GRE Subject Test: Biology : Understanding Transcription
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Example Questions
Example Question #1 : Understanding Transcription
Which of the following are commonly found in a eukaryotic RNA-polymerase-II-dependent promoter?
I. Shine-Delgarno sequence
II. TATA element
III. Ribosomal binding site
I, II, and III
II only
I and III
I only
II only
Of the three choices, the only element commonly found in a eukaryotic promoter is a TATA element. This is the site where TBP (TATA binding protein) binds and begins to recruit other transcriptional machinery.
The Shine-Delgarno sequence is commonly found on prokaryotic mRNA and serves as a ribosomal binding site. Because promoters are regions of DNA, both option I and II do not really apply.
Example Question #1 : Understanding Transcription
In eukaryotes, promoter sequences are regulatory elements found upstream of the transcription start site. Promoter sequences are required for transcription factors and RNA polymerase to recognize and bind to the DNA strand, thus promoting transcription of the genes on that strand and production of mRNA.
mRNA is ultimately translated into proteins, i.e. gene products. Consider a mutation in the promoter sequence that increases the affinity of RNA polymerase for the DNA strand. Compared to a sequence where the promoter sequence is wild-type, which of the outcomes below is most likely for this mutated promoter region?
Loss of the gene product
20% reduction in gene product
The process described above has nothing to do with quantity of gene product
Overexpression of the gene product
Altered tertiary structure of the gene product
Overexpression of the gene product
The binding of RNA polymerase and transcription factors is tightly modulated by promoter elements. If affinity was increased compared to a wild-type sequence, we would expect that RNA polymerase would bind more easily to the sequence and produce more mRNA. Nothing about the nature of this mRNA is altered (since the coding sequences are unchanged); there is simply more of it, which would mean overexpression of the protein for which it codes.
Example Question #2 : Understanding Transcription
What is the region of DNA where transcription factors and RNA polymerase bind, and that is also responsible for regulating transcription?
Enhancer
Promoter
Exon
Intron
Insulator
Promoter
The correct answer is promoter. The promoter is directly upstream of the start of transcription for a given gene. It is the site of transcription factor and RNA polymerase binding, and interacts with distant enhancers to regulate transcription.
Example Question #3 : Understanding Transcription
Eukaryotic transcription requires many proteins interacting in a coordinated fashion to drive the process of converting DNA to RNA. RNA polymerase, the enzyme that initiates transcription, needs a number of factors and components to being transcribing a gene. Which of the following answers is not one of these factors?
Each of these are required for initiation of transcription
Activators
Core promoter sequence
DNA polymerase
Transcription factors
DNA polymerase
DNA polymerase is a crucial factor required for replication of DNA, but is not a component utilized in the process of transcription. The core promoter sequence, activators, and transcription factors are all needed in order for RNA polymerase to begin the process.
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