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Gene Expression
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- 1Transcription factorsProteins which alter gene expression.
Activators- bind DNA and activate (increase) gene expression.
Repressors- bind DNA and repress (decrease) gene expression.
Transcription factors bind DNA sequences at or near the start of a gene or interact with other proteins which affect gene expression. - 2The trp OperonTryptophan metabolism in E.coli is controlled by a repressible gene system, the trp operon.
TrpR is a transcription repressor.
Represses transcription of the trp operon in the presence of tryptophan.
TrpR also regulates four other operons. - 3Control of the lac OperonThe lac operon is controlled by two transcription factors.
LacI, lac repressor, alters gene expression depending on the levels of lactose in the cell.
CAP- catabolite activator protein (CRP), alters gene expression depending on the level of glucose in the cell. - 4LacILacI is a transcription repressor.
Represses transcription of the lac operon in the absence of lactose.
Only regulates the lac operon.
LacI binds operator, preventing RNA polymerase binding, so no gene expression. - 5CAP (CRP)RNA polymerase binds weakly to the lac promotor so transcription is low.
E.coli needs to utilise lactose when there is low glucose.
Cyclic AMP (cAMP) is present when glucose is low.
High glucose, CAP- inactive.
Low glucose, CAP;cAMP- active.
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- CBBM Fichas sobre Gene Expression, creado por izzy-whizzy el 03/05/2013.
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- izzy-whizzy
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