Gene Expression 1 - Transcription Flashcards
Transcription
Makes messenger RNA copy of the information in a gene that codes for protein
Translation
Conversion of RNA message into protein at ribosome
What is the additional step of transcription in eukaryotes
- RNA processing
- RNA transport
What is a gene composed of
Specific base sequences organised in a way that allows DNA to be transcribed
What do genes contain that are NB for transcription
- Promoter
- Terminator
- Other regulatory sequences
Position of the promoters
- -10 (Pribnow box) & -35 bases before transcription start site
- (in the region preceding transcription and 10 nucleotides back)
Which enzyme catalyses transcription
RNA polymerase
What do the two alpha subunits of RNA polymerase do
The two alpha subunits assemble the enzyme & bind regulatory factors
What does the beta subunit of RNA polymerase do
Beta subunit has the polymerase activity (catalyses synthesis of RNA), which includes chain initiation & elongation
What does the omega subunit of RNA polymerase do
Restores denatured RNA polymerase to its functional form in vitro. Promotes enzyme assembly.
What does the sigma subunit of RNA polymerase holoenzyme do
1.Reduces affinity of enzyme for non specific DNA
2.Increases affinity for promoter sites
Provides specificity of enzyme by directing enzyme to appropriate transcription start sites.
When does the sigma factor dissociate from core enzyme
Once a promoter has been bound and first few nucleotides have been bound together
How is the initiation of transcription in eukaryotes more complex
- RNA polymerase does not directly recognize the core promoter sequences.
- Transcription factors mediate binding of RNA polyermase forming a transcription initiation complex.
What does RNA polymerase do during elongation
- Polymerase unwinds DNA ahead of it & rewinds DNA behind it
- This maintains an unwound region of about 17 base pairs in region of transcription
How is the template strand of DNA copied to RNA
Using complementary base pairing & insertion of appropriate ribonucleotides
Can RNA polymerase proofread??
YESSS
Can multiple RNA polymerases transcribe a single DNA molecule at the same time
YESS OFC
How does termination of transcription occur in prokaryotes
Rho dependent or Rho independent process - both lead to release of mRNA transcript
How does termination of transcription occur in eukaryotes
- LEss understood
- Occurs in conjunction with polyadenylation of the transcripts
Steps of Rho dependent termination
- Rho protein binds to single stranded RNA as it exits from polymerase enzyme complex
- Moves along the mRNA strand
- Uses a helicase activity to release the mRNA from enzyme complex
How does Rho independent termination occur
Termination due to specific sequence in terminator DNA
In what direction does addition of nucleotides occur in template strand (by RNA polymerase)
Nucleotides added in the 5’ to 3’ direction by RNA polymerase
Directionality of template strand
3’ to 5’
In what direction does the coding DNA strand run in
Runs in the 5’ to 3’ direction
What does the coding DNA strand contain that is the same in the mRNA strand
The same nucleotide sequence
