Freeze Fracture and Freeze Etch

Freeze-Fracture reveals the distribution of proteins in cell membranes. Specimens are fixed, dehydrated and cryo-protected, then rapidly frozen in a cryogen. While frozen, they are fractured with a metal knife, breaking open the cell membranes and exposing transmembrane proteins. Specimens are contrasted by metal shadowing, as above.

Freeze-fracture image of cell plasma membrane: small particles represent transmembrane proteins.

Freeze-fracture image of cell plasma membrane: small particles represent transmembrane proteins.

Freeze-etched specimens are prepared as for freeze-fracture, but before shadowing, some of the specimen ice is sublimed off. Following etching, the specimen is shadowed, providing beautiful images of the cell interior (organelles and cytoskeletal filaments) which is exposed during the etching process.

Freeze-fractured, freeze-etched flagellum showing microtubles and dynein arms.

Freeze-fractured, freeze-etched flagellum showing microtubles and dynein arms. (Courtesy of Dr George Witman, Cell Biology, UMass Medical School)