ABSTRACT
Proteins and nucleic acids often exist in multiple states. Molecular motors adopt a range of different conformations depending upon the presence or absence of bound nucleotides such as ATP as well as the presence or absence of the cytoskeletal tracks that they move on. One simple example of the way in which state variables can be used to describe the internal states of macromolecules is for ion channels. One class of problems that people will return to repeatedly is the structure and function of ion channels. Ion channels are transmembrane proteins that mediate the transport of ions in and out of cells. The interesting case for ion channel dynamics arises when the energy balance between the open and closed states is altered by the presence of some driving force. Regulation of protein activity by covalent attachment of phosphate groups is one of the most important regulatory modes in all of biology.
