Nucleosome inhibits?

Practice Question Solving
1

What do nucleosomes inhibit?

  1. RNA polymerase
  2. tRNA
  3. Assembly of transcription factors

A. 1 and 2 only

B. 1 and 3 only

C. 2 and 3 only

D. 1, 2 and 3

E. 3 only

The correct answer is E. May I know the reason ?

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Nucleosomes help regulate transcription because they make certain parts of the DNA is accessible. This means that only certain genes are allowed to be expressed. If there were no nucleosomes then all genes and ALL parts of the DNA would be expressed. Nucleosomes can inhibit the stage of transcription initiation by occupying key regulatory DNA sequences near the promoter and transcriptional start sites of genes to regulate transcription :)) Hope this helps!!

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Wouldnt the nucleosomes also inhibit RNA polymerase from binding to the promoter site and beginning transcription as well? If for example the nucleosomes where in really tightly packed form, no transcription can take place. Please let me know if Im mistaken:D

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Yes, good point Darius! I read that too however I also did read that nucleosomes inhibit the initiation of transcription but allow chain elongation with the displacement of histones and since RNA polymerase is used for elongation it doesn’t affect it directly I believe. I get your point though because RNA polymerase DOES bind to the promoter sequence but maybe since the question talks about the nucleosome INHIBITING something, I believe it doesn’t inhibit RNA polymerase, but just the process of transcription by sort of “interrupting” it? This isn’t a great explanation but I hope this makes sense?:))

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Yes I get it now, thanks Raya!

Basically the RNA polymerase can do whatever it wants since nucleosomes do not prevent it from continuing with the transcription it has already begun, but instead what is inhibited is the production of certain proteins (like transcription factors) which cannot begin their production when nucleosomes condense and block promoter sites.

The wording of this question makes it a lot more difficult than it should be I guess:D

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Exactly!! IMAT is infamous for making questions extremely confusing, gotta watch out for them :))

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