Phosphoglycerides: Study with Video Lessons, Practice Problems & Examples

Phosphoglycerides, or glycerophospholipids, are a type of phospholipid with a glycerol backbone and two fatty acids. They feature a hydrophilic head, consisting of a phosphate group and an amino alcohol, and hydrophobic tails. Key classes include cephalins, with an ethanolamine head, and lecithins, with a choline head. These lipids are crucial for forming lipid bilayers in cell membranes, influencing membrane rigidity based on fatty acid composition. Understanding their structure and classification is essential for grasping cellular functions and lipid interactions.

Phosphoglycerides Concept 1

Everyone, in this video, we're going to take a look at phosphoglycerides. With phosphoglycerides, we can say they belong to a class called phospholipids. These are just lipids that contain a phosphate group attached to a Glycerol or Sphingosine backbone. Like fatty acids, phospholipids are amphipathic, meaning they contain portions that are polar and nonpolar. They have a hydrophilic head and a hydrophobic tail. If we take a look at our phospholipid, it is better depicted in terms of the bonds involved. For a simpler view, we have our hydrophobic head here and our hydrophobic tail. These can organize themselves to help create what we call a lipid bilayer. Remember, when we talk about lipids, we break them down into hydrolyzable and non-hydrolyzable categories. Our phospholipids belong to the hydrolyzable portion, which includes Glycerol Lipids and Sphingolipids. The portion we are concerned with is our Phospholipids which contain Phosphoglycerides and Sphingomyelins. Looking at the key differences, with Phosphoglycerides, we have Glycerol as our backbone, two fatty acid chains, and a phosphate group connected to an amino alcohol. With sphingomyelin, the backbone is Sphingosine. We still have a fatty acid, and we have our phosphate with Amino Alcohol. In addition to this, phospholipids are a major component of all cell membranes, and the rigidity of the lipid bilayer depends on the identity of the fatty acids that compose the phospholipids. They are an incredibly important category of lipids because they are components of all cell membranes that we talk about in biological systems. Keep in mind some of these key points when it comes to our phospholipids.

Phosphoglycerides Example 1

Which one of the following is not a component of phospholipids?

So we did talk about phospholipids being involved with fatty acids because it is underneath the umbrella term of fatty acids. Phosphate. We said that phospholipids, an important aspect of them, is that they contain a phosphate group. It can be connected to a glycerol molecule or a sphingosine molecule. Cholesterol. Cholesterol here is not a component of phospholipids, and in fact, it belongs under the category of steroids. So here, this would be our answer. Then finally, Glycerol. Glycerol can be a vital component of phospholipids. It forms a potential backbone in terms of the attachment of the phosphate group. So this would also be a component of phospholipids. So here the only answer that's correct is option c. Cholesterol is not a component of phospholipids.

Phosphoglycerides Concept 2

In this video, we talk about our phosphoglycerides. Now we're going to say here that our phosphoglycerides, also called our Glycerophospholipids, are phospholipids with a Glycerol backbone and 2 fatty acids. Now, here we're going to say again they're composed of a head and a tail region. The head is a phosphate group extended with an Amino Alcohol head group, and the tails, there are 2 fatty acids attached through Ester Bonds. Now, here we're going to say they are classified based on the Head Group Attached to the Phosphate Group. If we take a look here at our types of Phosphoglycerides, we have our two classes, which are our Sphingolipids and our Lecithin. Here, the differences come with the different types of head groups involved.

With Cephalin, the head group is an Ethanolamine. And here Nitrogen is making 4 bonds, so it is positively charged, Its groups would be Hydrogens. An example of this would be this structure. We can see the head group here, our Ethanolamine. We have our phosphate group. We have our glycerol backbone in blue. And then, notice that we have 2 fatty acids. They could be saturated or unsaturated. They could be the same. They could be different. Now, here with Lecithin, its head group is different. Here, its head group is Choline. Notice that here, instead of having hydrogens attached to nitrogens, we have methyl groups and there are 3 of them. Here we have our head group, our phosphate group, we have our glycerol backbone, and our 2 fatty acids. Again, they could be saturated or unsaturated; that's not important here. The defining characteristics of these two classes are in the types of head groups attached.

