Some Membranes Have Relatively Large Pores

Some Membranes Have Relatively Large Pores 

Mitochondria, Gram negative bacteria, and chloroplasts have double envelopes of membranes. As we discussed, their inner membranes are impermeable to ions and polar molecules other than those that are transported by specific 

Gap junctions are formed from hexagonal arrays of a rod-shaped protein. Arrays in the membranes of adjacent cells line up to form intercellular channels that can transmit small molecules from cell to cell in some tissues. (Source Adapted from L. Makowski, D. L. D. Caspar, W. C. Phillips, and D. A. Goodenough, Gap junction structures. II. Analysis of the x-ray diffraction data,./. Cell Biol. 74 629, 1977.) 

Gap junctions close if the Ca2+ concentration of the cell rises above normal physiological levels. Because the Ca2+-ATPase ordinarily keeps the cytosolic Ca2+ concentration below 10-7 M, a large increase in [Ca2+] could be a signal that a cell has exhausted its energy supplies, and the closing of gap junctions under these conditions could serve to cut off the drain of materials from living cells to neighboring cells that have died. 

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Two Phosphorylated Forms of the Enzyme Some Membranes Have Relatively Large Pores Other Specific Interactions Mediated by Membrane... 

Some Membranes Have Relatively Large Pores... 

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