Exam 16: Regulation of Gene Expression in Prokaryotes

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

The cAMP-CAP complex and RNA polymerase bind more efficiently to the lac operon together than either does alone.What term is applied to this increased efficiency of binding?

State whether the following statement is true or false,then give your reasoning.The terminating "hairpin" loop occurs in the trp operon when sufficient tryptophan is present.

What two important domains within a riboswitch involve the ligand-binding site?

Attenuation involves the termination of mRNA synthesis.

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.

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

(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 β-galactosidase in the lac system. (d)Show by diagram the manner in which lactose brings about transcription of the three structural genes of the lac operon. (e)Explain why certain mutations in the regulator gene (I-)of the lac system result in maximal synthesis of β-galactosidase,permease,and transacetylase even in the absence of the inducer (lactose).

The trp operon is typically characterized as being both under negative control and repressible.

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 enzyme permease cleaves the linkage between glucose and galactose residues in lactose.

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

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

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

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?

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?

The trp and lac operons are both subject to forms of control that are typically called negative.

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?

Present a detailed description of the actions of the regulatory proteins in inducible and repressible enzyme systems.

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