In prokaryotes, control of gene expression often requires the binding of transcription factors to operons
What is an operon?
☐ | A | The binding site for a repressor protein | |
☐ | B | Any group of genes responsible for the metabolism of lactose | |
☐ | C | A cluster of genes under the control of promoter | |
☐ | D | A regulatory gene |
The lac operon of E. coli contains genes involved in lactose metabolism. The genes are expressed only when lactose is present and glucose is absent.
Two regulators turn the operon "on" and "off" in response to lactose and glucose levels: the lac repressor and catabolite activator protein (CAP). The lac repressor will inhibit transcription of the operon genes by binding to the operator, however if lactose is present the repressor is unable to bind to the operator. CAP acts as a glucose sensor and will activate transcription of the operon when glucose levels are low.
Use the information to complete each cell of the table with a Yes or No.
Condition | Lac repressor bound to operator? | CAP bound to CAP binding site? | Binding of RNA polymerase? | Transcription of operon? |
High glucose, high lactose | ||||
High glucose, low lactose | ||||
Low glucose, high lactose | ||||
Low glucose, low lactose |
Explain why the repressor protein is inhibited in the presence of lactose.
The lac operon controls the production of the enzyme β-galactosidase and two other structural proteins.
Discuss the importance of the survival of E.coli on the mechanisms of the lac operon.
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