Scientific Roots of Protocell Research 

Contemporary protocell research has a number of scientific roots. One is the long tradition of work on the origin of life. The question of how life might be obtained from nonliving materials is similar to that of how contemporary life originated, since contemporary life presumably arose from nonliving materials, but these two questions lead us in very different directions. The methods and conditions used to make protocells might be radically unlike those actually involved in life’s origins, and it is an entirely open question whether such new forms of life would or could ever evolve into anything like naturally existing life-forms. The understanding of life obtained from making protocells, however, should contribute to research on the origin of life as well as benefit from it. Research on the origin of life naturally spawned several of the research threads that comprise current protocell efforts. A particularly important thread is the concept of the RNA world, which concentrates on RNA as the primary element in origin of life scenarios (see, e.g., Gilbert, 1986; Orgel, 1994). The connection with protocell research comes when RNA chemistry is integrated with container structures (cf. Szostak, Bartel, and Luisi, 2001; Deamer, 2008; Stano et al., 2008). 

Protocell research may also be seen as an endeavor within thefield of artificial life. The phrase‘‘artificial life’’is much broader and refers to any attempt to synthesize the essential features of living systems. Artificial life traditionally falls into three branches, corresponding to three synthesis methods.‘‘Soft’’artificial life creates computer simulations or other purely digital constructions that exhibit lifelike behavior.‘‘Hard’’artificial life produces hardware implementations of lifelike systems, usually in robotics.‘‘Wet’’artificial life involves the creation of lifelike systems in a wet lab, in most cases based on carbon chemistry in water. The holy grail of wet artificial life is the construction of protocells. While PACE does not aim to deliver an artificial cell, because of the amount of work still to be done, it is an important focus of PACE to clarify our current chemical potential to solve the problems still outstanding in order to achieve this.

Another strand of human activity that produces living cells that are not found in nature is represented by the recent success of synthetic biology efforts to alter metabolic pathways of existing contemporary cells by genetic manipulation (for an overview see Baker et al., 2006). These techniques may produce a range of more or less artificial cells, depending on the extent of genetic modification and the resulting distance from naturally existing life. If synthetic biology is characterized as the attempt to engineer new biological systems, then protocell research can be viewed as a branch of synthetic biology (see the introduction to part IV in Rasmussen et al., 2008). 

Astrobiology is concerned with the search for life elsewhere in the universe, so it and protocell research share an interest in the fundamental properties of living systems. While the artificial life community asks what is minimal life and how can it be useful, the astrobiology community asks where life comes from and whether it exists only on the Earth. In contrast with astrobiology, protocell research does not need to justify the cosmological or geochemical origins of its starting materials. However, the possibility of detecting alien life on other planets or moons adds many intriguing questions, which however will not be addressed in PACE. 

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