Practice question

Lipid linkage expands repertoire of membrane association beyond hydrophobic transmembrane spans enabling reversible targeting. Four major classes documented: N-myristoylation fourteen-carbon saturated fatty acid amide linked to N-terminal glycine after methionine removal catalyzed by N-myristoyltransferase cotranslationally; S-palmitoylation sixteen-carbon palmitate thioester linked to cysteine catalyzed by DHHC palmitoyl acyltransferases reversible by thioesterases controlling trafficking; prenylation fifteen-carbon farnesyl or twenty-carbon geranylgeranyl thioether linked to C-terminal CAAX cysteine by farnesyltransferase and geranylgeranyltransferases followed by proteolysis by RCE1 and carboxyl methylation by ICMT; GPI anchoring where preassembled glycolipid comprising ethanolamine phosphate oligosaccharide glucosamine mannose inositol diacylglycerol attached to C-terminal cleavage site via transamidase embedding in outer leaflet. These moieties embed in one leaflet providing raft affinity, polarized sorting and assembly of signalosomes for Ras Rab Src G-alpha and alkaline phosphatase families distinct from multipass integral proteins like channels that cross bilayer via peptide helices. Each modification uses distinct metabolite donors myristoyl-CoA palmitoyl-CoA farnesyl diphosphate and preassembled GPI precursor dictating substrate specificity and cellular localization.