Exam 16: Regulation of Gene Expression in Bacteria

The accompanying table lists several genotypes associated with the lac operon in E.coli.For each,indicate with a "+" or a "-" whether fi- galactosidase would be expected to be produced at induced levels. 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)

Explain why lacO^c mutations are cis- acting while lacI mutations can be trans- acting.

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?

Regarding the trp operon,trpR^- maps to a considerable distance from the structural genes.The mutation either inhibits the interaction with tryptophan or inhibits repressor formation entirely.In the presence of tryptophan in the medium,would you expect the trp operon to be transcriptionally active? Explain.

Through genetic analysis,Jacob and Manod were able to make predictions about the lac operon.However,which of the following techniques confirmed their predictions?

Usually,bacteria only make tryptophan when tryptophan is absent or available in low concentration.However,a particular bacterial mutation makes tryptophan all the time whether or not tryptophan is present.What could explain this phenotype?

In the lac operon,the product of structural gene lacZ is capable of __________.

Some lac operon mutations allow for beta galactosidase to be expressed constitutively even in the absence of lactose.Which of the following lac genotypes would allow for this constitutive expression?

If lactose is accumulating outside of E.coli and is unable to enter,then which structural gene of the lac operon is most likely mutated?

Genetic regulation in bacteria can involve alterations in RNA secondary structure.What phenomenon occurs in the trp operon that involves such alterations?

Present an overview of bacterial gene regulation in terms of growth efficiency.

a)Describe by labeled diagram the structural components of the lac operon in E.coli. b)State the function of the lac regulator gene. c)State the function of fi- galactosidase in the lac system. d)Show by diagram the manner in which lactose brings about transcription of the three structural genes of the operon. e)Explain why certain mutations in the regulator gene I^-)of the lac system result in maximal synthesis of fi- galactosidase,permease,and transacetylase even in the absence of the inducer lactose).

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

A protein,like the lac repressor,is said to be __________because when it binds lactose,it structurally changes and its chemical activity also changes.

Small noncoding RNAs regulate gene expression in bacteria by __________ .

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?

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

Describe what is meant by a gratuitous inducer.Give an example.

What is an allosteric molecule?

Compare and contrast positive and negative controls of gene expression in bacteria.