bis_104_pq_27_ans_ss_i_2009

bis_104_pq_27_ans_ss_i_2009 - (1) presence of microsomes:...

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BIS 104 PQ 27 ANS SS I 2009 27. a. Provide a one or two sentence description of the signal peptide hypothesis. Secretory proteins contain a signal sequence at their NH2-terminus that directs the emerging polypeptide and ribsomes 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. Polypeptides lacking this specific signal sequence do not follow this pathway for translation. 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.
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Unformatted text preview: (1) presence of microsomes: Since the mRNA has no signal sequence code, the translation system would synthesize native 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. c. Why is the procedure described in (b) above an important control for the in vitro experiments described by Lingappa? It demonstates 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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bis_104_pq_27_ans_ss_i_2009 - (1) presence of microsomes:...

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