Now, here finally we can say that phosphoglycerides again are the most abundant lipids in all cell membranes. Remember, they help to make the lipid bilayer. That's why they're found in so many I mean, all cell membranes, right. So just keep this in mind when we're talking about our phosphoglycerides; we have 2 classes. Those classes depend on the type of head group attached.

Phosphoglycerides Example 2

This example question asks, what is the basis of the classification of Glycerophospholipids? Now remember, we said that it is the type of head group that's attached to our phosphate that determines the classification for Glycerophospholipids. So we take a look here, it's not about the fatty acid molecule of carbon 1, the number of double bonds in the carbon 2 fatty acid, or the fatty acid molecule of carbon 2. Again, it is the head group that's attached to the phosphate group. And remember, here we can have either an Ethanolamine Group as the Head Group or a Choline as the Head Group. In both cases, we have a Nitrogen making 4 bonds and therefore it's positively charged. With an Ethanolamine head group, we have Nitrogen connected to 3 Hydrogens, an Ethyl group then connected to an Alcohol. And then for Choline, the Nitrogen is not connected to Hydrogens but to 3 methyl groups and it still possesses a positive charge. So in this particular question, it's the head group attached to the phosphate group that deals with the classification of our Glycerophospholipids.

Which one of the following statements accurately describes the difference between cephalins and lecithins?

• A. Cephalins contain saturated fatty acids while lecithins have unsaturated fatty acids.
• B. Lecithins and cephalins have different backbone molecules.
• C. The head groups in cephalins and lecithins are ethanolamine and choline, respectively.
• D. Lecithins do not have a head group.

Phosphoglycerides Concept 3

Now, when it comes to drawing Glycerophospholipids, we're going to say it requires recalling the structures of the fatty acids and head groups. Alright. So, here it says draw the structure of a Glycerophospholipid that contains 2 lauric acid Acetyl groups and ethanolamine bonded to the phosphate group. Alright. So, here, the way we're going to approach this is step 1, we're going to draw the Glycerol backbone with the phosphate group at carbon number 3. So remember, we're going to say this is 1,2,3, we're going to say instead of 2 OH groups at carbon 1 and 2, we're going to write only oxygen atoms. So here, carbon 1 and 2 we have an oxygen here and an oxygen here, we already have our Phosphate group connected to Carbon 3. Next, we're going to say step 2, extend the Phosphate group at Carbon 3 with CH₂CH₂ group and Ethyl group. And we're going to say we're going to complete the head group with a NH₃⁺ group because it's ethanolamine, or we're going to complete it with a nitrogen connected to 3 methyl groups, and it's also positive if it's a choline group. So here we're going to say we have CH₂, CH₂ attached. They told us it's an ethanolamine, so it's going to be an NH₃⁺ group attached. And then let's see. So then we're done with that portion. And then finally, it says draw the 2 fatty acyl groups. So here we're going to say, remember, we don't include the OH group of the fatty acid from the 2 oxygen atoms at carbons 1 and 2. Alright. So we have our ethanolamine group attached, and they're telling us within this question it's 2 lauric acid Acetyl groups. Remember, lauric acid is going to be a saturated fatty acid. It has 12 carbons in total, and it has no pi bonds. So we just have to draw that out. So 2, 4, 6, 8, 10, 12. Same thing here. 2, 4, 6, 8, 10, 12. So here, this would be the structure of our Glycerophospholipid based on the description at the beginning of the example question.

Draw a glycerophospholipid with lauric acid at C1, myristic acid at C2, and choline bonded to phosphate.

• A.
• B.
• C.
• D.

Draw a cephalin with stearic acid at C1 and oleic acid at C2.

• A.
• B.
• C.
• D.

Phosphoglycerides can undergo saponification reaction. Draw products of complete basic hydrolysis of following cephalin. (Hint: 5 products are formed.)

