13 terms

gene control

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how do prokaryotes (E.coli) regulate the expression of lactose specific genes
lac operon
what does E.coli do when there is no glucose and there is lactose available?
it switches so that its is able to metabolise lactose
how does E.coli do this ?
it induces the production of two enzymes
operon
genes function as single transcription unit
I or regulatory gene
codes for the repressor protein lac I
P
promoter region where RNA polymerase binds to
Lac O
operator region
structural genes : lac z , lac y and
lac z: B galactosidase
lac y : galactoside permease
lac a : B galactoside transacetylase
under normal conditions (glucose present)
lac I binds to region o
this blocks RNA polymerase from binding to the promoter region so it can't transcribe structural genes.
therefore no mRNA for lac z and lac y is produced and so no translation.
lactose present (no glucose)
lactose binds to lac I
it undergoes a conformational change
therefore stops lac I from binding to lac o
so nothing blocks the promoter
RNA polymerase can bind promoter region and so transcription of structural genes lac z and lac y.
what controls the transcription of eukaryotic genes?
transcription factors located in nucleus
what are transcription factors?
proteins / short non - coding pieces of RNA.
role of transcription factors?
they activate or repress RNA polymerase
it also contains a binding site specific to a sequence of DNA bases found in promoter region of gene)