Chapter 6: 6.3 Prokaryotic Transcription Flashcards
How many steps can transcription be broken down into? What are they?
3 steps:
1. Initiation
2. Elongation
3. Termination
What enzyme synthesizes the complementary RNA strand?
RNA polymerase
What is the site that transcription starts at designated as?
+1
Define:
Sigma factor
Subunit of RNA polymerase
* Can bind to specific DNA sequences within the promoter region of a gene
In the Inititation stage:
What does the sigma subunit bind to?
- The -35 box
- The -10 box
Where are the -35 and -10 boxes located?
In the promoter region
Why is it called the -35 box and the -10 box?
- -35 box = ~35 bases upstream from the +1 site
- -10 box = ~10 bases upstream from the +1 site
In the Inititation stage:
Where do the remaining subunits of RNA polymerase bind?
To the promoter
What is the RNA polymerase complex referred to as?
Holoenzyme
In the Inititation stage:
The RNA polymerase is able to orient itself near the – —- and to move in the direction of ————-
- +1 site
- Transcription
In the Inititation stage:
RNA polymerase:
1. Binds to ——– ——
2. It reads DNA – – –
3. It synthesizes RNA in – – –
- Template strand
- 3’ to 5’
- 5’ to 3’
True or False:
The promoter sequence is the same between genes and bacteria
False, they can vary but are still recognized by Sigma because they are relatively similar
Comparing the sequences for the -35 box and -10 box of different genes can yield what?
A consensus sequence
* The most common nucleotide at a particular position
State:
The consensus sequence of -34 region
TTGACG
State:
The consensus sequence of -10 region
TATAAT
The closer to consensus a sequence is…
The higher the affinity the Sigma has for the promoter
In the Elongation stage:
When does the elongation start?
Starts when the polymerase releases the sigma subunit
In the Elongation stage:
What happens?
(4 points)
- RNA polymerase orientates at the +1 site
- Moves along the template strand in the 3’ to 5’ direction
- Creates a complementary RNA copy by base pairing
- Uses Uracil instead of Thymine (RNA)
In the Elongation stage:
The RNA strand is created ————- to the template strand
Complementary
True or False:
The RNA strand is identical to the coding (non-template) strand
True
In the Termination stage:
What are the two types of termination signals?
- Rho-dependent termination
- Formation of a hairpin (Rho-independent)
Describe:
Rho-dependent termination
Uses a protein called Rho that binds to the new RNA strand and causes RNA Polymerase to fall off upon their encounter
How does Rho-independent termination work?
- RNA polymerase reaches a termination sequence in the DNA
- Region with C-G folds onto itself to form a hairpin loop
- The region with a run of A-U is not very stable, and in combination with the hairpin, causes the polymerase to dissociate
In the Rho-independent termination:
What is a termination sequence?
Typically a region of DNA with lots of C and G nucleotides and a poly A sequence
In the Elongation stage:
What does a formation of a hairpin loop cause?
Causes polymerase to pause
