Model 1 below shows the promoter of a regulated gene in E. coli . The promoter r
ID: 45399 • Letter: M
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.
3. Would transcription regulator X work as efficiently if it bound where Y does? What about the opposite scenario (Y bound where X normally is)?
4. a. One gene in the lac operon encodes the b-galactosidase enzyme which breaks the disaccharide lactose down into the monosaccharides glucose and galactose. The regulation of the lac operon depends on whether the cells are grown on media containing lactose or glucose. Why is this logical?
b. Which transcriptional regulator is responding to the presence of glucose?
c. Which transcriptional regulator is responding to the presence of lactose?
X and Y are transcription regulator proteins Amount of Transcript (Compared to Maximum) Condition sigma faclor 5% A: Glucose Lactose RNA polymerase B: Glucose only 0.1% C: Glycerol Only 0.5% 100% D: Lactose onlyExplanation / Answer
3. No, because Y specifically binds to the region and inhibits the transcription under the presence of glucose, and glycerol only. If X binds where Y does, it would not inhibit transcription. But when Y bound where X normally is, would result in the effective inhibition of the transcription.
4. a. This is logical because, breakdown of lactose using b-galactosidase is a most energy consuming process. So, in order to avoid energy loss, bacteria first utilizes the glucose as the main source of energy.
b. Y is responding to the presence of glucose.
c. No transcriptional regulator is responding to the presence of lactose.
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