The Chemistry and Physics of Life

Our idea of the interior of a cell at the molecular scale is often rather naif. If one could see the interior of a cell with molecular resolution, one would not see an aqueous solution of molecules with the cellular organelles suspended. The molecular crowding, in particular the macromolecular crowding, inside a cell is such that the interior of a cell is more like a gel than a solution. Molecular packing is so dense that it is hard for macromolecules to diffuse freely. The ubiquitous presence of the cytoskeleton and macromolecular assemblies in a space that is highly restricted due to cellular organelles makes the interior of cells tightly packed (Fig. 2.1). Nevertheless, it is a highly hydrated environment, where solvation is made by water molecules (Fig. 2.1) and voids are filled by water that solubilizes ions and small molecules. Thus, virtually all exposed molecules in a cell are under the chemical and physical influence of water. The interior of a cell is not an aqueous solution, but the chemical reactions of the living cells are typical chemical reactions of aqueous solutions.