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14 Cards in this Set
- Front
- Back
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Trp operon: What does it stand for?
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tryptophan operon
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When is maximal expresssion of the Trp operon?
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When tryptophan is absent from growth media.
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Tryptophan functions as a...
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corepressor.
It binds to the TrpR repressor protein. This allosteric alteration allows the repressor to bind with the promoter. |
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Would a trpR- mutant completely express the trp genes if tryptophan was present?
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No. only 33% expression of the gene. Something else is block transcription
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Control of gene expression by premature termination of transcription is called...
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attenuation
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What is the alternate stem loop structure for an attenuated trp Gene?
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base pairs at region 1,2
base pairs at region 3,4 |
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What is the alternate stem loop structure for an expressive trp Gene?
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base pairs at region 2,3
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Why does the translation stop with the attenuated version?
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Because the leader sequence codes for two tryptophans. If tryptophan is present, the ribosome moves along quickly, there is no delay, and regions 3,4 base pair
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Why does translation continue with the alternate version, non attenuated?
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Because there is no tryptophan to bind with the two codons UGGUGG in the leader sequence. This causes the ribosome to pause, allowing the 2,3 regions to bind.
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Structure of the trp operon
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Promotor
Operator Leader (attenuation site) trpE trpD trpC trpB trpA |
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Proteins act in ___
DNA sites act in ___ |
Trans
Cis |
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Lac Z gene encodes ___ which ____
Lac Y Lac A |
B-galactosidase, cleaves lactose in glucose and galactose
Lac Permease, (idk) transacetylase, adds an acetyl group to lactose and other B galactoside sugars. |
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Constitutive mutants
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Synthesize certain enzymes irrespective of environmental conditions.
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Repressor binding domains
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One for the operator.
One for the inducer |
