LABORATORY REVIEW
MOLECULAR BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Glucose is available, lactose not available
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Sucrose not available, pentose is available
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Pentose not available, sucrose is available
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Glucose not available, lactose is available
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Detailed explanation-1: -Glucose must be unavailable: When glucose is unavailable, cAMP binds to CAP, making CAP able to bind DNA. Bound CAP helps RNA polymerase attach to the lac operon promoter. Lactose must be available: If lactose is available, the lac repressor will be released from the operator (by binding of allolactose).
Detailed explanation-2: -In the absence of lactose the lac repressor blocks the expression of the lac operon by binding to the DNA at a site, called the operator that is downstream of the promoter and upstream of the transcriptional initiation site.
Detailed explanation-3: -Step 2: The explanation for the correct answer Lactose must also be present, second. The lac operon won’t be transcriptionally active unless lactose and glucose are both presents. The binding of the CAP protein enhances lac operon transcription in the absence of glucose.