Why does the Lac Operon shut down sometimes after the addition of lactose in the medium where E coli was growing ? why low level expression of Lac Operon is always required ?
Answers
The function of lac operon is to codes for proteins required to transport lactose into the cell and to break it down. CAP helps bacteria to use alternative carbon sources in the absence of glucose. The lac repressor so ensures that the lac operon is shut off in the absence of lactose. This arrangement helps the control region of lac operon to respond to and integrate two different signals.
i. lactose must be present
ii. glucose must be absent
Any of the other three possible signal combinational maintains the group of genes in the off state.
The Lactose Operon or Lac Operon is a basic and fundamental component in the DNA structure of E.coli bacteria. It supports the metabolic activity of lactose and its movement.
Presence of lactose in the medium of the E.coli growth stops the binding of the repressor to operon, allowing the polymerase to bind with the operon and perform the genetic transcription .
Later, when the cells utilize entire content of the lactose present, repressor becomes bond free. Now, it binds to the operon and inhibits the transcription process. Finally, the operon shuts down.
It is possible for bacterial cells to use lactose in the medium, only if there is availability of permease in the bacteria. Permease can be formed only when there is low level expression of the Lac Operon.