The lac operon - TRUE or FALSE: Group of answer choices Before the induction of the lac operon, lactose transporters are completely absent from the cell membrane.

False.

Explanation:

The lac operon is an operon required for the transport and metabolism of lactose in Escherichia coli bacteria, as well as in some other enteric bacteria. It has three adjacent structural genes, a promoter, a regulator and an operator. The lac operon is regulated by several factors, including the availability of glucose and lactose.

The lac operon is under a type of negative regulation, where the genes can always be transcribed, except when the Lac I repressor protein is attached to the operating region, for which it presents a high affinity. In this case, the promoter of the lac gene I is constitutive, for which the Lac I protein is permanently expressed and remains united in tetramer form to the operative region, preventing the transcription of the structural genes.

In the presence of lactose, lactose is the inductor of the operon. It is capable of binding to the repressor protein Lac I and generating a conformational change that decreases its affinity for the operating region. In this way, the operator region remains free, RNA polymerase can freely transcribe the structural genes and β-galactosidase can degrade lactose to glucose and galactose.

In absence of lactose, Lac I repressor protein maintains its high affinity for the operator region, preventing RNA polymerase to transcribe structural genes. In this way, the system remains closed with the consequent energy saving for the bacteria.

The lac operon is an inducible circuit which encodes the genes for the transport of lactose into the cell. But before the induction of it (in absence of lactose), the lactose transporter is not really completely absent from the membrane. There are some active lactose carriers at the basal level.

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