Saturated chains have no double bonds; unsaturated have one or more.
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Fatty acids are long hydrocarbon chains with a carboxylic acid head group. Saturated fatty acids, such as stearic acid, contain only single carbon-carbon bonds, so the chains are straight and pack closely, giving higher melting points and solid fats. Unsaturated fatty acids contain one or more C=C double bonds, and cis double bonds, as in oleic acid, introduce a kink that disrupts packing and lowers the melting point. Omega-3 and omega-6 polyunsaturated acids are essential because humans cannot add double bonds beyond carbon 9 counted from the carboxyl end, so they must come from food. The degree of saturation strongly influences the fluidity of membranes and of foods.
Key ideas: Saturated chains have only single C-C bonds, pack tightly and have higher melting points (stearic acid about 70 C). Natural unsaturated acids usually have cis double bonds that kink the chain, lowering melting point (oleic acid about 13 C). Omega-3 means the first double bond is on carbon 3 from the methyl end. Linoleic and linolenic acids are essential.
Common mistakes and connections: A mistake is to read omega numbering from the carboxyl end, which is the delta system instead. Another is assuming all unsaturated fats are healthy. Catalytic hydrogenation converts unsaturated to saturated. Links to trans fats, membrane fluidity and iodine value.
Melting points of C18 fatty acids. Each added cis double bond adds a kink that disrupts packing and lowers the melting point. The interactive lesson shows this as a live animation or chart.
Oleic acid melts at about 13 C, while stearic acid, with the same chain length but no double bonds, melts at about 69 C.
Saturated chains have no double bonds; unsaturated have one or more.
Saturated and Unsaturated Fatty Acids is a intermediate topic in Biochemistry, Environment & Industry. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Biochemistry, Environment & Industry first: Vitamins, Hormones, Fats and Oils.
The next topics in Biochemistry, Environment & Industry are Trans Fats and Phospholipids.
Yes. The interactive lesson includes a self-check question on Saturated and Unsaturated Fatty Acids, and the Biochemistry, Environment & Industry quiz draws on every topic in this area.
Saturated and Unsaturated Fatty Acids is topic 19 of 127 in Biochemistry, Environment & Industry.
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