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.
rigidity kf or its persistence length x; we use the latter representation in this section and introduce kf in Section 2.3. Mathematically, the persistence length is a measure of the length scale over which the orientation of a curve undergoes a significant change in direction. For molecules whose variation in shape is governed by thermal fluctuations, x and kf are directly proportional to each other through x = kf/kBT, from which one sees that the stiffer the filament (larger kf) the longer the
been realized by encapsulation of smaller vesicles, hydrogels, or aqueous two-phase systems. These provide primitive models for microcompartmentation of the cytoplasm. The following subsections introduce experimental models of cytoplasm, and are organized based on whether the model systems are bulk solutions or microvolumes. 1 Towards a Minimal Cytoplasm 9 1.2.1 Bulk Cytoplasm Models In vitro experiments can be become more realistic models of the intracellular environment even by very
self-assembly. Liquid water is essential for all life today, and it is highly implausible that life, as known on Earth, can exist in its absence. Possible energy sources include sunlight, if life began on the Earth’s surface, or energy arising from chemical disequilibria in submarine or subterranean sites. Selfassembling compounds must have been available to provide building blocks for polymer synthesis and formation of boundary structures. The first forms of life were represented by
of biosynthetic products. The first suggestion that membranes played a role in the origin of life was put forward by Haldane (1929) who wrote that “The cell consists of numerous halfliving chemical molecules suspended in water and enclosed in an oily film. When the whole sea was a vast chemical laboratory the conditions for the formation of such films must have been relatively favourable…” Goldacre (1958) proposed that the first membranes could have been produced by wave action disturbing films
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