In a truly interdisciplinary fashion, organic chemists and molecular biologists have engineered novel systems that allow externally applied light to regulate protein confirmation in living systems. These highly engineered systems typically involve two distinct parts. The first part is a small molecule, photosensitive chromophore that responds to light by changing shape or conformation. At one end of this molecule is usually a ligand or an effector molecule and at the other, sometimes a chemically reactive group that targets a particular amino acid. The second part of these systems is typically a genetically modified protein that has been designed to present a reactive site on the surface of a cell to allow facile chemical coupling of the photoswitch to the protein. These two parts together allow for light to regulate cellular activity by mediating membrane voltage or protein conformation.