Biological membranes, such as those surrounding animal cells, are made up of lipids and proteins. Because these molecules do not usually mix well, they are distributed within different regions of the membrane. These two lipids are required for the generation of cholesterol-dependent raft domains, which are necessary for signaling within the plasma membrane. However, it was not clear how SMs interacted with other molecules of raft domains, until researchers developed new fluorescent synthetic molecules that structurally mimic SMs and can be studied in live cells.