Question Video: Outlining the Difference Between a Saturated and Unsaturated Fatty Acid | Nagwa Question Video: Outlining the Difference Between a Saturated and Unsaturated Fatty Acid | Nagwa

Question Video: Outlining the Difference Between a Saturated and Unsaturated Fatty Acid Biology • First Year of Secondary School

Which of the following best explains the difference between a saturated and an unsaturated fatty acid? [A] Saturated fatty acid chains have only single bonds between the carbon atoms, whereas unsaturated fatty acid chains have one or more double bonds between the carbon atoms. [B] Unsaturated fatty acid chains have only single bonds between the carbon atoms, whereas saturated fatty acid chains have one or more double bonds between the carbon atoms. [C] A saturated fatty acid chain contains double the number of carbon atoms that an unsaturated fatty acid chain contains. [D] Saturated fatty acids contain a higher proportion of oxygen than unsaturated fatty acids.

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Video Transcript

Which of the following best explains the difference between a saturated and an unsaturated fatty acid? (A) Saturated fatty acid chains have only single bonds between the carbon atoms, whereas unsaturated fatty acid chains have one or more double bonds between the carbon atoms. (B) Unsaturated fatty acid chains have only single bonds between the carbon atoms, whereas saturated fatty acid chains have one or more double bonds between the carbon atoms. (C) A saturated fatty acid chain contains double the number of carbon atoms that an unsaturated fatty acid chain contains. Or (D) saturated fatty acids contain a higher proportion of oxygen than unsaturated fatty acids.

This question asks about the difference between saturated and unsaturated fatty acids. So, first let’s remove the answer choices so we have some space to remind ourselves about the basic structure of fatty acids. As you can see here, fatty acids are composed of a carboxyl group attached to a hydrocarbon chain and are a major component of lipids. The carboxyl group is hydrophilic; it’s charged and will interact with charged or polar molecules, like water. On the other hand, the hydrocarbon chain doesn’t contain any charge and is therefore hydrophobic. This diagram is specifically showing the structure of a saturated fatty acid, but what does this mean? Let’s take a closer look at the atoms in the hydrocarbon chain to understand this better.

As the name suggests, the hydrocarbon chain of a fatty acid only contains carbon and hydrogen atoms. Saturated fatty acids only contain single bonds between adjacent carbon atoms in the hydrocarbon chain. This means that the hydrocarbon chain is fully saturated with hydrogen atoms. In other words, they contain the maximum number of atoms of hydrogen, and hydrogen atoms are bonded to a carbon atom in every available location on the chain.

Because of their chemical structure, fats containing saturated fatty acids can lie flat against each other and form a solid at room temperature. Unsaturated fatty acids have at least one double bond between the carbon atoms in the hydrocarbon chain. Each double bond between carbon atoms takes the place of two hydrogen atoms, resulting in fewer hydrogen atoms in the hydrocarbon chain overall and causing the structure to kink. This results in lipids that are liquid at room temperature because the kink in the fatty acid hydrocarbon chain means they do not fit together as easily as saturated fatty acids.

With this information, let’s take a look at the answer choices again. First, we can eliminate answer (C). The classification of these molecules into saturated or unsaturated fatty acids has nothing to do with the number of carbon atoms in the hydrocarbon chain. In fact, both saturated and unsaturated fatty acids come in a wide range of lengths. Next, we can eliminate answer (D), as both fatty acid types have the same proportion of oxygen atoms in their carboxyl group.

This means that the correct answer is (A), as (A) and (B) are the exact opposite of each other and (A) correctly describes the difference between the carbon-carbon bonds in saturated and unsaturated fatty acids. Saturated fatty acid chains have only single bonds between the carbon atoms, whereas unsaturated fatty acid chains have one or more double bonds between the carbon atoms.

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