BIOLOGICAL CLASSIFICATION
VIRUSES
|
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
|
|
|
lactose is absent in the cell
|
|
|
glucose is present in the cell
|
|
|
lactose is present in the cell
|
|
|
tryptophan is present
|
Detailed explanation-1: -The lac operon of E. coli contains genes involved in lactose metabolism. It’s expressed only when lactose is present and glucose is absent.
Detailed explanation-2: -Transcription of the lac operon normally occurs only when lactose is available for it to digest. Presumably, this avoids wasting energy in the synthesis of enzymes for which no substrate is present. A single mRNA transcript includes all three enzyme-coding sequences and is called polycistronic.
Detailed explanation-3: -The genes are expressed only when lactose is present and glucose is absent. The operon is turned on and off in response to the glucose and lactose levels: catabolite activator protein and lac repressor. The lac repressor blocks the transcription of the operon. In the presence of lactose, it stops acting as a repressor.
Detailed explanation-4: -The Lactose operon expresses as long as the Lactose is present. When all lactose is converted into glucose and galactose, the reaction stops.