Phosphatidylinositol (PI) is a type of phospholipid found in cell membranes. It plays a crucial role in cellular signaling and membrane dynamics. PI consists of a glycerol backbone, two fatty acid tails, and a phosphate group linked to inositol, a six-carbon sugar alcohol. In addition to its structural role, PI can be phosphorylated to form various derivatives, such as phosphatidylinositol 4,5-bisphosphate (PIP2). These derivatives are important for signaling pathways, including those involved in cell growth, metabolism, and cellular communication.