exam 4 back - 1 There are large arrays of mutations...

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1. There are large arrays of mutations associated with cancerous cells, but one general type is those that alter the responsiveness of the cells to apoptotic signals. A. How would the cells be affected if there were amino acid substitution mutations in the aspartic acid residues of procaspases? Procaspases are themselves cleaved at aspartic acid residues by caspases to become fully active. An alteration in this amino acid would result in procaspases that couldn’t be activated and apoptosis would not occur. Even with many other signals apoptosis ultimately relies on executioner caspases to cleave molecular components of the cell. B. Name one protein that if constitutively expressed would allow a cell to avoid apoptosis if it was extrinsically stimulated. Explain how this protein will work to prevent apoptosis if it is always present. There are a large number of possibilities here. IAPs serve to block or degrade active caspases. Dummy receptors and/or dummy caspases (FLIP) block initial perception of extrinsic signals. The intrinsic pathway is also often engaged so blockages of that pathway are acceptable too (however this connection should be clearly stated). These components could include Bcl-2 or, from the survival signaling pathways, Akt kinase (which inactivates a BH3-only protein) or MAP-kinase which inactivates Hid (an anti-IAP). 2. Cells depend heavily on their cytoskeletons and motor proteins for a variety of functions. A. Neurons have to transport vesicles over very long distances. Assuming that processivity could be compensated for, explain one change to a motor protein which would allow for faster axonal transport? Any one of the following: Faster rates of ATP hydrolysis would move the motor protein through its step cycle faster. Longer lever arms or linker regions would allow each step to move a greater distance in the same amount of time. Spending less time of each hydrolysis cycle bound to the track would speed up the process (making it more like running instead of walking). B. The Golgi apparatus is divided and reestablished at the end of cell division through the use of motor proteins. This organelle is oriented to be near the center or nucleus of the new cells. Would addition of kinesin inhibitors interfere with the proper division and localization of the Golgi apparatus? Why or why not? It should not inhibit this process because the Golgi is specifically positioned near the centrosome/nucleus. In the coordinate system of the cell, the center is towards the minus ends of the microtubules, which would require minus-end directed motor proteins, specifically dyneins. Credit can be given for answers yes as long as the minus end directed kinesin family member is specified instead. 3. The molecular process of stimulation and contraction of a muscle cell is an example of several general processes
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This note was uploaded on 12/30/2010 for the course BIO 320 taught by Professor Staff during the Spring '08 term at University of Texas.

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exam 4 back - 1 There are large arrays of mutations...

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