Question

Draw and describe the regulation of the Escherichia colilac operon in the following situations:

1.         In the absence of lactose (disregard presence or absence of glucose).

2.         In the presence of lactose (disregard presence or absence of glucose).

3.         In the absence of glucose (disregard presence or absence of lactose).

Finally, describe where in the gene expression process this regulation is taking place.

Answer 1

© Absence of Lactose : RNA polymerase EL P D Laut ya) E-POST Repressor - - Presence of Lactose RNA polymerase Trip To 12 YA B A Repressed Lactose

3- Absence of glucose - Lactose present: CAMP DHA А рецp3 TO1Pozul CAP Sites CAP @ Pozyral Lactose absent a

1. In the absence of the lactose, repressor molecule is attached to the operator gene. So there will not be transcription of the Z,Y and A genes Operon is in off position.

2. In the presence of the lactose, the repressor is removed from the operator gene. This helps in RNA polymerase moving over the Z,Y and A genes to trascibe them. The operon is on now.

3. In the absence of glucose, the operon may be off if the lactose is not there. It will be on if the lactose is present. CAP and cAMP are important in the regulation of the Lac Operon. Absence of the glucose activates the production of cAMP which binds to CAP protein and the complex binds to the CAP site in the DNA which will activate the operon if lactose present. If the lactose is absent, then the operon will be off because repressor will be still bound to the operator gene.

OPerator gene is called the switch of the operon. If the switch is on , operon is on, other wise the operon is off. When repressor attaches to the Operator, the switch is off. When the repressor is detached from the operator, the operon is on. So the regulation is through the repressor molecule attached to the operator gene.