Genes On The Operon
I - Regulatory genes - Codes for the repressor protein that stops RNA polymerase binding to the operator region.
P - Promoter - RNA polymerase binds here to begin the transcription of the structural genes.
O - Operator - The repressor protein binds here and overlaps the promoter to prevent RNA polymerase from binding.
Z - Strucutral gene for B-Galactosidase - This is an enzyme that hydrolyses lactose into glucose and galactose.
Y - Structural gene for Lactose Permease - This enzyme transports lactose into the cell.
When Lactose is Absent
1. The regulatory genes code for the repressor protein which is then synthesised.
2. The repressor protein binds to the operator region and covers part of the promoter region so that RNA polymerase cannot bind.
3. The structural genes cannot be synthesised.
When Lactose is Present
1. Lactose binds to the repressor protein. This causes it to change shape so that is can no longer bind to the operator region.
2. RNA polymerase can now bind to the promoter region and transcribe the structural genes.
3. The structural genes are synthesised.
4. B-Galactosidase hydrolyses lactose into galactose and glucose.
5. Lactose permease is involved in the transport of lactose into the cell.