Gene Transcription & RNA modification pt 2 (2) Flashcards
Describe the initiation stage of bacterial transcription
- After sliding along the DNA, the sigma factor recognizes a promoter & RNA polymerase holoenzyme forms a closed complex
- An open complex is formed & short RNA is made
- Sigma factor is release & the core enzyme is able to move along the DNA & make RNA (mRNA)
The RNA transcript (mRNA) is made during __________ stage
Elongation Stage
Template strand (antisense strand)
The DNA strand that is a template for RNA synthesis
In RNA synthesis A binds to what?
U (G-C)
mRNA is made in ________ direction with no proofreading
5’ to 3’ direction
Transcription can occur in _______ direction depending on which strand is the template strand, if the bottom strand is the template then transcription occurs from left to right but if the top strand is the template then it occurs from right to left
Opposite direction
Describe the elongation stage in bacterial transcritption
- RNA polymerase slides along the DNA creating an open complex as it moves
- The template strand is used to make a complementary copy of RNA resulting in an RNA-DNA hybrid
- RNA polymerase moves along the template strand in a 3’ to 5’ direction & RNA is synthesized in the 5’ to 3’ direction
- The complementary rule is A-U/ G-C in RNA
Bacterial transcription is terminated by either an _________ or _________
RNA - binding protein or intrinsic terminator
Termination
End of RNA (mRNA) synthesis
__________ occurs when the RNA-DNA region is forced to sperate which releases the new RNA transcript (mRNA)
Termination
In E. coli (bacteria) what are the 2 different mechanisms for termination?
- rho (p) - dependent model (termination)
2. rho (p) - independent model (termination)
rho (p) - dependent model (termination)
Require the use of p -protein to end transcription
What are the 2 sequences in rho-dependent termination?
- A sequences from the terminator called rut site which acts as a recognition site for binding rho (p) proteins to mRNA
- Stem loop region, where the stem loop forms from complementary sequences which causes RNA polymerase to puase the synthesis of mRNA which allows the p-protein to catch up to the stem loop & past it to break the hydrogen bonds between DNA & RNA
The _______ functions as a helicase & separates the RNA -DNA hybrid region (binds to rut site & moves towards the 3’ end)
p- protein
rho (p) independent (intrinsic) termination
Doesn’t need p- protein
What are the two sequences in rho-independent termination?
- U-A (U rich region) bonds at the 3’ that has weak U-A bonds
- Stem loop
Describe the rho-independent termination process?
- Stem loop stalls RNA polymerase, NusA stabilizes the pausing
- While RNA polymerase pauses the weakly bound U-rich sequences is not able to hold the RNA-DNA hybrid together, termination occurs by RNA polymerase & mRNA falling off
Describe the process of rho-dependent termination
- p protein binds to the rut site in RNA & moves towards the 3’ end
- RNA polymerase transcribes a region that forms a stem loop & the stem loop causes RNA polymerase to pause
- During the pause the p protein catches up to the open complex & seperates the RNA-DNA hybrid
Transcription in ________ is more complex because it is larger, has organelles & is multicellular
Eukaryotes
What are the 3 RNA polymerase in Eukaryotes?
- RNA polymerase 1
- RNA polymerase 2
- RNA polymerase 3
RNA polymerase 1
Transcribe all of the genes for ribosomal RNA (rRNA) (translation)
RNA polymerase 2
Transcribe all protein-encoding genes, therefore responsible for synthesis of mRNA (messenger RNA)
RNA polymerase 3
Transcribe all the genes for tRNA (transfer RNA) (translation)
Both RNA polymerase in prokaryotes & eukaryotes have the same shape which is a ________
Hand Shape