Illustration of a cell membrane, showing the role played by lipids (orange) in membrane biochemistry. Here, two receptors (one yellow, one red) are shown floating in lipid ‘rafts’, areas with higher concentrations of cholesterol compared to the surrounding phospholipid bilayer that makes up the normal membrane structure. The phospholipids consist of a phosphate head (blue) and a fatty acid tail (orange). Membrane receptors are specialized proteins that receive chemicals as part of signaling between cells and the surrounding environment. Created for Sigma Aldrich.