Chemoton

The term chemoton (short for 'chemical automaton') refers to an abstract model for the fundamental unit of life introduced by Hungarian theoretical biologist Tibor Gánti.[1] It is the oldest known computational abstract of a protocell. Gánti conceived the basic idea in 1952 and formulated the concept in 1971 in his book The Principles of Life (originally written in Hungarian, and translated to English only in 2003). He surmised the chemoton as the original ancestor of all organisms, or the last universal common ancestor.[2]

Autocatalytic reaction of chemoton

The basic assumption of the model is that life should fundamentally and essentially have three properties: metabolism, self-replication, and a bilipid membrane.[3] The metabolic and replication functions together form an autocatalytic subsystem necessary for the basic functions of life, and a membrane encloses this subsystem to separate it from the surrounding environment. Therefore, any system having such properties may be regarded as alive, and it will be subjected to natural selection and contain a self-sustaining cellular information. Some consider this model a significant contribution to origin of life as it provides a philosophy of evolutionary units.[4]

Property

Chemoton is a protocell that grows by metabolism, reproduce by biological fission, and has at least rudimentary genetic variation. Thus, it contains three subsystems, namely autocatalytic network for metabolism, a lipid bilayer for structural organisation, and a replicating machinery for information. Unlike cellular metabolic reactions, metabolism of chemoton in autonomous chemical cycle and is not dependent on enzymes. Autocatalysis produces its own structures and functions. Hence, the process itself has no hereditary variation. The model reaction however asserts that another molecule (T in the diagram) is spontaneously produced that is incorporated into the structure. This molecule is amphipathic like membrane lipids, but it is highly dynamic, leaving small gaps that close and open frequently. This unstable structure is important for new amphipathic molecules to be added, so that a membrane is subsequently formed. This will become a microsphere. Due to metabolic reaction, osmotic pressure will build up inside the microsphere, and this will generate a force for invaginating the membrane, and ultimately division. In fact, this is close to the cell division of cell wall-less bacteria, such as Mycoplasma. Continuous reactions will also invariably produce variable polymers that can be inherited by daughter cells. In advanced version of the chemoton, the hereditary information will act as a genetic material, something like a ribozyme of the RNA World.[5]

Significance

Origin of life

The primary use of the chemoton model is in the study of the chemical origin of life. Because chemoton itself can be, though in theory, as a primitive or minimal cellular life as it satisfies the definition of what a cell is (that it is a unit of biological activity enclosed by a membrane and capable of self-reproduction). Experimental demonstration showed that a synthesised chemotron can survive in a wide range of chemical solutions, it formed materials for its internal components, it metabolised its chemicals, and it grew in size and multiplied itself.[6]

Unit of selection

As it is scientifically hypothesised that the first replicating systems must be simple structure, most likely before any enzymes or templates existed, chemoton provides a plausible scenario. As an autocatalytic but non-genetic entity, it predates the enzyme-dependent precursors of life, such as RNA World. But being capable of self-replication and producing variant metabolites, it possibly could be an entity with the first biological evolution, therefore, the origin of the unit of Darwinian selection.[7][8][9]

Artificial life

Chemoton has laid down the foundation of some aspects of artificial life. The computational basis has become a topic of software development and experimentation in the investigation of artificial life.[2] The main reason is that chemoton simplifies the otherwise complex biochemical and molecular functions of living cells. Since the chemoton is a system consisting of a large but fixed number of interacting molecular species, it can effectively be implemented in a process algebra-based language such as the BlenX programming language.[10][11]

See also

References
  1. Marshall, Michael (14 December 2020). "He may have found the key to the origins of life. So why have so few heard of him? - Hungarian biologist Tibor Gánti is an obscure figure. Now, more than a decade after his death, his ideas about how life began are finally coming to fruition". National Geographic Society. Retrieved 15 December 2020.
  2. Hugues Bersini (2011). "Minimal cell: the computer scientist's point of view". In Muriel Gargaud; Purificación López-Garcìa; Hervé Martin (eds.). Origins and Evolution of Life: An Astrobiological Perspective. Cambridge University Press. pp. 60–61. ISBN 9781139494595.
  3. Van Segbroeck S, Nowé A, Lenaerts T (2009). "Stochastic simulation of the chemoton". Artif Life. 15 (2): 213–226. CiteSeerX 10.1.1.398.8949. doi:10.1162/artl.2009.15.2.15203. PMID 19199383. S2CID 10634307.
  4. Hoenigsberg HF (2007). "From geochemistry and biochemistry to prebiotic evolution...we necessarily enter into Gánti's fluid automata". Genet Mol Res. 6 (2): 358–373. PMID 17624859.
  5. John Maynard Smith; Eors Szathmary (1997). The Major Transitions in Evolution. Oxford University Press. pp. 20–24. ISBN 9780198502944.
  6. Csendes T (1984). "A Simulation study of the chemotron". Kybernetes. 13 (2): 79–85. doi:10.1108/eb005677.
  7. Laurent Keller (1999). Levels of Selection in Evolution. Princeton University Press. p. 52. ISBN 9780691007045.
  8. Munteanu A, Solé RV (2006). "Phenotypic diversity and chaos in a minimal cell model". J Theor Biol. 240 (3): 434–442. doi:10.1016/j.jtbi.2005.10.013. PMID 16330052.
  9. Pratt AJ (2011). "Prebiological Evolution and the Metabolic Origins of Life". Artificial Life. 17 (3): 203–217. doi:10.1162/artl_a_00032. PMID 21554111. S2CID 6988070.
  10. Zachar I, Fedor A, Szathmáry E (2011). "Two different template replicators coexisting in the same protocell: stochastic simulation of an extended chemoton model". PLOS ONE. 6 (7): 1380. doi:10.1371/journal.pone.0021380. PMC 3139576. PMID 21818258.
  11. Dematté L, Larcher R, Palmisano A, Priami C, Romanel A (2010). "Programming Biology in BlenX". Systems Biology for Signaling Networks (Systems Biology series). 1. pp. 777–820. doi:10.1007/978-1-4419-5797-9_31. ISBN 978-1-4419-5796-2.

Further reading
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