Because the carboxyl group is a polar group, fatty acids are soluble in water. Most fatty acids in cells contain 16 to 18 carbon atoms per molecule. Saturated fatty acids have no double bonds between their carbon atoms. Unsaturated fatty acids have double bonds in the carbon chain. Glycerol is a water-soluble compound with three hydroxyl groups.
Triglycerides are glycerol joined to three fatty acids by condensation.
Phospholipids are like neutral fats except one fatty acid is replaced by phosphate group or a group with both phosphate and nitrogen. Phospholipids arrange themselves in a double layer in water, so the polar heads face outward toward water molecules and nonpolar tails face toward each other away from water molecules. Cholesterol is a precursor of other steroids, including aldosterone and sex hormones. Testosterone is the male sex hormone. Functions vary due primarily to different attached functional groups.