Protobionts

Protobionts are simple, cell-like structures proposed as precursors to living cells in origin-of-life research. They are aggregates or compartments of abiotic molecules enclosed by a boundary, such as a lipid membrane, a protein coat, or a polymeric shell. Protobionts are envisioned to maintain a distinct internal environment and carry out basic, life-like chemical processes, but they are not considered fully living because they generally lack a self-sustained, information-bearing system capable of reliable replication and Darwinian evolution on their own.

Common model systems studied as protobionts include coacervates, proteinoid microspheres, and lipid vesicles (liposomes). Coacervates form droplets rich in polymers that can concentrate reactants and catalyze reactions. Proteinoid microspheres arise from heated amino acids and can swell, take up nutrients, and, under some conditions, exhibit growth or division-like behavior. Lipid vesicles form bilayer membranes that self-assemble in water, encapsulate enzymes or nucleic acids, and create a defined interior while allowing selective exchange with the surroundings.

In origin-of-life research, protobiont-like systems are used to explore how compartmentalization, metabolism, and primitive replication might co-occur, and how environmental conditions could drive growth and division. They help address questions about how life-like properties could emerge from non-living matter, although protobionts remain hypothetical constructs rather than established steps in a universal pathway to life.