An overview of TAG metabolism as a dynamic process that allows its lipid participants to play numerous inter-related roles within cells is presented. For most synthetic pathways each step is catalyzed by a single enzyme unless specific regulation is required. Yet, in the glycerol-3-phosphate pathway of TAG synthesis, investigators have confirmed four independent GPAT isoforms, three AGPAT isoforms, three PAP isoforms, and two DGAT isoforms. The non-backcrossed mice resist weight gain on a high-fat diet. Their subdermal fat depots are absent, and their gonadal and brown adipose fat pads and adipocytes are smaller. The differences in fat pad size are not solely due to absent GPAT4 activity within the tissue, because although NEM-sensitive GPAT activity in brown adipose is 50% lower than in wild-type brown adipose, gonadal NEM-sensitive GPAT activity is identical.