Sphingolipid Recap: Study with Video Lessons, Practice Problems & Examples

Sphingolipids are classified based on their variable head groups, influencing both their structure and function. Key classes include ceramides, sphingomyelins, cerebrosides, globosides, and gangliosides. Ceramides are the simplest, with a hydrogen atom as the head group. Sphingomyelins contain phosphocholine, while cerebrosides have a single sugar unit. Globosides feature multiple sugar residues, and gangliosides possess complex oligosaccharides with sialic acid. Understanding these variations is crucial for grasping lipid functionality and interactions within biological membranes.

Sphingolipid Recap

In this video, we're going to begin our review or our recap of sphingolipids. So let's first start by revisiting our lipid map. And so we know that we're currently exploring the fatty acid based lipids. And already in our previous lesson videos, we've covered the glycerolipids including triacylglycerols and glycerophospholipids, as well as the most common variable head groups of these glycerophospholipids. And we've also covered the sphingolipids, including sphingophospholipids and sphingomyelin, as well as the sphingoglycolipids, including cerebrosides, globosides, and gangliosides. And so here in this topic, we're specifically doing a review of the sphingoglycolipids, which would include everything that we see highlighted right here. And so essentially we're just doing a review of what we have circled right here. And, what we have circled here is really just going to show up in our table down below which we'll talk about in our next lesson video. So I'll see you guys there to do some more review.

Sphingolipid Recap

And so again, everything that we're going to be talking about in this video is really just a review from our previous lesson videos. And so, if you're already feeling good about the classes of single lipids, then feel free to skip this video if you'd like. But if not, stick around because this video might help you guys put everything together. And so again, we're going to be reviewing the different classes of sphingolipids. So, essentially, reviewing this branch right here of our lipid map. And just like Glycerophospholipids over here are classified according to their variable head groups, sphingolipids are also classified according to their variable head groups. Notice down below what we have is the structure of a typical sphingolipid. Notice that the variable head group is right here. And so, simply by changing the variable head group, we can change the class of sphingolipid. Not only does the variable head group dictate the structure and class of the sphingolipid, again, but it's also going to dictate the function of the sphingolipid as well. Now, very similarly to Glycerophospholipids, sphingolipids over here can also vary in their fatty acid length and degree of saturation. So, these can vary among the molecules in each class. And so if we take a look at this table down below, again, it's really just going to be a review from our previous lesson videos. Notice we have the sphingolipid class here in the first column and then we have the variable head group that's associated, over here in the second column. And so you might recall that ceramides are practically the simplest type of sphingolipid. And that's because their variable head group is literally just a hydrogen atom. So you just put a hydrogen atom here, and you've got yourself a ceramide. And the amide here in the ceramide lets you know that the fatty acid in the variable fatty acid here is going to be linked via an amide linkage. And really that's the most distinct feature of the sphingolipid classes. All the sphingolipids. Now, the next row that we have here are the sphingomyelin class of sphingolipids and these are, you might recall, sphingophospholipids and so here we're showing you phosphocholine as the variable head group. And you can see that it has a phosphate group and, it has this choline group over here as well. And then notice down below we're showing you cerebrosides which are, a type of sphingoglycolipid and the glyco here is indicating sugar. So, we can go ahead and write sugar here. And so you can see that it does indeed have just one sugar unit. For example, here, we're showing you Glucosyl Cerebroside which means that it has a glucose residue as the variable head group. And then if we wanted to get a globoside, which you might notice is not on this table, but if we wanted to get a globoside, all we would have to do is add a second sugar residue. So multiple sugar residues would give us the globoside. And so, down below, last but not least, what we have are the gangliosides, which you might recall, containing complex oligosaccharide as the variable head group that is going to be branched as we can see here and it contains a sialic acid residue. And the sialic acid residue is typically NEU5Ac. And so this here concludes our review of sphingophospholipids and the classes of sphingophospholipids. And if you take some time to be able to review the lipid map and review this table down below, then you guys should be good on sphingolipids. And we'll also be able to get some practice applying all of these concepts in the next couple of practice videos. So I recommend you guys try those out, and I'll see you guys there.

