Medicine & USMLE


  1. Fatty Acids
  2. Triacylglycerols
  3. Phospholipids
  4. Sphingolipids
  5. Terpenes
  6. Steroids
  7. Waxes


Waxes are a type of lipid that contain an ester surrounded on both sides by long, hydrocarbon chains. Esters are non-polar or hydrophobic molecules, making them dissolve well in oil, but poorly in water. These properties make them biologically useful for coatings that seal in or repel water.

Key Points

  • Waxes
    • Structure:
      • Ester with two hydrocarbon chains on both sides
      • Waxes are synthesized when a long-chain alcohol nucleophilically attacks a long-chain fatty acid
    • Role:
      • Ear wax
      • Covers feathers of aquatic birds and leaf surfaces of some plants
    • Unique Properties:
      • Water-repellant
    • Nonpolar/hydrophobic