One of the fundamental steps in understanding the origin of organic life on Earth (and perhaps in other astrobiological environments) is to model how and where the first cells formed. And they’ve just found a key piece of the puzzle.
The role of fats in cell formation
The early Earth’s water environments contained fats, or lipids. New work led by Sunil Pulletikurti of the Scripps Research Institute in California describes a way in which simple lipid vesicles (small spheres or sacs filled with liquid) could form protocells in water environments rich in nutrients from the early Earth.
Cages are not waterproof compartments isolated from the aquatic environment. From the very beginning of evolution, they must have had membranes that filtered nutrients and eliminated waste. These properties are fundamental to allowing us to experiment with the processes that occurred in the primitive aquatic environment where life may have originated.
According to research by Pulletikurthy and co-authors, these spherical lipid vesicles in turbulent fluid environments may be precursors to the membranes of modern cells.
The researchers studied the chemical process of adding phosphate groups to a molecule—phosphorylation. This process could lead to the formation of phospholipids, which, unlike other fats, are capable of forming double-stranded protocells.
The formation of double-stranded protocells can enable a wide range of chemical reactions within them and provide membrane stability. And so he got to the birth of the first cell.
Scripps Research Institute
RNA world
Jan Gebicki and Mark Hicks pointed out the role of lipid molecules in the formation of cell membranes back in the seventies. Fats are involved in the provision of proteins and act as a barrier to the free flow of solutes inward, which is an important aspect in allowing the cell to maintain itself on its own.
Subsequently, Ting F. Zhu and Jack W. Szostak demonstrated that protocells constructed from large multilamellar fatty acid vesicles could replicate in a continuously stirred environment. Thus, ribonucleic acid (RNA) molecules encapsulated in these protomembranes could be distributed into daughter vesicles.
In their observations, Gebitsky and Hicks indicated that they were approaching the synthesis in the laboratory of a full-fledged protocell: endowed with a self-replicating genome and a self-replicating membrane compartment.
The relative simplicity of this mechanism would have allowed it to occur under the prebiotic conditions of the early Earth.
Zhu and Shostak (2009)
The key role of phosphorus
Interest in the properties of phosphorus in chemical evolution has a long history. The recently deceased brilliant physicist Enric Macia has already pointed out certain initial ways of introducing this chemical element into living matter. Not too much phosphorus can form phosphate groups in aqueous solution, and this detail may be key to the transition to more advanced membranes.
In fact, modern cell membranes are composed of fatty acids linked to glycerol (one of the major breakdown products of lipids), in which the fatty acid is replaced by a phosphate group.
The phosphate group is hydrophilic (it absorbs water very easily and does not mix with fats) and binds to glycerol. This combination forms the “head” of the structure, and the “tails” are hydrophobic fatty acid chains.
Both molecules have opposite chemical properties (amphipathic). These are key characteristics that ensure the stability of the structure.
At this point we will have the basic structure of what could be the first living cell.
Demand for the first living forms
New research suggests that the first cells, the first living systems, may have had different early “preferences” for replacing certain components of glycerol.
New research by Sunil Pulletikurti and co-authors indicates that in this biological evolution, cyclic phospholipids played an important role not only in early prebiotic protocellular chemistry: they also contributed to the chemical evolution of protocells from structurally simple to functionally more complex. .
For all this to be possible, it must be based on a double membrane structure.
Josep M. Trigo
Contribution of open space
Membranes played a significant role in shaping the properties of the first cells and in their subsequent evolution. But we cannot forget the importance of knowing what was in that first aquatic environment where the origin of life occurred.
Understanding these processes in aquatic environments requires studying the availability of these components in primitive environments subject to a continuous influx of elements from space, including in the form of minerals with the catalytic properties of complex organic compounds.
As simple as it may seem, modeling the exact conditions under which such events occurred is challenging.