Transcription Flashcards
What is transcription?
Synthesis of RNA from DNA template
What is transcription catalyzed by?
RNA polymerase
How many subunits if RNA polymerase made of?
multiple (alpha, beta, beta prime, omega, sigma70)
What does transcription require?
A template:
- RNA strand synthesized is complimentary to the “template strand” of DNA
- The other DNA strand has the same sequence of the RNA strand w/ exception of the thymine (which is replaced with Uracil)
- Ribonucleoside Triphosphate (ATP, cTP, UTP, and GTP)
What direction does transcription occur in?
5’ to 3’ direction
What is base +1?
First base that gets initiated/incorporated, initiates mRNA strand
What is upstream of transcriptional start site?
The promotor
What is the the promotor?
Where RNA polymerase binds
What recognizes the promotor?
alpha subunit to facilitate initiation
What components of the promotor?
-10 sequence, “pribnow box”
-35 sequence
(both on coding strand)
TATAAT
-10 Sequence, “pribnow box”
TTGAcA
-35 sequence
What happens after RNA polymerase binds to promotor?
- 17 bp segment of DNA unwinds
- Results in an open “promotor complex”
- RNA synthesis proceeds in 5’ to 3’ direction
RNA synthesis can start without a ________.
Primer
In bacteria, most newly synthesized RNA have ___ or ____.
pppG, pppA (1st nucleotide still with phosphate attached)
Name two methods that can terminate RNA synthesis
- Formation of an RNA hairpin from the transcribed gc-rich stop signal. On the mRNA transcript, a sequence of 4 or more uracils follow the hairpin.
- Rho (p) protein activity: Uses ATP to “catch up” to RNA polymerase complex and then dislodge it.
What is the Lac Operon?
Model system to examine transcriptional regulation (when transcription is turned on and of)
What are the three components of the Lac Operon?
x, y, z, i-gene
What is X in the lac operon?
B-Galactosidase
What is the purpose of B-Galactosidase?
Breaks the glycosidic linkage in lactose between galactose and glucose (disaccharide into two monosaccharides)
What is Y in the lac operon?
Permease
What is the purpose of Permease?
allows lactose into bacterial wall (B/c lactose is very polar, making it difficult to pass through on its own)
What is Z in the lac operon?
Transacetylase
What is the purpose of Transacetylase ?
- Assists with the metabolism of sugars
2. Transfers acetyl groups
What is the i-gene in the lac operon?
Responsible for synthesis of repressor protein
What is the repressor protein responsible?
tells us when transcription is turned on/off
How does the repressor protein turn transcription off?
When it binds downstream to the 3’ end of the promotor (prevent RNA polymerase from binding to the promotor)
What turns transcription back on?
1, 6-Allolactose (Variation of Lactose, which is usually a 1,4 linkage)
How does 1, 6-Allolactose turn transcription on?
By binding to repressor protein to inhibit repressor protein from binding to promotor
What is another way transcriptional regulation can occur in the lac operon?
Via glucose regulation
______ prefer to utilize _________ before breaking down _________.
e. coli, glucose, lactose
What binds to cyclic AMP to for cAMP-cap complexes?
catabolite activator protein
What is the function of cAMP-cap complexes?
To help recruit RNA polymerase to the promotor?
When glucose is _______, cAMP levels are low.
abundant
When glucose levels are abundant, cAMP levels are ___.
low
What happens when cAMP levels are low and there are few cAMP-cap complexes?
Lac operon has low levels of transcription
When _____ is scarce, cAMP levels are high.
glucose
When glucose is scarce, cAMP levels are ____.
high
What happens when cAMP levels are high and there are many cAMP-cap complexes?
Lac operon has high levels of transcription
