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protocell
A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a stepping-stone to the origin of life. A central question in evolution is how simple protocells first arose and how they could differ in reproductive output, thus enabling the accumulation of novel biological emergences over time, i.e. biological evolution. Although a functional protocell has not yet been achieved in a laboratory setting, the goal to understand the process appears well within reach.
==Overview==
Compartmentalization was important in the origins of life. Membranes create enclosed compartments that are separate from the external environment, thus providing the cell with functionally specialized aqueous spaces. Because lipid bilayer of membranes is impermeable to most hydrophilic molecules (dissolved by water), the cell must have membrane transport systems that are in charge of import of nutritive molecules as well as export of waste.〔Book: "Molecular Biology of the Cell." Alberts B., Johnson Lewis, et al. 2004.〕 It is very challenging to construct protocells from molecular assemblies. An important step in this challenge is the achievement of vesicle dynamics that are relevant to cellular functions, such as membrane trafficking and self-reproduction, using amphiphilic molecules. On the primitive Earth, numerous chemical reactions of organic compounds produced the ingredients of life. Of these substances, amphiphilic molecules might be the first player in the evolution from molecular assembly to cellular life.〔Deamer, D.W.; Dworkin, J.P. "Chemistry and Physics of Primitive Membranes." Top. Curr. Chem. 2005, 259, 1–27.〕〔Walde, P. "Surfactant Assemblies and their various possible roles for the origin(s) of life." Orig. Life Evol. Biosph. 2006, 36, 109–150.〕 A step from vesicle toward protocell might be to develop self-reproducing vesicles coupled with the metabolic system.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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