This practice question states that phosphoglycerides can undergo a saponification reaction. Remember, saponification is just base-catalyzed hydrolysis. Draw products of the complete basic hydrolysis of the following, Suffulan. Here, there's a hint that there are 5 products that are going to be formed. Now, here, Suflin, because our head group here represents an ethanolamine. Remember, this is our head group right here. If we're going to do basic hydrolysis, we would sever ester-like linkages here. So, technically this would be 1. Even though it's with a phosphate group, in essence, it's acting like an ester group would. We're doing basic conditions which would mean that we wouldn't have this protonated amine at the end. We'd have its neutral form. And here, we've just created our ethanolamine group. It's basic condition, so we create a phosphate group as well. Right. So this right here. Then we'd have the creation of our glycerol backbone. Alright. So this is our glycerol backbone right here. Alright. Plus, we'd have our carboxylate anions. Just remember, basic conditions, we're not able to create carboxylic acids as products. So we just create our carboxylate anions. So 2, 4, 6, 8, 10, 12, 14, 16. 2, 4, 6, 8, 10, 12, 14, 16, plus this last one here, 2, 4, 6, 8. 2, 4, 6, 8. Then we have our pi bonds. 2, 4, 6, and then 8 here. So these would represent our 5 products formed from the basic hydrolysis of our starting material in the form of this phosphoglyceride molecule.

Here’s what students ask on this topic:

What are phosphoglycerides and why are they important in cell membranes?

Phosphoglycerides, also known as glycerophospholipids, are a type of phospholipid that consist of a glycerol backbone, two fatty acids, and a phosphate group attached to an amino alcohol. They are amphiphatic, meaning they have both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions. The hydrophilic head contains the phosphate group and amino alcohol, while the hydrophobic tails are the fatty acids. Phosphoglycerides are crucial for forming lipid bilayers in cell membranes, which are essential for maintaining cell structure and function. The composition of fatty acids in these lipids influences the rigidity and fluidity of the membrane, impacting various cellular processes.

What are the key differences between cephalins and lecithins in phosphoglycerides?

Cephalins and lecithins are two key classes of phosphoglycerides, differentiated by their head groups. Cephalins have an ethanolamine head group, where nitrogen is bonded to three hydrogen atoms, making it positively charged. Lecithins, on the other hand, have a choline head group, where nitrogen is bonded to three methyl groups, also resulting in a positive charge. Both types have a glycerol backbone, two fatty acids, and a phosphate group, but the specific head group attached to the phosphate distinguishes them. These differences in head groups can affect the properties and functions of the phosphoglycerides in cell membranes.

How do phosphoglycerides contribute to the formation of lipid bilayers?

Phosphoglycerides contribute to the formation of lipid bilayers due to their amphiphatic nature. The hydrophilic heads, which consist of a phosphate group and an amino alcohol, face the aqueous environments inside and outside the cell, while the hydrophobic tails, made up of fatty acids, face each other, away from water. This arrangement forms a bilayer, creating a semi-permeable membrane that separates the cell's interior from its external environment. The lipid bilayer is fundamental for cell membrane integrity, allowing selective transport of substances and facilitating various cellular functions.

What role do fatty acids play in the rigidity of the lipid bilayer formed by phosphoglycerides?

The fatty acids in phosphoglycerides play a significant role in determining the rigidity and fluidity of the lipid bilayer. Saturated fatty acids, which have no double bonds, pack closely together, making the bilayer more rigid. In contrast, unsaturated fatty acids, which contain one or more double bonds, create kinks in the tails, preventing tight packing and increasing membrane fluidity. The specific composition and ratio of saturated to unsaturated fatty acids in phosphoglycerides influence the physical properties of the cell membrane, affecting its flexibility, permeability, and overall function.

How are phosphoglycerides classified based on their head groups?

Phosphoglycerides are classified based on the type of head group attached to the phosphate group. The two main classes are cephalins and lecithins. Cephalins have an ethanolamine head group, where nitrogen is bonded to three hydrogen atoms, making it positively charged. Lecithins have a choline head group, where nitrogen is bonded to three methyl groups, also resulting in a positive charge. These head groups determine the specific properties and functions of the phosphoglycerides in biological membranes, influencing interactions with other molecules and the overall behavior of the lipid bilayer.