Phosphatidylserine

Phosphatidylserine (PS) synthesis in mammalian tissues is provided by the base exchange reaction, in which the ethanolamine of phosphatidylethanolamine is exchanged for free serine (Fig. 1). This reaction, although reversible, is used primarily to produce the PS required for membrane synthesis. PS has a net negative charge. 

Figure 1:  Synthesis of phosphatidylcholine from phosphatidylserine in the liver. ( is a fatty acid hydrocarbon chain.) = phosphate; CO2 = carbon dioxide.