Dynamic Dark-Field Electron Microscopy

1976 ◽  
Vol 34 ◽  
pp. 482-483
Author(s):  
G.B. Haydon ◽  
R.A. Crane ◽  
C.R. Zercher
Keyword(s):  
Electron Microscopy ◽  
Optical Axis ◽  
Dark Field Image ◽  
Dark Field ◽  
Annular Ring ◽  
Field Electron ◽  
Field Electron Microscopy ◽  
Dark Field Electron

Dynamic dark-field electron microscopy as described here provides capabilities not present with other methods. An annular ring of any selected diameter is used to illuminate the specimen. Diffraction rings selected by the objective aperture are integrated photographically to produce the dark-field image.All methods of dark-field electron microscopy eliminate the incident illumination from the image and utilize only a selected portion of the scattered electrons and each has its limitations (1):1. Movement of the objective aperture off of the optical axis introduces spherical aberation which increases as the 4th power of the distance from the axis.2. Tilting the beam either mechanically or electrically allows only those electrons scattered in one direction to be imaged.

Imaging a Protein α-Helix by Dark Field Electron Microscopy

1981 ◽  
Vol 39 ◽  
pp. 34-35
Author(s):  
D. W. Andrews ◽  
F. P. Ottensmeyer
Keyword(s):  
Electron Microscopy ◽  
Visual Recognition ◽  
Dark Field Image ◽  
Relevant Information ◽  
Dark Field ◽  
Biologically Relevant ◽  
Field Electron ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Α Helix

Elucidation of the fine structure of a protein, beyond its gross conformation, requires images of better than 10 Å resolution. In order to achieve such a resolution the normal techniques of staining the molecule must be avoided by substituting a technique such as dark field electron microscopy. However, to form a dark field image of such high resolution requires an exposure of approximately 1500 e/Å2. Exposures of this magnitude are so high that serious doubt has been expressed regarding the extent to which an image formed under these circumstances is an accurate representation of the molecule. Images of myokinase, protamine, glucagon, secretin, and ACTH indicate that reproducible 5-10 Å detail is present in the micrographs. Furthermore, for bacitrin, valinomycin, and the growth stimulators LMW-CSA N and B, biologically relevant information of 3-5 Å is present in averages prepared from a collection of images or even in single molecular images. Visual recognition has been used as a criterion to assess radiation damage in images of isolated molecules of protamine.

Evaluation of the dark field method for large association of spread DNA

1978 ◽  
Vol 36 (2) ◽  
pp. 190-191
Author(s):  
Douglas C. Barker
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Mitochondrial Dna ◽  
Extraction Method ◽  
Field Method ◽  
Dark Field ◽  
Kinetoplast Dna ◽  
Field Electron ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A number of satisfactory methods are available for the electron microscopy of nicleic acids. These methods concentrated on fragments of nuclear, viral and mitochondrial DNA less than 50 megadaltons, on denaturation and heteroduplex mapping (Davies et al 1971) or on the interaction between proteins and DNA (Brack and Delain 1975). Less attention has been paid to the experimental criteria necessary for spreading and visualisation by dark field electron microscopy of large intact issociations of DNA. This communication will report on those criteria in relation to the ultrastructure of the (approx. 1 x 10-14g) DNA component of the kinetoplast from Trypanosomes. An extraction method has been developed to eliminate native endonucleases and nuclear contamination and to isolate the kinetoplast DNA (KDNA) as a compact network of high molecular weight. In collaboration with Dr. Ch. Brack (Basel [nstitute of Immunology), we studied the conditions necessary to prepare this KDNA Tor dark field electron microscopy using the microdrop spreading technique.

Structure and Interaction of Protamine by Dark Field Electron Microscopy

1976 ◽  
Vol 34 ◽  
pp. 160-161
Author(s):  
D.P. Bazett-Jones ◽  
F.P. Ottensmeyer
Keyword(s):  
Electron Microscopy ◽  
Dark Field ◽  
Amino Acid Sequences ◽  
Dimensional Structure ◽  
3 Dimensional ◽  
Field Electron ◽  
Proposed Model ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Positively Charged

It has been shown for some time that it is possible to obtain images of small unstained proteins, with a resolution of approximately 5Å using dark field electron microscopy (1,2). Applying this technique, we have observed a uniformity in size and shape of the 2-dimensional images of pure specimens of fish protamines (salmon, herring (clupeine, Y-l) and rainbow trout (Salmo irideus)). On the basis of these images, a model for the 3-dimensional structure of the fish protamines has been proposed (2).The known amino acid sequences of fish protamines show stretches of positively charged arginines, separated by regions of neutral amino acids (3). The proposed model for protamine structure (2) consists of an irregular, right-handed helix with the segments of adjacent arginines forming the loops of the coil.

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