Why Are Lipids Hydrophobic?

If a substance is hydrophobic, it does not dissolve in water. Lipids are hydrophobic because lipids are nonpolar molecules and water molecules are polar.

Background

Lipids are a group of molecules that includes fats and oils, waxes, phospholipids, steroids (such as cholesterol) and other related compounds.

Polar Molecules

A polar molecule has two bonded atoms that do not share electrons. Polar molecules are only attracted to other polar molecules. Polar molecules are hydrophilic because they dissolve in water by forming hydrogen bonds.

Nonpolar Molecules

Nonpolar molecules are not attracted to polar molecules and are called hydrophobic because they do not dissolve in water.

Hydrocarbon Backbones

According to Carnegie Mellon, lipid molecules are hydrophobic because they consist of long, 18-22 carbon-hydrocarbon backbones and contain only a small amount of oxygen.

Fun Fact

One type of lipids, called phospholipids, are amphipatic, that is, both hydrophillic and hydrophobic.

References

• Clinton Community College: Organic Chemistry Lecture
• Tel Star: The Structure and Function of the Cell Membrane