Glycosidic Bond: Videos & Practice Problems

A glycosidic bond is an acetal or ketal linkage between a sugar's anomeric carbon and another group, forming glycosides. These bonds arise from dehydration synthesis, releasing a water molecule, and can be broken by hydrolysis. The two primary types are O glycosidic bonds (with oxygen) and N glycosidic bonds (with nitrogen). Naming involves the configuration of the anomeric carbon (alpha or beta) and the carbon numbering, sometimes indicated by arrows or commas. Understanding these concepts is crucial for grasping carbohydrate chemistry and its applications in biochemistry.

Glycosidic Bond

In this video, we're going to begin our lesson on glycosidic bonds. A glycosidic bond is defined as an acetal or a ketal linkage between a sugar's anomeric carbon and another chemical group. This other chemical group could be another monosaccharide, which would allow monosaccharides to be covalently linked together and form a chain. However, this other chemical group could also be another class of molecules, such as a protein or a lipid for that matter. Moving forward through our course, we're going to talk about different types of glycosidic bonds.

It's important to note that glycosidic bonds will actually form via dehydration synthesis reactions, which means that it's going to release a water molecule, and we'll be able to see that down below in our image. It's also important to note that compounds that contain glycosidic bonds can be generally referred to as glycosides, and so you might find that your professor will use this term, as will your textbooks. If we take a look at our image down below, notice on the left-hand side we have 2 separate individual glucose molecules. On the left side, we have the alpha configuration and on the right-hand side, we have the beta configuration that's going up on the same side of the highest numbered carbon.

Through a dehydration synthesis reaction, we can remove a water molecule, visible here in these glucose molecules. When we remove that water molecule through the dehydration synthesis reaction, we can form a new bond, the glycosidic bond, which is the bond between a sugar's anomeric carbon (the anomeric carbon is shown here) and another chemical group. Here, the other chemical group is another monosaccharide, again allowing monosaccharides to be covalently linked together and form chains. Because this entire compound contains a glycosidic bond, it can be generally referred to as a glycoside.

Note that the glycosidic bond can also be broken through a hydrolysis reaction, which is the opposite reaction of dehydration synthesis. This will hydrate the molecule. Notice that water is coming back in and used to cleave the glycosidic bond. Moving forward in our course, we're going to be talking about different types of glycosidic bonds, and this is the conclusion to our introduction of glycosidic bonds. That being said, I'll see you guys in our next video.

The molecular formula of glucose is C₆H₁₂O₆. What is the molecular formula for an oligosaccharide made by linking 10 glucose molecules together by dehydration synthesis? (Hint: Consider how many glycosidic bonds form).

• A. C₆₀H₁₂₀O₆₀
• B. (C₆H₁₂O₆)₁₀.
• C. C₆₀H₁₀₂O₅₁.
• D. C₆₀H₁₀₀O₅₀.

Answer: (C)

Glycosidic Bond

In this video, we're going to introduce O-glycosidic bonds and N-glycosidic bonds. Among the many types of glycosidic bonds, these are really the two primary types that you should know moving forward. The first type is the O-glycosidic bond, which is just a glycosidic bond between an anomeric carbon of a sugar and an oxygen atom. The "O" is, of course, for the "o" in the oxygen. The second type of glycosidic bond is the N-glycosidic bond, which is a glycosidic bond between the anomeric carbon of a sugar and a nitrogen atom. Here, the "N" is for nitrogen.

If we take a look at our image on the left-hand side, notice that we have a sugar here, and the sugar's anomeric carbon is this carbon atom that we see right here, numbered with number 1. Notice that the anomeric carbon is bound to an oxygen atom here. This bond that we see here is going to be referred to as an O-glycosidic bond. Now, notice over here on the right-hand side of our image, we have another sugar. Again, the sugar's anomeric carbon is carbon number 1 right here. Notice that the anomeric carbon is bound to a nitrogen atom, and this chemical bond that we see here is an N-glycosidic bond.

Moving forward through our course, we will see O-glycosidic bonds and some N-glycosidic bonds as well. It's important to keep this in mind. That concludes our introduction to O and N glycosidic bonds, and I'll see you guys in our next video.

Glycosidic Bond

In this video, we're going to talk about the naming of glycosidic bonds. Glycosidic bonds are named based on 2 criteria that we have listed down below. The first criterion is the configuration of the anomeric carbon involved in the glycosidic linkage or the configuration of the anomeric carbons, plural, involved in the glycosidic linkage. Of course, we know from our previous lesson videos that the configuration of anomeric carbons includes either the alpha configuration or the beta configuration.

