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Ch.23 Lipids
Chapter 23, Problem 23.31

Are the carbon–carbon double bonds in naturally occurring fatty acids primarily cis or trans?

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Understand the structure of fatty acids, which are long hydrocarbon chains with a carboxylic acid group at one end.
Recognize that fatty acids can have carbon–carbon double bonds, which can exist in two geometric isomers: cis and trans.
Recall that in the cis configuration, the hydrogen atoms attached to the carbon atoms of the double bond are on the same side, causing a bend in the chain.
In the trans configuration, the hydrogen atoms are on opposite sides of the double bond, resulting in a straighter chain.
Note that naturally occurring fatty acids predominantly have cis double bonds, which contribute to the fluidity of cell membranes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cis and Trans Isomerism

Cis and trans isomerism refers to the spatial arrangement of atoms in a molecule. In cis isomers, similar groups are on the same side of a double bond, while in trans isomers, they are on opposite sides. This difference in arrangement can significantly affect the physical properties and biological functions of fatty acids.
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Fatty Acids

Fatty acids are carboxylic acids with long hydrocarbon chains, which can be saturated or unsaturated. Unsaturated fatty acids contain one or more double bonds between carbon atoms. The configuration of these double bonds (cis or trans) influences the fatty acid's melting point, fluidity, and overall health effects.
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Biological Importance of Fatty Acids

Fatty acids play crucial roles in biological systems, serving as key components of cell membranes and energy sources. The predominance of cis double bonds in naturally occurring fatty acids contributes to membrane fluidity and flexibility, which are vital for proper cellular function. Understanding the structure of these fatty acids is essential for studying nutrition and health.
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