Final answer:
The molecule formed when the R substitution attached to sphingosine is phosphorylcholine is known as sphingomyelin, an important sphingolipid and phospholipid found in cellular membranes, especially in the myelin sheath of nerve cells.
Step-by-step explanation:
If the R substitution attached to sphingosine is phosphorylcholine, the molecule is sphingomyelin. Sphingomyelins belong to a class of sphingolipids, which are essential components of cellular membranes. Sphingomyelins are particularly important in the composition of the myelin sheath of nerve cells and are implicated in diseases like multiple sclerosis when the myelin is damaged.
Sphingomyelins are also classified as phospholipids because they contain a phosphoric acid group. The phosphatide structure can be broken down into the following parts: a ceramide unit made up of sphingosine and a fatty acid, and a phosphorylcholine attached to the primary alcohol group of ceramide.