Which of the following is TRUE of sphingolipids?

A) They always contain glycerol and fatty acids. 

B) They may be charged, but are never amphipathic.

C) Phosphatidylcholine is a typical sphingolipid. 

D) They contain only one esterified variable fatty acid. 

E) Cerebrosides, globosides and gangliosides are sphingolipids. 

• A. They always contain glycerol and fatty acids.
• B. They may be charged, but are never amphipathic.
• C. Phosphatidylcholine is a typical sphingolipid.
• D. They contain only one esterified variable fatty acid.
• E. Cerebrosides, globosides and gangliosides are sphingolipids.

Sphingolipid Recap Example 1

Alright. So at this point in our course, we've covered a lot of different types of lipids and introduced a lot of prefixes, including glycero, sphingo, and glyco. And so I can admit it can be pretty confusing at times. Here, what we have is an example problem that's hopefully going to help put things in perspective for you guys. This example problem wants us to appropriately match each of the following 6 lipid molecules that we see down below with one of the listed types of lipids that we see here.

Taking a look at this first lipid molecule, one of the first things that you guys should notice about this is that it has a glycerol-based backbone. Here what we have is a platform that is derived from glycerol. Another thing that you guys should notice is that we've got these hydrocarbon chains here and so these are certainly going to be our fatty acids. Another thing that you guys should note is that these fatty acids are linked to the glycerol via these ester linkages that we see here. We can go ahead and label these as esters. What's important to note is that there are actually 3 fatty acid chains linked to a glycerol molecule. This is going to be a glycerolipid. But because there are specifically 3 fatty acid chains, of course, that is going to correspond with the trie. The tri is indicating that there are 3, and so, of course, this is going to be a triacylglycerol and so down below, we can go ahead and label this as a triacylglycerol and then, what we can do is go ahead and cross this off our list.

Notice that we have this trans double bond that is present here. And, we have this 18 carbon platform. This is going to be a sphingosine-based form. We know that this is going to be some kind of sphingolipid. Another way to recognize that this is a sphingolipid is that notice that this fatty acid chain is actually linked not via an ester linkage like what we had over here. It's actually being linked via an amide linkage and so here what we can do is label this as an amide and again, that's another way to identify this as not being a glycerol molecule and as being a sphingosine molecule. You can see here that there is a phosphate group attached to this sphingosine molecule and so that must mean that this is a sphingophospholipid. The only sphingophospholipid that we talked about in our previous videos was sphingomyelin and so here what we have is a phosphoethanolamine head group and so, what we can do is go ahead and label this as a sphingomyelin molecule. We can cross it off our list.

Moving on to the next lipid molecule, what we need to recognize is again, what we have here is a glycerol-based platform. So this is going to be another glycerolipid. This time, notice that there is a phosphate group attached to this glycerol backbone. We know that this must be a glycerophospholipid. We've got these 2 fatty acid chains and they are linked to the glycerol backbone via ester linkages once again. The head group here branching off of this platform actually does resemble another glycerol molecule that we have over here. Really this is another glycerol molecule that is branching off of this glycerophospholipid. This means that it must be some kind of glycerophospholipid that has a glycerol in it. You might recall from our previous lesson videos that phosphatidate was actually the simplest glycerophospholipid. The phosphatide here is indicating that this is a glycerophospholipid. The ill glycerol is saying that there's a glycerol molecule branching off and so essentially, what we're saying is that here because we have another glycerol molecule branching off. This must be a phosphatidylglycerol molecule and indeed, it is. We can go ahead and label that down below. Then, of course, we can cross this off our list up above.

Looking at this platform, this is not going to be a glycerol platform. Instead, what we can see is that there is a trans double bond here and we've got this 18 carbon amino alcohol once again. You can see the amide linkage here once again. This means that this is going to be a sphingosine platform right here. The fatty acid chain here is linked via the amide. Notice that this time, the variable head group does not have a phosphate group like it did previously. The variable head group here is actually a sugar residue and you might recognize this sugar residue as being a glucose molecule and so there's only one glucose here. There's only one sugar residue branching off of this sphingosine platform here. Because there's only one sugar residue, of course, this is going to correspond with the cerebroside from our previous lesson video. We can go ahead and label this as a cerebroside. That's how we identify that one.

