Ice drives the emergence of functional protocells
A defining feature of living systems is the high local concentration of diverse molecular components within membrane-bounded compartments. How did such an organization arise de novo, without complex molecular machinery or pre-existing cellular structures that could template their own reproduction? Prebiotic environments may have provided the physical driving forces needed to bring dispersed molecular components together and organize them into functional compartments. Here, we show that a freeze-thaw (FT) process can couple molecular concentration, the formation of cell-sized membrane compartments, and the activation of a biochemical system. In situ imaging showed that chemically diverse solutes and membrane material were co-concentrated within ice-confined liquid regions during slow freezing. Subsequent slow thawing gave rise to cell-sized giant vesicles that capture the concentrated molecules. Crucially, we show that these sequential processes can assemble a multicomponent transcription-translation system (PURE system) within vesicle compartments, enabling protein synthesis from diluted mixtures with little or no detectable activity in bulk solution. By demonstrating that functional cellular organization can emerge from otherwise inactive molecular components, our study suggests that environmental FT processes provide a physical route for the transition from chemical to biological organization, with implications for the emergence of life on Earth and beyond.