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BIOLOGY 153 - Cells, Metabolism, and Heredity

Spring 2001

The transmission electron microscope (TEM) is used to support lab sessions for over 70 students in the Spring Intro Bio course. The TEM provides another way to look at material that is also examined biochemically. In the lab exercise from the week of Feb. 12, using both techniques made it possible to gather independent but mutually supportive evidence that the enzyme succinate dehydrogenase is localized specifically to the mitochondria.

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Fig. 1  Electron micrograph (left) from the starting material, a cauliflower mash prepared in lab. This mash will be further processed and then used to study a subcellular component, the mitochondria, by spectroscopic means. The TEM image shows the starting material, which predictably consists of large and small broken cell fragments, clumps of dispersed DNA (chromatin), and free mitochondria.



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Fig. 2  Electron micrograph (right) from the pellet that resulted when the original mash was centrifuged at 600xG. Large cell fragments and clumped chromatin are the major constituents of this preparation. There are few, if any, mitochondria. (Approx. the same magnification as Fig. 1.)



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Fig. 3  Electron micrograph (left) from the pellet that resulted when the supernatant from the 600xG spin  was centrifuged at 10,000xG. Very small cell fragments and many mitochondria are present in this sample. When measured spectroscopically, this sample demonstrated high levels of succinate dehydrogenase, an enzyme that is specific to mitochondria.  (Approx. the same magnification as Fig. 1.)


Fig. 4  A greatly magnified mitochondrion (below), which can be identified by its double limiting membrane and the presence of internal membrane invaginations called cristae. (Approx. 15X the magnification as Fig. 1.)
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