Reconstructing the Emergence of Cellular Life through the Synthesis of Model Protocells

The complexity of modern biological life has long made it difficult to understand how life could emerge spontaneously from the chemistry of the early earth. The key to resolving this mystery lies in the simplicity of the earliest living cells, together with the ability of the appropriate molecular building blocks to spontaneously self-assemble into larger structures. In our view, the two key components of a primitive cell are not only self-assembling, but also self-replicating, structures: the nucleic acid genome and the cell membrane. Here, we summarize recent experimental progress toward the synthesis of efficient self-replicating nucleic acid and membrane vesicle systems and discuss some of the issues that arise during efforts to integrate these two subsystems into a coherent whole. We have shown that spontaneous nucleic-acid-copying chemistry can take place within membrane vesicles, using externally supplied activated nucleotides as substrates. Thus, membranes need not be a barrier to the uptake of environmentally supplied nutrients. We examine some of the remaining obstacles that must be overcome to enable the synthesis of a complete self-replicating protocell, and we discuss the implications of these experiments for our understanding of the emergence of Darwinian evolution and the origin and early evolution of cellular life.