Transcription Flashcards
What is the role of RNA polymerase in transcription and what are its key components?
Role: enzyme that catalyzes the formation of new RNA
Key components include:
- Multiple subunits that
form the complex
enzyme
- The sigma subunit
(sigma factor) that
positions RNA
polymerase at the site
of transcription initiation
RNA pol I vs II vs III
I : transcribes rRNA genes,
II : transcribes mRNA and miRNA, protein coding
III : transcribes tRNA
What is a promoter in transcription?
the DNA sequence that RNA polymerase binds to in order to initiate transcription.
Key features of Promoter in Transcription
-1. Two sets of sequences upstream (5’) of the transcription start site (+1)
- The -10 and -35 regions where the sigma factor binds
- A consensus sequence that many genes share
RNA Pol Bacteria vs Eukaryotes
Bac: only utilized RNA pol I
Euk: has three versions of RNA pol with respective functions I, II, & III
How is there cell diversity if all genetic info is identical?
behavior of cells is determined not just by what genes are inheriteded, but by what genes are expresses at certain times —> regulation of gene expression
Bacterial Transcription Initiation
Multistep:
- Sigma factor guides RNA Pol to bind to DNA ( -10 and -35 regions)
- Sigma protein assists RNA pol to read start signals from DNA
- DNA unwinds and becomes single stranded DNA (ssDNA)
- Transcription begins and joined free nucleotides together
BAC transcription- Elongation
RNA POl continues to unwind the DNA in the 3’ to 5’ direction while winding in the 5’ direction
Elongation continues until RNA pol reaches termination signal (typically GC rich invertes repeat followed by several A residues)
BAC transcription - termination
RNA Pol reaches termination signal
The RNA formed from transcription of the term site will form stem-loop structure
After transcription of these residues, the RNA is released from RNA pol and will dissociate from DNA template
Types of RNA
Associated with protein-coding genes
–> Messenger RNA
(mRNA)
Used for regulation of gene expression in eukaryotes
–> Micro RNA (miRNA)
–> Long non-coding RNA
(lncRNA)
Associated with RNA processing, translation, and protein transport
–> Ribosomal RNA (rRNA)
–> Transfer RNA (tRNA)
–> Small nuclear RNA
(snRNA)
–> Small cytoplasmic RNA
(scRNA)
General Transcription factors
proteins that bind to DNA to activate the transcription of genetic information into messenger RNA
TATA box
The TATA box is a DNA sequence that’s important for transcription, the process of producing RNA from DNA
Euk Transcription Initiation
- 5 general transcription factors are required AT minimum for formation of the transcription complex and initiation of transcription
- A general transcription factor binds to the promoter
- This binding recruits a second general transcription factor
- RNA polymerase II binds to this complex WITH a third factor
- Two more factors are added forming the “preinitiation complex”
Euk transcription Elongation
- RNA polymerase leaves the promoter region after synthesizing 9–10 RNA nucleotides
- Unzip DNA
- Add Nucleotides
- Move histones
- Form base pairs
Euk transcription- Termination
Less is known about this process
- A specific residue in the CTD is phosphorylated which creates a binding site for an RNA endonuclease
- The RNA endonuclease will recognize and cleave a non-coding sequence after the mRNA, freeing it
- An exonuclease will degrade the remaining RNA sequence and cause RNA polymerase II to dislodge from the DNA