Biology Reference
In-Depth Information
other line of research is the one which will be the subject of this article. It concerns the
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A minimal cell is broadly defined as the cell containing the minimal
and sufficient number of macromolecular components to be recognized as living
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minimal cells.
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or at
least displaying some of the basic functions of a living cell (e.g. protein synthesis,
metabolism, or self-reproduction). This is a program of chemical SB, based on vesicles, as
supramolecular surfactant aggregates, and the basic operation is chemical manipulation.
This kind of investigation is important for determining the minimal structural conditions
for cellular life, and is fundamental for the origin of life
in particular for the origin of
cellular life. The relevance of this study is also apparent if one considers that the
simplest bacterial form of our present life contains 400
500 genes, and therefore each
compartment has many thousands of molecular components: conceivably, life cannot
have started from the very beginning with this high complexity, and therefore the study
of a minimal cell may shed light on those protocellular structures preceding the full-
fledged genome cells.
In this article we will briefly highlight the main results obtained in this field, we will also
consider some novel developments in the filed, such as the
cell colonies
(aggregates of
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minimal cells), and the recent surprising finding of the spontaneous
overcrowding
of
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biological macromolecules in vesicles.
THE CONCEPTUAL FRAMEWORK OF SEMISYNTHETIC
MINIMAL CELLS
The concept of minimal cells was developed in the context of origin of life research.
For understanding how primitive living cells could be originated from the association
and the dynamic organization of nonliving components, our research group initiated a
research field focused on the construction of cell-like compartments that could display
living-like properties such as growth, internal metabolism, self-reproduction, etc. by
using chemical and biochemical approaches. These investigations, which have been
recognized as a branch of SB, are currently carried out by several groups and
encompass different aspects of cellular organization (an overview of these aspects can
be found in a recently published topic).
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The starting point for our discussion is the theory of autopoiesis (self-production),
developed in the 1970s by Humberto Maturana and Francisco J. Varela.
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Autopoiesis is a
distinctive feature of all living systems. It describes how a living system is organized in
terms of the internal transformation of its components. In particular, by referring to
unicellular organisms (which are the best example to describe what is an autopoietic
mechanism), the genetic/metabolic network of a cell is a set of biochemical processes that
produce all its own molecular components, which in turn interact between each other
giving rise to the biochemical processes that produce (
Fig. 14.1A
).
Moreover, the autopoietic network needs to be limited by a semipermeable boundary (also
created autopoietically) for self-containment, and that distinguishes the autopoietic unit
(the cell, in this case) from the environment. Note that this definition focuses on the
dynamic organization of the molecules that constitute the autopoietic unit (e.g. the cell),
rather than their chemical identity or their lifetime. Autopoiesis provides a framework for
the construction of synthetic cells in the laboratory and can be considered as a blueprint of
cellular life. This gives rise to two considerations. First,
can be
thought of and designed as molecular systems composed of the minimal number of
molecules that, by interacting with each other, give rise to an autopoietic dynamic and an
autopoietic self-confinement. Second, considering that early living cells were certainly
simpler than modern (evolved) cells, the construction of minimal autopoietic cells in the
laboratory might reveal what are the key steps, the criticalities, the emergent properties, and
minimal autopoietic cells
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