THERMODYNAMICS OF COMPLEXITY - THE LIVE CELL

Thermodynamics has always been a remarkable science in that it studies macroscopic properties that are only partially determined by the prop erties of individual molecules. Entropy and free energy only exist in constellations of more than a single molecule (degree of freedom). The y are the so-called emergent properties. Tendency towards increased en tropy is an essential determinant for the behaviour of ideal gas mixtu res, showing that even in the simplest physical/chemical systems, (dys )organisation of components is crucial for the behaviour of systems. T his presentation aims at illustrating the thesis that the aforesaid ho lds a fortiori for the living cell: Much of the essence of the live st ate depends more on the manner in which the molecules are organised th an on the properties of single molecules. This is due to the phenomeno n of 'Complexity'. BioComplexity is defined here as the phenomenon tha t the behaviour of two functionally interacting biological components (molecules, protein domains, pathways, organelles) differs from the be haviour these components would exhibit in isolation from one another, where the difference should be essential for the maintenance and growt h of the living state, For a true understanding of this BioComplexity, modem thermodynamic concepts and methods (nonequilibrium thermodynami cs, metabolic and hierarchical control analysis) will be needed. We sh all propose to redefine nonequilibrium thermodynamics as: The science that aims at understanding the behaviour of nonequilibrium systems by taking into account both the molecular properties and the emergent pro perties that are due to (dys)organisation. This redefinition will free nonequilibrium thermodynamics from the limitations imposed by earlier near-equilibrium assumptions, resolve the duality with kinetics, and bridge the apparent gap with metabolic control analysis. Subsequently, the complexity of the control of the energy metabolism of E. coli wil l be analysed in detail. New control theorems will be derived for newl y defined control coefficients. It will become transparent that molecu lar genetic experimentation will allow one to penetrate into the mecha nisms of the complex regulation of energy metabolism. (C) 1998 Elsevie r Science B.V.