Carbohydrates - Online Tutor, Practice Problems & Exam Prep

Carbohydrates, or saccharides, are carbon-based molecules with hydroxyl groups, classified into monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides, like glucose (C₆H₁₂O₆), are single units, while oligosaccharides consist of 2-20 linked units, and polysaccharides contain over 20. They serve vital functions, including structural support (e.g., cellulose in plants, chitin in animals) and energy storage (e.g., starch in plants, glycogen in animals). The formation of polysaccharides involves dehydration synthesis, creating glycosidic bonds, while hydrolysis breaks them down into monosaccharides.

Carbohydrates

In this video, we're going to begin our lesson on carbohydrates. Now, carbohydrates can be defined as carbon-based molecules that are hydrated with many hydroxyl groups, which recall are just a functional group that look like this with an oxygen and a hydrogen atom. And so when we take a look at our image down below of carbohydrates, one thing that you'll notice is that there are plenty of these hydroxyl groups throughout their structures and so that is definitely a characteristic feature of carbohydrates. Now, carbohydrates are also referred to as saccharides, and so saccharides is really the Greek word that means sugars, and so sugars are carbohydrates. Now, when the term carbohydrates was originally coined way back in the 1800s, it was actually referring to compounds that had the exact chemical formula of Cn(H2O)n where you had some number of carbon atoms being hydrated by some number of water molecules, and that's exactly where it got its name from. The carbo for the carbons and the hydro or the hydrates for the water molecules that are hydrating the carbon atoms. Now, it turns out that simple carbohydrates are carbohydrates that fit this chemical formula exactly. For example, glucose is a carbohydrate that fits this chemical formula exactly. And glucose is, the most abundant carbohydrate, and it's the one that you guys should all be familiar with. And we'll be able to see an example of glucose down below in our image. But not all carbohydrates fit this chemical formula exactly, and so there are some complex carbohydrates, and complex carbohydrates are going to be carbohydrates that can slightly differ from this chemical formula here, and they can also have other types of atoms such as phosphorus, nitrogen, or sulfur atoms too. So let's take a look at our example down below to distinguish between the simple and complex carbohydrates. So notice on the left-hand side over here, when we take a look at its chemical formula and we count up the total number of carbon atoms, the total number of hydrogen atoms, throughout, and, the total number of oxygen atoms throughout, what we'll see is that there are a total of 6 carbon atoms, a total of 12 hydrogen atoms, and a total of 6 oxygen atoms. And so what you'll notice is that there are 6 water molecules that we can make out of the C6H12O6, and those water molecules are hydrating the 6 carbon atoms. And so this is going to be a molecule that fits the chemical formula up above exactly. And so this is going to be an example of a simple carbohydrate. More specifically, this is the chemical structure of glucose. And once again, glucose is the most abundant carbohydrate, and you should, start to, recognize its chemical formula of xmlns="http://www.w3.org/1998/Math/MathML">C6H12O6 because at some point in your course, you will need to know this chemical formula. Now, over here on the right-hand side, what we're showing you is a complex carbohydrate, and we can tell that it's a complex carbohydrate because its chemical formula does not match the one that we have up above. And so notice that it has a total of 6 carbon atoms, but when you count the hydrogen atoms there are 11 of them, and when you count the oxygen atoms there are actually 9 of them, and there's also 1 phosphorus atom as well, which you can see up above right here. And so this is a complex carbohydrate not because it has a circular shape, but because its chemical formula does not fit the one, up above exactly. And so, moving forward, we're mainly gonna be focusing on simple carbohydrates but it's good for you to also know that complex carbohydrates also do exist. And so this here concludes our introduction to carbohydrates and we'll get to talk more and more about carbohydrates as we move forward in our lesson. So I'll see you all in our next video.

Which of the following chemical formulas represents that of a simple carbohydrate?

• A. C₂H₂O₂.
• B. C₆H₁₂O₆.
• C. C₅H₄O₃.
• D. C₃H₆O₉.

