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.

Why is it essential that bacterial cells be able to regulate the expression of their genes? What are the energetic and evolutionary advantages of regulated gene expression? Is the expression of all bacterial genes subject to regulated expression? Compare and contrast the difference between regulated gene expression and constitutive gene expression.

Answer these questions concerning promoters.What is the common structure of a bacterial promoter with respect to consensus sequences?

Contrast positive versus negative control of gene expression.

Contrast the role of the repressor in an inducible system and in a repressible system.

For the lac genotypes shown in the following table, predict whether the structural genes (Z) are constitutive, permanently repressed, or inducible in the presence of lactose.Genotype Constitutive Repressed InducibleI⁺O⁺Z⁺ xI⁻O⁺Z⁺I⁻OᶜZ⁺I⁻OᶜZ⁺/F'O⁺I⁺OᶜZ⁺/F'O⁺IˢO⁺Z⁺IˢO⁺Z⁺/F'I⁺

For the genotypes and conditions (lactose present or absent) shown in the following table, predict whether functional enzymes, nonfunctional enzymes, or no enzymes are made.

The locations of numerous lacI⁻ and lacIˢ mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI⁻ mutations were found to occur in the 5′-upstream region of the gene, while lacIˢ mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene?