Medicine & USMLE


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


Terpenes are a group of lipids composed of individual units called isoprene. Isoprene is a 5-carbon structure that fits together in various ways to make all the different terpenes! One of the most important terpenes to know is a compound called squalene. Squalene is important because it eventually becomes cholesterol, which is a crucial biomolecule in our bodies! Finally, terpenes are non-polar, hydrophobic molecules that dissolve well in oil but poorly in water!

Key Points

  • Terpenes
    • Structure:
      • Terpenes are a type of lipid composed of isoprene units
        • Isoprene: 5-carbon unit with the formula (C5H8)n
        • Monoterpene: 2 Isoprenes (10 C)
        • Sesquiterpene: 3 Isoprenes (15 C)
        • Diterpene: 4 Isoprenes (20 C)
        • Triterpene: 6 Isoprenes (30 C)
          • Squalene is an triterpene
    • Roles:
      • Precursor to cholesterol and steroids
        • Isoprene → monoterpene → squalene cholesterol → steroid hormones
    • Unique Properties:
      • Terpenoids (a.k.a. isoprenoids) are terpenes with additional functional groups, usually oxygen
    • Nonpolar/hydrophobic