Prebiological Membranes and Their Role in the Emergence of Early Cellular Life.

Membrane compartmentalization is a fundamental feature of contemporary cellular life. Given this, it is rational to assume that at some stage in the early origins of life, membrane compartments would have potentially emerged to form a dynamic semipermeable barrier in primitive cells (protocells), protecting them from their surrounding environment. It is thought that such prebiological membranes would likely have played a crucial role in the emergence and evolution of life on the early Earth. Extant biological membranes are highly organized and complex, which is a consequence of a protracted evolutionary history. On the other hand, prebiotic membrane assemblies, which are thought to have preceded sophisticated contemporary membranes, are hypothesized to have been relatively simple and composed of single chain amphiphiles. Recent studies indicate that the evolution of prebiotic membranes potentially resulted from interactions between the membrane and its physicochemical environment. These studies have also speculated on the origin, composition, function and influence of environmental conditions on protocellular membranes as the niche parameters would have directly influenced their composition and biophysical properties. Nonetheless, the evolutionary pathways involved in the transition from prebiological membranes to contemporary membranes are largely unknown. This review critically evaluates existing research on prebiotic membranes in terms of their probable origin, composition, energetics, function and evolution. Notably, we outline new approaches that can further our understanding about how prebiotic membranes might have evolved in response to relevant physicochemical parameters that would have acted as pertinent selection pressures on the early Earth.