The Origin of Cell Boundaries and Metabolism

Abstract

The wide gap between the properties of non-living phenomena and the simplest living forms cannot be explained without some intermediate stages (Ruiz-Mirazo et al. 1999). Although some achievements of life suggest that a continuum might have existed between non-life and life (Browning 1869, Hazen 2001), many features of life appear to have emerged in a stepwise way. The addition of a boundary capable of separating the interior from the exterior is one of those achievements of life showing a pronounced stepwise (phase transition) character. Many authors believe that the formation of phase-separated systems (PSSs) was necessarily one of the earliest if not the absolute precondition for the origin of the living state (Oparin 1938, 1968, Oró and Lazcano 1990, Lyubarev and Kurganov 1995, Turian 1999). This seclusion from the external environment was given a variety of names such as compartmentalization, cellularization, territorial separation, segregation or encapsulation (Oparin 1924, 1968, Haldane 1929, Fox 1964, Edwards and Peng 1998, Edwards et al. 1998, Deamer 1998, Arrhenius 2002, Guimarães 2002). A variety of names was also used to describe the earliest PSSs, such as coacervates (Oparin 1921, 1968), bioids (Decker 1973), proteinoid microspheres (Fox and Dose 1977), aggregates (Kaplan 1978), marigranules, marisomes (Yanagawa and Egami 1980), liposomes (Deamer 1986, Schmidli et al. 1991), jee-wanu’ meaning life particles’ in Sanskrit (Badahur and Ranganayaki 1970), probotryoids (Russell et al. 1994), microvesicles, microspheres (Turian 1999) or droplets (Dyson 1997).