Now we're down to just 2 more molecules and, looking at this one on the left, what you'll notice is again, it has a glycerol-based backbone. You can see that there are no amide linkages. Instead, we have the ester linkages once again. We have these fatty acid chains that are connected via the ester linkages, and then we have a phosphate group branching off of the glycerol. We know again that this is another glycerophospholipid. The variable head group here looks like an amino acid. It has an amino group, a carboxyl group, a central carbon, and a central hydrogen, and then this would be the R group. At a closer look, if this oxygen right here were a hydroxyl group, then that would be the amino acid serine. So this is going to be a serine head group here. Once we consider that, we know that this must be the phosphatidylserine here. The phosphatid is going to be the phosphatidate prefix indicating a glycerophospholipid. The ill indicates the branching of a serine molecule. Then of course, we can cross that one off our list. We also already covered cerebroside previously and so the only one that's left now is linoleate and that one may not sound familiar because this is the common name of a fatty acid and although we have not yet talked about the common naming system in a lot of detail, this is a fatty acid. You can see that there's a long hydrocarbon chain here and we've got the carboxylic acid group over here and so this is indeed going to be linoleate. This concludes our practice problem here and hopefully, the strategies that we use to determine each of these molecules will be able to help you guys out. I'll see you guys in our next video.

Match the following lipid types with the correct description.

A) Fatty acid. _____                                     1. Membrane lipids with a glycerol backbone.                   

B) Triacylglycerol. _____                             2. Phospholipid especially common in nerve cells.

C) Phospholipid. _____                               3. One of the simplest forms of a glycolipid.

D) Sphingosine. _____                                4. Lipids covalently attached to carbohydrate groups.

E) Glycerophospholipid. _____                  5. Chains of hydrogen-bearing carbon atoms with a carboxylic acid.

F) Sphingomyelin. _____                            6. Complex glycolipids with a sialic acid residue. 

G) Glycolipid. _____                                    7. A complex amino alcohol backbone for membrane lipids. 

H) Cerebroside. _____                               8. Major class of membrane lipids. 

I) Ganglioside. _____                                  9. Long-term storage form of fatty acids.

Alright. So this practice problem wants us to match the following lipid types in this left column with the correct description in this right column. Of course, there are many different strategies you can use to solve this problem, and we're just going to go through one of those strategies. Option A here says, fatty acid, and we know already that fatty acids are just long hydrocarbon chains with a carboxylic acid group at the very end. The option that best suits a fatty acid is going to be option 5: "Chains of hydrogen-bearing carbon atoms with a carboxylic acid group at the very end." So, we can go ahead and put a 5 here to match it with number 5 and then go ahead and cross off 5 from our list. Moving on, what we have is, for B, triacylglycerol, which has the word glycerol embedded in it. We know that it's going to have a glycerol molecule as the platform and the 'tri' here indicates that there are 3 fatty acid chains that are ester-linked to it. We also talked about the functions of triacylglycerols in our previous lesson video. So we know that they act as long-term energy storage of fatty acid molecules, and the answer that best suits that is going to be 9. We can go ahead and cross off 9 from our list. Next, what we have are phospholipids, and phospholipids are lipids that contain at least one phosphate group. We know that phospholipids are going to be a major component of all cell membranes. Because that's true, the best answer that matches here is 8, "a major class of membrane lipids." We can go ahead and put 8 here to match it with 8. Next, what we have is sphingosine. Sphingosine is the alternate platform to glycerol, and we know it as a complex amino alcohol backbone for specific membrane lipids. We can go ahead and match it with number 7 here and cross off 7 from our list. Then, we have glycerophospholipids. It has the 'glycero' prefix, so we know that it's going to have a glycerol platform molecule, and it also has the 'phospho' prefix. So, we know that they're going to have phosphate groups attached. Glycerophospholipids are going to be membrane lipids with a glycerol backbone. We can go ahead and match this to option 1 and cross off 1 from our list. Next, we have sphingomyelin. You might recall sphingomyelin is a sphingophospholipid and it's specifically found in the myelin sheath, which is a membranous structure around the axons of nerve cells. These are going to be sphingophospholipids that are especially common in nerve cells. So, we can go ahead and label that as 2 and cross that off our list. Next, we have glycolipids, which really are just lipids that are covalently attached to carbohydrates (the 'glyco' prefix here not to be confused with the 'glycero' prefix). The 'glyco' prefix means carbohydrates or sugars. So, lipids that are covalently attached to carbohydrate groups would be glycolipids. We can go ahead and put 4 here, and cross off 4. And you might recall from our previous lesson videos that cerebrosides and gangliosides are really specific types of glycolipids. Cerebrosides specifically only have one single sugar residue as the head group and so that makes them one of the simplest forms of a glycolipid. We can go ahead and put 3 here and cross that off our list. Last but not least, we have the ganglioside, which is going to be the complex glycolipid with a sialic acid residue. We can go ahead and match it to that. That concludes this practice problem, and I'll see you guys in our next video.

