The graph below shows a growth curve of E.coli growing in a defined medium containing equal molar amounts of glucose and lactose.

Figure 23.1
Based on your knowledge of the regulation of the lac operon,the best explanation of these results is that
A)early on, due to the presence of lactose, the bacteria utilize the lac operon. Glucose is used later.
B)the bacteria are utilizing both sugars simultaneously.
C)the presence of glucose causes the formation of cAMP catabolic repressor protein (CR
P)complexes, which shut down the lac operon until the glucose is used up.
D)glucose is used first. Once glucose becomes limiting, intracellular cAMP increases, forming cAMP-CRP complexes that activate the lac operon to use lactose.
E)none of the above

Question

The graph below shows a growth curve of E.coli growing in a defined medium containing equal molar amounts of glucose and lactose.

Figure 23.1
Based on your knowledge of the regulation of the lac operon,the best explanation of these results is that
A)early on, due to the presence of lactose, the bacteria utilize the lac operon. Glucose is used later. 
B)the bacteria are utilizing both sugars simultaneously. 
C)the presence of glucose causes the formation of cAMP catabolic repressor protein (CR
P)complexes, which shut down the lac operon until the glucose is used up. 
D)glucose is used first. Once glucose becomes limiting, intracellular cAMP increases, forming cAMP-CRP complexes that activate the lac operon to use lactose. 
E)none of the above

Quizplus · Accepted Answer

The graph shows that glucose is used first, followed by a period of slower growth, and then a later period of faster growth when lactose is utilized. This is consistent with the regulation of the lac operon, where the presence of glucose causes catabolite repression of the lac operon until glucose is used up, and then the intracellular concentration of cAMP increases, leading to formation of cAMP-CRP complexes that activate the lac operon to use lactose.

The Graph Below Shows a Growth Curve of E