The role of non-genomic information in maintaining thermodynamic stability in living systems.

Living systems represent a local exception, albeit transient, to the second law of thermodynamics, which requires entropy or disorder to increase with time. Cells maintain a stable ordered state by generating a steep transmembrane entropy gradient in an open thermodynamic system far from equilibrium through a variety of entropy exchange mechanisms. Information storage in DNA and translation of that information into proteins is central to maintenance thermodynamic stability, through increased order that results from synthesis of specific macromolecules from monomeric precursors while heat and other reaction products are exported into the environment. While the genome is the most obvious and well-defined source of cellular information, it is not necessarily clear that it is the only cellular information system. In fact, information theory demonstrates that any cellular structure described by a nonrandom density distribution function may store and transmit information. Thus, lipids and polysaccharides, which are both highly structured and non-randomly distributed increase cellular order and potentially contain abundant information as well as polynucleotides and polypeptides. Interestingly, there is no known mechanism that allows information stored in the genome to determine the highly regulated structure and distribution of lipids and polysacchariedes in the cellular membrane suggesting these macromolecules may store and transmit information not contained in the genome. Furthermore, transmembrane gradients of H$^+$, Na$^+$, K$^+$, Ca$^+$, and Cl$^-$ concentrations and the consequent transmembrane electrical potential represent significant displacements from randomness and, therefore, rich potential sources of information.Thus, information theory suggests the genome-protein system may be only one component of a larger ensemble of cellular structures encoding and transmitting the necessary information to maintain living structures in an isoentropic steady state.