There are two central themes underlying the concepts in this book. The first is that the function of a molecule depends on its structure and that biological macromolecules can assemble spontaneously into functional structures. The second theme is that any biological macromolecule must work together with other molecules to carry out its particular functions in the cell, and this depends on the ability of molecules to recognize each other specifically. Clearly, to understand the molecular mechanism of any biological process, we must understand the energy of the physical and chemical interactions that drive the formation of specific structures and promote molecular recognition