Cell Metabolism

A living cell comprises a large number of compounds of distinct natures; water dominates this inventory, ca. 70% (w/w) on average, due to its unique physicochemical properties—namely, its role as universal solvent. In fact, water exhibits a great capacity to solubilize polar compounds, for being a polar molecule itself—at the expense of (stabilizing) mutual attraction to positive and negative (integer or partial) charges in the solute. This is complemented by its ability to solubilize apolar compounds, by maximizing the intensity of hydrogen bonds between water molecules themselves—at the expense of a structured clathrate of water molecules, located at fixed, optimized relative distances and orientations, built around the solute molecules. Formation of such supramolecular entity is accompanied by decrease in Gibbs’ energy, sufficient to override any increases thereof associated with (unfavorable) interactions between dipoles in water molecules and hydrophobic moieties in solute molecules. In addition, its liquid state within a range of temperatures that encompass most temperatures found on the Earth crust supports reasonable rates of mass transfer—intermediate between the too low rates in solids or the too high rates in gases; and of heat transfer—intermediate between the too low rates in gases and the too high rates in solids.