Quiz Questions: Chapter 26 Flashcards
What is the function of a sigma factor?
The sigma factor binds the consensus sequence of a gene’s promoter and leads to the loading of RNAP
Do all genes recognized by an RNA holoenzyme with a specific sigma
factor recognize the same promoter sequence? Explain.
No. Not all genes have the same promoter sequence that is recognized by an individual sigma factor. There are certain instances where organisms produce different sigma factors that search for different promoter sequences to control gene expression.
Sigma factors contain specific domains that have specific functional
activities. What is the main function of domain 2, domain 4,
and domain 1?
How does the loop between domains 3 and 4 come into play?
-sigma domain 4 (makes contact and binds strongly to -35 region of promoter, a-helix, turn, a-helix structure. sits in major groove or -35); -sigma domain 2 (allows RNAP to melt and unzip DNA at -10 region) ; Sigma domain 1 (mimicks DNA, has negatively charged AA, sits inside RNAP acts as dsDNA (molecular mimicry), makes space for DNA so it can feed into RNAP). The sigma 4-3 loop comes into play by exiting out of the RNA exit channel causing initiation
How does prokaryotic transcription start?
When Sigma 4/3 loop exits RNA exit channel
What are the mechanisms by which prokaryotic transcription stops?
Understand how these two manners differ. How do these differ from
eukaryotic transcriptional termination?
(Each happen 50% of the time) 1) Rho-dependent transcription termination. (Depends on a protein and a DNA sequence) ; Rho protein (ATP dependent helicase binds to rut site on RNA (C-rich areas) being produced. Slides along mRNA molecule toward elongating RNAP and separates it from the DNA template by pulling. 2) Rho-independent prokaryotic transcription termination (Transcribed RNA forms terminator hairpin; poly u region. interactions between U’s of RNA and A’s of DNA cause RNA to fall off. )
What is the CTD tail? What are some of the functions of it? Know the
phosphorylation states and what they signify.
Cyan; alternating b-turn subunit; in RNAP II; hydrophillic and phosphorylatable; important for transcription, splicing, termination and capping of RNA (recruit proteins) and RNA processing ; when CTD is not phosphorylated transcription occurs.
What are the functions of the 5’ cap. How is it added on the RNA.
-capping occurs when ser 5 is phosphorylated; nucleotide is added in wrong direction ( connected via 5 prime end with 3’OH on end); 7 methyl guanine (methylation allows for binding to protective proteins); tethered to ctd tail ; 1) protects from exonuclease activity (exonuclease can’t work because of incorrectly placed nucleotide) 2) RNA transport into cytoplasm 3) Translation
