Bio Qbank 1 Question 28

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z3lan
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Bio Qbank 1 Question 28

Post by z3lan » Thu Apr 11, 2019 5:06 pm

Why wouldn't the sense RNA base pair with the anti-sense DNA and prevent its transcription?
NS_Tutor_Mathias
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Re: Bio Qbank 1 Question 28

Post by NS_Tutor_Mathias » Sun Apr 14, 2019 1:23 am

D is kind of the best answer, because cells are relatively suicide-happy in a pinch. Thank you for bringing up all the questions that need a little bit of love in the future ;)

As far as your question goes, DNA/RNA pairing is not that stable that it would out-compete DNA hybridization handily, and the primary transcript is rapidly spliced (making it not perfectly complementary anymore!) and then exported from the nucleus through nuclear pores on proteins called exportins (this is very cell bio stuff, which shows up on some FLs, but is probably less likely to show up on more modern MCAT questions). This whole thing is called the Ran-GAP/GEF system, in case you run into in a passage. Either way, it would cease to be present to even partially hybridize with DNA and thereby inhibit transcription. I'm fairly certain RNA doesn't even stay hybridized after RNA Pol II leaves, as it is effectively pushed out and away while the complementary DNA strand re-hybridizes.

So there you have a variety of reasons why excess sense-RNA is not likely to inhibit transcription. So at least that should make sense. Transcription of the gene should be unaffected, provided no cascade of reactions due to the function of said excess-protein occurs. I am fairly certain that, in reality, this would normally lead to at least cell-cycle arrest followed by eventual apoptosis.


The question should at least specify that this excess primary transcript is produced by RNA Polymerase II, as other options would be that excess tRNA or ribosomes are being made and some of those have more direct feedback loops for transcriptional regulation. "Antisense gene" is also a strange way to phrase things - the MCAT does, as a rule, not make up any terms even in incorrect answers. Antisense strand maybe? The antisense strand is also called the template strand, or in an intuitive sense that is the useful part of the gene. To call that an 'anti-sense gene' is audacious in a way.
z3lan
Posts: 126
Joined: Thu Feb 28, 2019 5:24 pm

Re: Bio Qbank 1 Question 28

Post by z3lan » Mon Apr 15, 2019 12:45 am

I had thought that antisense gene sounded a bit odd! In any case, the main takeaway from this question seems to be that even though sense RNA could base pair to the template strand, it would be unlikely to impair transcription because a) it would be spliced and b) it would dissociate from the sense strand because it would be outcompeted by DNA polymerase/excess nucleotides floating around. And if there are big abnormalities in the nucleus you're likely to get apoptosis. Thanks for the clarification. Hopefully I'm not abusing the forum too much. My professors tend to get on my case that I ask too many questions!
NS_Tutor_Mathias
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Re: Bio Qbank 1 Question 28

Post by NS_Tutor_Mathias » Mon Apr 15, 2019 3:43 am

Best I can tell DNA is hybridized with itself again as RNA Pol II moves further downstream. It's a structural arrangement thing - don't worry about it, the MCAT will not ask you to make that kind of judgement call, or to put it simply: There is no such interaction that you will be tested on.

As far as using the forums goes: Participation is great and getting student feedback on questions is very helpful. We work to continuously maintain and improve all our materials. Professors tend to have a large student body and teaching undergrads makes up only a small portion of their responsibilities but a large fraction of their headaches. We here at NextStep are just here to help you do well on the MCAT though, so if asking questions helps you, go for it - and you should never feel guilty for doing so!
NS_Tutor_Katelyn
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Re: Bio Qbank 1 Question 28

Post by NS_Tutor_Katelyn » Mon Apr 15, 2019 1:54 pm

z3lan wrote:
Mon Apr 15, 2019 12:45 am
I had thought that antisense gene sounded a bit odd! In any case, the main takeaway from this question seems to be that even though sense RNA could base pair to the template strand, it would be unlikely to impair transcription because a) it would be spliced and b) it would dissociate from the sense strand because it would be outcompeted by DNA polymerase/excess nucleotides floating around. And if there are big abnormalities in the nucleus you're likely to get apoptosis. Thanks for the clarification. Hopefully I'm not abusing the forum too much. My professors tend to get on my case that I ask too many questions!
Just to follow up on this, no, you're not abusing the forum! Please feel free to continue posting and utilizing it.
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