produced by the environment, and then assembled into structures that led to the first cells. However, there have been many other types of molecules formed alongside biomolecules on early Earth, and it is possible that life began using very simple chemistry unrelated to modern biomolecules, then evolved through increasingly complex stages to give rise to the structures found in modern cells
Previous work conducted at ELSI showed that moderate temperature drying of the simple organic compounds known as alpha-hydroxy acids, which are found in meteorites and many simulations of prebiological chemistry, spontaneously polymerizes them into mixtures of long polyesters. Building on this work, Jia and colleagues took the next step and examined these reactions under the microscope, and found that these mixed polyester systems formed a gel phase and spontaneously self-assembled when rewetted to form simple cell-like structures
The most challenging aspect of this work was devising new methods to characterize the droplets' properties and functions, as no one had analyzed such systems before. Jia noted that the team was fortunate to have such a diversity of multidisciplinary expertise, including chemists, biochemists, material scientists and geologists. After determining their composition and showing their propensity to self-assemble, the next question was whether these cell-like structures might be able to do something chemically useful. Modern cell membranes perform many crucial functions that help maintain the cell, for example, retaining macromolecules and metabolites in one place, as well as providing a constant internal environment that can be very different from the one outside the cell.
They then tested the ability of these structures to sequester molecules from the environment and found that they accumulated large dye molecules to a remarkable degree. They then showed that these droplets could also host RNA and protein molecules and still allow them to be functionally catalytic. Furthermore, the team showed that the droplets could help in the formation of a lipid layer on their surface, suggesting that they could have helped scaffold protocell formation
Jia and colleagues are not sure these structures are the direct ancestors of cells, but they It is possible that such droplets could have enabled the assembly of protocells on Earth. The new compartmentalization system they have found is extremely simple, they note, and could form easily in primitive environments throughout the universe. Says Jia, "This allows us to imagine non-biological systems on the early Earth that could still have had a hand in the origins of life, which suggests that there may be many other non-biological systems that should be targets of future investigations of this type . " He thinks the development of these or similar model systems could allow a better study of the evolution of various chemical systems representative of the complex chemistries likely to be found on primitive planetary bodies
"The early earth was certainly a messy place chemically, Jia explains, "and often, most origins of life studies focus on modern biomolecules under relatively 'clean' conditions. It may be important to take these messy mixtures and see if there are interesting functions or structures that can arise from them spontaneously. " The authors now think that by systematically increasing the chemical complexity of such systems, they will be able to see how they evolve over time and eventually find divergent and emerging properties
"We have this new experimental system we can now play with, we can begin to study phenomena such as the evolution and evolution of these droplets, and if the physical rules governing the formation of the droplets are fairly universal in nature then we hope to study similar systems to discover whether they can also form microdroplets with novel properties, "adds Jia.
Finally, while the team is currently focusing on understanding the origins of life, they note that this basic research could have applications in other areas, for example, drug delivery and personalized medicine. "This is just a wonderful example of how unpredictable projects can be developed when a team of diverse scientists from around the world come together to try and understand new and interesting phenomena," said team member Jim Cleaves, also of ELSI.
Study reveals a simple chemical process that may have led to the origin of life on Earth
Tony Z. Jia et al., Membraneless polyester microdroplets as primordial compartments at the origins of life, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1902336116
Scientists discover new chemistry that can help explain the origins of cellular life (2019, July 23)
retrieved 23 July 2019
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