This freeze fracture micrograph shows a region of membrane from the midpiece of opossum Didelphis virginiana sperm. This region of the sperm is notable for the repeating longitudinal bands composed of 3-5 intramembranous particles (IMPs). This micrograph by Gary Olson is Figure 7 from Chapter 1 (The Cell Surface) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.
With the freeze-fracture technique, tissue is rapidly frozen and cracked to shear along zones of weakness. Cleavage of membranes occurs along the hydrophobic interior of the lipid bilayer to reveal views of a "p-face" (the outwardly-facing inner half of the membrane) and an "e-face" (the inwardly-facing outer half of the membrane), and a metallic replica is made of the fractured surface. The intramembranous particles represent integral membrane proteins.
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