Well, fatty acids are these biological molecules that consist of a long hydrocarbon chain and a terminal carboxylate group. Now, the terminal carboxylate group gives the molecule hydrophilic polar properties, while the long hydrocarbon chain gives the fatty acids hydrophobic nonpolar properties. So what do our cells use fatty acids for? Well, fatty acids have four important functions inside our cells. Number one is fatty acids are fuel molecules. And as we'll shortly see, our cells can break down fatty acids to actually generate high energy ATP molecules.