Freeze fracture examination of the plasma membrane, a. View of the plasma membrane seen on edge, with arrow indicating the preferential plane of splitting of the lipid bilayer through the hydrophobic portion of the membrane. When the membrane splits, some proteins are carried with the outer leaflet, though most are retained within the inner leaflet, b. View of the plasma membrane with the leaflets separating along the cleavage plane. The surfaces of the cleaved membrane are coated, forming replicas; the replicas are separated from the tissue and examined with the TEM. Proteins appear as bumps. The replica of the inner leaflet is called the P-face; it is backed by cytoplasm (protoplasm). A view of the outer leaflet is called the E-face; it is backed by extracellular space, c. Electron micrograph of a freeze fracture replica shows the E-face of the membrane of one epithelial cell and the P-face of the membrane of the adjoining cell. The cleavage plane has jumped from the membrane of one cell to the membrane of the other cell, as indicated by the clear space (intercellular space) across the middle of the figure. Note the paucity of particles in the E-face compared with the P-face, from which the majority of the integral membrane proteins project. (Courtesy of Dr. Giuseppina d'Elia Raviola.)

cell membrane collagen IV


K+o pumps receptors structural proteins

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