BIOL Chapter 13 Review

Insert the correct terms that relate to regulation of eukaryotic transcription.

A protein that binds to DNA and blocks activation of a small number of genes is a/an repressor. A protein that binds to DNA and activates transcription of some genes is a/an activator. Modification of bases in DNA, usually resulting in inhibition of transcription, results from methylation. The idea that gene regulation involves multiple factors is called combinatorial control. Function of activators and repressors can be modulated by binding of small effector molecules, protein-protein interactions, or covalent modifications.

What is a major disadvantage to a bacterial cell of having an operon?

If there is a mutation in a regulatory region, none of the proteins will be synthesized.

Evaluate the statements below and determine which is the BEST reason that bacterial cells use operons and polycistronic RNA.

Initiation of transcription of all genes in a biochemical pathway is regulated simultaneously.

How is it possible for a single gene to encode more than one polypeptide?

Introns can be removed from pre-mRNA in different combinations.

How does the cell recognize that lactose needs to be metabolized?

Lactose is converted into allolactose, which inhibits the lac repressor.

Transcription is carried out by the enzyme

RNA polymerase.

What is the MOST important reason a cell exhibits tight transcriptional control over the regulation of gene expression?

Regulation at the transcriptional level is energetically efficient for the cell.

Genes that encode proteins are first transcribed to mRNA, and then are translated into protein. What is the MOST important factor determining the control of gene expression?

The level of transcription (when a gene is transcribed to mRNA)

If lacI were mutated such that could no longer bind DNA, what effect would this have on the regulation of the operon?

The repressor protein would not function properly, and the lac operon would be over expressed.

If lacO were mutated, what effect would this have on lactose metabolism?

The repressor would not properly bind to the operator, and the lac operon would be over expressed.

Which of the following statement(s) about basal transcription factors is(are) TRUE?

They are essential for transcription and they cannot increase the rate of transcription by themselves.

Which statement represents the best explanation for why eukaryotes use basal, or general, transcription factors?

They give the cell tight control over transcription.

Distinguish between the characteristics associated with each of the four types of gene regulation.

Transcriptional - An activator binds to an enhancer - A repressor binds near a promoter Post-transcriptional - The correct removal of introns of a pre-mRNA is prevented - Stability of an mRNA is regulated -Export of an mRNA to the cytoplasm is blocked Translational - The ability of an mRNA to bind to ribosomes is changed - THe 5' end of an mRNA forms a shape that blocks translation Post-translational - A phosphate group is added to a protein making it inactive - The rate of degradation of a protein is increased

The lac repressor is inactivated by binding to which of the following?

allolactose

A regulatory element that can function from a large distance (e.g. tens of thousands of base pairs) from a promoter is called

an enhancer.

The trp operon consists of ________ genes that encode tryptophan biosynthesis enzymes.

five

In the absence of tryptophan, the trp repressor is

inactive and cannot bind to the operator.

The lac repressor binds to what site within the lac operon?

lacO

Which of the following is not part of the lac operon?

lacl

At which of the following level(s) can gene expression be regulated in eukaryotes?

passage of mRNA through the nuclear membrane, destruction of the mRNA, and rate of protein synthesis

RNA polymerase binds to the

promoter.

The most efficient control of eukaryotic gene expression is achieved at the level of

transcription initiation.

In the presence of tryptophan, tryptophan binds to the

trp repressor.

The assembly of transcription factors begins

upstream from the transcription start site.