NS FL 9 biochem q13

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khadeja
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NS FL 9 biochem q13

Post by khadeja » Mon Apr 16, 2018 9:09 am

Don't endonucleases intrinsically have a nuclear localization signal?
NS_Tutor_Andrew
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Re: NS FL 9 biochem q13

Post by NS_Tutor_Andrew » Tue Apr 17, 2018 4:27 pm

Hi khadeja,

Not as far as I know? That would be very surprising b/c restriction endonucleases are derived from prokaryotes, which do not have nuclei. If you've come across a source that says otherwise, though, by all means please let me know, I'd be curious and would be happy to help make sense of what's going on here :).
Andrew D.
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khadeja
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Re: NS FL 9 biochem q13

Post by khadeja » Tue Apr 17, 2018 5:36 pm

It was a CRISPR-Cas related question in some NS FL; the experimenter transferred the Cas proteins to eukaryotes but forgot to add the localization sequence. without that the Cas endonucleases did not reach the DNA... I guess that's what the context was
NS_Tutor_Andrew
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Re: NS FL 9 biochem q13

Post by NS_Tutor_Andrew » Tue Apr 17, 2018 5:41 pm

Right! (I think that's this question, FL 9 B/B 13) -- the researchers would have had to add a nuclear localization signal precisely b/c the Cas protein wouldn't have one by default.
Andrew D.
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ds07164
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Re: NS FL 9 biochem q13

Post by ds07164 » Thu Apr 19, 2018 5:39 pm

I had a question about this question today also. I do not understand how choice D is incorrect. Choice D reads:"Humans are diploid, so the homologous chromosome compensated to allow for lipid metabolism." In the question stem, it stated that: "A researcher incorporates all the prokaryotic genes for CRISPER-Cas into a human chromosome...." In my interpretation, I thought it meant "a" as in only one, and therefore the homologue could compensate. The answer description for why it is wrong does not suggest this at all, so any help would be great.
NS_Tutor_Andrew
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Re: NS FL 9 biochem q13

Post by NS_Tutor_Andrew » Fri Apr 20, 2018 3:12 pm

Hi ds07164,

That's an excellent question. I think what's going on is that choice D is tempting if you envision Crispr-CAS as a defective version of the genes required for lipid metabolism, so the question scenario would be similar to a single-knockout model. Instead, as described by the passage, Crispr-CAS is a new set of genes that encode cRNA that then target specific genes, and this final step is possible regardless of how many chromosomes encode the gene. So the idea is that the scenario in the Q is (1) Crispr-CAS insertion --> (2) cRNA synthesis from Crispr-CAS --> (3) cRNA + Cas9 interfere with targeted lipid genes (regardless of which chromosome they're on).

Hopefully this helps clarify the question!
Andrew D.
Content Manager, Next Step Test Prep.
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