Phosphatidylinositol (PI) is a class of glycerophospholipids consisting of a glycerol backbone esterified with two fatty acids and a phosphate group linked to myo-inositol. It is a key component of eukaryotic cell membranes, particularly enriched in the inner leaflet of the plasma membrane. PI serves as a precursor for important signaling molecules: hydrolysis by phospholipase C yields diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3), which act as second messengers regulating calcium release and protein kinase C activation. Phosphorylation by PI kinases produces PIP2 and PIP3, critical for membrane trafficking, cytoskeletal dynamics, and pathways like PI3K/Akt in cell growth and survival. In food science, PI occurs naturally in soy lecithin and other plant/animal lipids used as emulsifiers.