Glycerol 3 Phosphate Acyltransferase (GPAT) is an enzyme that plays a crucial role in the initial step of triglyceride and phospholipid synthesis. It catalyzes the esterification of glycerol-3-phosphate with a fatty acyl-CoA, producing lysophosphatidic acid. This process is essential in the formation of the lipid bilayers that make up cellular membranes.