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Transcription
The process by which DNA is used as a template to make RNA, which can then be used to make proteins
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What is the enzyme that catalyzes transcription?
RNA polymerase
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What are the subunits for RNA polymerase?
Alpha, omega, beta, beta', and sigma
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What do the subunits do?
They are receiving proteins
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What is the actual composition of the enzyme?
Alpha2omegabetabeta'sigma
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What is the core enzyme?
Alpha2omegabetabeta'
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What is the holoenzyme?
Alphaomegabetabeta'sigma
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What is the purpose of the sigma subunit?
Provides specificity to the enzyme; the core enzyme will make RNA, but only randomly
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What is the DNA strand called that is used to make RNA?
The template strand
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What is the direction called that the enzyme travels?
Downstream
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What is the promoter?
The region where transcription starts. The first base to be transcribed is the TSS.
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What is the pribnow box?
10 base pairs upstream of the TSS; part of the promoter.
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What is the -35 element?
Found -35 BPs upstream of the TSS; together with the pribnow box and TSS is called the promoter.
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What is the UP element?
Found between -40 and -60, it is included with the core promoter to make the extended promoter.
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When does the sigma subunit detach?
After the enzyme binds to the core promoter and transcribes about 10 BPs.
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What is the transcription bubble?
About 17 BPs long, it unwinds the the DNA and splits it apart to be read; produces - supercoiling downstream and + upstream.
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What is the rate of transcription?
Non-constant.
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What are termination sites?
They tell the enzyme to stop; consist of 2 inverted repeats. Also called intrinsic terminination.
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How does termination proceed?
Creates a hairpin coil which stops transcription by causing 2 weak H-bonds with U and T.
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What is rho-dependent termination?
The rho protein chases down the enzyme and forms the hairpin, which slows transcription and causes it to dissociate.
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What are the 4 ways transcription is regulated?
Alternative sigma factos, enhancers, operons, and transcription attenuation
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How do alternative sigma factors regulate transcription?
Different sigma factors place the RNA polymerase differently on the DNA, causing another set of proteins to be produced.
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What are enhancers?
DNA sequences that are upstream from the extended promoter that can be bound to proteins called transcription factors.
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How do enhancers regulate transcription?
Transcription factors bind to the enhancers which cause a change in transcription.
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What do promoters bind to?
RNA polymerase
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What do enhancers bind to?
Transcription factors
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What is a response element?
Causes a change in metabolic condition, such as causing the production of a heat-shock protein.
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What is a silencer?
Turns genes off.
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What is an operon?
An organized region where all the genes for a metabolic pathway are turned on; ex: lac operon in E. coli
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What three genes comprise the lac operon?
Beta-galactosidase, lactose permease, transacetylase
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What is a repressor protein?
Binds to the operon so that the enzyme cannot bind.
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What is an inducer?
Turns an operon on.
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In E. coli, what acts as an inducer?
Allolactose causes a conformational change by binding to the repressor, which makes it fall off and allows RNA polymerase to attach and transcribe.
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