Chapter 12 Flashcards
Describe Positive Control
1) Activators + Effectors: without effectors, no transcription but with effector, transcription is activated
2) Activators + Inhibitors: with inhibitors, no transcription but with inhibitor, transcription is activated
Describe Negative Control
1) Repressors + Inducers: without inducer, repressor can block transcription but with inducer, transcription is allowed
2) Repressors + Corepressors: with corepressor, repressor can block transcription but without corepressor, transcription is allowed
An example of negative control where a repressor binds when an inducer is absent to prevent transcription is the ___________
lac operon
B-galactosidase & Permease
breaks B-galactosidase linkage of lactose to produce glucose and galactose, also converts lactose to allolactose (inducer)
imports lactose into cell
The lacI repressor is ______________ expressed and represses transcription of the lac operon. This means there is no expression of lacZ (__________________), lacY (_______________), and lacA (_____________________).
constitutively, B-galactosidase gene, permease gene, transacetylase gene
T or F: even though repressor proteins are constitutively expressed to repress the expression of the lac operon, there is some basal level of expression which in the presence of lactose, allows allolactose to be produced, inhibiting the repressor and allowing transcription of lac genes.
True
Repressor Mutation
prevents repressor from binding to operator, leading to constitutive expression even in the absence of the inducer (allolactose)
Operator Constitutive Mutation
prevents repressor from binding, leading to constitutive expression even in the absence of the inducer (same as repressor mutation)
T or F: when there’s low glucose, there is lots of cAMP which leads to a higher expression of the lac operon but when there’s high glucose, there’s not much cAMP, leading to a lower expression of the lac operon
True
Super Repressor Mutation
prevents inducer from suppressing repressor, transcription is repressed even in the presence of the inducer - even when cAMP is present
The trp operon has ________ that work together to synthesize the amino acid tryptophan, these genes work in sequential steps.
5 genes
T or F: When tryptophan is present, it acts as a corepressor, so transcription is low (there is a basal level) and the repressor binds to trpO.
True
Expression of the trp operon is also ____________, meaning the level of expression is influenced by the level of ____________
attenuated, tryptophan
If a hairpin loop between repeat regions ___ & ___ form, transcription stops early after trpL is transcribed but the rest of the trp operon is not transcribed. However, if a hairpin loop forms between repeat regions ___ & ___, then the rest of the trp operon is transcribed
3 & 4 (when there’s rapid translation of trpL due to lots of trytophan), 2 & 3 (when three’s slow translation of trpL due to lack of tryptophan)
