Glycerophospholipids and sphingolipids are the main membrane lipids used in biological systems. The most common types of membrane lipids are phosphatidylethanolamine and phosphatidylcholine, which are both types of glycerophospholipids. It's worth noting that prokaryotes cannot synthesize phosphatidylcholine and use a different structure. Let's take a look at phosphatidylcholine. Similar to triacylglycerides, it has a glycerol backbone attached to two fatty acids and a phosphate group. In phosphatidylcholine, a choline is attached to the phosphate, whereas in phosphatidylethanolamine, a different molecule is attached but maintains the same glycerol backbone. Additional membrane lipids include phosphatidylserine and phosphatidylinositol, though they are not the major ones.
Turning our focus to sphingolipids, their structure is somewhat similar to that of phosphatidylcholine, with choline, a phosphate group, and a single fatty acid. However, instead of glycerol and another fatty acid, sphingolipids contain a molecule called sphingosine. This small but significant difference gives sphingolipids different properties and uses. This particular sphingolipid is called sphingomyelin, and all sphingolipids use a sphingosine backbone. This distinction in structure—whether having two fatty acids and a glycerol backbone versus using a sphingosine backbone with only one fatty acid—is the basic separation between sphingolipids and glycerophospholipids.
