The joining of a fatty acid to a carbon skeleton using oxygen. The resultant product is a monoglyceride, diglyceride, or triglyceride (triacylglyceride). Triacylglycerides are formed in a stepwise fashion. First, a fatty acid (usually a saturated fatty acid) is attached at carbon 1 of the glycerophosphate. The phosphate group at carbon 3 is electronegative and because it pulls electrons toward it, it leaves carbon 1 more reactive than carbon 2. The fatty acid (as acyl CoA) is transferred to carbon 1 through the action of a transferase. The attachment uses the carboxy end of the fatty acid chain and makes an ester linkage releasing the CoA. Now the molecule has electro¬ negative forces at each end—the phosphate group on carbon 3 and the oxygen plus carbon chain at carbon 1. Now carbon 2 is vulnerable and reactive and another carbon chain can be attached. In this instance, the fatty acid is usually an unsaturated fatty acid. At this point, the 1,2 diacylglyceride- phosphate loses its phosphate group so that carbon 3 is now reactive. The 1,2 diacylglyceride can either be esterified with another fatty acid to make triacylglyceride or can be used to make the membrane phospholipids, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, cardiolipin, and phosphatidylserine.