The second criterion that we use to name glycosidic bonds is the numbering of the carbon atoms involved in the glycosidic linkage. Sometimes, in the names of glycosidic bonds, you'll find that arrows are used in the names. Single-headed arrows like this one right here, pointing in only one direction, suggest that only one anomeric carbon is involved in the bond. Whereas, double-headed arrows like this one right here, pointing in both directions, suggest that 2 anomeric carbons are involved in the glycosidic bond.

Alternatively, the name of a glycosidic bond might not have any arrows at all. Instead of having arrows, it will use commas. Commas can also be used to replace the arrows, and that's also perfectly acceptable.

Glycosidic Bond Example 1

And so if we take a look down below at our image, notice that we have these 3 different disaccharides in each of these 3 different boxes. And so the goal is to name the following glycosidic bonds in each of these disaccharides. So we can start with this one over here on the far left and notice that we have 2 sugar units. We've got this sugar unit right here and then we've got this other sugar unit over here. And of course, if we want to name the glycosidic bonds, then we're going to need to consider the configuration of the anomeric carbon or carbons involved in the glycosidic linkage. And so we need to find the anomeric carbon of this sugar over here on the left-hand side. And recall that the anomeric carbon is the only carbon atom bonded to 2 oxygen atoms. So that would be this carbon atom right here which is assigned the lowest possible number, carbon 1. And notice that it's bonded to this ring oxygen and this other oxygen over here. And notice that the glycosidic linkage that we see here is an O-glycosidic linkage since the anomeric carbon is bonded to an oxygen atom. And so what we need to realize here is that this glycosidic linkage is actually pointing in a downwards direction. In the opposite direction of the highest-numbered carbon, which is pointing upwards. And so it seems as if this glyco bond is reaching down to the ants and so that is going to be an alpha configuration. And so, this is, indeed, going to be alpha. And, what we'll notice is that the anomeric carbon of the sugar over here on the right-hand side is actually way over here on the right. So it's actually not participating in this glycosidic linkage over here. And so, what that means is we're not going to consider the configuration of this anomeric carbon in the naming of this glycosidic bond. So now with that, we're done with this first step here. We can move on to the second step which is again, going to be the numbering of the carbon atoms involved in the glycosidic linkage. And so notice that we have, the anomeric carbon of the sugar on the left as C1. And notice that the carbon atom over here of this sugar on the right-hand side is actually C4 since, again, its anomeric carbon is over here as one. And then when we number these, this carbon ends up being C4. And so what that means is that, we have an alpha one four glycosidic linkage. And so really this is the name of this linkage that we see here. It's an alpha one four glycosidic linkage. Now notice that we only have a single-headed arrow right here because we only have 1 anomeric carbon involved in the bond. However, an alternative way to write this name of the glycosidic bond is to replace this arrow with a comma. And so an alternative way to write this would be an alpha one comma and alpha 1 comma 4 glycosidic bond. And again, that, is perfectly acceptable.

So now moving on to this second dissect right here in the middle. Again, notice we have 2 sugar units, 1 up here on the top and then one down here on the bottom. And so what you'll notice here is that for the top sugar, the anomeric carbon is again this lowest-numbered carbon right here. And what you'll notice is that the linkage that's forming here is an O-glycosidic linkage since the anomeric carbon is bonded to an oxygen atom. And the O-glycosidic linkage seems to be going again in a downwards direction here, away in the opposite direction of the highest-numbered carbon, which is going up. And so, what this means is that, we're definitely going to have an alpha configuration again. And so we can put alpha down here. And then notice for this sugar way down here, its anomeric carbon is actually way over here. And so it's not involved in this glycosidic linkage here. And so for that reason, we're not going to include the configuration of this animere carbon in the naming of this glycosidic linkage. So now that we're done with the configuration, we can move on to the numbering of the carbon atoms. And so again, we can see that carbon number 1 of the top sugar is involved in the glycosidic linkage, so alpha 1. And then notice that it's actually carbon number 6 of the bottom sugar that's involved in the glycosidic linkage. So this is an alpha one 6 glycosidic linkage right here. And so again, notice that we have a single-headed arrow here because there's only 1 anomeric carbon involved in the glycosidic linkage. But an alternative way to write this would be to replace the arrow again with a comma. And so, we could rewrite this as just an alpha one comma 6 glycosidic linkage, and that is again perfectly acceptable.

