What is the Difference Between Phospholipids and Sphingolipids

The main difference between phospholipids and sphingolipids is that phospholipids consist of a glycerol backbone whereas sphingolipids consist of a sphingosine backbone. Furthermore, phospholipids are the major component of lipids in the cell membrane while sphingolipids are the second major component of lipids in the cell membrane.

Phospholipids and sphingolipids are two classes of lipids mainly found in the cell membrane of all living organisms.

Key Areas Covered

1. What are Phospholipids
     – Definition, Structure, Function
2. What are Sphingolipids
     – Definition, Structure, Function
3. What are the Similarities Between Phospholipids and Sphingolipids
     – Outline of Common Features
4. What is the Difference Between Phospholipids and Sphingolipids
     – Comparison of Key Differences

Key Terms

Cell Membrane, Glycerol, Phospholipids, Sphingolipids, Sphingosine

What are Phospholipids

Phospholipids are the main form of lipids found in the cell membrane of all living organisms. Generally, a phospholipid molecule consists of two fatty acid groups attached to the glycerol backbone. Also, it contains a simple organic molecule like choline or ethanolamine attached to the backbone via a phosphate group. This simple organic molecule serves as the polar head group while the two fatty acid chains serve as the two non-polar tails. Furthermore, the main function of phospholipids is to form the lipid bilayer, maintaining the cell membrane structure. However, phospholipids are not a type of fat and it is not stored in fat cells.

Figure 1: Phospholipids int he Cell Membrane

Furthermore, triglycerides are another type of lipid found in the cell. They are a form of fat stored in the fat cells. Triglycerides have three fatty acid molecules attached to the glycerol backbone. Also, they help to maintain the structure of the cell membrane while serving as an energy source.

What are Sphingolipids

Sphingolipids are the second most abundant form of lipids in the cell membrane. They mainly occur in the cell membranes of nerve cells and brain cells. The backbone of sphingolipids is a sphingosine molecule. A sphingosine molecule consists of a three-carbon moiety, which contains two alcohol groups and an amino group. The three-carbon moiety is then attached to a long hydrocarbon chain. Also, based on the side chains attached to the sphingosine molecule, there are two types of sphingolipids. They are sphingophospholipids and glycolipids. In sphingophospholipids, the sphingosine backbone is attached to a fatty acid chain and a simple organic molecule such as choline is attached to the sphingosine backbone separately via a phosphate group. Sphingomyelin is an example of a sphingophospholipid.

Figure 2: Sphingomyelin

However, in glycolipids, the polar head group attached via the phosphate group to the backbone is replaced by a carbohydrate moiety. Cerebrosides are a type of glycolipids present in the nerve cell membrane and Gangliosides are the most complex form of glycolipids in the nerve cells.

Similarities Between Phospholipids and Sphingolipids

• Phospholipids and sphingolipids are two classes of lipids in the cell membrane.
• Both types of lipids have at least one fatty acid group bound to the backbone.
• Also, phospholipids and some sphingolipids have a phosphate group bound to the backbone, forming a polar head group.

Difference Between Phospholipids and Sphingolipids

Definition

Phospholipids refer to a lipid containing a phosphate group in its molecule, e.g. phosphatidylcholine, while sphingolipids refer to a class of compounds which are fatty acid derivatives of sphingosine and occur chiefly in the cell membranes of the brain and nervous tissue. Thus, this is the fundamental difference between phospholipids and sphingolipids.

Backbone

Besides, the main difference between phospholipids and sphingolipids is that the backbone of phospholipids is glycerol molecule while the backbone of sphingolipids is a sphingosine molecule.

Head Group

Moreover, phospholipids contain a head group attached to the backbone via a phosphate group while sphingolipids contain a head group attached to the backbone via a phosphate group or a carbohydrate group attached to the backbone. Hence, this is another difference between phospholipids and sphingolipids.

Fatty Acid Groups

Furthermore, one other important difference between phospholipids and sphingolipids is that the phospholipids contain two fatty acid groups attached to the backbone while sphingolipids do not contain the first fatty acid group.

Abundance in the Cell Membrane

Phospholipids are the most abundant form of lipids in the cell membrane while sphingolipids are the second most abundant form of lipids in the cell membrane.

Examples

Lecithin or phosphatidylcholine is an example of phospholipids while sphingomyelin is an example of a sphingophospholipid.

Conclusion

Phospholipids are the main form of lipids in the cell membrane. The backbone of phospholipids is a glycerol molecule. Phospholipids contain a fatty acid group and a polar head group attached to the backbone via a phosphate group. In comparison, sphingolipids are the second most abundant form of lipids in the cell membrane. However, the backbone of sphingolipids is a sphingosine molecule. The main difference between phospholipids and sphingolipids is the structure of the molecule and the abundance in the cell membrane.

References:

1. “Phospholipids and Related Complex Lipids.” SMC Homepage, Available Here.
2. “Sphingolipids.” Chemistry LibreTexts, Libretexts, 23 Feb. 2019, Available Here.

Image Courtesy:

1. “Cell membrane detailed diagram 4” By derivative work: Dhatfield (talk)Cell_membrane_detailed_diagram_3.svg: *derivative work: Dhatfield (talk)Cell_membrane_detailed_diagram.svg: LadyofHats Mariana Ruiz – Cell_membrane_detailed_diagram_3.svg (CC BY-SA 3.0) via Commons Wikimedia  
2. “Sphingomyelin core structure colored” By Hbf878 – Own work (CC0) via Commons Wikimedia