Cholesterol

Cholesterol is a sterol (or modified steroid), a lipid molecule and is biosynthesized by all animal cells because it is an essential structural component of all animal (not plant or bacterial) cell membranes that is required to maintain both membrane structural integrity and fluidity. Cholesterol enables animal cells to dispense with a cell wall to protect membrane integrity and cell viability, thus allowing them to change shape and move about (unlike bacteria and plant cells which are restricted by their cell walls).

Cholesterol also serves as a precursor for the biosynthesis of steroid hormones and bile acids. Cholesterol is the principal sterol synthesized by animals. All kinds of cells in animals can produce it. In vertebrates the hepatic cells typically produce greater amounts than other cells. It is almost completely absent among prokaryotes (bacteria and archaea), although there are some exceptions such as Mycoplasma, which require cholesterol for growth.

According to the lipid hypothesis, since cholesterol (like all fat molecules) is transported around the body (in the water outside cells) inside lipoprotein particles, elevated cholesterol concentrations (hypercholesterolemia) — potentially offers a lower cost way to detect elevated concentrations of LDL particles; possibly even low concentrations of functional HDL particles — both variations strongly associated with cardiovascular disease because LDL particles promote atheroma development in arteries (atherosclerosis).