Practice question

Fluid Mosaic Model postulated by Singer and Nicolson in 1972 integrated thermodynamic considerations and experimental data that membranes behave as two-dimensional fluid solutions. Phospholipids and sphingolipids undergo rapid lateral diffusion measured 1-3 µm2/s, rotation around axis, transbilayer flip-flop rare without flippase catalysis, demonstrated by Frye and Edidin fusion of human and mouse fibroblasts where surface antigens intermix within 40 minutes, and later single-particle tracking revealing Brownian, confined, and directed motions due to cytoskeletal fences. Integral membrane proteins float in lipid sea, some tethered via ankyrin to spectrin cortex, others partitioning into cholesterol-rich ordered rafts enriched in sphingomyelin for signaling. Peripheral proteins attach via ionic interactions or lipid anchors myristoylation, palmitoylation. Lipid asymmetry is maintained by ATP-dependent P4-ATPases. Membrane is not static nor rigid, lipids and proteins can move laterally, asymmetry persists except during apoptosis, enabling processes like immune synapse, vesicular budding, and hormone reception that require reorganization of components in plane of membrane.