Electron microscopist

Somlyo Moving away from the intestine, I seem to remember that many years ago Geoff Burnstock convinced a poor electron microscopist to serially section a smooth muscle cell in the vas deferens, which he thought would be about 25 jim long. It turned out to be several times longer than this, and they showed that in the vas deferens smooth muscle there were neural synapses. 

Many electron microscopists appreciate the value of the array of sophisticated, light microscopic techniques that are currently available (Chapter 1). In fact, volumes regarding correlative LM and EM are making... 

The 50 S subunit as seen by electron microscopists is an asymmetric, trinodal particle. Three protuberances—the so-called L7/L12 stalk, the nose, and the LI-shoulder—appear on a hemispherical body. The models proposed by various groups are shown in Fig. 5. 

The wave theory eqnations essentially have the form of a mnltiple scattering theory based on plane waves. In the limit of small Bragg angles Takagi s eqnations rednce to the Howie-Whelan eqnations, well known to electron microscopists. 

Another type of device used in nanoscale research, the carbon nanotube, is not so much a tool as an invaluable raw material from which to make nanoscale objects. Carbon nanotubes were discovered in 1991 by the Japanese electron microscopist Sumio Iijima (1939- ). In his research, Iijima vaporized a sample of carbon between two electric arcs and then used an STM to analyze the soot formed. He found that the soot consisted of very large numbers of long cylinders only a few nanometers in diameter, but hundreds or thousands of nanometers in length. Iijima called these structures carbon nanotubes. 

The tobermorite obtained in the hydration of tricalcium silicate (Ca3Si02), / -dicalcium silicate (/ -Ca2Si04), portland cement, and concrete is a colloid, with a specific surface area of the order of 300 sq. meters per gram. To give an idea of how the elementary particles of tobermorite look, Figure 7 is an electron micrograph of a few particles (obtained by L. E. Copeland and Edith G. Schulz at the Portland Cement Association Research and Development Laboratories). These particles look like fibers, but if you watch them closely, you see that they are very thin sheets, rolled up as one would roll up a sheet of paper. At the lower end the sheets are partly unrolled. When one prepares tobermorite by the reaction of lime and silica, one usually obtains crumpled sheets, which are not rolled up. The electron microscopists tell us that the sheets are very thin, of the order of a single unit cell in thickness. 

Ribosomes were first isolated by differential centrifugation and then examined by electron microscopy. This and related work by George Palade in the early 1950s earned him the Nobel prize in 1975. For a time ribosomes were known to electron microscopists as Palade s granules. 

A macrophage is a cell type that is involved in the engulfing of foreign material, such as bacteria and damaged host cells. In view of this specialized phagocytic function, draw what you think an electron microscopist would see in a cross section of the cell. 

In addition, this CTF is attenuated by an envelope or damping function, which depends on the coherence of the beam, specimen drift, and other factors (6,71,72). Figure 14.5 shows a few representative CTFs for different amounts of defocus on a normal and a FEG microscope. Thus, for a particular defocus setting of the objective lens, phase contrast in the electron image is positive and maximal only at a few specific spatial frequencies. Contrast is either lower than maximal, completely absent, or it is opposite (inverted or reversed) from that at other frequencies. Hence, as the objective lens is focused, the electron microscopist selectively accentuates image details of a particular size. 

Electron microscopists see the third layer as a moderately osmiophilic sheath that probably contains some crosslinked sulfur (64). The sheathed filaments look like tubes 70 A in diameter their radial orientation within the plane of SC cells probably accounts for the keratin pattern observed by Brody (31) with the electron microscope (64, 81). Baden s (82)... 

The regions of the presynaptic membrane where fusion of vesicles and the plasmalemma occur are limited to what has been termed the active zones. Closely associated with these active zones are what electron microscopists believe may be clusters of calcium ionophores necessarv for the entry of Ca + for the initiation of exocytotic release. Other morphological entities at the active zone have also been identified, but their physiological role in transmitter release has not been elucidated. It should be noted that numerous freeze-fracture micrographs taken of active synapses reveal many more vesicle fusions than would be predicted for one or two release events. These observations are not consistent with the one vesicle-one quantum hypothesis that was briefly discussed earlier. To date, no explanation for the discrepancy between the number of vesicles and the number of quanta released has been proposed except to suggest that the vesicle, in fact, only releases a fraction of the quantum, which has been termed a microquantum. 

How realistic is this view A considerable amount of evidence has become available that a substantial quantity of the cellular water assumes a structured form/ Moreover, the penetrating studies of the electron microscopists have now revealed that surrounding all cellular organelles and pervading the whole cytoplasm is a delicate fine structure, the cytoskeleton, comprising microtubules, microfilaments, and a variety of other structural elements such as intermediate filaments/" In motile cells the cytoskeleton is particularly extensive and it seems likely that an architecture of similar nature exists in all cells. 

The Section entered into a close working relationship with the Department of Virology, headed by Joseph Melnick, at the University Medical School Baylor, Houston, TX (where this author served as visiting professor). The top electron microscopist Baylor professor, Ferenc Gyorkey, chief physician at the Pathology... 

---