For the lac operon to be transcribed, two conditions must both be met at the same time. What are they?
AGlucose must be very low or absent, and lactose must be present
BGlucose must be abundant, and lactose must be absent
CEither glucose is present or lactose is present, but not both at once
DTryptophan must be absent, and glucose must be abundant
Answer & Solution
Correct answer: A. Glucose must be very low or absent, and lactose must be present
1. The lac operon is a typical inducible operon that encodes genes for acquiring and processing lactose.
2. For the lac operon to be activated, glucose must be very low or non-existent.
3. Second, lactose must also be present at the same time.
4. Only when both conditions are satisfied is the lac operon transcribed, which rules out the option requiring only one condition or neither.
5. Tryptophan availability governs the separate trp operon, not the lac operon, so that option does not apply here.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 16 "Gene Expression", section The lac Operon: An Inducer Operon_
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