Figure 1.

The proposed models of cell membranes. A An updated fluid mosaic membrane model that contains information on membrane domain structures, membrane-associated cytoskeletal, and extracellular structures. Reprinted from Nicolson (2014) with permission from Elsevier. B Lipid raft domains in cell membranes. Reprinted from Lillemeier et al. (2006) with permission from National Academy of Sciences, U.S.A. C Proposed protein layer-lipid-protein island (PLLPI) model of the cell membrane. The proteins on the ectoplasmic side of the cell membrane form a dense protein layer to show a smooth feature; the proteins on the cytoplasmic side tend to form dispersed microdomains (left). The total height of the cell membrane is 20 nm, which is composed of ectoplasmic protein layer (4 nm), lipid bilayer (4 nm), and cytoplasmic protein layer (12 nm) (right). Reprinted from Zhao et al. (2014) with kind permission from the Public Library of Science