There are several connections between metabolism of fats and fatty acids to other metabolic pathways. As noted, phosphatidic acid is an intermediate in the synthesis of triacylglycerols, as well as of other lipids, including phosphoglycerides. Diacylglycerol (DAG), which is an intermediate in fat synthesis, also acts as a messenger in some signaling systems. Fatty acids twenty carbons long based on arachidonic acid (also called eicosanoids) are precursors of the classes of molecules known as leukotrienes and prostaglandins. The latter, in turn, are precursors of the class of molecules known as thromboxanes. The ultimate products of beta oxidation are acetyl-CoA molecules and these can be assembled by the enzyme thiolase to make acetoacetyl-CoA, which is a precursor of both ketone bodies and the isoprenoids, a broad category of compounds that include steroid hormones, cholesterol, bile acids, and the fat soluble vitamins, among others.