Because of this, polar molecules are important in helping to establish the three-dimensional structure or orientation of other larger molecules. When placed in water, the polar ends of the fatty acid molecules are attracted to water molecules, which are also polar. The nonpolar carbon chains are at the same time repelled by the water. As a result, fatty acid molecules are oriented on the water's surface. Of particular importance to living things is the orientation of phospholipid molecules, which are a combination of a fat molecule with a phosphate group.
Phospholipids are among the most important parts of cell membranes.
They tend to become oriented on surface or boundary regions in a manner similar to the fatty acids on water. It is partly in this way that cell membranes are given a distinct structure. Second, polarity is important in understanding both the geometry and the chemical characteristics of large molecules, such as proteins. Proteins are so large that they may possess a number of polar groups on one molecule. The specific geometry of proteins exists in part because polar groups on one part of the molecule attract polar groups on another part of the same molecule.