In this module:

Cholesterol

The four-ringed lipid cholesterol forms the basis for another class of lipids. Cholesterol is a building block for many important molecules used for various purposes in higher organisms. It is partially oxidized in the liver to bile salts, which act like detergents to solubilize fatty acids in foods and allow them to be absorbed by the body. Many hormones, including estrogens and testosterone, are also derived from cholesterol. The diagram below shows the structures of cholesterol, glycocholate (the most common bile salt), estradiol and testosterone (two well-known hormones that are derivatives of cholesterol). As you can see, all four are amphiphiles, since they have hydrophobic and polar regions.

Intracellular Signaling

Some stimuli, such as the smell of bell peppers in olfactory receptor cells, activate an enzyme that breaks up phospholipids into smaller molecules. These molecules, derivatives of glycerol and fatty acids, then act on other enzymes in the cell.