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BIO320_HW3.2011.answers - start and stop-transfer signals...

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Name _____________________________________ BIO320 HW-3 Membrane Traffic Problem 1) Examine the multipass transmembrane protein shown in Figure 1. What would you predict would be the effect of converting the first hydrophobic transmembrane segment to a hydrophilic segment? Sketch the arrangement of the modified protein in the ER membrane. Assume that the portions labeled 1-6 are >100 aa each. In the unmodified protein, the first transmembrane segment served as a start-transfer signal, oriented so that it caused the N-terminal segment to pass across the ER membrane. The next transmembrane segment is also a start-transfer signal, but oriented so that it passes C-terminal protein across the membrane until it reaches the next transmembrane segment, which serves as a stop-transfer signal. Two more pairs of similarly orientated
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Unformatted text preview: start- and stop-transfer signals give rise to the final arrangement. Eliminating the first start-transfer signal would not affect the function of the second transfer signal, which would initiate transfer of C-terminal segments just as it did in the unmodified, original protein. This conclusion is also reached by the fact that there are more than 100 amino acids at the N-terminus of the modified protein before the first transmembrane segment. The glycosylation sites near the N-terminus of the protein can only be modified if they are in the ER lumen. Thus, the mutant protein will not be glycosylated. Page 1 of 1...
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