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40 Cards in this Set
- Front
- Back
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What is Transcription
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Synthesis of RNA from a DNA template
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Which direction is new mRNA made?
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5' to 3'
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Which direction is the template strand DNA read?
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3' to 5'
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What is another term for the template strand of DNA?
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Anti-sense strand
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Does RNA Polymerase need a primer?
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No
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Does RNA Polymerase have 3' to 5' exonuclease activity like DNA polymerase?
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No
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How many types of RNA can E. Coli RNA Polymerase generate?
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All 3, mRNA, tRNA, rRNA
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Which subunit of E. Coli RNA polymerase binds it to the promoter on DNA?
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sigma-70
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How many types of RNA can eukaryotic RNA polymerase generate?
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1 each
∴ there are 3 RNA polymerases |
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Which type of eukaryotic RNA polymerase generates which RNA?
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Type 1 for most rRNA
Type 2 for mRNA Type 3 fo small RNAs, such as tRNA and 5S rRNA |
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How do different types of RNA polymerase know which type of RNA to make?
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By recognizing and binding to their specific type of promoters
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What does α-Amanitin do?
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Binds very tightly to RNA polymerase II and III at high conc.
Inhibits RNA synthesis Doesn't do anything to RNA polymerase I |
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How do RNA polymerase know its target DNA strand and location to start?
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Recognition site
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Why is recognition sites said to be cis acting?
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They are close-by and on the same strand as the gene they regulate
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What are said to be trans acting?
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Proteins that bind to recognition to regulate expression
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Promoter region in prokaryotes?
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the TATAAT, aka TATA or Pribnow box
*consensus sequence (ie average) |
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What is the significance of a AT rich sequence near the start site of transcription?
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Aids in strand separation
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What controls the frequency of transcription?
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1. Promoter-proximal elements (close to promoter)
2. Enhancer (May be far away) |
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How do promoter-proximal elements and enhancers influence transcription frequency?
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By interacting with proteins that stabilize RNA polymerase binding to promoter
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Eukaryotic promoter Region (3)
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- At -25, also known as TATA box, or Hogness Box
- Other consensus sequences involved in RNA pol binding, further upstream - Enhancers, beyond promoter region, increases effectiveness of promoters |
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Trascription Factors
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- Eukaryotes
- Protein - Bind TATA box - Facilitate binding of RNA pol II (for mRNA) |
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TF-IIH roles
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ATP-dependent DNA helicase in both transcription and DNA repair
- mutation leads to xeroderma pigmentosum |
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How can rate of transcription be increased?
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Bind regulatory DNA binding proteins to gene regulatory sequences (gene-specific TFs or trans-activators)
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Steps of Bacterial Transcription
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1. RNA pol search for promoter sites on DNA
2. Binding with sigma factor to promoter →DNA strands unwind and separate 3. RNA pol finds correct RNA nucleotide and form phosphodiester bond (Sigma factor released after initial transcription) 4. Terminates when encounters transcription termination signal |
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Transcription Termination Signal
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Hairpin loop in the transcript, preceding some U residues
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What is Rho factor?
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- Termination protein
- ATP-dependent helicase - Binds nascent RNA and pulls it away from RNA pol & DNA |
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What is a cistron?
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A region of DNA that encodes a single polypeptide chain
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What is a polycistronic transcript?
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mRNA generated from an operon, with information to produce multiple different proteins
*in bacteria |
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When does a polycistronic transcript get translated?
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As it is being transcribed
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Does the polycistronic transcript contain introns?
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No, so it is not modified or trimmed
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How is rRNA produced in prokaryotes?
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- as one single long transcript
- cleaved into 16S, 23S, and 5S rRNA |
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Example of Prokaryotic gene expression control
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Induction of lac operon
- presence of lactose induce the galactosidase in lac operon to be expressed |
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Structure of the lac operon gene
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[Pi]-[inducer]-[P_lac]-[Operator]-[lac enzymes]
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Difference between Eukaryotic and prokaryotic transcription (3)
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- pre-mRNA
- eukaryotic mRNA only contains 1 polypeptide - trascription in nucleus, than translation in cytoplasm |
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Post-transcriptional modifications (3)
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- 5' cap
- 3' poly-A-tail - splicing |
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Function of 5' cap
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- slow degradation
- tag as ready for translation |
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What is spliceosomes?
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Complex of proteins and RNA molecules that perform splicing
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How does mature mRNA leave the nucleus?
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pores in the nuclear envelope
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What is Rifampicin?
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Antibiotic
Inhibits transcription by blocking enzyme active site |
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What is Actinomycin D?
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Antibiotic
Inhibits by binding to double strand DNA and preventing it from opening, so RNA pol cannot read it |
