Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when lactose enters the cell?
A) The repressor protein attaches to the regulator.
B) Allolactose binds to the repressor protein.
C) Allolactose binds to the regulator gene.
D) The repressor protein and allolactose bind to RNA polymerase.
E) RNA polymerase attaches to the regulator.

Question

Quizplus · Accepted Answer

When lactose enters the E. coli cell, some of it will be converted into allolactose. Allolactose acts as an inducer for the lac operon, which regulates the expression of genes involved in lactose metabolism. The lac operon contains a gene for a repressor protein that normally binds to the operator region of the operon, preventing transcription of the genes. However, when allolactose is present, it binds to the repressor, causing a conformational change that prevents it from binding to the operator. This allows RNA polymerase to transcribe the genes, leading to the production of enzymes that can break down lactose into usable energy for the cell.

Allolactose, an Isomer of Lactose, Is Formed in Small Amounts