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High-Tech Cellular Imaging
| Article
# : |
16844 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1989 |
2,292 Words |
| Author
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Peter J. Lea and Martin J. Hollenberg
Peter J. Lea and Martin J. Hollenberg are members of the
Department of Anatomy, faculty of medicine at the University
of Toronto, Ontario, Canada. They, with D.H. Cormack, are
authors of Stereo Atlas of the Cell (Toronto and Philadelphia:
B.C. Decker, 1989). |
What in the human body is too small to be seen with the naked eye but is as complex in structure and function as a modern city?
Imagine the complex activity that takes place in a city during one day--goods being manufactured and transported, food brought in via highway, garbage removed and transported, houses being built. The component of the human body that is comparable in complexity is, of course, a single cell. Analogous functions of all a city's efforts are constantly ongoing within the cell--the most basic component of life.
Now compare our relative ability to observe these two organized complexes. If we observed the city from the window of an airplane, how much detail could we see? At best, we could see high rises, houses, highways, and maybe some people, as small as ants. Until recently, the best imaging of the cell was comparable to such a view. Imagine if instead of seeing, say, an office building, we could see a single pencil on a desk in an office inside that building. In terms of relative scale, the technique of high resolution scanning electron microscopy now permits us to observe the three-dimensional structure of the actual working units, called organelles, inside a single cell!
Historical Perspective
Early microscopists studied cells and tissues using glass lenses and light to magnify to a maximum of about 1,000 diameters. The smallest object they could resolve was some 2/10,000 of a millimeter--about the diameter of a red blood cell. The big advantage of the transmission electron microscope (TEM) was its ability to use electrons and electromagnetic lenses to magnify the observed image. Modern TEM's can magnify up to one million diameters and resolve less than 1/10-millionth of a millimeter--the distance between two carbon atoms in a carbohydrate chain.
Most of the information about the microanatomy of cells and tissues has been obtained by the study of very thin sections in the TEM. The TEM is similar to the light microscope in that the electron beam goes through the specimen section, producing a flat, two-dimensional image. To obtain three-dimensional information from the TEM, many consecutive thin sections have to be photographed, and the three-dimensional image then has to be reconstructed from these two dimensional images. The resolution of biological material as observed in the TEM is approximately 2 nanometers; this means that the smallest object we can see would be two-millionths of a
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