sapling chapter 16

repressible

1. activating the repressor gene product inhibits transcription. 2. sufficient amounts of the gene product inhibit further transcription.

negative gene regulation

1. in the presence of iron, the dtxR repressor protein binds DNA, and the gene that encodes for the diphtheria toxin is not expressed. 2. in the absence of lactose, the lacR repressor protein binds the lac operon 3. in the presence of excess tryptophan, a repressor protein bind the operator of the trp operon and prevents the operon from being transcribed.

postive gene regulation

1. in the presence of lactose and low glucose, the lac operon is expressed 20-fold higher than in the absence of lactose. 2. in the presence of the sugar arabinose. an activator protein binds the promoter of the genes responsible for processing arabinose and induces their transcription.

steps of gene regulation by the lac operon from the introduction of lactose to the environment to when the cell begins to digest lactose

1. lactose is introduced to the environment 2. the repressor is inactivated by allolactose 3. the repressor is removed from the operator 4. RNA polymerase binds to the promoter region 5. lactose enzyme genes are expressed by the operon. 6. the cell begins to digest lactose

steps of gene regulation by the lac operon from the removal of lactose from the environment to when the cell no longer digests lactose.

1. lactose is scarce in the environment 2. the repressor is activated in the absence of lactose 3. the repressor binds to the operator 4. RNA polymerase is prevented from moving from the promoter 5. lactose enzyme genes are not transcribed 6. the cell no longer digests lactose

steps of the regulation of the trp operon in the order of occurrence.

1. level of tryptophan in the cell are low 2. RNA polymerase binds to the promoter, allowing transcription of the trp genes to proceed. 3. enzymes produced from the trp genes catalyze tryptophan production 4. level of tryptophan rise, and no more is required. 5. tryptophan activates the trp repressor protein. 6. the trp repressor protein binds to the operator 7. the trp protein blocks RNA polymerase from binding to the promoter. 8. transcription of the gene stops.

what is the function of the repressor in the E.coli lac operon?

A repressor is a type of protein that inactivates the expression of the lac operon genes by binding to the DNA of the lac operon.

Which statement describes an operon?

a gene cluster controlled by a single promotor that transcribes to a single mRNA strand.

what is the function of the promoter in the E.coli lac operon?

a promoter is a type of DNA sequences that activates the expression of the lactose genes by polymerase binding site for the lac operon.

a ribozyme is

an RNA catalyst

A mutant strain of E.coli produces beta-galactosidase in the presence and in the absence of lactose. Where in the operon might the mutation in this strain occur, and why?

in the operator region, where the mutation leads to the failure of the operator to normally bind the repressor in the lacl gene, which leads to an inactive lac repressor

Constitutive

the amount of gene product is constant.

A mutation at the operator site of an operon prevents the repressor from binding what effect will this mutation have on transcription in a repressible operon? what effect will this mutation have on transcription in an inducible operon?

the operon will always be transcriptionally active; the operon will always be transcriptionally active.

inducible

transcription is turned on when a specific molecule is present.