Can you think for how many long the lac operon would be expressed in the presence of lactose?

The lac operon depends on lactose to be expressed and hence lac operon works only in the presence of lactose. EXPLANATION: The lack operon is expressed based on availability of lactose. This reaction involves the glucose and galactose formation.

What happens to the lac operon When lactose is present?

When lactose is present, the lac repressor loses its DNA-binding ability. This clears the way for RNA polymerase to bind to the promoter and transcribe the lac operon.

What factor is required for the lac operon to be expressed in the presence of lactose?

Positive control (conditions: lactose only; permit expression of lac operon). If no glucose is present and lactose is present (see Fig. 16-13B), the gene products from the lac operon are needed to use the lactose for energy. Thus a regulatory factor, the CAP-cAMP complex is needed to permit expression of the operon.

How long is lac operon?

The lac operon of Escherichia coli spans approximately 5300 base pairs and includes the lacZ, lacY, and lacA genes in addition to the operator, promoter, and transcription termination regions.

What is positive regulation of lac operon?

The lac operon is therefore positively regulated by the absence of glucose catabolites (Figure 1). Figure 1: The lac operon is activated when intracellular glucose levels are low. When the concentration of intracellular glucose is low (upper panel), the levels of the signal molecule cAMP are high.

What happens to lac operon in presence of glucose?

As glucose is present, cAMP level is low so activator CAP remains inactive. Lac repressor remains bound to the operator and prevents binding of RNA polymerase. In this condition, no transcription of the lac operon occurs.

How does the lac operon regulate expression of the lac genes?

A repressor protein binds the operator (control) region upstream of the operon preventing transcription. When lactose is present outside the cell, it crosses the cell membrane and acts as an inducer of the operon. CAP promotes RNA polymerase transcription of genes leading to an increase of lac operon expression.

How would lac operon operates in in E coli?

Answer : When lactose is present , the lac genes are expressed because allolactose binds to the lac repressor protein and keeps it from binding to the lac operator. Small amount of allolactose are formed when lactose enters E. coli.

How does lactose promote transcription of lac operon?

a) How does lactose (allolactose) promote transcription of LacZ? 1) Lactose binds to the polymerase and increases efficiency. 3) Lactose binds to an activator protein, which can then help the RNA polymerase bind to the promoter and begin transcription.

What happens to the lac operon when both glucose and lactose are present?

If both glucose and lactose are both present, lactose binds to the repressor and prevents it from binding to the operator region. The block of lac gene transcription is thus lifted, and a small amount of mRNA is produced. This complex binds to the promoter region and stimulates the transcription of the three lac genes.

How does glucose regulate the lac operon?

Concerning the mechanisms that lead to the inhibition of the lac operon expression, it widely has been believed that glucose inhibits lac expression by reducing the level of cAMP and therefore by depriving the lac operon of a transcriptional activator (CRP–cAMP) necessary for its expression.