Eimembraanisten

Eimembraanisten is a term used in speculative biology and in some fictional settings to describe a proposed class of life forms that lack membrane-bound organelles and, more broadly, membranes surrounding cellular compartments. In this concept, cells organize their biochemistry through membrane-less condensates formed by phase-separated proteins and RNAs, rather than through vesicles and membranes. The term derives from ei- (non-) and membran- (membrane) with the standard suffix -isten.

In proposed models, eimembraanisten exhibit a cytoplasm organized by dynamic, membraneless compartments. They may possess a supportive cell wall or extracellular matrix, and rely on cytosolic enzyme complexes for metabolism. Reproduction is envisioned via fission or budding within an enclosed cytoplasmic milieu, with division controlled by protein networks that coordinate concentration and flow rather than membrane partitioning. Movement, if present, would be mediated by cytoskeletal elements or cytoplasmic streaming.

Ecologically, proponents associate eimembraanisten with environments where rapid reorganization of biochemical processes is advantageous, such as variable or extreme conditions. The concept is primarily a thought experiment in origin-of-life discussions and in science fiction, used to explore the necessity and evolution of membrane-bound compartmentalization.

Status: The eimembraanisten concept remains controversial and is not supported by empirical evidence in mainstream biology. It is mainly discussed as a theoretical model or fictional device to illustrate questions about cellular organization, membrane evolution, and the limits of life’s architectural diversity.