When E. coli is placed in a medium containing both glucose and lactose, why does cell growth stop temporarily when the glucose is used up?
A) Once glucose is depleted, the cell must use the lactose; before it can do this, it must express the lac operon and synthesize the enzymes needed to use lactose, which takes time.
B) Once lactose is depleted, the cell must use the glucose; before it can do this, it must express the lac operon and synthesize the enzymes needed to use lactose, which takes time.
C) Once glucose is depleted, the cell must use the lactose; before it can do this, it must express the lac operon-it can only do this if the culture medium is placed in the dark at 22ᵒC.
D) Glucose is the preferred medium of the cells-when it is available, they grow extremely fast, and this depletes all the energy in the cell which must be replaced before it can use lactose.
E) The presence of glucose denatures the lactose in the medium; once the glucose is depleted, the lactose has to regain its original shape before the cells can use it.

Question

Quizplus · Accepted Answer

Once glucose is depleted, the cell must switch to using lactose as a source of energy. However, to use lactose, the cell must first express the lac operon and synthesize the enzymes needed to break down lactose, which takes time. This temporary stop in growth is known as the diauxic shift.

When E Coli Is Placed in a Medium Containing Both Glucose