Final answer:
Lactose, when present in the cell and converted to allolactose, binds to the repressor protein, removing it from the operator and allowing RNA polymerase to transcribe the lactase gene.
Step-by-step explanation:
The molecule that determines if the lactase gene gets transcribed when its presence removes the repressor from the operator is lactose. This occurs because lactose, once inside the cell, is converted to allolactose. Allolactose serves as an inducer molecule that binds to the repressor and changes its shape, rendering it unable to bind to the operator DNA. When the repressor is removed, RNA polymerase can move through the operator region and begin the transcription of the lac operon genes responsible for lactose digestion.
The presence of lactose and its conversation to allolactose is essential for lifting the repression of the lactase gene. When lactose is absent, the repressor protein binds to the operator and prevents RNA polymerase from transcribing the operon, conserving energy and resources by not producing unnecessary proteins.
The molecule that determines if the lactase gene gets transcribed is mRNA. mRNA carries the genetic information from DNA to the ribosomes, where it is used to synthesize proteins.