Water is not a blank canvas for molecules of life

A fundamental consequence of cellular organization of living systems is that the aqueous milieu, bathing the cells, is also compartmentalized. Although water equilibrates readily across the elastic cellular boundary, passive permeation of solutes is strongly hindered. As a result, gradients of concentrations of ions, salt, and soluble biomolecules are readily established across the cellular boundary, producing osmotic activity of water. Drawing from recent experiments in our labs employing simple models for the cellular chassis (i.e., phospholipid membrane), this talk considers how the osmotic activity of water is transduced across cell-like compartments. It highlights how the dissipation in water activity couples with the compartmental boundary, mechanically remodeling the membrane shape and chemically reorganizing membrane components through a cooperative dynamics. Comparing these processes as elemental events in the homeostatic working of a living cell, these findings support the idea that water is not a mere solvent for life ¿ a blank canvas on which biomolecules become animated ¿ but an active medium that guides organization and dynamics of biomolecules in complex, subtle and essential ways.