Question Video: Describing the Basic Composition of the Three Main Biological Molecules: Proteins, Carbohydrates, and Lipids

Complete the statements to correctly describe the composition of biological molecules. a) A protein is made of many monomers called _. b) Many sugar molecules, like glucose, join together to form _. c) A basic lipid molecule is formed of one _ and three fatty acids.

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Video Transcript

Complete the statements to correctly describe the composition of biological molecules. (a) A protein is made of many monomers called blank. (b) Many sugar molecules, like glucose, join together to form blank. (c) A basic lipid molecule is formed of one blank and three fatty acids.

Key knowledge required to complete these statements correctly is the structure of biological molecules, also known as biological macromolecules. So, let’s review what these molecules are made of and the patterns in their structure as we go through this question. The question asks us to describe the composition of biological molecules. So, we need to describe how the parts of a biological molecule are put together. The biological molecules of concern here are three types of large molecules that we require from our food and in our bodies, and these include carbohydrates, proteins, and lipids. And specifically, we’ll be talking about fats. These types of molecules are called polymers.

The word polymer literally means many parts. And you can see in the diagram here that carbohydrates can be made of many parts. And typically, they’re many, many times larger than what we have shown here. The parts can be bonded into a single chain, as shown here, or they’re branched chain carbohydrates as well. A couple common examples of large or complex carbohydrates include starch, which is used for energy storage, and cellulose, a structural component of plant cell walls.

Polymers are made of many parts, and we call those parts monomers, which literally means one part. The monomer of carbohydrates are sugars and individual sugars are considered carbohydrates as well. In fact, some other carbohydrates are made of only two sugars bonded together, such as table sugar or sucrose. So, the number of sugars in a carbohydrate can range from one to thousands. Protein polymers also have a large range of sizes, and they bond together to form a single chain. A couple common examples of proteins that you may have heard of before are the hormone insulin and the structural protein collagen. The monomer unit of a protein is called an amino acid, and there’s 20 different kinds of amino acids that we build our proteins from.

Lipids are a little different, and while some references don’t consider lipids to be polymers, we will recognize them as polymers. And while lipids also include more than just fats, we’ll limit our scope to just fats here. Fats are made of a molecule of glycerol bonded to three fatty acid chains, which can vary in length and bond type. The monomer units of fats are glycerol and the fatty acids that attach to the glycerol. The fatty acids vary in length, and some of them can even have bends. The combination of the different fatty acids that attach to a glycerol give the fat its identity.

And it looks like we’re ready to complete the statements in the question. Statement (a) says, a protein is made of many monomers called blank. If we look at our table down here, proteins have a monomer unit called amino acids. Statement (b) says, many sugar molecules like glucose join together to form blank. And we now have the names of a couple example sugars in our table, glucose and fructose. So, if we put together many glucose sugars, we’ll get a larger carbohydrate. Statement (c) says that a basic lipid molecule is formed of one blank and three fatty acids. Looking at our diagram, we can see one, two, three fatty acids are connected to one glycerol.

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