This Data Analysis Problem does not appear in the textbook.
Source: Chalcroft, J. P., S. Bullivant. 1970. An interpretation of liver cell membrane and junction structure based on observation of freeze-fracture replicas of both sides of the fracture. J. Cell Biol. 47: 49–60.
Corresponding chapter(s) in the textbook: Chapter 15 (and 1)
Review the following terms before dealing with the figure: freeze-fracture electron microscopy, cell membrane, cell junction
The figure shows a freeze-fracture replica of two adjacent cells from mouse liver: the smooth face of one cell membrane (indicated by –) and the more particulate face (+) of the other cell membrane are apparent. The circled arrow at the bottom of the micrograph indicates the direction of heavy metal shadowing.
1. Briefly describe the steps of the freeze-fracture technique.
2. What are the particles that appear on both the – and + membrane faces? Suggest an explanation for why some of the particles appear on the –, while others appear on the + face.
3. G1 and G2 indicate regions of the membranes that are thick with a type of cell-to-cell junction that allows the flow of small molecules and ions between the cells. What type of junction is represented by these regions?