Membrane Self-Assembly Processes: Steps Toward the First Cellular Life

Abstract

This review addresses the question of the origin of life, with emphasis on plausible boundary structures that may have initially provided cellular compartmentation. Some form of compartmentation is a necessary prerequisite for maintaining the integrity of interdependent molecular systems that are associated with metabolism, and for permitting variations required for speciation. The fact that lipid-bilayer membranes define boundaries of all contemporary living cells suggests that protocellular compartments were likely to have required similar, self-assembled boundaries. Amphiphiles such as short-chain fatty acids, which were presumably available on the early Earth, can self-assemble into stable vesicles that encapsulate hydrophilic solutes with catalytic activity. Their suspensions in aqueous media have therefore been used to investigate nutrient uptake across simple membranes and encapsulated catalyzed reactions, both of which would be essential processes in protocellular life forms.

Development of an artificial cell, from self-organization to computation and self-reproduction

“…Natural lipids form small unilamellar spherical vesicles spontaneously upon suspension in aqueous solutions due to the favorable packing parameter of phospholipids (74,75). Soft matter and protocell research have provided many ways to fabricate cell-like compartments with pure amphiphilic molecules (76)(77)(78). Some of these methods are used to encapsulate pure proteins inside phospholipid vesicles to study cellular processes.…”

Lifeness signatures and the roots of the tree of life

“…They might also have a much simpler and rudimentary lipidic membrane that would split without any molecular regulatory system but simply thanks to physical pinching forces (e.g. Monnard and Deamer 2002), or even no lipid-based membrane at all but mineral compartments in a hydrothermal chimney (e.g. Martin and Russell 2003).…”

“…fatty acids) following their abiotic synthesis and their concentration in pools or droplets of water; such vesicles might have indeed been the first types of membranes encountered on the primitive Earth; yet they remain very fragile, sensitive to concentration, temperature and pH (e.g. Monnard and Deamer 2002). In stage III, the addition of other molecules such as sterols or amphiphilic polypeptides could have resulted in slightly more robust vesicles that would be stable across a broader set of chemical conditions, and that would be larger as well (e.g.…”

On What It is to Fly Can Tell Us Something About What It is to Live

“…For instance, it appears very likely that, over time, membranes evolved very much in complexity: the abiotic synthesis of amphiphilic molecules, such as fatty acids, and their concentration and self-assembly might have resulted into vesicles, likely to be the first types of membranes encountered on the primitive Earth; yet such vesicles are very sensitive to concentration, temperature and pH (e.g. Monnard and Deamer 2002); the addition of other molecules such as sterols or amphiphilic polypeptides could have resulted, in a second step, in more robust vesicles, stable across varying chemical conditions, and larger as well (e.g. Luisi 2002); in a third step, the insertion of specialized transporters and active catalysts might have led to vesicles able to create and maintain chemical disequilibria; and the subsequent additions of other more complex organic compounds such as polysaccharides, energytransduction components or surface-layers components would have resulted in the appearance of the extremely sophisticated and multi-function membranes of current organisms (e.g.…”