Cellular life

The central role played by DNA in cellular life guarantees a place of importance for the study of its chemical and physical properties. It did not take long after Watson and Crick described the now iconic double helix structure for a question to arise about the ability of DNA to transport electrical charge. It seemed apparent to the trained eye of the chemist or physicist that the array of neatly stacked aromatic bases might facilitate the movement of an electron (or hole) along the length of the polymer. It is now more than 40 years since the first experimental results were reported, and that question has been answered with certainty. 

Morowitz, H. (1992), Beginnings of Cellular Life Metabolism Recapitulates Biogenesis, Yale University Press, New Haven, CT. 

Did cellular life develop in a later phase of evolution ... 

We must give first an outline of the non-metal pathways which we observe in all cells. We start here because we know nothing about their abiotic chemistry but assume that cellular life arose from it. We shall assume that the basic requirement of all metabolism is the energised and catalysed synthesis of polysaccharides, lipids, proteins and nucleic acids. These are polymers (see Table 4.5), formed from monomers, all of which could have always arisen when energy was applied to the... 

Margulis, L. and Schwartz, K.V. (1998). Five Kingdoms (3rd ed.). Freeman and Co., New York Morowitz, H.J. (1992). Beginnings of Cellular Life. Yale University Press, New York Pope, M.T., Still, E.R. and Williams, R.J.P. (1980). A Comparison between the chemistry and biochemistry of molybdenum and related elements. In M. Cougwan, (ed.), Molybdenum and Molybdenum Containing Enzymes. Pergamon Press, Oxford, Chap. 1... 

The combination of the material of the first four chapters led us then to give an outline of the thermodynamic systems chemistry common to all cells. We offered little explanation of the origins of cellular life, as such an explanation could well remain beyond our insight. We then concerned ourselves with the way in which the... 

Vertebrates contain several proteins that maintain the integrity of the blood plasma circulatory system. These contain domains that are specific to vertebrates (Gla, FN1, FN2) (Patthy, 1985), domains that are found in different contexts in invertebrates and/or protists (FBG, APPLE, KR) (Xu and Doolittle, 1990 Eschenbacher et al., 1993 Wilson et al., 1993) and a domain that is found in all cellular life (trypsin-like serine protease, Tryp SPc). The invertebrate versions of these domains, however, are found in molecular contexts that differ considerably from their vertebrate extracellular counterparts, indicating that although these nonenzy-... 

Kletsas, D., Pratsinis, H., Gioni, V., Pilichos, K., Yiacoumettis, A. M., and Tsagarakis, S. (2007). Prior chronic in vivo glucocorticoid excess leads to an anabolic phenotype and an extension of cellular life span of skin fibroblasts in vitro. Ann. N. Y. Acad. Sci. 1100, 449-454. 

Let us consider some of the further implications of Figure 1.1. The view that cellular life can be arrived at from inanimate matter may imply in principle the possibility of reproducing it in the lab. Why not, if all we need is a bunch of molecules in a properly reactive environment This way of thinking is the basis of the experimental work on the origin of life. In fact, the best way to demonstrate the validity of this view would be to make life in the laboratory - the age-old Faustian dream. We do not know how the process of the transition to life really occurred in nature, so how can we reproduce it in the laboratory The answer to this question is conceptually simple, as pointed out by Escheiunoser and Kisakiirek (1996) ... 

The idea of the high probability of the occurrence of life on Earth, although phrased differently and generally with less emphasis, is presented by other significant authors. For instance, H. J. Morowitz in his well-known book on the emergence of cellular life (1992, p. 12), states ... 

Of course, this is too much of a big picture and to define fife at this level may indeed appear impossible. However, one can scientifically tackle this question by looking at life in its simplest expression, namely microbes and other uiucellular organisms. This is a first, important clarification, which also eliminates (at least for most scientists) the notions of soul or consciousness from the picture. In other words, let us talk only about microbial fife, and try to give a definition of cellular life. 

Is it the case that all components of our cellular life are thermodynamically stable Of course not. We have around us many compounds in our biochemistry that are not under thermodynamic control - think of important compounds such as adenonine triphosphate (ATP), phospholipids, RNA, DNA, proteins. .. Nowadays, these compounds are formed thanks to the action of enzymes, which are often specialized for catalyzing the synthesis of products under kinetic control. 

The autopoietic analysis of life is based on cellular life, the main argument for this being simply that there are no other forms of life on earth. We all know that even the simplest cells are extremely complex, encompassing hundreds of genes and other macromolecules. However, beyond this complexity, the question of what a cell really does, lends itself to a relatively simple answer. Consider Figure 8.1, which schematizes a cell. The first thing one observes is the boundary, a semi-permeable, spherical closed membrane that discriminates the cell from the medium. Here the term semi-permeable means that certain substances (nutrients and other chemicals)... 

Figure 8.2 The cyclic logic of cellular life. The cell, which is equivalent to an autopoietic unit, is an organized bounded system that determines a network of reactions that in turn produces molecular components that assemble into the organized system that determines the reaction network that... and so on.

Varela, 1998). This characterizes the system as an autonomous identity that can be dehned as auto referential. It produces its own rules of existence and therefore has a particular type of bio-logical coherence. These internal rules of the system are what dehne cellular life. 

We go back now to the question of whether and to what extent autopoiesis is the necessary and sufficient condition for cellular life. In the early days of autopoiesis, Maturana and Varela explicitly wrote (Maturana and Varela, 1980, p. 82) that autopoiesis is necessary and sufficient to characterize the organization of living systems and Gail Fleischaker, in the previously cited review on autopoiesis... 

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