DNA-dependent synthesis of RNA Eukaryotic Transcription Flashcards
Central Dogma
- nucleic acids store information
DNA transcription = RNA
RNA translation = proteins
T or F: RNA can hybridize with DNA genome
TRUE; RNA can hybridize with DNA genome
Differentiate transcription vs replication
Transcription:
- only specific genes at one time = only portions are transcribed
- one strand
Replication:
- both strands of DNA are replicated
- whole strand is replicated
Which strand is used by RNA polymerase to synthesize RNA from DNA ‘bubble’ ?
Antisense (non-coding) strand
- complementary to coding strand
- produces RNA product that is similar to coding strand
Different cell types have __ DNA genomes but vary __ of genes from cell to cell
Different cell types have SIMILAR DNA genomes but vary EXPRESSION of genes from cell to cell
Why is RNA Polymerase II important in synthesis processes ?
- synthesizes all proteins in higher cells
- largest polymerase (12 subunits)
- serines in sequence are susceptible to covalent modification
- active site holds DNA
Which polypeptide chains make up the active site in RNA Polymerase II ? What is the substrate for the active site ?
B’ homolog and B homolog
- dsDNA (substrate) is separated in a transcription bubble
Phases of transcription (4):
- Assembly
- Initiation
- Elongation
- Termination
Sequence selectivity is needed for __
ELONGATION not initiation
What are eukaryotic promoters ? What is their purpose ?
- integrated sequences in DNA
- accessory proteins identify promoters and recruit RNAP to start transcription
Enhancers can be located __ and __
Enhancers can be located upstream (-ve) and downstream (+ve) the transcription site
- they are not precise
What are enhancers in transcription ?
DNA sequences downstream or upstream the transcription site
What is TATA binding protein ?
- part of TFIID
- first protein to bind promoter in initiation (along with TBP-Associated factors)
- via H bonding and VWF
- binding distorts DNA/ unwinds duplex
TBP- TATA Binding Protein
Describe the Pre-initiation Complex
- TBP component of TFIID binds TATA box of promoter
- TFIIA and TFIIB bind
- TFIIF binds to RNAP II = subsequently escorts it to promoter complex
- TFIIE and TFIIH (helicase) are recruited = opens complex
- RNAPII starts transcription
When does the Pre-initiation complex change from a closed to open system ?
When TFIIE and TFIIH (helicase) are recruited = completes PIC complex and unwinds DNA = transcription bubble
Does the TBP/TFIIB/TFIIA subunit follow RNAP II or remain at the promoter ?
TBP/ TFIIB/ TFIIA remain at promoter for next RNAP II to bind
Are inactive and active genes repaired with equal efficiency ?
No; active genes are already being transcribed and have recruited TFIIH for nucleotide-excision repair complex
- inactive genes are still wound DNA (less efficient to repair)
What is a mediator in transcription ?
- interacts with assembled PIC to initiate transcription
- regulates expression of both protein-coding and most non-coding RNA genes
- gene expression in response to developmental/ environmental cues
Do eukaryotes have precise transcription termination sites ?
No, termination sites are imprecise
- after transcription, eukaryotic transcripts have variable 3’ ends
- undergo (post-transcription) endonucleolytic cleavage = more consistent 3’ ends
3 molecules that selectively inhibit RNA polymerase
- Rifampin
- Actinomycin D
- α-amanitin
How does Rifampin cause selective inhibition of RNAP II?
- prevents promoter clearance
- antibiotic; inhibits bacterial β subunit of RNAP
How does Actinomycin D cause selective inhibition of RNAP II?
- inhibits bacterial AND eukaryotic RNAP
- intercalates into dsDNA; prevents movement of RNA and RNAP along template
How does α-amanitin cause selective inhibition of RNAP II?
- inhibits eukaryotic RNAP
- blocks RNAP II, and blocks RNAP III at higher concentrations
TFIID binds which promoter element ?
TATA box
