Carbohydrates - Online Tutor, Practice Problems & Exam Prep

Carbohydrates, or saccharides, are carbon-based molecules characterized by hydroxyl groups. They are classified into three size classes: monosaccharides (single units like glucose), oligosaccharides (2-20 linked units), and polysaccharides (more than 20 units). Polysaccharides form through dehydration synthesis, creating glycosidic bonds, while hydrolysis breaks them down. Key functions include structural support, as seen in cellulose and chitin, and energy storage, exemplified by starch in plants and glycogen in animals. Understanding these concepts is essential for grasping the diverse roles of carbohydrates in biological systems.

Carbohydrates

In this video, we're going to begin our lesson on carbohydrates. Carbohydrates can be defined as carbon-based molecules that are hydrated with many hydroxyl groups, which are just a functional group with an oxygen and a hydrogen atom. When we take a look at the image below of carbohydrates, one thing that you'll notice is that there are plenty of these hydroxyl groups throughout their structures, which is definitely a characteristic feature of carbohydrates. Carbohydrates are also referred to as saccharides, the Greek word that means sugars, so sugars are carbohydrates. When the term carbohydrates was originally coined way back in the 1800s, it referred to compounds that had the exact chemical formula of CnH2On where you had some number of carbon atoms being hydrated by some number of water molecules. The "carbo" for the carbons and the "hydro" or the hydrates for the water molecules that are hydrating the carbon atoms. Simple carbohydrates are carbohydrates that fit this chemical formula exactly. For example, glucose is a carbohydrate that fits this chemical formula exactly and is the most abundant carbohydrate and the one that you should all be familiar with. We'll be able to see an example of glucose below in our image. Not all carbohydrates fit this chemical formula exactly, so there are some complex carbohydrates. Complex carbohydrates can slightly differ from this chemical formula and can also have other types of atoms such as phosphorus, nitrogen, or sulfur atoms. Let's take a look at our example below to distinguish between simple and complex carbohydrates.

Notice on the left-hand side, when we look at its chemical formula and count the total number of carbon atoms, hydrogen atoms, and oxygen atoms, what we'll see is that there is a total of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. You'll notice that there are 6 water molecules that we can make out of the H12O6, and those water molecules are hydrating the 6 carbon atoms. This is a molecule that fits the chemical formula above exactly. This is an example of a simple carbohydrate, more specifically, the chemical structure of glucose. Once again, glucose is the most abundant carbohydrate, and you should start to recognize its chemical formula of C6 H12O6 because, at some point in your course, you will need to know this chemical formula. Over on the right-hand side, showing a complex carbohydrate, we can tell it is complex because its chemical formula does not match the one above. Notice that it has a total of 6 carbon atoms, but 11 hydrogen atoms, 9 oxygen atoms, and also 1 phosphorus atom. This complex carbohydrate is not labeled as such because of its circular shape but because its chemical formula does not fit the formula exactly. Moving forward, we're mainly going to focus on simple carbohydrates, but it's good for you also to know that complex carbohydrates exist. This concludes our introduction to carbohydrates, and we'll talk more about carbohydrates as we move forward in our lesson. 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.

• A. C₂H₂O₂.
• B. C₆H₁₂O₆.
• C. C₅HO₃.
• D. C₃H₆O₉.

3 Size Classes of Carbohydrates

In this video, we're going to introduce 3 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" 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 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 1 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 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 carbohydrates 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 2 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 2 sugar units linked together. So this would be more specifically a disaccharide since "di" is a prefix meaning 2. And then, here what we have is a trisaccharide since "tri" is a prefix meaning 3 and there are 3 sugar units linked together. But once again, anywhere between 2 to 20 would be considered oligosaccharides, and so these are some oligosaccharides.

Now the third size class of carbohydrates 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 20 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 20 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 3 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. And so recall from our previous lesson videos that dehydration synthesis reactions would be needed to link individual monosaccharides together in order to build polysaccharides. And so once again, the synthesis part of dehydration lets us know that we're going to be building or synthesizing the polysaccharides. Now, the covalent bonds that link individual monosaccharides together are going to be referred to as glycosidic bonds. And so glycosidic bonds are once again the covalent bonds that link monosaccharides together. And then last but not least, recall that the hydrolysis reaction is what's going to be needed to break down. So hydrolysis is used to break down polysaccharides into individual monosaccharides.

