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Question Video: Identifying Lipids from a List of Types of Biological Molecules Biology

Which molecules from the examples given are classified as types of lipids?


Video Transcript

Which molecules from the examples given are classified as types of lipids?

This question provides us with a list of biological molecules. Then it asks us to determine which of these molecules will be considered types of lipids. So first, we’ll recall some facts about lipids. And then we’ll look at the structures of the molecules in the list provided, and we’ll use what we know to determine which of these are lipids. Let’s recall that lipids are molecules that are insoluble in water. They’re generally composed of carbon atoms, hydrogen atoms, and few oxygen atoms. And they’re characterized by their possession of what’s known as a hydrocarbon chain. Here, I’ve drawn simplified diagrams of each of the biological molecules listed. Can you identify them based on their structure?

If you said triglyceride, nucleic acid, phospholipids, cholesterol, and cellulose, then you know your biological molecules. In order to answer our question, let’s take note of two things here. First, we’re looking for lipids, which is a type of biological macromolecule. Well, nucleic acids are their own category of macromolecule. And cellulose is an example of what we call a carbohydrate. Our four types of biological macromolecules are proteins, lipids, nucleic acids, and carbohydrates.

Since nucleic acids and cellulose belong to other categories, we know that they’re not lipids. The second thing to note here is that lipids are characterized by the possession of a hydrocarbon chain. We can see hydrocarbon chains in the triglyceride molecule, the phospholipid molecule, and the cholesterol molecule.

Nucleic acids are composed of a phosphate group, a sugar, and a nitrogen-containing base. They do not possess hydrocarbon chains. And cellulose is made of a repeating pattern of sugars, also without hydrocarbon chains. Since triglycerides, phospholipids, and cholesterol possess hydrocarbon chains, we know that they’re classified as types of lipids.

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