When glucose and lactose are present in an Escherichia coli cell, ____.
A)the lac operon will be turned off
B)the lac operon will be on, and lactose will be used first
C)the lac operon will be on, but glucose will be used first
D)both glucose and lactose will be used at the same rates
E)the cell will produce starch from the sugars

Question

​When glucose and lactose are present in an Escherichia coli cell, ____.
A)​the lac operon will be turned off
B)​the lac operon will be on, and lactose will be used first
C)​the lac operon will be on, but glucose will be used first
D)​both glucose and lactose will be used at the same rates
E)​the cell will produce starch from the sugars

Quizplus · Accepted Answer

Escherichia coli cells preferentially use glucose as a carbon source, and the presence of glucose will inhibit the transcription of the lac operon. Even in the presence of lactose, E. coli will first use up the available glucose before switching to the use of lactose. Therefore, the lac operon will be turned on, but glucose will be used first, and then lactose will be used.

​When Glucose and Lactose Are Present in an Escherichia Coli

When Glucose and Lactose Are Present in an Escherichia Coli