Practice question

Lipid-linked proteins associate with membranes via covalent attachment of hydrophobic moieties rather than simple non-specific interactions. Several distinct modifications exist: N-myristoylation adds 14-carbon myristate to N-terminal glycine after methionine removal via amide linkage, palmitoylation S-acylates internal cysteine via thioester that is reversible, prenylation attaches 15-carbon farnesyl or 20-carbon geranylgeranyl to C-terminal cysteine in CAAX motif via thioether, and glycosylphosphatidylinositol anchor attaches to C-terminus via phosphoethanolamine bridging to glycan core terminated by phosphatidylinositol lipid inserting into outer leaflet. GPI anchoring provides stable extracellular membrane tethering for enzymes like alkaline phosphatase and adhesion molecules like CD59 complement regulator, conferring localization to lipid rafts and enabling regulated release via phospholipases. Contrary to notion of only extracellular occurrence without post-translational processing, lipidation occurs co- or post-translationally in cytoplasm, endoplasmic reticulum and Golgi and determines membrane targeting and signaling localization. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.