Carbohydrates - Online Tutor, Practice Problems & Exam Prep

Carbohydrates

In this video we're going to begin our lesson on carbohydrates. So of course, you guys have learned about carbohydrates before in your old courses, and so you might already remember that carbohydrates are a structurally and functionally diverse class of molecules, but all carbohydrates are carbon-based molecules and they're all rich in hydroxyl groups or OH groups, and so in the science world, carbohydrates are commonly referred to as saccharides, which is the Greek word for sugars. And so carbohydrates, saccharides, and sugars are all practically synonyms of one another. It's important to note that when the term carbohydrates was originally coined way back in 1800, it actually referred to compounds that had this exact formula right here, CnH2On, where n≥3. As you can see by this formula, there's going to be some number of carbon atoms, and for each carbon atom, there's going to be the same number of water molecules. You can see how there are going to be carbon atoms that are hydrated by these water molecules.

Now, the term simple carbohydrates refers to molecules that fit this exact formula. However, not all carbohydrates fit this formula exactly. There are derivatives of these simple carbohydrates, and so your professors and your textbooks will refer to these carbohydrates as complex carbohydrates. Complex carbohydrates can actually slightly differ from this formula. On top of that, they can also have other atoms too, such as phosphorus atoms, nitrogen atoms, or sulfur atoms as well. If we take a look at our image down below at these carbohydrates, notice over here on the left, we have a carbohydrate that if it doesn't look familiar to you now, it will, glucose, which you guys have all learned about before in your previous courses. Now, glucose, as you can see here, is a simple carbohydrate, and we can tell by just looking at its chemical formula. Notice if we count up the number of carbons that this molecule has, there are 6 carbons. If we count up the hydrogens, we'll count 12 hydrogens. If we count up the oxygens, we'll see that there are 6 oxygens. You can see that for every carbon, there is a water molecule. So the carbons are being hydrated, and this formula fits the formula that we talked about above exactly. And so that's why this is a simple carbohydrate.

Now, over here on the other hand, notice what we have is a complex carbohydrate. And we can tell because notice, if we look at the chemical formula, that there is indeed a phosphorus atom here. You can see the phosphorus atom and so already, it's starting to differ from that formula we talked about previously. Then if you count the number of carbon atoms in this molecule, you'll count 6 carbon atoms. If you count the hydrogens, you'll count 11 hydrogens, and if you count all of the oxygens including these oxygens up here, you'll count 9 oxygens. Clearly, this chemical formula here differs from the formula we talked about before, but even though this structure has a different chemical formula, it's still referred to as a carbohydrate because it's actually a derivative of this carbohydrate over here. Moving forward, this is important to keep in mind that we will talk about carbohydrates that differ from this standard chemical formula. And so, this concludes our introduction to carbohydrates and we'll be able to get a little bit of practice in our next video. So I'll see you guys there.

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

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

Carbohydrates

In this video, we're going to talk about the three size classes of carbohydrates, which, again, you guys probably already covered before in your previous courses, so we're just going to brush right on through this. And so the very first size class of carbohydrates is going to be the smallest size class, and this, of course, is going to be the monosaccharides. Mono, a prefix meaning singular, and saccharide, a prefix meaning sugar or carbohydrate. And so this literally translates to a single carbohydrate unit, otherwise known as just a monomer. And recall that monomers are the tiny little Lego pieces that are used to build larger polymers. Now the second size class of carbohydrates is going to be the intermediate size class, and this is going to be the oligosaccharides. Oligo, a prefix meaning a few. And so this is going to be carbohydrates that contain somewhere between two to about 20 covalently linked monosaccharides. Now the third and final size class of carbohydrates is going to be the largest size class, and this, of course, is going to be the polysaccharides. Poly, a prefix meaning many. And so these are going to be carbohydrates that contain greater than 20 covalently linked monosaccharides. So if we take a look at our image down below, we can visually see each of these size classes. So the first, the monosaccharides, is the smallest size class. So it consists of just individual single carbohydrate units. And, of course, there are many, many different types of monosaccharides, and moving forward in our course, we'll talk about some of those different types. Now the second size class is going to be the oligosaccharides. And so this again, includes any carbohydrate that contains between 2 to 20 covalently linked monosaccharides. So more specifically, if there are two monosaccharides linked together, then this is referred to as a disaccharide, di, a prefix meaning 2, but, really, a disaccharide is just a type of oligosaccharide. And then, of course, if there are three monosaccharides linked together, then this is going to be a trisaccharide. Tri, a prefix meaning 3. But, again, di and trisaccharide fall under the categorization of oligosaccharides. And then, of course, our third and final size class of carbohydrates is going to be the polysaccharides, which consists of carbohydrates that have greater than 20 covalently linked monosaccharides. And so here you can count 21 making this a polysaccharide. And, again, as we move forward in our course, we're going to talk about each of these different size classes in a lot more detail. So, you can consider this just the introduction. So, that concludes this video and I'll see you guys in our next one.

