Fatty acid molecules have an acidic carboxyl group at one end and what feature on the rest of the molecule?

• A. A long chain of hydrophobic carbon atoms
• B. A glycerol backbone
• C. A cholesterol backbone
• D. A phosphate group

Answer: (A)

Fatty acids are carboxylic acids with a long, nonpolar hydrocarbon tail. The acidic carboxyl group at one end provides polarity, while the rest of the molecule is a lengthy chain of carbon and hydrogen that is hydrophobic. This hydrocarbon tail is what makes fatty acids insoluble in water and capable of packing tightly for energy storage. In many lipids, fatty acids are attached to a glycerol backbone to form triglycerides, or to a glycerol-phosphate head in phospholipids, but the fatty acid portion itself remains the long hydrophobic chain. The glycerol backbone, cholesterol backbone, and phosphate group describe other parts of lipid structures, not the fatty acid tail.