Freeze-fractured membranes, figure

Figure 8-15 Freeze-fractured membranes of two erythrocyte "ghosts." The upper fracture face (PF) shows the interior of the membrane "half" closest to the cytoplasm. The smooth region is lipid and contains numerous particles. The lower face, the extracellular half (EF), possesses fewer particles.

FIGURE 8.19 Replica of a freeze-fractured membrane. In the freeze-fracture technique, the lipid bilayer is split parallel to the surface of the membrane. The hydrocarbon tails of the two layers are separated from each other, and the proteins can be seen as hills in the replica shown. In the other layer, seen edge on, there are valleys where the proteins were. (From Singer, S.J, in G. Weissman and R. Claiborne, Eds., Cell Membranes Biochemistry, Cell Biology, and Pathology, New York HP Pub., 1975, p. 37.)... 

Figure 25. Freeze fractured replica. P-fracture face of the plasma membrane in 15h aplanospore of Valonia veniricosa. The clustered TC s are shown, suggesting the build-up of new axis for microfibril orientation.

FIGURE 20-30 Rosettes. The outside surface of the plant plasma membrane in a freeze-fractured sample, viewed here with electron microscopy, contains many hexagonal arrays of particles about 10 nm in diameter, believed to be composed of cellulose synthase molecules and associated enzymes. 

Figure 18-2 (A) Schematic diagram of mitochondrial structure. (B) Model showing organization of particles in mitochondrial membranes revealed by freeze-fracture electron microscopy. The characteristic structural features seen in the four half-membrane faces (EF and PF) that arise as a result of fracturing of the outer and inner membranes are shown. The four smooth membrane surfaces (ES and PS) are revealed by etching. From Packer.8...

Freeze-fracture electron microscopy studies of the membranes of E. coli and A. vinelandii by Reusch et al.24 provide evidence of structural changes that support the fluorescence data (Figure 10). Freeze-fracture micrographs of log-phase cells show a typical mosaic of particles and pits on both concave and convex surfaces of the plasma membranes. However, as complexed PHB was increasingly incorporated into the membranes, as determined by analysis of the purified membranes and evidenced by the intensity of the thermotropic transition at - 56 °C, the micrographs revealed the formation of small semi-regular plaques in the plasma membranes (arrows) that possess shallow particles. The plaques grew in size and frequency as the concentration of membrane PHB and intensity of the PHB/polyP transition increased. 

Figure 10. Representative freeze-fracture electron micrograph of competent E. coli DH1. The micrograph shows the typical appearance of small semi-regular plaques (arrows) in the plasma membranes of E. coli DH1 cells after treatment to make them genetically transformable by the method of Hanahan.146 These cells have sharp thermotropic transitions at -56 °C when examined as in Figure 9A.24...

Figure 5.10 Electron micrographs of L-cells of Streptomyces hydroscopicas [73]. The freeze-fractured texture shows the periodically curved lipid bilayer. The curvature is weakly expressed in a and very distinct in fi. Two attached lamellar bodies and the imderlying membrane are shown in fe. The bar (in fi) is 500 nm.

Figure 4 Freeze-fracture micrograph illustrating the gap junction plaque in the membrane between two cells.

Fig. 19. Chloroplast thylakoid-membrane structure revealed by freeze-fracture electron microscopy. The oxygen-evolving (BBY) PS-II particle its preparation (A) and electron micrographs (B). The inside-out and rightside-out vesicles preparation, structure, and properties (C) and electron micrographs (D). Figure source (A) and (B) Dunahay, Staehelin, Seibert, Ogilvie and Berg (1984) Structural, biochemical and biophysical characterization of four oxygen-evolving photosystem II preparations from spinach. Biochim Biophys Acta 764 190, 185 (C) and (D) from Andersson and Akerlund (1978) Inside-out membrane vesicles isolated from spinach thylakoids. Biochim Biophys Acta 503 465, 468. Figure (B) kindly furnished by Dr. Andrew Staehelin.

Although the hydrophobic barrier created by the fluid lipid bilayer is an important feature of membranes, the proteins embedded within the lipid bilayer are equally important and are responsible for critical cellular functions. The presence of these membrane proteins was revealed by an electron microscopic technique called freeze-fracture. Cells are frozen to very cold temperatures and then fractured with a very fine diamond knife. Some of the cells are fractured between the two layers of the lipid bilayer. When viewed with the electron microscope, the membrane appeared to be a mosaic, studded with proteins. Because of the fluidity of membranes and the appearance of the proteins seen by electron microscopy, our concept of membrane structure is called the fluid mosaic model (Figure 18.13). 

Figure 5.5 Cross section and surface of a microporous polysulfone sheet used in composite reverse osmosis membranes (a) total cross section of a polysulfone sheet cast on a nonwoven polyester fabric, then delaminated prior to freeze-fracture for SEM (note fiber trecks on backside of the sheet) (b) backside of sheet showing cellular structure, which extends through 85% of the sheet thickness (c) transition region from cellular to nodular structure near film surface (d) dense nodular structure at the surface (e) high magnification of the extreme top surface cross section (f) high magnification view of the surface structure showing tha texture of the top surface.

Most of the proteins of PS II are embedded within the photosynthetic membrane although portions are exposed to the aqueous media on the inside and on the outside of the membrane. A fully developed PS II is composed of hundreds of Chi a and Chi b molecules, carotenoids, plastoquinones (Figure 1), a-tocopheryl quinone or a-tocopherol, cytochrome b-559, the Mn-protein responsible for O2 evolution, and other electron transport agents. The diameter of a fully-developed PS II has been estimated at 160 A from electron micrographs of freeze-fractured photosynthetic membranes (46). The bulk of the chlorophyll molecules in PS II have only an antenna function, i.e., they absorb photons (reaction 1) and transfer the resultant electronic... 

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