Transcription Flashcards
What are the three classes of RNA?
rRNA
mRNA
tRNA
What is transcription?
The process that is responsible for synthesizing the three major classes of RNA
The synthesis of RNA is under the direction of a ______ template.
DNA
Each type of RNA participates in the synthesis of proteins by what other process?
translation
What is the first step in gene expression?
transcription
Transcriptional control is important in gene expression for _____ genes.
many
Do transcriptional mechanisms differ between prokaryotes and eukaryotes?
yes
Prokaryotes have _______ of RNA polymerase(s) and eukaryotes have ________ of RNA polymerase(s).
a single type
3 different types
How many subunits does the prokaryotic RNA polymerase consist of?
4 subunits
What are the holoenzyme subunits and the core polymerase subunits of the prokaryote RNA polymerase?
holoenzyme- alpha 2, beta, beta prime, sigma
core polymerase- alpha 2, beta, beta prime
What is the sigma subunit and what does it do?
It is the specificity factor and it directs the core enzyme to transcribe specific genes
How does the sigma subunit direct the core enzyme to transcribe specific genes? and what does this stimulate?
It causes tight binding between RNA polymerase and the regions of DNA known as the promoters. This stimulates the initiation of transcription.
What does the tight binding of the RNA polymerase to the DNA depend on?
localized melting
What is the open-promoter complex?
the complex that is formed when the RNA polymerase is allowed to tightly bind tot the DNA template
The melting of DNA and the tight binding of RNA polymerase can only occur in the presence of what?
sigma
How does sigma promote the binding of multiple RNAPs to the template DNA?
Once it has successfully allowed the RNAP to bind to the template DNA it then disassociates from the RNAP leaving it tightly bound to the DNA and the sigma is free to participate in the binding of another RNAP at another location.
Promoter regions have specific base sequences that attract what to bond?
RNA polymerase
What is the -10 box?
A promotor sequence that is 6-7bp long and located 10 base pairs upstream of the start of transcription.
WHat was the -10 box originally called?
Pribnow box
What is the -35 box?
a second promoter sequence that is found 35 base pairs upstream form the transcription start site.
How far does RNA polymerase extend when it binds in an open-promotor complex?
at least -44 to +3
what are UP elements?
sometimes very strong promoters contain another region located between -40 and -60 to which the RNA polymerase is additionally added to. This region is known as the Up elements.
What other region is the promotor region also associated with?
Three Fis sites between -60 and -150
What is the Fis protein and what are its binding sites?
transcription activator and the 3 Fis sites
Do the Fis sites bond to RNA polymerase?
no
What do the Fis sites represent?
A group of transcription activating elements that help activate transcription without the direct binding to RNA polymerase
what are enhancers?
group of transcription activating elements that help activate transcription without the direct binding of RNA polymerase
What antibiotics are inhibitors of prokaryotic transcription and what organism do they come from?
Rifamycin B —> Streptomyces mediterranei
Rifamycin —> synthetic form of Rifamycin B
Does Rifamycin B and Rifamycin inhibit initiation in eukarotes as well?
No
Does Rifamycin B and Rifamycin inhibit elongation in prokaryotes?
No
When does the termination of transcription occur?
When the bacterial RNA polymerase reaches a terminator at the end of a gene being transcribed
What are the two types of E coli. terminators? and what is the relative abundance of each type?
- intrinsic terminators-Rho independent
- Rho-dependent terminator
Equal numbers of both
What does Rho independent termination depend on in prokaryotes?
It depends on the presence of an inverted repeat that is immediately followed by a T-rich region in the nontemplate strand.
What does the inverted repeat allow that terminates transcription?
It creates a hairpin structure
A model strong efficient terminator includes what two things and how does it trigger termination?
The hairpin structure along with the associated poly (U) tail work together to trigger termination by causing the RNA polymerase to dissociate from the template.
What is the difference between Rho-independent and Rho-dependent termination in E.coli?
Rho-dependent and Rho-independent lack any resemblance to one another and Rho-dependent termination is unable to form hairpin structures.
What is the protein factor that is required for termination in the Rho-dependent sites?
Rho protein
What is the structure of the Rho protein and what does it do?
It is a helicase that unwinds the RNA-DNA and RNA-RNA double helices
Where must the specific recognition sequence for the Rho protein to recognize and terminate transcription be located?
On the newly synthesized RNA strand
How does Rho go about terminating the transcription of RNA?
It binds to the recognition sequence on the RNA and then migrate towards the RNA polymerase that is paused at the termination site and then proceeds to unwind the RNA-DNA duplex at the transcription bubble.
All cells do not express their genes continuously and this is die to what?
The excessive energy expenditure would be required
Cells will only express certain genes when those spefic gene products are required. true or false?
true