Approaches to the minimal cell

We come back now to the origin of life and the evolution of early cells. We have seen in the first chapters of this book the endeavor of people working with the aim of clarifying the pathway to the transition to life starting from simple molecules. This is the so-called bottom-up approach, the narrative by which a continuous and spontaneous increase of molecular complexity has transformed inanimate matter into the first self-reproducing entities, and from those, life at large. 

The bottle neck of the bottom-up approach is the difficulty of reproducing on paper and/or in the laboratory those processes which have been moulded by contingency - such as the synthesis of specific macromolecular sequences. 

The point of this procedure is not to synthesize a fully fledged modem cell, but the simplest possible form of it. To clarify this point, the notion of the minimal cell needs to be discussed is more detail. 

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There are artificial life approaches to the minimal cell, with the idea of creating forms of life other than those based on nucleic acids and proteins. Do you believe that this is possible Towards which structures would you move ... 

Going back to the synthetic biology discussed in this book, I mentioned also that the construction in the laboratory of the early cell using the bottom-up approach is made difficult by the clouds of contingency, and added that there is instead confidence in a different approach to the minimal cell. This is the semi-synthetic approach seen in the previous chapter, which utilizes extant enzymes and/or genes. 

Luisi, P. L. and Oberholzer, T. (2001). Origin of life on Earth molecular biology in liposomes as an approach to the minimal cell. In The Bridge between the Big Bang and Biology, ed. F. Giovanelli. CNR Press, pp. 345-55. 

There is another approach to the construction of the living cell, as indicated in Figure 11.1. This is to utilize the extant nucleic acids and enzymes and insert them into a vesicle, and re-construct in this way a minimal living cell. 

Figure 11.1 The semi-synthetic approach to the construction of the minimal cell.

What can be done in order to approach the construction of the minimal cell In principle, the complexity of the core of the liposomes should be increased so as to reach the minimal genome. 

In real biological systems, a cell is capable of duplicating and reproducing itself with the same genetic content. This is due to complex systems of regulation, which is not really compatible with the experimental set up of minimal cells. For the time being, some alternative approaches to the question of self-reproduction should be envisaged. (Luisi et al., 2006). 

Luisi, P.L., Walde, P., Oberholzer, T. (1994). Enzymatic RNA synthesis in self-reproducing vesicles An approach to the construction of a minimal synthetic cell. Ber. Bunsenges. Phys. Chem. 98, 1160-1165. 

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