Slide Preparation and Staining: Transmission
electron microscopy (TEM)
Throughout the course we will be examining a
number of specimens that were imaged using transmission electron microscopy
(TEM). TEM uses an electron beam that transmits or passes through areas of
specimens providing shades of white to light gray (electron lucent) or is
absorbed or deflected by other areas producing shades of dark gray to black
(electron dense). TEM provides very high resolution (3 nm) and magnification up
to 40,000X (compared to 1000X for light microscopy), allowing for visualization
of ultrastructural features (e.g. protein complexes, organelles, plasma
membrane) within cells and tissues. To achieve this very high resolution and
magnification, specimens imaged using TEM must be highly preserved with
fixatives such as glutaraldehyde. To impart high contrast, these specimens are
also treated with special stains containing heavy metals (e.g. osmium tetroxide,
lead citrate, and uranyl citrate). Compare the images below of the same cells
imaged using the light and transmission electron microscopes. Note that
ultrastructural features of organelles and macromolecular complexes (e.g.
glycocalyx, glycosylated proteins and lipids on the plasma membrane of
microvilli) are easily visualized in TEM images.
