"Scientists think that the protobionts are the evolutionary precursors of prokaryotic cells. Protobionts may be originated as an array of microspheres of diverse organic and inorganic compounds enclosed by lipidic membranes. Proteins, carbohydrates, lipids, and other organic substances were the most important autocatalytic organic compounds. Water was a very important factor in the assembly of the protobionts' endoplasm. After this event, several microspheres could self-organize into organelles that were able to perform specific functions; for example, lysosomes, peroxysomes, vacuoles, etc."
"A protobiont is an aggregate of abiotically produced organic molecules surrounded by a membrane or a membrane-like structure."
Obcells as proto-organisms (PubMed)
Abstract only (2001). Suggests that the prior existence of membranes was necessary for the evolution of the genetic, bioenergetic, and structural aspects of the cooperative macromolecular coevolution required for evolving the genetic code. Suggests that "membranes initially functioned as supramolecular structures to which different replicators attached and were selected as a higher-level reproductive unit: the proto-organism."