The Molecular Structure of Ion Channels Understanding the physical structure of ion channels is obviously the key to sorting out how they actually work. For instance, much insight into the detailed operation of ion channels has come from recent X-ray crystallographic studies of a bacterial K+ channel. This particular molecule was chosen for analysis because the large quantity of channel protein needed for crystallography could be obtained by growing vast numbers of bacteria. The channel is formed by subunits that each cross the plasma membrane twice; between these two membrane-spanning structures is a loop that inserts into the plasma membrane.