So now moving on to our final disaccharide over here on the right-hand side. Again, notice that we have 2 sugars units, involved in this disaccharide, highlighted as shown. And so we want to look for the anomeric carbon. And so, of this sugar over here, notice the anomeric carbon is right here. And, notice that it's forming an O-glycosidic linkage since the anomeric carbon is bonded to this oxygen atom right over here. And so notice that this glycosidic linkage seems to be going in an upwards direction here. It goes upwards and then it curls, it's curling back downwards. But initially, it's going upwards in the same direction as the highest-numbered carbon. And so, of course, this is going to be a beta configuration since the bumps of the beta go on the same side. These two arrows are going in the same side. So this is a beta configuration. So we can put beta here. And then when we take a look at this sugar over here, notice that its anomeric carbon is not over here this time. Instead, its anomeric carbon is right over here. Since this is the carbon atom that's bonded to 2 oxygen atoms. The ring oxygen and this oxygen over here. And so notice that with this anomeric carbon, it's also forming an O-glycosidic linkage since it's bonded to this oxygen. But with this anomeric carbon, notice that the bond is actually going in a downwards direction initially here. And so, it's going in the opposite direction as the highest-numbered carbon which is going up. And so what that means is that for this sugar over here on the right, we need to consider the configuration since it's involved in the glycosidic linkage. And so, what you'll note is that it's going to have an alpha glycosidic linkage, and we can put that over here. And notice that because 2 anomeric carbons are involved in this glycosidic linkage, that we have a double-headed arrow right here. So now that we've considered the configuration of both anomeric carbons, we can move on to the numbering of the carbon atoms involved in the glycosidic linkage. And of course because we have 2 anomeric carbons involved, they're both going to be assigned the lowest possible number here. And so, they're both going to be assigned to number 1. So we have a beta one right here, and then an alpha one, right here. And so this entire glycosidic linkage right here is going to be called a beta one alpha one glycosidic linkage. And again, the double-headed arrow can be replaced by a comma. So it could also be written as beta 1 comma alpha one glycosidic linkage. So this is another acceptable way to write this glycosidic linkage. And so the best way to understand the naming of glycosidic bonds is to get practice applying these concepts. So as we move forward in our course, we'll be able to get some more practice doing that. And so I'll see you guys in our next video.

What is the name for the glycosidic linkage in the following glycoside?

• A. 1, 1 glycosidic linkage.
• B. 1, 2 glycosidic linkage.
• C. 1, 4 glycosidic linkage.
• D. 1, 6 glycosidic linkage.

Answer: (B)

Determine the name of the glycosidic bond of the following disaccharide.

• A. α-1,2-glycosidic bond.
• B. β-1,3-glycosidic bond.
• C. α-1,4-glycosidic bond.
• D. β-1,4-glycosidic bond.
• E. α,β-1,3-glycosidic bond.

Answer: (D)

Which two molecules below do NOT contain a 1,4 glycosidic linkage?

• A. A & B.
• B. B & C.
• C. C & A.
• D. D & C.
• E. E & D.

Answer: (E)

Label & name every glycosidic bond in the branched oligosaccharide below:

Alright. So this practice problem wants us to label and name every glycosidic bond in the branched oligosaccharide down below right here which notice has a total of 6 sugar units. And so of course, if we want to label and name every glycosidic bond, we're first going to need to be able to identify where these glycosidic bonds are. And so let's go ahead and highlight the glycosidic bond. So notice that we have one here, we've got one here, we've got one here, we've also got one here, and we've got one over here as well. And so, what you'll notice is that the glycosidic bonds that are highlighted in yellow look very similar to each other, whereas, the glycosidic bond here in blue and the one over here in green look a bit different. So, we're going to start with the glycosidic bond here in yellow. Now, we know from our previous lesson videos that when it comes to naming glycosidic bonds, the anomeric carbon is going to be key, and so let's go ahead and identify the anomeric carbon for each of these 6 sugar units. Recall that the anomeric carbon is the only carbon atom that's going to be bonded to 2 oxygen atoms and so this is an anomeric carbon. So is this one. So is this one. So is this one. This is an anomeric carbon and so is this one right here. And so these are the 6 anomeric carbons circled in red for each of these 6 sugar units. And of course, we know that when we're numbering the anomeric carbons, we want them to have the lowest possible number. And so focusing here on the bonds highlighted in yellow, notice that the lowest number for these anomeric carbons is going to be number 1 for these sugars here. And so, of course, that means that when we're looking at this sugar unit over here on the far left, this carbon atom is going to be carbon 6, the highest numbered carbon, and so notice that with this again, yellow background glycosidic bond that the glycosidic bond itself is going in somewhat of a downwards direction. It's going downwards in the opposite direction of the highest numbered carbon. And so that means that it's reaching down for the ant and this is going to be an alpha configuration. And so, of course, this is the only anomeric carbon involved in this glycosidic bond. So it's just going to be, the alpha here that we need to consider, so we can write alpha below it. And of course, this is an alpha one so far. And then, we need to figure out what is the number of this carbon over here. So we already identified this anomeric carbon as number 1 over here. So this would be number 2. This would be number 3. And then this one here would be number 4. And so what you'll notice is that this is, this glycosidic linkage here is an alpha $1 \rightarrow 4$ glycosidic linkage. So, this yellow one here matches, this yellow one and this yellow one are matching. Moving on to the one in blue and notice that we have the anomeric carbon here which is carbon 1. And, if we continue the numbering system, this is carbon 4. That means that this one will be carbon 5, and this will be carbon 6. Notice that the glycosidic bond here on the anomeric carbon is going in a downwards direction and the opposite direction of the highest numbered carbon. And so that means that this is going to be an alpha configuration. And so, what you'll notice is that this is going to be an alpha $1 \rightarrow 6$ glycosidic linkage right here. We now move to our final glycosidic linkage, this green one over here. And again, notice that the anomeric carbon seems to be going in an upwards direction here. The glycosidic bond seems to be going in an upwards direction in the same direction as its highest numbered carbon. They're both going up. And so when they're going in the same direction, we think about the bumps of the beta being on the same side. And so that means that this is going to have this anomeric carbon will have a beta configuration. And so It's, of course, going to be beta one, because it's on the first carbon here. This is going to be a beta $1 \rightarrow 4$ glycosidic linkage here in green. So we've got a total of 5 glycosidic linkages. The ones in yellow here are alpha $1 \rightarrow 4$ glycosidic linkages. The one in blue is an alpha $1 \rightarrow 6$ glycosidic linkage, and the one in green is a beta $1 \rightarrow 4$ glycosidic linkage. And so this concludes our practice problem, and I'll see you guys in our next video.

Here’s what students ask on this topic:

What is a glycosidic bond and how is it formed?

A glycosidic bond is an acetal or ketal linkage between a sugar's anomeric carbon and another chemical group. This bond can form between two monosaccharides, linking them covalently to create a chain, or between a sugar and another molecule like a protein or lipid. Glycosidic bonds are formed through a dehydration synthesis reaction, which involves the removal of a water molecule. This process can be reversed by hydrolysis, where water is added to break the bond. Understanding glycosidic bonds is crucial for studying carbohydrate chemistry and its applications in biochemistry.

What are the different types of glycosidic bonds?

The two primary types of glycosidic bonds are O glycosidic bonds and N glycosidic bonds. An O glycosidic bond forms between the anomeric carbon of a sugar and an oxygen atom, while an N glycosidic bond forms between the anomeric carbon of a sugar and a nitrogen atom. These bonds are essential for linking sugars to other molecules, such as forming polysaccharides or glycoproteins. Understanding these types helps in grasping the structural diversity and functional roles of carbohydrates in biological systems.

How are glycosidic bonds named?

Glycosidic bonds are named based on two criteria: the configuration of the anomeric carbon (alpha or beta) and the numbering of the carbon atoms involved in the linkage. The configuration indicates whether the anomeric carbon is in the alpha or beta form. The numbering specifies which carbon atoms are connected by the bond. Sometimes, arrows or commas are used in the names to indicate the involvement of one or two anomeric carbons. This naming convention helps in identifying the specific structure and type of glycosidic bond in complex carbohydrates.

What is the difference between alpha and beta glycosidic bonds?

Alpha and beta glycosidic bonds differ in the configuration of the anomeric carbon involved in the bond. In an alpha glycosidic bond, the anomeric carbon's hydroxyl group is positioned below the plane of the sugar ring, while in a beta glycosidic bond, it is positioned above the plane. This difference in configuration affects the three-dimensional structure and properties of the resulting carbohydrate. For example, starch contains alpha glycosidic bonds, making it more easily digestible, whereas cellulose contains beta glycosidic bonds, making it more rigid and less digestible.

How do dehydration synthesis and hydrolysis relate to glycosidic bonds?

Dehydration synthesis and hydrolysis are two key reactions involving glycosidic bonds. Dehydration synthesis forms glycosidic bonds by removing a water molecule, linking two monosaccharides or a sugar and another molecule. This process is essential for building complex carbohydrates like polysaccharides. Conversely, hydrolysis breaks glycosidic bonds by adding a water molecule, splitting the linked sugars or sugar-molecule complexes. This reaction is crucial for carbohydrate digestion and metabolism, allowing the breakdown of complex sugars into simpler, absorbable forms.