Model 1 below shows the promoter of a regulated gene in E. coli. The promoter re

Question

Model 1 below shows the promoter of a regulated gene in E. coli. The promoter region of the lac operon (DNA depicted below) is shown under four different growth conditions and the resulting effects on transcription are reported. Use this model to answer questions 1-5 about how the genes in the lac operon are regulated. X and Y are transcription regulator proteins Amount of Transcript (Compared to Maximum) Condition sigma factor A: Glucose Lactose 5% RNA polymerase B: Glucose only 0.1% C: Glycerol Only 0.5% 100% D: Lactose only

Explanation / Answer

1. A = X is an activator

B = Y is a repressor

2. Because in condition A, glucose also present which lower down the concentration of cAMP. Thus cAMP-CAP complex can not form and efficient transcription will not occur. E.coli lac promoter is weak unless it binds with CAP.

3. If X is bound then the effects of Y is a little low. It means Y is less able to repress transcription.

4. A = Y

B = X

C = In D condition beta galactosidase will produce at high levels

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