3 Size Classes of Carbohydrates

In this video, we're going to introduce three different size classes of carbohydrates that we have numbered down below. And the numbers here correspond with the numbers that we have throughout our image. Now, what you'll notice is that for all three of these size classes the word "saccharide" here is present, which recall from our last lesson video means "sugar." And so, saccharide is present in all three of these size classes, which means sugar, and that's referring to carbohydrates. And so, really these three different size classes, they differ in the root word, their prefix. And so the very first size class is going to be the monosaccharide. Now recall that mono is a prefix that means just one or singular. And so monosaccharides are going to be a single carbohydrate unit, or in other words, monosaccharides are the monomers of carbohydrates, and that is very, very important for you all to note. Now an example of a monosaccharide is glucose, which once again is the most abundant monosaccharide. And so, it's one that you all should start to familiarize yourself with a little bit. And so when we take a look at our image down below, notice number 1 is the monosaccharide, which is just a single carbohydrate unit or just a single hexagon here, if you will.

Now the second size class of carbohydrate is going to be the oligosaccharide. And so oligo is a prefix that means a few. And so oligosaccharide, when you put it together, means a few sugars. So somewhere between two and 20 covalently linked monosaccharides would be classified as oligosaccharides. So when we take a look at our example down below at number 2, the oligosaccharides, we're showing you two types. We're showing you, one here that has two sugar units linked together. So this would be more specifically a disaccharide since di is a prefix meaning two. And then, here what we have is a trisaccharide since tri is a prefix meaning three, and there are three sugar units linked together. But once again, anywhere between two to twenty would be considered oligosaccharides, and so these are some oligosaccharides.

Now the third size class of carbohydrate that you all should be familiar with are the polysaccharides. And once again, poly is a prefix that means many, and so these are going to have greater than twenty covalently linked monosaccharides together. And, polysaccharides are, of course, going to be the polymer form of the carbohydrate. And so when we take a look at our image down below at the polysaccharides here, notice that it has more than twenty covalently linked monosaccharide units together, and so we start to form the polysaccharide. Moving forward, we're going to talk about some specific examples of polysaccharides and their functions, so keep that in mind. But for now, this here concludes our introduction to the three size classes of carbohydrates: monosaccharides, oligosaccharides, and polysaccharides, and we'll be able to get some practice moving forward in our course. So I'll see you all in our next video.

Formation & Breakdown of Polysaccharides

In this video, we're going to talk about the formation and the breakdown of polysaccharides. Recall from our previous lesson videos that dehydration synthesis reactions are needed to link individual monosaccharides together in order to build polysaccharides. The synthesis part of dehydration lets us know that we're going to be building or synthesizing the polysaccharides. The covalent bonds that link individual monosaccharides together are referred to as glycosidic bonds. Once again, glycosidic bonds are the covalent bonds that link monosaccharides together. Lastly, recall that the hydrolysis reaction is what's needed to break down polysaccharides into individual monosaccharides.

When we look at our image below, we can see the formation of a sugar called maltose from two glucose molecules. Notice on the far left, we have these two separate monosaccharides, one over here and one over there, which are two separate glucose monosaccharides. If we wanted to join these two separate glucose monosaccharides together like what we have here, then we're going to need a dehydration synthesis reaction, which dehydrates the molecule, releasing a water molecule. Also, what forms is a covalent bond linking the two separate monosaccharides. When these two are linked together, the covalent bond that links them is referred to as a glycosidic bond just as indicated above. As soon as these two glucose monosaccharides are joined together, it becomes a new sugar that we call maltose. This is a maltose disaccharide starting to build our polysaccharide here.

