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Ques RE: proteins synthed at RER

Discussion in 'Step I' started by audramill, Jun 19, 2008.

  1. audramill

    audramill miss akay 10+ Year Member

    Jun 17, 2005
    San Francisco
    Which of the following best explains why proteins synthesized in the rough endoplasmic reticulum and secreted from eukaryotic cells have a shorter length than would be predicted by their respective mRNAs?

    A. Cleavage of 5ยข segments of nascent polypeptides being synthesized on polyribosomes in the endoplasmic reticulum

    B. Covalent binding of nascent polypeptides to specific membrane proteins during their synthesis

    C. Nonspecific protease activity during passage of these proteins through the endoplasmic reticulum membrane

    D. Shortening of the carboxy terminus because hydrophobic amino acids remain within the membrane
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  3. tfom08

    tfom08 2+ Year Member

    May 2, 2008
    Haha, I remember this because I had to look it up when I took the test. By the way, you should put a spoiler on this thread if you got this question from where I think it's from. I went with A although I was unsure because I don't know if peptides have a 5' end. But I was guessing by 5', that means amino terminus of the peptide, which is what is cleaved off as the hydrophobic signaling part of the RER synthesized peptide. I think D is a distractor because as far as I know, the carboxy terminus does not get cleaved in the RER membrane, it is the amino terminus. Perhaps a cell bio expert can help.
  4. rox

    rox ossified 7+ Year Member

    Jul 9, 2006
    Far away
    I'd choose A.
  5. Its_MurDAH

    Its_MurDAH The DaVinci Savant 10+ Year Member

    Jun 28, 2005
    Los Angeles
    yea, that just sounds right...

    I did that a lot on the real thing: pick an answer the "seemed" right. Bad way to approach such an important test. whatever.

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