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Tuesday 18 October 2011

The term autopoiesis (self-production) refers to a theory that describes the behavior of all biological systems, from cells to organisms.

This theory was introduced in the Seventies by the two Chilean biologists Humberto R. Maturana and Francisco J. Varela (Maturana and Varela 1980).

Within the context of synthetic biology (SB) and the construction of synthetic cells, autopoiesis is an extremely powerful conceptual tool to define in general terms what are the structural and functional requirements of a molecular biosystems in order to mimic the basic living features of natural ones.

The analysis is particularly simple when we focus on the lowest complexity level, namely the single cell.

A minimal autopoietic system (e.g., an autopoietic cell) can be seen as a self-bounded molecular assembly, characterized by the following dynamics.

Components from the environment (A, B) are assimilated by the structure and transformed into the components of the cell (S, M).

Together with these transformations, which are actually anabolic processes, waste material is produced (Y, W) by catabolic processes.

It is possible to define two main processes:
- (1) synthesis of the boundary components (A to S) and self-assembly of S into a semi-permeable membrane;
- (2) synthesis of all internal components (M) at the expenses of B (B to M and W).

Thanks to these two processes, which are actually coupled, the autopoietic cell:
- (1) constructs its own boundary;
- (2) constructs all other internal components, which in turn give rise to processes that produce all components, that in turn give rise to processes … and so on.

The functions of the autopoietic cell are therefore defined recursively according to a circular logic.

Notably, the whole system is out-of-equilibrium and thermodynamically open, because it exists only in the act of continuously transforming the nutrients (A, B) into the waste products (Y, B), and by exploiting the free energy of this transformation in order to maintain its internal organization.

It is important to remark that, despite the ceaseless formation and destruction of the elements (lower hierarchical level) of the autopoietic system, the whole system (at an higher hierarchical level) maintains its own identity.

The autopoietic cell is a self-organizing entity (see self-organization and auto-assembly where its main features (self-producing, self-bounding, homeostasis) are emergent properties.

Another important aspect of autopoietic systems, is that in their description it is not needed to identify a central control unit, because the property of being autopoietic is not associated with a particular molecule or function, but stems from the coordinated and collective system dynamics, which is also strongly coupled with the environment.

Figure also tells us that depending on the relative rate of anabolic and catabolic processes, the autopoietic cell can grow, stays in homeostatic state, or dies, depending on which aspect of metabolism is prevailing in certain conditions.

Open References

- Synthetic biology of minimal living cells: primitive cell models and semi-synthetic cells. Stano P. Syst Synth Biol. 2010 Sep;4(3):149-56. PMID: 21886680 [Free]