This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Transcription in Eukaryotes : Activators and Repressors”.
1. Promoter proximal elements is positioned ________________
a) Outside the core promoter
b) Downstream to start site
c) Within the enhancer
d) Just before the start site
Explanation: The promoter proximal elements are a part of core promoter. They occur downstream to the promoter start site. Enhancers on the other hand are much farther and outside the core promoter.
2. TATA box in eukaryotes would be present in _________________
a) Housekeeping genes
b) Developmentally regulated genes
c) Cytoskeletal genes like that for actin
d) Highly specialized genes.
Explanation: The highly specialized genes are likely to have a TATA box within their promoter. On the other hand the rest genes have TATAless promoters.
3. TFIIB can bind to a promoter element in the core promoter of eukaryotes. This element is __________
Explanation: BRE stands for TFIIB recognition site. It is here that the element can bind. On the other hand TFIID binds at the TATA box.
4. Which of these is not a promoter element?
a) TATA box
c) CCAAT box
Explanation: The CCAAT box is a part of the upstream activating elements which is upstream to the promoter. It is recognized by CTF or CCAAT recognizing Transcription Factor. The remaing options are part of core promoter.
5. Which would be an appropriate method to detect the core promoter regions in a eukaryotic gene?
c) Linker scanning
d) S1 endonuclease
Explanation: In linker scanning method a small segment of the DNA is removed from promoter region and replaced with a random segment to see its effect on the transcription rate. Thus, as absence of promoter would lead to less transcription this method can be used to detect promoter elements.
6. Repressors are active only when they are at the proximity of the RNA polymerase as they directly associate with the pre-initiation complex. State whether this is true or false.
Explanation: Although often repressors directly associate with RNA polymerases it can also act by the means of a mediator as enhancers do. So, they could be close or far from the transcription start site.
7. Which of these class III promoter type resemble class II?
a) Type I
b) Type II
c) Type III
d) Type IV
Explanation: The Type III of class III promoter is a non-classical class III promoter which resembles type II. It has a TATA box, PSE and an upstream DSE. There is no 4th type of class III promoter and type I and II don’t resemble class II.
8. If you make a chimeric factor with the DNA binding element of an activator and a functional domain of a repressor, how will this factor behave?
a) It will act like a repressor
b) It will act like an activator
c) It will not be able to bind the DNA so although it binds via the repressing domain it won’t cause repression
d) Repression domain will be non-functional
Explanation: As activators and repressors have a domain organization it is seen that if a DNA binding domain is provided it doesn’t affect the activity. As long as the factor binds to the correct cis element it will still be a functional repressor.
9. Which of this element is not orientation independent?
c) Upstream activating element
d) Promoter proximal elements
Explanation: While upstream activating element is orientation independent, enhancers and silencers are position as well as orientation independent. On the other hand promoter proximal elements are orientation dependent.
10. Which of these promoter elements has a high propensity of developing mutation given the eukaryotic gene was inserted in prokaryotes?
a) CCAAT box
b) CPG islands
c) TATA box
Explanation: This is because prokaryotic methylases would methylate the C bases of the CPG region. Then it there is a de-amination of C base, it will resemble a T base which is not as easily distinguishable as U by UDG. So, this region is very mutagenic.
Sanfoundry Global Education & Learning Series – Cytogenetics.
To practice all areas of Cytogenetics, here is complete set of 1000+ Multiple Choice Questions and Answers.