This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: membrane structure and function, Subject name: Biochemistry
Which impoant component of cell wall has carbohydrate moiety? 
Select and explain. 
A. Phosphoglyceride, B. Triacylglycerol, C. Sphingomyelin, D. GM2 Gangliosides
D: GM2 Gangliosides
Answer: D: GM2 Gangliosides 
Explanation: This group of glycosphingolipids contains one or more sialic acid residues. They are present in high concentrations in the CNS and also on surface of membranes. The major gangliosides of brain are GM1, GM2, and GM3. For ganglioside synthesis, the active form of NANA (N-acetyl neuraminic acid) used is its CMP derivative. The NANA is attached by the hydroxyl group of its 2nd carbon to the 3rd hydroxyl group of sugars.Ref: DM Vasudevan, page no: 168