Carbohydrates

In this video, we're going to do a side-by-side comparison of proteins and carbohydrates, and we'll point out some of the key differences between these two different classes of molecules. So notice over here in this table, in this column we have proteins and in the next column, we have carbohydrates. And so this is going to allow us to do a side-by-side comparison. Now if we start to fill out this table, notice the first row here says monomer. And, of course, we know from our older lesson videos that the monomers of proteins are going to be amino acids. And so here we have a little image to represent the structure of amino acids. And, of course, we learned in our last lesson video that the monomer of carbohydrates is going to be a monosaccharide. Mono meaning singular and saccharides meaning sugar. And so here we have a little image to represent the structure of monomers. And, of course, we know from our older lesson videos that the types of bonds that link together amino acids, like methionine and valine here, these bonds are referred to as peptide bonds. Now, the type of bond that links together carbohydrates, on the other hand, like these two carbohydrates right here, this bond is not a peptide bond. Instead, this bond that links together monosaccharides is referred to as a glycosidic bond. And so later in our course in a different topic, we'll talk a lot more details about these glycosidic bonds. But for now, you can see that this is one of the key differences between proteins and carbohydrates, the type of bond that's used to link together the monomers. Now the third row here says number of linkage points, and this is referring to how the monomers can be linked together. And so when it comes to proteins and amino acids, amino acids really have just two linkage points in general. Amino acids can either be linked via their free amino group or they can be linked to other amino acids via their free carboxyl group. And so because they can really only be linked at the amino group or the carboxyl group, this means that in terms of proteins, they're generally going to be linear. And so you can see here we have a protein, magic here that is linear in its formation because it really only has these two linkage points. However, when it comes to carbohydrates on the other hand, if we look at the number of linkage points, what you'll see is that there are many, many different linkage points and because there are many linkage points, it means that it's possible for both linear and branch structures to be common. And so here, you can see we have a linear carbohydrate, and over here we have a branched carbohydrate. And so again, later in our course, we'll be able to talk about more details about these different types of carbohydrates, linear versus branched. But for now, you can see that this is one of the key differences between proteins and carbohydrates. Proteins are normally linear, whereas carbohydrates are commonly linear and branched. Our last and final row here says, is the molecule built from a template? Now when it comes to proteins, you might recall that transcription is the process that builds proteins using an mRNA template. And so, yes, proteins are built from a template. They're built from an mRNA template. However, when it comes to carbohydrates on the other hand, they are not built from a template. Instead, there are enzymes that build these carbohydrates not using a template. And so we'll be able to talk a little bit more about this as we move through our course. But for now, this concludes our compare and contrast of proteins and carbohydrates, and as we move forward, we'll be able to apply these concepts. So I'll see you guys in our next video.

Which of the following is a monosaccharide?

• A.
• B.
• C.
• D.

Carbohydrates

Alright. So in this video, we're going to give you guys a little introduction to carbohydrate functions. Recall that we already mentioned in some of our previous lesson videos that carbohydrates are incredibly diverse when it comes to their biological structures and functions.

Some of their biological functions include acting as or participating in each of these four things that we have listed down below. Notice that the numbers for each of these four things correspond with the numbers that we have in the images. The very first biological function of carbohydrates is that they act as short-term energy sources, which is likely a function that you guys already knew about. It's interesting to note here that carbohydrate oxidation is the central energy-yielding pathway in practically every single cell. Acting as a short-term energy source is one of the primary functions of carbohydrates. It's such a primary function that later in a different section of our course, when we're talking about carbohydrate metabolism, we're going to talk a lot of details about the ability of carbohydrates to act as short term energy suppliers. For now, if we take a look at our image down below, you can see that we've got this little thunderbolt here to remind you guys that carbohydrates can provide a spark of energy.

Now the second biological function that we have is that carbohydrates can act as structural and protective components. As we move forward in our course, we'll see that carbohydrates actually make up part of the structures of nucleotides as well as part of the structures of plant and bacterial cell walls. If we take a look down below, at our image number 2, you can see that we've got this wall here that's built of carbohydrates.

The third function that we have is that carbohydrates participate in cell communication. Of course, what this means is that carbohydrates are going to participate in cell recognition, cell adhesion, and cell coordination. We'll talk a lot more about cell communication and biosignaling later in our course. But for now, if we take a look at our image number 3, you can clearly see that we've got some cells that are communicating and carbohydrates are indeed going to participate in this communication, the cell communication.

The fourth and final function that we have listed here is that carbohydrates can designate intracellular localization. Basically, what this is saying is that carbohydrate modifications to different molecules can determine the area that that molecule is going to end up in within the cell. Carbohydrate modifications can also determine metabolic fates of those molecules. If we take a look at our image number 4 down below, you can see that we've got a cell right here and inside of the cell, we have all of these different organelles: the nucleus, mitochondria, rough ER, smooth ER. You'll notice that we've got this blue circle molecule, and attached to our blue circle molecule is a carbohydrate. The attachment of carbohydrate, would be considered a carbohydrate modification, and you can see that that can determine the intracellular localization. So you can see that our covalently modified carbohydrate molecule is moving locations within the cell from this area over to this area. Again, this is another type of function that we can talk more about as we move along through our course. But for now, this is just a general introduction to carbohydrate functions. You can see all the different things that they are able to help a cell do. And so this concludes our intro, and I'll see you guys in our next video.