320Fall09Homework9_key - Cell Biology (BIO 320), Fall 2009,...

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Cell Biology (BIO 320), Fall 2009, Dr. Bushart Homework set #9 (Lectures 21-23) 1. Tight junctions require the presence of functional adherens junctions to form correctly. Even if they were stable in the absence of adherence junctions, why would cells connected only by tight junctions not be able to effectively hold together? Tight junctions are formed by contact between transmembrane proteins, just like junctions formed by cadherins. However, tight junctions do not connect to cytoskeletal elements. A lipid bilayer on its own is pretty weak against pulling forces and so we would expect cells only being held together by tight junctions to rip apart under mechanical stress (perhaps like the intermediate filament- and desmosome-based blistering disorders). 2. Why would you not expect caspases or cytochrome c to be the transmitted element leading to the excessive apoptosis that occurs during heart attack or stroke? How might this compare or contrast to excessive apoptosis seen in plants? Gap junctions could be transmitting signals from the necrotic cells to surrounding neighbors. These signals could be inducing apoptosis, however it cannot be direct transport of caspases or cytochrome c because these are proteins and too large to travel through the gap junctions of animal cells.
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This note was uploaded on 01/25/2010 for the course BIO 51055 taught by Professor Bushart during the Fall '09 term at University of Texas at Austin.

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320Fall09Homework9_key - Cell Biology (BIO 320), Fall 2009,...

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