Which of the following best describes the biological role of the lac operon?

It ensures that bacterial cells produce lactose only when no other food sources are available.

It prevents other sugars from being metabolized until all available lactose has been used.

It ensures that a cell produces enzymes involved in lactose metabolism in a constitutive manner.

It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.

It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.

Correct. The cell expends energy to produce the proteins necessary for lactose metabolism only when lactose is present.

The placement of the operator sequence between the promotor and the structural genes is critical to the proper function of the lac operon.

True

False

True

Correct. When the repressor binds to the operator, RNA polymerase cannot transcribe the structural genes.

Under the system of genetic control of the tryptophan operon, ________.

when there are high levels of tryptophan in the medium, transcription of the trp operon occurs at high levels

when there is no tryptophan in the medium, transcription of the trp operon occurs at high levels

when there are high levels of tryptophan in the medium, transcription of CAP (CRP) occurs at high levels

no transcription occurs under any nutritional circumstance because negative controls inhibit transcription

when there are high levels of tryptophan in the medium, ribosomes "stall" and reduce the levels of tryptophan synthesized

when there is no tryptophan in the medium, transcription of the trp operon occurs at high levels

Which of the following occurs as a result of an abundance of tryptophan in E. coli?

The leader sequence is not transcribed.

The 5 trp genes (TrpA – TrpE) are not transcribed.

The 5 trp genes (TrpA – TrpE) are transcribed, but not translated.

Stalling of the ribosome at trp codons in the leader sequence

The 5 trp genes (TrpA – TrpE) are not transcribed.

Correct. When trp is abundant, the genes involved in tryptophan synthesis are negatively regulated at the level of transcription.

Which of the following features of the trp operon is likely least essential to the process of attenuation?

Trp codons near the beginning of the leader sequence

Transcription and translation of the leader sequence occur simultaneously.

The ability of sequences within the leader mRNA to pair with one another

The order of the structural genes, E, D, C, B, A

The order of the structural genes, E, D, C, B, A

Correct. Because each gene encodes an enzyme involved in the trp synthetic pathway, the order in which the genes occur is likely not important in terms of the attenuation process.

Attenuator systems such as the one described for regulation of tryptophan synthesis would be just as likely to occur in eukaryotes as in prokaryotes.

True

False

False

Correct. Regulation by attenuation requires that translation of a given transcript can begin before transcription is completed. This is not possible in eukaryotes, as the two processes are spatially separated by the nuclear membrane.

What are transcription factors?

Regulatory motifs that bind to the promoter region of a gene

Regulatory DNA sequences that bind to the promoter region of a gene

Regulatory proteins that bind to specific DNA sequences

Regulatory DNA sequences that bind to a protein

Regulatory proteins that bind to specific DNA sequences

Transcription factors are proteins that bind to specific DNA recognition sequences in the promoter or enhancer elements of a gene.

Which of the following elements is not a DNA binding domain?

Zinc finger

Gal4p

Helix-turn-helix

Leucine zipper

Gal4p

Gal4p is a yeast protein that contains a DNA binding domain.

Alternative splicing is an example of gene regulation that occurs after the synthesis of mRNA.

True

False

True

Alternative splicing is a form of mRNA processing and occurs after mRNA synthesis.

_______ _____ changes in DNA/chromosome structure that can influence overall gene output

Chromatin remodeling

____ sequences in DNA to which transcription factors and RNA polymerase bind to initiate transcription

Promoters

_____ cis-acting DNA sequences to which transcription factors bind to regulate transcription. They can act over distances of thousands of base pairs and can be upstream, downstream, or internal to the gene they affect

Enhancers

_____ _____ bind DNA and regulate transcription

transcription factors

The addition of a 5' cap and poly A tail, and removal of introns are all steps in ___ ___ and ____

RNA processing and transport

RNA processing contributes to ___ ___, which regulates translation

mRNA stability

What is the role of the lacZ gene product, the enzyme ß-galactosidase?

It converts simple sugars to lactose.

It converts lactose to glucose and galactose.

It facilitates the entry of lactose into the bacterial cell.

It removes the toxic by-products of lactose digestion from the bacterial cell.

It converts lactose to glucose and galactose.

It is essential that this conversion occur if lactose is to be used as an energy source, since glucose enters intermediary metabolism and glycolysis to provide the cell with carbon and energy.

What is the effect on transcription of the structural and regulatory genes of the lac operon when lactose is present in the environment?

The genes are transcribed for only a single generation and then are shut off.

Transcription of the structural genes occurs.

Lactose represses the synthesis of the repressor.

Transcription does not occur.

Transcription of the structural genes occurs.

Lactose changes the structure of the repressor such that it is unable to bind to the operator site, which in turn allows RNA polymerase to transcribe the structural genes.