Practice question

Functional spectrum of lipid-linked proteins encompasses dynamic localization and signal integration far beyond simple tethering. N-myristoylated and palmitoylated kinases like Src family and non-receptor tyrosine kinases concentrate at inner leaflet raft domains upon growth factor stimulation scaffolding MAPK, PI3K pathways regulating proliferation and cytoskeletal remodeling. Small GTPases Ras Rab and Arf require prenylation plus secondary palmitoylation for vesicular transport from endoplasmic reticulum through Golgi to plasma membrane controlling vesicle budding and fusion. GPI anchors of hydrolytic enzymes ecto-5 prime nucleotidase and alkaline phosphatase provide apical sorting in polarized epithelia, high mobility for substrate encounter, and release by phospholipase for soluble enzyme generation. Structural roles include linking extracellular matrix. Passive diffusion across bilayers however occurs through solubility of small nonpolar molecules like O2 CO2 or via aqueous channels porins aquaporins and carriers exchanging down gradient driven by concentration. Lipid anchors do not generate aqueous pores therefore cannot mediate passive diffusion requiring channel proteins with selectivity filters.