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The Structure of Lipids – Saturated Vs. Unsaturated Fatty Acids

The structure of lipids consists of a long carbon chain and a polar head. Discover the difference between the structure of saturated fatty acids and the structure of unsaturated fatty acids.

Fats and oils are classified as lipids. These molecules are insoluble in water and are great sources of energy. The structure of lipids vary between different types of fats, but they all share similar features. Each consists of several carbon atoms linked together by chemical bonds. At the top of the carbon chain sits a polar molecule, usually a carboxyl group (COOH).

The Carbon Chain

The carbon chain can range in length from a few carbon atoms to a few dozen carbon atoms. This part of the fatty acid is non-polar, meaning it is insoluble in water. The carbon chain of fatty acids which comprise the cell membrane face the interior space between the phospholipid bilayer.

Polar Head

The carboxyl group atop the carbon chain is polar, meaning it is soluble in water. The polar head of fatty acids comprising the cell membrane face either the exterior environment or the interior of the cell.

Saturated Fatty Acids

The structure of saturated fatty acids consists of carbon chains that don’t have any double bonds. Some examples include the 12 carbon molecule lauric acid and the 16 carbon molecule palmitic acid.

Unsaturated Fatty Acids

The structure of unsaturated fatty acids feature at least one double bond in the carbon chain. Oleic acid is an 18 carbon unsaturated fatty acid with one double bond. Another example is linoleic acid, which features two double bonds.


Nelson, David L. Lehninger Principles of Biochemistry 4th ed. W.H. Freeman and Company. 2005

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