Practice question

Detergent resistant membrane fractions shotgun lipidomics consistently show enrichment sphingolipids relative glycerophospholipids quantitative evidence rafts composition bias and lateral organization. Sphingomyelin ceramide cerebrosides gangliosides share sphingosine backbone hydrogen bonding capacity amide hydroxyl groups predominantly saturated very long chains eighteen to twenty four carbons promoting all trans extended conformation high Tm above thirty seven degrees favoring condensation cholesterol into liquid ordered phase where acyl packing tight yet laterally mobile diffusion moderate. Phosphatidylcholine kinked oleoyl chain phosphatidylserine negative charge unsaturated tails favor liquid disordered phase depleted rafts non raft domains. Estimates SM two to three fold gangliosides four fold enrichment rafts versus whole plasma membrane via mass spectrometry imaging super resolution microscopy. Thicker hydrophobic core rafts sorts proteins longer transmembrane helices seventeen versus fifteen amino acids explaining apical sorting polarized epithelial cells. Compositional bias underlies fluorescence microscopy using cholera toxin B GM1 as raft marker and functional assays showing sphingolipid cholesterol depletion blocks signaling sorting mechanisms thoroughly examined in membrane biology and examination questions regarding microdomains composition and functional consequences for protein trafficking.