Niemann-Pick disease type A is caused by acid sphingomyelinase deficiency, leading to sphingomyelin accumulation in lysosomes. Sphingomyelin is structurally unique among membrane phospholipids because:
- A It contains glycerol as the backbone
- B It is the only phospholipid found in the outer leaflet of the plasma membrane
- C It contains sphingosine (a long-chain amino alcohol) as the backbone, not glycerol, and has a phosphocholine head group ✓
- D It contains an ether-linked fatty acid (plasmalogen)
Correct answer: C. It contains sphingosine (a long-chain amino alcohol) as the backbone, not glycerol, and has a phosphocholine head group
Explanation
Sphingomyelin is a sphingolipid based on sphingosine (an 18-carbon amino alcohol with a trans double bond), not glycerol. A fatty acid is attached to sphingosine via an amide bond forming ceramide; phosphocholine is then esterified to ceramide's C1 hydroxyl, making sphingomyelin. Unlike glycerophospholipids (which have glycerol backbone and two ester-linked fatty acids), sphingomyelin has one amide-linked fatty acid. Plasmenyl-phospholipids (plasmalogens) have ether-linked fatty acids at sn-1; these are glycerophospholipids found in heart and brain.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.