Here’s what students ask on this topic:

What are the main classes of sphingolipids and their variable head groups?

Sphingolipids are classified based on their variable head groups, which influence their structure and function. The main classes include:

• Ceramides: Simplest form with a hydrogen atom as the head group.
• Sphingomyelins: Contain phosphocholine as the head group.
• Cerebrosides: Have a single sugar unit, such as glucose or galactose.
• Globosides: Feature multiple sugar residues.
• Gangliosides: Possess complex oligosaccharides with sialic acid (typically Neu5Ac).

Understanding these variations is crucial for grasping lipid functionality and interactions within biological membranes.

How do sphingolipids differ from glycerophospholipids?

Sphingolipids and glycerophospholipids differ primarily in their backbone structures and head groups. Sphingolipids have a sphingosine backbone, while glycerophospholipids have a glycerol backbone. The head groups of sphingolipids can be hydrogen, phosphocholine, or various sugars, whereas glycerophospholipids typically have phosphate-containing head groups like phosphatidylcholine or phosphatidylserine. Additionally, sphingolipids are linked via an amide bond to fatty acids, while glycerophospholipids are esterified to fatty acids. These structural differences lead to distinct functional roles in cellular membranes and signaling pathways.

What is the role of ceramides in sphingolipid metabolism?

Ceramides are central to sphingolipid metabolism and serve as the simplest form of sphingolipids. They act as precursors for more complex sphingolipids like sphingomyelins, cerebrosides, globosides, and gangliosides. Ceramides are involved in various cellular processes, including apoptosis, cell differentiation, and response to stress. Their role in signaling pathways is crucial for maintaining cellular homeostasis and function. The amide linkage in ceramides, formed between the fatty acid and sphingosine backbone, is a key structural feature that influences their biological activity.

What are gangliosides and their significance in biological membranes?

Gangliosides are a class of sphingolipids characterized by complex oligosaccharides with sialic acid residues, typically Neu5Ac. They are abundant in the outer leaflet of the plasma membrane, particularly in neural tissues. Gangliosides play critical roles in cell-cell recognition, signal transduction, and modulation of membrane protein functions. Their complex carbohydrate structures allow them to participate in interactions with other molecules, influencing processes like neurodevelopment, immune responses, and pathogen entry. Understanding gangliosides is essential for studying neurological diseases and membrane dynamics.

How do variable head groups affect the function of sphingolipids?

The variable head groups of sphingolipids significantly influence their function and interaction within biological membranes. For example:

• Ceramides: Involved in apoptosis and stress responses.
• Sphingomyelins: Contribute to membrane structure and signaling.
• Cerebrosides: Participate in cell recognition and signaling.
• Globosides: Involved in cell-cell interactions and immune responses.
• Gangliosides: Play roles in neurodevelopment, signal transduction, and pathogen interactions.

These head groups determine the specific biological roles and interactions of sphingolipids, making them crucial for cellular function and communication.