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bis_104_pq_23_ans_fall_08 - size alpha globin protein not...

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BIS 104 PQ 23 23. a) Give a one or two sentence description of the signal peptide hypothesis. Secretory proteins contain a signal sequence at their N-terminus that directs the emerging polypeptide and ribosome to the ER membrane. The polypeptide is then moved into the cisternal space of the ER through a protein-lined aqueous channel in the ER membrane. b) Describe the results you would expect to observe if you added mRNA coding for alpha globin to a cell-free translation system in (1) the presence, or (2) in the absence of added microsomes. (1) presence of microsomes: Since the mRNA has no signal sequence code, the translation system would synthesize native
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Unformatted text preview: size alpha globin protein, not associated with the microsomes. Therefore, a single protein band on SDS gel, that would be digestible by protease. (2) absence of microsomes: Same as above; only native alpha globin protein is made. (In describing your results remember that the protein products from the cell-free system are analyzed by SDS-PAGE). c) Why is the procedure described in (b) above an important control for the in vitro experiments described by Lingappa? It demonstrates that native alpha globin protein, in the absence of a signal sequence, does not associate non-specifically with an in vitro preparation of microsomes....
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