T. Clark Brelje, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
Robert L. Sorenson, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
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Freeze fracture of a more complex specimen as seen by scanning electron microscope (SEM). This micrograph is optional because the previous examples are sufficient to explain this technique.
The absence of nuclei identifies this view as only the cytoplasm of one or more cells.
Plasma Membranes - a pair cross the middle of the image with another one at the bottom of the image.
Protoplasmic face (or P-face; cyan) - most proteins (or complexes of proteins) remain embedded in the inner half of the plasma membrane adjacent to the cytoplasm.
Extracellular face (or E-face; yellow) - fewer particles are bound to the outer half of the plasma membrane adjacent to the extracellular space
The a small region of the cytoplasm adjacent to the plasma membrane is seen for the upper cell, while a narrow cross-section of the cytoplasm is seen for the lower cell.
The most prominent feature is a stack of flattened, membrane-enclosed structures known as cisternae. They are a characteristic feature of endoplasmic reticulum in many cell types. The apparent absence of ribosomes attached to their surface identifies them as smooth endoplasmic reticulum.
Plasma Membranes - protoplasmic face (or P-face) (cyan) and extracellular face (or E-face) (yellow)
Several organelles can be identified in the lower cells. Mitochondria (red) and endoplasmic reticulum (green) can be seen in the lower cell.
A circular structure (~500 nm in diameter) contains internal folds of membrane. This suggests it is a mitochondria fractured in cross-section revealing cristae.
A longitudinal depression appears to contain fragments from two parallel membranes. This suggests the fracture jumped between the inner and outer mitochondrial membranes on the underside of the missing mitochondria.
Plasma Membranes - upper membrane and lower membrane [protoplasmic faces (or P-face) (cyan) and extracellular faces (or E-face) (yellow)].