If we wanted to break down this maltose disaccharide into its individual monosaccharides, we would need a hydrolysis reaction. Recall that lysis means to breakdown or cleave, which is going to break down or cleave the glycosidic bond to release the two separate monosaccharides. There's a lot of review here, but one of the main takeaways is once again that the bond between individual monosaccharides is referred to as a glycosidic bond. This concludes our introduction to the formation and breakdown of polysaccharides, and I'll see you all in our next video.

Monosaccharides are linked together via a ______________ reaction, forming a _____________bond.

• A. Hydrolysis ; Glycosidic.
• B. Dehydration synthesis ; Hydrogen.
• C. Hydrolysis ; Peptide.
• D. Dehydration synthesis ; Glycosidic.
• E. Hydrolysis ; Hydrogen.

Which of the following chemical reactions results in energy release when glycosidic bonds are broken?

• A. Condensation reaction.
• B. Dehydration synthesis reaction.
• C. Hydrolysis reaction.
• D. Hydrogen bonding.

Carbohydrate Functions

In this video, we're going to talk about carbohydrate functions. And so it turns out that carbohydrates are structurally and functionally diverse, meaning that they can do many different things for the cell because they can take on so many different types of structures. However, that being said, there are just 2 main functions that you should be aware of when it comes to carbohydrate functions. And so, the first function that you should be aware of is structural support. Some carbohydrates are used specifically to build the structures of cells, either within cells or on the outside of cells. For example, cellulose and chitin are two classic examples of some polysaccharides that are used for structural support. There are others as well, for example, peptidoglycan might be one that you may or may not have heard of, but we're going to focus specifically on cellulose and chitin. Now the second primary main function that you should know carbohydrates have is energy storage; carbohydrates are specifically used for short-term energy storage. For example, starch and glycogen are both examples of carbohydrates that are used for short-term energy storage.

Let's take a look at our example below to focus on the polysaccharides that are in plants and animals and the functions that they have. Notice that we have this image below of this grid where the first column we have the function, whether it is structural support like this Bob the Builder guy, or energy storage like these batteries over here. Then we have the polysaccharides that are found specifically in plants, here in this column, and the polysaccharides that are found specifically in animals over here in this column. Notice that we're showing you 2 structural support carbohydrates, one in plants and one in animals, and we're also showing you 2 energy storage carbohydrates, once again one in plants and one in animals. It's a helpful grid here.

When we're talking about structural support, a classic example of a polysaccharide in plants that's used for structural support is cellulose. Cellulose is the most abundant carbohydrate found in plant cell walls. When we take a look at plants like this leaf right here and we zoom in on its structure, what you'll notice is that the cell walls of these plants contain cellulose. It's used to build cell walls, and that's why it is structural support. A structural support carbohydrate in animals is chitin. Chitin is a structural support carbohydrate that's found in the exoskeletons of insects and crustaceans such as lobsters. If we were to zoom into the exoskeleton shell here of this lobster, we would see that chitin is found within its structure. Chitin's structure is complex, and we don't need to worry about its particular structure so much. Just knowing that chitin is an example of a structural support carbohydrate that's used to build the structures of exoskeletons.

In terms of energy storage, we're showing you two examples: in plants, plants mainly store their energy in the form of starch. Starch is the storage form of glucose specifically in plants, and you'll find lots of starch inside of potatoes like this one over here. Over here, we have an animal liver, and in animals, they store their energy in the form of glycogen. Glycogen is a polysaccharide or carbohydrate whose main function is to store glucose in animal cells. This here concludes our introduction to carbohydrate functions, and we'll be able to get some practice applying these concepts in our next few videos. So I'll see you all there.

Animal cells store energy in the form of _________, and plant cells store energy in the form of ___________.

• A. Sucrose ; glucose.
• B. Disaccharides ; monosaccharides.
• C. Starch ; glycogen.
• D. Cellulose ; chitin.
• E. Glycogen ; starch.

Which polysaccharide is an important component in the structure of lobsters and insects?

• A. Chitin.
• B. Cellulose.
• C. Starch.
• D. Glycogen.
• E. Polypeptides.