Practice question

Sphingolipids are defined by long-chain amino alcohol sphingosine, 18 carbons with amino group at C2 and hydroxyls at C1 and C3, rather than glycerol used in phosphoglycerides. Synthesis starts with serine palmitoyltransferase condensing serine and palmitoyl-CoA to 3-ketosphinganine, reduced to sphinganine, then N-acylated by ceramide synthase family CerS1-6 to dihydroceramide and desaturated by DES1 to ceramide. Ceramide is central metabolic hub; addition of phosphocholine headgroup by sphingomyelin synthase SMS1 in Golgi yields sphingomyelin, while addition of glucose by glucosylceramide synthase yields glucosylceramide precursor for lactosylceramide, globosides, and gangliosides via sequential glycosyltransferases. This explains why sphingolipid derivatives all retain amide-linked fatty acid, saturated acyl chain promoting ordered packing, extensive hydrogen bonding through amide and hydroxyl groups, and tendency to associate with cholesterol in membrane rafts. They are mostly neutral or zwitterionic, not constitutively anionic, and their backbone divergence from glycerolipids underlies distinct biophysical behavior crucial for myelin sheath, epidermal barrier, and signaling via ceramide and sphingosine-1-phosphate controlling fate decisions.