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320Fall2010Homework6 - Cell Biology(BIO 320 Fall 2010 Dr...

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Cell Biology (BIO 320), Fall 2010, Dr. Bushart Homework 6, for quizzes the week of 10/18 1. Acyl transferase catalyzes the addition of glycerol 3-phosphate to fatty acids in the membrane (the “growth step”). Imagine a cell lacking scramblase activity. Why would the expression of an additional acyl transferase having an ER signal peptide still not allow for even membrane growth in the absence of the scramblase? 2. What ensures that Sar1 and Rab proteins will associate with specific membranes? (In another way to think about it, why won’t Sar1 or Rabs randomly associate with any membrane after activation?) This has to do with the exposure of the amphipathic or hydrophobic region of these monomeric GTPases on conversion to the GTP-bound form. Having these regions exposed to the aqueous environment of the cytosol is not favorable so they will want to associate with membranes as soon as possible. By localizing specific GEFs to specific membranes we can fairly simply ensure that an activated Sar1 or Rab protein will associate with the same membrane the GEF is in.
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