CDP-choline and PtdEtn methylation pathways for PtdCho biosynthesis. Cho, choline; Cho-P, choline phosphate; CDP-Cho, CDP-choline; PtdMME, phosphatidylmonomethylethanolamine; PtdDME, phosphatidyldimethylethanolamine; SAM, S-adenosylmethionine; SAHC, S-adenosylhomocysteine.