The Minimal Cell: The Biophysics of Cell Compartment and the Origin of Cell Functionality
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In the last ten years there has been a considerable increase of interest on the notion of the minimal cell. With this term we usually mean a cell-like structure containing the minimal and sufficient number of components to be defined as alive, or at least capable of displaying some of the fundamental functions of a living cell. In fact, when we look at extant living cells we realize that thousands of molecules are organized spatially and functionally in order to realize what we call cellular life. This fact elicits the question whether such huge complexity is a necessary condition for life, or a simpler molecular system can also be defined as alive. Obviously, the concept of minimal cell encompasses entire families of cells, from totally synthetic cells, to semi-synthetic ones, to primitive cell models, to simple biomimetic cellular systems. Typically, in the experimental approach to the construction of minimal the main ingredient is the compartment. Lipid vesicles (liposomes) are used to host simple and complex molecular transformations, from single or multiple enzymic reactions, to polymerase chain reactions, to gene expression. Today this research is seen as part of the broader scenario of synthetic biology but it is rooted in origins of life studies, because the construction of a minimal cell might provide biophysical insights into the origins of primitive cells, and the emergence of life on earth. The volume provides an overview of physical, biochemical and functional studies on minimal cells, with emphasis to experimental approaches. 15 International experts report on their innovative contributions to the construction of minimal cells.
minimal metabolism (~65% in term of number of genes in the minimal genome, see Gil et al. 2004), is already a process of considerable complexity, and, moreover, is – to date – the only experimentally feasible synthetic model. 11.3 In Vitro Protein Expression with a Minimal Set of Enzymes Cell-free protein synthesis system is a biotechnological tool to perform protein synthesis in a test tube. Although conventional cell-free systems are based on cellextracts such as E. coli (Liu et al. 2005) or
genome of M. genitalium (Mushegian and Koonin 1996). Subsequent comparative genomic and experimental studies have yielded a range of estimates for the minimal genome complement (Carbone 2006) and the concept of what constitutes a minimal gene set has evolved as greater amounts of sequence data have become available. A recent study involving 573 bacterial genomes identified an “extended core” set of ~250 protein families present in almost all species (Lapierre and Gogarten 2009) which may be
Minimal Cell and Life’s Origin: Role of Water and Aqueous Interfaces 115 b acteria. This process could represent not only a potentially significant energetic pathway that may be broadly relevant for nature, but also as argued below, a central protagonist for the origin of life. 7.7 Exclusion Zones and Protons A prime attribute of the interfacial exclusion zone is separation of charge. The zone itself is ordinarily negative, while the region beyond is positive. This positive potential is
vesicles. Indeed if the rate of amphiphile formation substantially exceed the reproduction rates of the metabolic network elements (genetic codes and catalytic species), these species will be rapidly diluted in the expanding internal aqueous compartment, and so that newly formed vesicles lose the characteristics of the parent cell. Attempts have been recently made to closely link the replication of containers to an endogenous production of amphiphiles either using simple metal catalytic systems
cells (directly or via a relay) in such a way that, as in the spirit of the original imitation game, it can be interrogated by the latter, in a language sufficiently sophisticated so as to appropriately distinguish between alternative outputs from realizable experiments. We suggested, as an example, a cellular imitation game set-up (Fig. 9.1) where the chell might imitate a natural cell and where the latter plays the role of interrogator through properly configured screening and life-support