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01 juli 2014

Universal features of life according to Christian de Duve

In his Singularities: Landmarks on the Pathways of Life (2005) Nobel Prize winner Christian de Duve points out what he thinks are universal chemical features of life (p. 160):

"The deterministic view suggested by our analysis supports such a possibility, as it encompasses most of the key chemical features of life [1], including
  • membranes
  • bioenergetic couplings (at least at the substrate-level kind)
  • DNA genes
  • RNA mediators of gene expression
  • information transfers via base pairing
  • RNA-dependent protein synthesis
  • the universal genetic code
  • as well as a number of enzymes, coenzymes, ribozymes
To the extent that those features arose by a combination of deterministic chemistry and selective optimization, they were essentially bound to arise under the conditions that surrounded their birth and would similarly arise should these conditions be duplicated. Almost the only key feature that may have been decided by chance is chirality, although even here, there may have been some bias. (...) 
Furthermore, the message of cosmic chemistry should not go unheeded. When looking at a list of the compounds detected in outer space or in meteorites and other celestial objects, one is struck by the number of substances that are utilized by life. This can be hardly a meaningless coincidence." (p. 160).

If these are the universal characteristics of life, what are non-universal characteristics? These are specific sequences of DNA, RNA and proteins. For example, a base C at the 10th position of a gene, or a Leucine amino acid at the 133th position of a protein are a non-universal characteristics. I suppose, De Duve would agree that these are historical contingencies [2].

My conclusion: it follows from de Duve's list that things like left-handed amino acids, introns, the eukaryotic cel (with mitochondrion(-DNA), chloroplast(-DNA), eukaryotic chromosome) and the Tree of Life (with three domains eukaryotes, archaeans, and bacteria) are not universal features of life. That is: they are not expected on other planets harboring life. [conclusion added 3 Jul 2014]

Of course, the universal features of life are relevant for detecting life on Mars. A next blog will discuss that topic. 

Notes
  1. The Major Metabolic Pathways are potentially a universal feature of life. The enzymatic control of metabolic pathways is probably species-specific, certainly the DNA sequences of the enzymes are. [GK]
  2. Harold J. Morowitz "has long been a vigorous proponent of the view that life on earth emerged deterministically from the laws of chemistry and physics". See: 'A Theory of Biochemical Organization, Metabolic Pathways, and Evolution', Complexity Volume 4, Issue 6, pages 39–53, July/August 1999:
    "To provide a framework for distinguishing historical aspects of biology from the more deterministic ones consider the following abstraction: an ensemble of earths, a very large collection of identical planets in macroscopically identical solar systems 4.0 billion years ago before there were biological entities. Each of these earths will unfold in time and will have features that may be compared. There will be common properties that belong to the deterministic, domain, and distinctive features that are historical in nature." [added: 5 July 2014]

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