When E Coli Is Placed in a Medium Containing Both Glucose

question 85

Multiple Choice

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.

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