Exam 16: Regulation of Gene Expression in Prokaryotes

Regarding regulation of the trp operon, what might one appropriately call the amino acid tryptophan?

What experimental results would indicate that the mutation lacI^s is dominant to lacI⁺?

Describe the positive control exerted by the catabolite activating protein (CAP). Include a description of catabolite repression.

What term would be applied to a regulatory condition that occurs when protein is associated with a particular section of DNA and greatly reduces transcription?

Which term most appropriately refers to a regulatory protein in prokaryotes?

What is an allosteric molecule?

Monod discovered that if tryptophan is present in relatively high quantities in the growth medium, the enzymes necessary for its synthesis are repressed. How does this occur?

Certain mutations in the regulator gene of the lac system in E. coli result in maximal synthesis of the lac proteins (β-galactosidase, etc.) even in the absence of the inducer (lactose). Provide an explanation for this observation.

Within the control region of the trp operon is a section of DNA that is sensitive to levels of tryptophan in the system. What is the name of this region?

Under a system of positive control, transcription does not occur unless a regulator molecule directly stimulates RNA production.

What is the function of the lacY gene in the lac operon?

Regarding the lactose utilization system in E. coli, a gratuitous inducer is a molecule that is chemically analogous to lactose and induces the operon, but is not a substrate for the enzymes of the lac operon.

When referring to attenuation in regulation of the trp operon, it would be safe to say that when there are high levels of tryptophan available to the organism, ________.

The lac operon consists of three structural genes as well as the adjacent region of DNA known as the regulator.

Attenuation involves the termination of mRNA synthesis.

What symbols are used to describe constitutive mutations at specific regions of the lac regulatory system?

What term refers to a contiguous genetic complex that is under coordinated control?

The table below lists several genotypes associated with the lac operon in E. coli. For each, indicate with a "+" or a "-" whether functional β-galactosidase would be expected to be produced at induced levels. Genotype                 $\beta$ -galactosidase production                                 No Lactose         With Lactose (a) $\quad I + O + Z + / F ^ { \prime } I - O + Z +$ (b) $\quad I - O c Z + / F ^ { \prime } I = O + Z -$ (c) Is Oc $\mathrm { Z } + / \mathrm { F } ^ { \prime } \mathrm { I } + \mathrm { O } + \mathrm { Z } +$ (d) $I - O + Z + / F ^ { \prime } I - O + Z +$ $I ^ { + } =$ wild-type repressor $I ^ { - } =$ mutant repressor (unable to bind to the operator) $I s$ = mutant repressor (insensitive to lactose) $O ^ { + } =$ wild-type operator $O C =$ constitutive operator (insensitive to repressor)

Regarding the lactose utilization system in E. coli, a constitutive mutant is one in which the three enzymes are produced regardless of the presence or absence of lactose.

The catabolite repression system in E. coli essentially represses the lac operon when glucose is present. What evolutionary advantage would favor evolution of such a system?