Practice question

Glycosylphosphatidylinositol anchored proteins are synthesized in endoplasmic reticulum via en bloc transfer of preassembled GPI moiety to C-terminus after cleavage of hydrophobic signal, trafficked through Golgi where lipid remodeling occurs, and delivered to extracellular leaflet of plasma membrane where they reside in ordered lipid rafts enriched in cholesterol and sphingolipid. Attachment chemistry involves phosphoethanolamine bridging peptide carboxyl to glycan tetramannosyl glucosamine core linked via phosphodiester to phosphatidylinositol lipid with two fatty acyl chains inserted into outer leaflet; linkage includes both phosphodiester and glycosidic bonds between sugars. Thus statement about phosphodiester bond for attachment is realistic. They are not exclusively cytoplasmic side; GPI anchor orients extracellularly unlike myristoylation or prenylation inner leaflet. They are not synthesized in mitochondria but endoplasmic reticulum, and they interact with outer leaflet lipids rather than principally via hydrophobic interactions with integral membrane proteins, though lateral interactions in rafts influence signaling and apical sorting. Release by GPI-specific phospholipases provides regulatory mechanism.