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How do sphingolipids differ from phospholipids in cell membranes?

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A composite diagram shows the structural formulas, space-filling models, and simplified depictions of lipid molecules including stearic acid and phosphatidylcholine, and how these assemble into a micelle and lipid bilayer, with labels identifying hydrophilic heads and hydrophobic tails. — Lipid Structure and properties of two representative lipids. Both stearic acid (a fatty acid) and phosphatidylcholine (a phospholipid) are composed of chemical groups that form polar “heads” and nonpolar “tails.” The polar heads are hydrophilic, or soluble in water, whereas the nonpolar tails are hydrophobic, or insoluble in water. Lipid molecules of this composition spontaneously form aggregate structures such as micelles and lipid bilayers, with their hydrophilic ends oriented toward the watery medium and their hydrophobic ends shielded from the water.

Sphingolipids and phospholipids are both essential components of biological membranes, but they differ primarily in their chemical structure and biological roles.12

Structural Differences

Backbone: Phospholipids (specifically glycerophospholipids) are built upon a glycerol backbone, where two fatty acids are linked to carbons 1 and 2, and a phosphate group is attached to carbon 3. In contrast, sphingolipids are based on an 18-carbon amino alcohol called sphingosine (or its analog, phytosphingosine).324
Head Groups: While phospholipids typically feature a phosphate group and an alcohol, most sphingolipids possess a simple or complex sugar linked to the alcohol on carbon 1. The notable exception is sphingomyelin, which is a sphingolipid that contains a phosphorylcholine group, making it a structural analog of the phospholipid phosphatidylcholine.124

Functional and Distribution Differences

Location: Glycosphingolipids are found exclusively on the external surface of the cell membrane, where their sugar moieties function as antigens and receptors for signaling molecules.2
Diversity: Phospholipids are the most abundant lipids in biological membranes. Sphingolipids, particularly those containing sugars, exhibit significant diversity and are critical for specialized functions, such as acting as receptors or components of the myelin sheath surrounding nerves.324