ABSTRACT
This chapter applies reaction thermodynamics to equilibrium conformational transitions of proteins. It begins with a description of the structural variables associated with both proteins and nucleic acids, to underscore the structural complexity of macromolecular conformational transitions. The chapter analyzes conformational equilibrium of unimolecular protein folding reactions using this "two-state" model. To experimentally quantify conformational transitions, and to connect to energies, entropies, and the like, equilibrium conformational transitions are required. The chapter discusses an example of one such a reaction: the "folding–unfolding" reactions of proteins. With simple chemical systems, thermodynamic data on macromolecular conformational transitions are obtained as discrete points, not as smooth curves and functions. Nucleic acids have even more backbone conformational degrees of system per residue, reflecting the larger number of bonds per residue, although the side chain nucleobases are less variable due to their rigid planarity.
