List possible genotypes for lac operon haploids that have the following phenotypic characteristics:
The operon genes are constitutively transcribed, but the strain is unable to grow on a lactose medium. List two possible genotypes for this phenotype.

Bacterial strategies to evade natural or human-imposed antibiotics are varied and include membrane-bound efflux pumps that export antibiotics from the cell. A review of efflux pumps [Grkovic, S., et al. (2002)] states that, because energy is required to drive the pumps, activating them in the absence of the antibiotic has a selective disadvantage. The review also states that a given antibiotic may play a role in the regulation of efflux by interacting with either an activator protein or a repressor protein, depending on the system involved. How might such systems be categorized in terms of negative control (inducible or repressible) or positive control (inducible or repressible)?

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are constitutively transcribed, and the strain grows on lactose medium. List two possible genotypes for this phenotype.

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are inducibly transcribed, but the strain is unable to grow on a lactose medium. List one possible genotype for this phenotype.

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are never transcribed above a basal level, and the strain is unable to grow on a lactose medium. List two possible genotypes for this phenotype.

In a theoretical operon, genes A, B, C, and D represent the repressor gene, the promoter sequence, the operator gene, and the structural gene, but not necessarily in the order named. This operon is concerned with the metabolism of a theoretical molecule (tm). From the data provided in the accompanying table, first decide whether the operon is inducible or repressible. Then assign A, B, C, and D to the four parts of the operon. Explain your rationale. (AE=active enzyme; IE=inactive enzyme; NE=no enzyme.) Genotype tm Present tm Absent A⁺B⁺C⁺D⁺ AE NE A⁻B⁺C⁺D⁺ AE AE A⁺B⁻C⁺D⁺ NE NE A⁺B⁺C⁻D⁺ IE NE A⁺B⁺C⁺D⁻ AE AE A⁻B⁺C⁺D⁺/F'A⁺B⁺C⁺D⁺ AE AE A⁺B⁻C⁺D⁺/F'A⁺B⁺C⁺D⁺ AE NE A⁺B⁺C⁻D⁺/F'A⁺B⁺C⁺D⁺ AE+IE NE A⁺B⁺C⁺D⁻/F'A⁺B⁺C⁺D⁺ AE NE

Suppose each of the genotypes you listed in parts (a) and (b) of Problem 19 are placed in a partial diploid genotype along with a chromosome that has a fully wild-type lac operon.

Which partial diploids will be able to grow on a lactose medium?

Suppose each of the genotypes you listed in parts (a) and (b) of Problem 19 are placed in a partial diploid genotype along with a chromosome that has a fully wild-type lac operon.

Will the transcription of operon genes in each partial diploid be inducible or constitutive?

A bacterial operon is responsible for the production of the biosynthetic enzymes needed to make the hypothetical amino acid tisophane (tis). The operon is regulated by a separate gene, R. The deletion of R causes the loss of enzyme synthesis. In the wild-type condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. Mutations in the operator gene (O⁻) result in repression regardless of the presence of tis. Is the operon under positive or negative control? Propose a model for:

(a) Repression of the genes in the presence of tis in wild-type cells

(b) The mutations.