Electron micrograph membrane

Fig. 5. (a) Preparation method and (b) scanning electron micrograph of a typical expanded polypropylene film membrane, ia this case Celgard. 

Fig. 12. Scanning electron micrograph of an asymmetric Loeb-Sourirajan membrane.

Fig. 16. Scanning electron micrograph of a silicone mbber composite membrane.

Fig. 18. Cross-sectional scanning electron micrograph of a three-layered alumina membrane/support (pore sizes 0.2, 0.8, and 12 p.m, respectively).

Fig. 27. Scanning electron micrograph (a) and cross-sectional comparison (b) of screen and depth filters both having a nominal particulate cut-off of 0.4 flm. The screen filter (a Nuclepore radiation track membrane) captures particulates at the surface. The phase-inversion ceUulosic membrane traps the...

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

Membrane proteins in many cases are randomly distributed through the plane of the membrane. This was one of the corollaries of the fluid mosaic model of Singer and Nicholson and has been experimentally verified using electron microscopy. Electron micrographs show that integral membrane proteins are often randomly distributed in the membrane, with no apparent long-range order. 

FIGURE 17.27 (a) Electron micrograph images of foot structures of terminal cisternae. (b, c) Foot structures appear as trapezoids and diamonds on the surface of the membrane. 

FIGURE 21.23 Electron micrograph of sub-mitochondrial particles showing the 8.5-nm projections or particles on the inner membrane, eventnally shown to be Fj-ATP synthase. (Parsons, D. E, 1963. Science 140 985)... 

The mitochondrial complex that carries out ATP synthesis is called ATP synthase or sometimes FjFo-ATPase (for the reverse reaction it catalyzes). ATP synthase was observed in early electron micrographs of submitochondrial particles (prepared by sonication of inner membrane preparations) as round, 8.5-nm-diameter projections or particles on the inner membrane (Figure 21.23). In micrographs of native mitochondria, the projections appear on the matrixfacing surface of the inner membrane. Mild agitation removes the particles from isolated membrane preparations, and the isolated spherical particles catalyze ATP hydrolysis, the reverse reaction of the ATP synthase. Stripped of these particles, the membranes can still carry out electron transfer but cannot synthesize ATP. In one of the first reconstitution experiments with membrane proteins, Efraim Racker showed that adding the particles back to stripped membranes restored electron transfer-dependent ATP synthesis. 

ATP synthase actually consists of two principal complexes. The spheres observed in electron micrographs make up the Fj unit, which catalyzes ATP synthesis. These Fj spheres are attached to an integral membrane protein aggregate called the Fq unit. Fj consists of five polypeptide chains named a, j3, y, 8, and e, with a subunit stoichiometry ajjSaySe (Table 21.3). Fq consists of three hydrophobic subunits denoted by a, b, and c, with an apparent stoichiometry of ajbgCg.ig- Fq forms the transmembrane pore or channel through which protons move to drive ATP synthesis. The a, j3, y, 8, and e subunits of Fj contain 510, 482, 272, 146, and 50 amino acids, respectively, with a total molecular mass... 

The processes for manufacturing microporous membranes can be broadly divided into wet processes and dry processes. Both processes usually employ one or more orientation steps to impart porosity and/or increase tensile strength. Figure 2 shows scanning electron micrographs of surfaces of separators made by each process. 

Figure 2. Scanning electron micrographs of surfaces of microporous membranes made by wet and dry processes. (a) Setela microporous membrane (net process) (b) Celgard microporous membrane (dry process).

Fig. 16.7. Scanning electron micrograph of a section of an asymmetric polyamine ultrafiltration membrane showing finely porous skin layer on more openly porous supporting matrix.

Figure 3. Electron micrographs of myelinated axons of Xenopus laevis. Upper figure Cross section of axon showing microtubules in groups in association with membrane-bound organelles. Lower figure Longitudinal section of axon showing neurofilaments and microtubules in close proximity to membrane-bound organelles. (Courtesy of Dr. R. Smith.)...

Figure 6.16 Top Electron micrographs of iron-overloaded human spleen (a) and of an avian species (Order passeriformes) (b), showing clumps of densely stained material throughout the tissue, haemosiderin. Bottom Electron micrographs of siderosomes from (a) human spleen and (b) an avian species (Order passeriformes). Iron-rich particles can be seen within the membrane-bound structure. Hexagonal arrangements and clusters of unbound ferritin are also seen. Unstained, magnification x 120000. Reprinted from Ward etal., 2000. Copyright (2000), with permission from Elsevier Science.

In addition, however, one can speculate about another possible application of stabilized vesicles in living systems tumor cells usually are not attacked by cells of the immune system. On the other hand it is impressive to see what happens if they are not able to elude the cells of the immune system. Antigens of cancer cells can be recognized e.g. by sensitized mice lymphocytes and the result is a destruction of the membrane of the malignant cell as demonstrated via electron micrographs by Old (12). 

Between 1955 and 1960 various sub-mitochondrial preparations were developed to give vesicles comprising only sealed inner mitochondrial membranes. Cooper and Lehninger used digitonin extraction Lardy and Kielley Bronk prepared sub-mitochondrial particles by sonication. At this time, too, Racker and his colleagues isolated Fq/F1 particles from mitochondria and showed that a separated FI particle behaved as an ATPase. The F0 portion had no enzymic properties but conferred oligomycin sensitivity on the FI ATPase. The orientation of these sub-mitochondrial vesicles (inside-out or vice-versa) was shown by the position in electron micrographs of the dense (FI) particles which in normal intact mitochondria project into the matrix and so define the surface of the inner mitochondrial membrane. 

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