Abstract
Contemporary biological cells are highly sophisticated dynamic compartment systems which separate an internal volume from the external medium through a boundary, which controls, in complex ways, the exchange of matter and energy between the cell’s interior and the environment. Since such compartmentalization is a fundamental principle of all forms of life, scenarios have been elaborated about the emergence of prebiological compartments on early Earth, in particular about their likely structural characteristics and dynamic features. Chemical systems that consist of potentially prebiological compartments and chemical reaction networks have been designed to model pre-cellular systems. These systems are often referred to as “protocells”. Past and current protocell model systems are presented and compared. Since the prebiotic formation of cell-like compartments is directly linked to the prebiotic availability of compartment building blocks, a few aspects on the likely chemical inventory on the early Earth are also summarized.
Highlights
Whether we will ever unravel how living systems originated on Earth—or possibly somewhere else—is doubtful, as pointed out, e.g., by Lazcano [1], “perhaps we will never know exactly how life originated”
If an extrapolation is made through a phylogenomic analysis towards previously existing, extinct, life forms, one arrives at the conclusion that even the last universal common ancestor (LUCA)— called “urancestor” [4]—must have been already rather complex, conceptually probably not very different from today’s forms of life
The self-assembly of potentially prebiological organic molecules into compartments has been explored under the various assumptions which reflect the constraints that could have prevailed on the early Earth. These studies can be categorized in three main groups: studies of molecules and processes which lead to compartments which are composed of (i) a single species of building blocks [108,109]; (ii) of molecule mixtures composed of a single type of building block; and (iii) more recently hybrid systems that comprise of mixtures of several types of building blocks or mixtures of compartment forming building blocks and other molecules [118,119]
Summary
Whether we will ever unravel how living systems originated on Earth—or possibly somewhere else—is doubtful, as pointed out, e.g., by Lazcano [1], “perhaps we will never know exactly how life originated”. Considering the general importance and the various roles of compartments in contemporary cells (both in terms of general cell identity and processes) [3], it is very likely that the formation of some type of compartment already occurred in early prebiotic times [4,6,9] In this short review, the focus lies in a compilation of some of the ideas about prebiotic compartmentalization, its possible relevance for the emergence of complex reaction networks (i.e., metabolism), and, by extension, for the. Due to the extensive body of work in which the term “protocell” is used for naming artificial compartments, as micrometer- or submicrometer-sized reactor systems for possible biotechnological applications [25,26,27], we will limit ourselves to examples that are of potential prebiotic relevance
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