The epigenetic cell

Nature s solution of this problem is both simple and extraordinary. The linear information of nucleotides is used to assemble a linear sequence of amino acids, and then this polypeptide chain folds on itself (because of the electrical forces that exist between amino acids) and spontaneously assumes a specific three-dimensional structure. It is as if one wrote the word apple and then observed the word folding on itself and becoming a real apple. 

The information difference that exists between the linear order of polypeptides and the three-dimensional order of proteins can be illustrated with a simple example. The linear order of 100 punctiform amino acids is specified by 100 coordinates, while their three-dimensional organisation requires 300 coordinates (three for each amino acid). Protein folding, or self-assembly, amounts therefore to adding the 200 missing coordinates to the 100 coordinates provided by the genes. And since the complexity of a system is determined by the number of parameters that are required to describe it, it is clear that protein folding is a phenomenon that produces an increase of complexity. 

A proper definition of the cell cannot ignore this fundamental characteristic, and must mention it explicitly. We arrive in this way at a new definition of the cell that can be expressed in various ways  

The increase of complexity, in conclusion, is a qualifying property of life. This requires a new definition of the cell and will allow us, as we will see, to discover a new logic at the basis of life. 

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