Lecture 29 - Gene Expression: Transcription Flashcards
Gene sequences have specific regions (punctuated). Mention all 5 regions and their role in the process of transcription.
o Regulatory sequence (control differential gene expression)
o Promoter (start of transcription)
o Coding Sequence (template for elongation of transcription)
o Terminator (stop of transcription)
o Untranslated sequences (start and stop of translation)
The transcription machinery is the ___________.
RNA polymerase
Three process of the transcription process: ________.
- Initiation
- Elongation
- Termination
How does RNA polymerases determine which gene sequence to transcript? Compare between how this process occurs in prokaryotes and eukaryotes.
In both cases, RNA polymerases look for consensus sequences in the promoter region. Consensus means similar base sequences in the promoter region. The only difference between prokaryotes and eukaryotes are the base sequence itself and its location.
Prokaryote RNA polymerase is composed of ___ subunits and a detachable _______. Together they form a compound called the ________.
5 subunits (extra: 2α, 1β, 1β’, 1ω)
σ factor
Holoenzyme
Explain the process of the prokaryotic transcription initiation. Answer in the context of promoter binding and remember to use key words.
The σ factor (as a part of the holoenzyme) binds to the consensus sequence in the promoter region, forming the “closed complex”.
RNA polymerase then switches to “open complex” and opening up the DNA strand to form the “transcription bubble”.
σ factor then dissociates, allowing the RNA polymerase to start RNA elongation.
Prokaryotic RNA polymerases subunit have different roles. Mention 2 of them and their function.
σ factor: recognize the promoter region α: determine the DNA to be transcribed β: catalyze polymerization β: binds and open DNA template ω: unknown
Compare and contrast between eukaryotic and prokaryotic transcription initiation process.
Similarities:
- RNA poly. unwinds DNA to form transcription bubble
- σ and general transcription factors must dissociate for RNA ploy. to move along DNA
Differences:
- Prokaryote binding involves the binding of the whole holoenzyme, which consists of RNA poly. and σ factor. Eukaryote binding involve binding of Basal factors, which then recruit RNA poly. sequentially.
-Specific transcription factors (activators and repressors, etc) is present in eukaryotic initiation to control rate of transcription. Not present in prokaryote.
Differ between the DNA coding strand and the template strand.
DNA coding strand (non-template): strand that is similar to the mRNA produced except for U instead of T.
DNA template strand: strand used to generate the complementary mRNA sequence
What are the roles of activators and repressors in eukaryotic transcription initiation?
Activators binds the pre-initiation complex to the enhancer gene sequence upstream, which leads to an increase in the rate of transcription. However, when repressor binds the complex to a silencer gene sequence, it blocks the binding of the activator protein, hence slowing down the rate.
In transcription, RNA always grows from the _____ end.
5’ –> 3’
How is a eukaryotic transcription termination different from its prokaryotic counterpart?
A eukaryotic termination process differs for each type of RNA polymerase. For RNA polymerase II, as the polymerase passes the termination sequence, the RNA is then cleaved by the cleavage complex, and the mRNA and RNA poly. dissociate from the strand.
As the RNA poly. encounters the chain termination sequence, the RNA forms a hairpin structure (as some of its sections are self-complementary).RNA and RNA polymerase dissociate from DNA.
What is added to the template strand to produce the mRNA strand?
NTP (RNA nucleoside Triphosphate)
Note: added to the 3’ end of the RNA strand.
Name an example of a DNA gene sequence that does not contribute to the transcribe RNA.
promoter gene sequence, terminator sequence, enhancer & silencer sequence, etc