So when we take a look at our image down below, we can see the formation of a sugar called maltose from 2 glucose molecules. Notice on the far left over here, we have these 2 separate monosaccharides, one over here and one over here, and these are 2 separate glucose monosaccharides. And so if we wanted to join these 2 separate glucose monosaccharides together like what we have over here, then we're going to need of course a dehydration synthesis reaction which we know dehydrates the molecule, releasing a water molecule. And, also what forms is a covalent bond linking the 2 separate monosaccharides. And so when these 2 are linked together, the covalent bond that links them is referred to as a glycosidic bond just like what we indicated up above. And so, notice that as soon as these 2 glucose monosaccharides are joined together, it becomes a new sugar that we call maltose, and so this is a maltose disaccharide starting to build our polysaccharide here.

And so if we wanted to break down this maltose disaccharide into its individual monosaccharides then of course we're gonna need the hydrolysis reaction. And recall lysis is that root that means breakdown or cleave and so that's going to break down or cleave the glycosidic bond here to release the 2 separate monosaccharides. And so 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. So this here 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.

• 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.

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

Carbohydrate Functions

In this video, we're going to briefly discuss carbohydrate functions. It's important to note that carbohydrates can actually be very structurally and functionally diverse, meaning that they can have many different types of structures and many different types of functions. However, for the purposes of our course, we're going to focus on 2 main functions that you should be aware of.

The first main function of carbohydrates that you should be aware of is structural support, so some carbohydrates are going to be used to build structures. For example, cellulose is a Polysaccharide that is used as structural support in plants. Thus, cellulose is used to build plant cell walls. Chitin is another example of a structural support polysaccharide that's used in animals such as insects and crustaceans. There are other examples of structural support polysaccharides such as peptidoglycan, which is used to build the cell walls of bacteria.

Now, the second main function that you should be aware of that carbohydrates tend to have is energy storage. There are some polysaccharides that are going to be used primarily for short-term energy storage. For example, the polysaccharide starch is used as energy storage in plants and the polysaccharide Glycogen is used for energy storage in animals.

If we take a look at our image down below, we'll be able to summarize some examples of these polysaccharides and their functions in plants and animals. You'll notice that in this column, we have the function of the polysaccharide, then in this column, we have the polysaccharides that are found in plants and in this column, we have the polysaccharides found in animals. When it comes to the function, there are two primary functions that you should be aware of: structural support, which is used to build things just like this house here is being built, and energy storage just like these batteries here store energy.

When it comes to polysaccharides in plants, an example of structural support polysaccharide in plants is Cellulose. Cellulose is going to be the most abundant carbohydrate and it is going to be found in plant cell walls. Notice that here we have a leaf and we're zooming into the cell walls of the cells that make up that leaf, you'll find cellulose. Here we have an image that represents cellulose, again a polysaccharide, a carbohydrate for structural support making the cell wall.

For animals, a polysaccharide that is involved with structural support is again going to be chitin. Chitin is going to be found in the exoskeletons of insects and crustaceans such as lobsters, for example, and so the hard shells that make up the lobsters here when you zoom into them you'll find the polysaccharide chitin.

When it comes to energy storage in plants, a classic example is going to be starch. When you think of starch you might think of potatoes, for example. So here we have a potato, and potatoes are going to have lots and lots of starch. Here we have an image that represents starch and again starch is a storage polysaccharide, which stores, glucose specifically in plants. And so, plants will store their glucose as starch.

On the right over here, what we have is an animal liver, and the animals will use the polysaccharide Glycogen as an energy storage polysaccharide. Notice here within the liver we have this molecule here which represents the glycogen polysaccharide and it is a storage form of glucose specifically in animals. Once again here, carbohydrates can have many different types of functions, but mainly structural support and energy storage.

Notice that plants and animals have these characteristic polysaccharides that are found in each of them with specific functions. This here concludes our brief lesson on carbohydrate functions and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

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.

• 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.

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