Cholesterol is a cholestanoid consisting of cholestane having a double bond at the 5,6-position as well as a 3beta-hydroxy group. It is an animal sterol found in the body tissues (and blood plasma) of vertebrates.
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.