Ceramide is synthesized in the endoplasmic reticulum from the amino acid serine. Ceramide is an impoant second messenger regulating pathways such as apoptosis, cell cycle, cell differentiation and senescence. Sphingomyelins are formed when ceramide reacts with phosphatidylcholine to form sphingomyelin plus diacylglycerol. It occurs mainly in the golgi apparatus and to lesser extend in the plasma membrane. Ref: Botham K.M., Mayes P.A. (2011). Chapter 24. Metabolism of Acylglycerols & Sphingolipids. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.