Thermodynamics of Far-From-Equilibrium Systems, Biochemistry, and Life in a Warming World

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Abstract: Recent advances in the formulation of thermodynamics for far-from-equilibrium systems has suggested multiple avenues for re-assessing the limits to life. However, biologists are largely unaware of these developments. Here I apply these new thermodynamics to a fundamental problem of life – the response to temperature. The classic paradigm posits that biological performance declines at higher temperatures because enzymes that catalyze biochemical reactions lose structural stability in ways not sensitive to reaction characteristics or environmental conditions (other than temperature). However substantial evidence suggests that biological performance declines at temperatures well below those at which proteins begin undergo irreversible structural change. An alternative explanation arises from thinking of reactions as dependent on the movement of molecules to and from enzymes. Within this “reaction-displacement” description of reactions, empirical data show that molecular movement processes (diffusion, transport) increase more slowly with temperature than do molecular collisions. Consequently, thermodynamic calculations reveal that biochemical reactions may become increasingly unable to achieve the necessary increase in entropy of surroundings required by the second law of thermodynamics. These calculations reveal an optimum temperature for reactions that depends on many factors other than change in enzyme stability, including enzyme concentration and type of reaction, e.g., energy generating versus synthesis of complex biomolecules. The resulting model makes unprecedented explanations of hot mitochondria and nuclei in cells, a decline in plant, and thus food, nutritional content at warmer temperatures, coral bleaching, and reduced biomass or elimination of higher trophic levels under warmer conditions.