HRR: Fundamentals of Gene Expression: Transcription I Flashcards
Transcription Template
RNA synthesis is template directed.
The template strand of DNA
is always transcribed in 3´ to 5´ direction by RNA Polymerase
Transcription Enzyme:
RNA Polymerase
Enzymatic Reaction
(RNA)n + NTP —(Mg2+)–> (RNA)n+1 + PPi
NTP= ATP, CTP, UTP, GTP
Processivity***
RNA Polymerases are processive enzymes that transcribe the template strand at rate of 50 nucleotides/sec.
Main Steps of Transcription
- Termination
- Initiation
- Elongation
do RNA have proofreading?
-why does this matter?
Polymerases do not have
3´ to 5´ exonuclease (proofreading) activity
t/f both RNA and DNA synthesis, require a primer ed.
RNA polymerase initiates RNA synthesis de novo by joining 2 ribonucleotides together to form the first 3´to 5´ phosphodiester bond.
Unlike DNA synthesis, a primer is not required.
Elongation Reaction of RNA Polymerases
Elongation Reaction of RNA Polymerases
Elongation Reaction of RNA Polymerases
note
t/f RNA has many different RNA polymerase
FALSE
RNA Polymerase: Prokaryotes have one type of RNA Polymerase
Subunit Composition Number a b b´ s 2 1 1 1 Function Binds regulatory proteins with w subunit Phosphodiester bond formation, Grasps DNA Grasps DNA template Promoter recognition and initiation
Subunit Composition Number a b b´ s 2 1 1 1 Function Binds regulatory proteins with w subunit Phosphodiester bond formation, Grasps DNA Grasps DNA template Promoter recognition and initiation
Gene Promoter: DNA sequence in the template strand of a gene that binds to RNA Polymerase.
In prokaryotes, the promoter of most genes has 2 consensus sequences as shown below.
. Gene Promoter: DNA sequence in the template strand of a gene that binds to RNA Polymerase.
In prokaryotes, the promoter of most genes has 2 consensus sequences as shown below.
A consensus sequence is derived by
A consensus sequence is derived by determining the base found most frequently
at each position in the promoter region of the gene.
- Initiation Step of Transcription
RNA Polymerase holoenzyme binds to DNA nonspecifically
- Initiation Step of Transcription
RNA Polymerase holoenzyme binds to DNA nonspecifically
RNA Polymerase searches for ____ site
by “sliding” along double-stranded DNA.
-stops when :
RNA Polymerase searches for promoter site
by “sliding” along double-stranded DNA.
The s subunit binds SPECIFICALLY to the promoter
sequences to form the closed promoter complex
closed promotor complex
bold
RNA Polymerase unwinds 17 base pairs of DNA around
the initiation site to form the open promoter complex.
RNA Polymerase unwinds 17 base pairs of DNA around
the initiation site to form the open promoter complex.
open promotor complex
the sigma subunit is released
The first phosphodiester bond
is formed during initiation.
The first phosphodiester bond
is formed during initiation.
unwound DNA
location
_____ subunit is released upon
completion of the initiation step.
sigma subunit is released upon
completion of the initiation step.
Elongation by core RNA Polymerase
Elongation by core RNA Polymerase
. Initiation Step of Transcription
. Initiation Step of Transcription
RNA Polymerase Holoenzyme
• There is only one RNA Polymerase in prokaryotes. However, the RNA Polymerase
holoenzyme can initiate transcription of specific genes via the s subunit.
• Multiple s subunits exist, each one binds preferentially to a consensus sequence in the
promoter of a certain gene. Thus, specificity of the RNA Polymerase for a given promoter
is dependent on the s subunit that is part of the holoenzyme.
TTGACA TATAAT -35 -10 +1 s70 TNNCNCNCTTGAA CCCATNT \+1 s32 CTGGGNA TTGCA \+1 s54 Standard Promoter Promoter for heat shock genes Promoter for nitrogenstarvation genes Once the s subunit binds specifically to the consensus sequence, helicase activity in the RNA Polymerase holoenzyme unwinds 17 bp of DNA to form an open promoter complex.
Open Promoter Complex
Once the s subunit binds specifically to the consensus sequence, helicase activity in the
RNA Polymerase holoenzyme unwinds 17 bp of DNA to form an open promoter complex.