Cholesterol is a major component of all biological membranes; ~25% of total brain lipid is cholesterol.
Cholesterol is a lipid that makes up about 20-25% of the structural components of the cell membranes. It determines the fluidity and permeability of the membrane, making it permeable to water but not to ions and protons.
Cholesterol also regulates the functions of the transporters and signaling proteins present on the plasma membrane. The major sites of cholesterol synthesis are small intestine and liver. Cholesterol is used to prepare immune-stimulating complexes to enhance cellular and humoral responses.