Practice question

Fluid mosaic model does not imply unrestricted random diffusion all components; regulated anchoring is prevalent and functionally critical. Many membrane proteins undergo co translational or post translational lipidation targeting membranes microdomains. N myristoylation by NMT attaches fourteen carbon myristate via amide to N terminal glycine exposing after methionine removal in Src Yes Lck non receptor kinases localizing to plasma membrane rafts. S palmitoylation by DHHC PAT family forms reversible thioester on cysteine in Ras PSD95 SNAP25 enhancing raft partitioning and stabilizing membrane orientation regulated by APT thioesterases. Prenylation farnesyl fifteen or geranylgeranyl twenty via FTase GGTase on CaaX cysteine of Rab Rho ensures transient association regulated by GDI. GPI anchoring in ER involves transamidase replacing C terminal signal with ethanolamine phosphate mannose three glucosamine PI core tethering alkaline phosphatase Thy1 CD59. Cytoskeletal fencing ankyrin spectrin actin further corrals diffusion. Hence some proteins tethered by lipids distribution patchy thickness regulated hydrophobic mismatch rather than protein abundance alone concept essential for exams understanding membrane organization beyond fluid mosaic simplicity.