The transcription of -galactosidase and permease is inducible in lac⁺ bacteria with a wild-type lac operon. Explain the mechanism by which lactose gains access to the cell to induce transcription of the genes.

Verified step by step guidance

1. Lactose is a disaccharide that cannot directly enter the bacterial cell through passive diffusion due to its size and polarity.
2. In the absence of lactose, the lac operon is repressed by the lac repressor protein, which binds to the operator region, preventing transcription of the downstream genes.
3. When lactose is present in the environment, a small amount can enter the cell through the basal level of permease activity, which is always present at low levels.
4. Once inside the cell, lactose is converted into allolactose, which acts as an inducer by binding to the lac repressor protein.
5. The binding of allolactose to the repressor causes a conformational change, reducing its affinity for the operator region, thus allowing RNA polymerase to bind to the promoter and initiate transcription of the lac operon genes, including those for β-galactosidase and permease.

Key Concepts

Lac Operon

The lac operon is a set of genes in bacteria that are responsible for the metabolism of lactose. It consists of structural genes that code for enzymes like β-galactosidase and permease, which are necessary for lactose utilization. The operon is regulated by the presence or absence of lactose, allowing the bacteria to conserve energy by only expressing these genes when lactose is available.

Inducible System

An inducible system is a type of gene regulation where the expression of certain genes is turned on in response to specific signals, such as the presence of a substrate. In the case of the lac operon, lactose acts as an inducer that binds to the repressor protein, causing it to release from the operator region of the operon. This allows RNA polymerase to access the promoter and initiate transcription of the genes needed for lactose metabolism.

Lactose Permease

Lactose permease is a membrane protein that facilitates the transport of lactose into bacterial cells. It is encoded by the lacY gene within the lac operon. Once lactose is inside the cell, it can be converted into allolactose, which then binds to the repressor protein, triggering the transcription of the lac operon genes. This transport mechanism is crucial for the induction of the operon and subsequent lactose metabolism.