According to the original fluid mosaic model, membrane proteins freely move in the plane of the lipid bilayer (lateral diffusion) like protein icebergs in a sea of lipids." However, the fluid mosaic model has been refined since its description in 1972. Complete the following statements, which describe some of the refinements of the fluid mosaic model as it relates to protein mobility. Choose the answer that best completes each sentence. Vesicles may form a locally rigid, non-lipid matrix surrounded by the fluid lipid matrix. 2. Membrane (lipid) rafts membrane domains rich in sphingolipids and cholesterol, are regions with reduced lipid and protein mobility Protein-protein interactions can be attached to proteins or can "fence in" proteins 3 Cytoskeletal elements reducing protein mobility