Biology - Homework Ch 14

What is NOT a mechanism used by enhancers and repressors to affect gene expression?

All of these are mechanisms used by enhancers or repressors to affect gene expression.

Which of the following statements about enhancers is TRUE?

Enhancers are sequences to which activators bind.

Select the BEST description of the complexity of eukaryotic gene expression as compared to prokaryotic gene expression.

Eukaryotic transcription is usually influenced by many transcription factors while prokaryotic transcription is usually influenced by only a few transcription factors.

Valid reasons for a cell to regulate gene expression include its ability to: keep a gene product available under all conditions.

False

Valid reasons for a cell to regulate gene expression include its ability to: synthesize mRNA for every gene in the genome at all times.

False

Why does the concentration of glucose have an effect on the transcription of the lac operon?

Glucose is the preferred sugar for the bacteria. If it is present, lactose metabolism is suppressed.

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.

The nematode C. elegans has approximately 19,000 genes, while humans have 25,000. Although the number of genes is similar, humans can make more than 4x as many proteins as C. elegans. What is the most plausible explanation for this phenomenon?

In humans, more pre-RNAs can be alternatively spliced to generate different mRNAs.

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.

Which of the following statements about chromatin is TRUE?

Modifying the accessibility of chromatin leads to complex regulation of eukaryotic gene expression.

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.

Assembly of basal transcription factors begins at the ________ sequence in the promoter.

TATA

How is the lac operon affected by negative control?

The Lac Repressor binds to the operator in the absence of lactose.

The trp operon of E. coli controls expression of five enzymes that are involved in the biosynthesis of the amino acid tryptophan. A trp repressor protein (trpR) binds to the trp operator to prevent transcription when tryptophan is present. When would the tryptophan synthesis enzymes be made if the trpR gene was mutated?

The enzymes would be made in the presence or absence of tryptophan.

Which of the following statements best describes the consequence of a mutated activator on expression of a transcriptional target gene?

The gene will be expressed, but in less than optimal quantities.

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.

In both the lac and trp operons of E. coli, a repressor binds to an operator to block transcription. Identify the most accurate description of these operons.

The trp operon is repressible while the lac operon is inducible.

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.

Valid reasons for a cell to regulate gene expression include its ability to: execute a specific program of development (e.g. to become a blood cell or immune cell).

True

Valid reasons for a cell to regulate gene expression include its ability to: make additional cells of the same type in response to a demand.

True

Valid reasons for a cell to regulate gene expression include its ability to: stop synthesis of a cellular component when there is enough available in the cell.

True

Valid reasons for a cell to regulate gene expression include its ability to: synthesize enzymes to metabolize a particular nutrient.

True

A protein that binds to DNA and activates transcription of some genes is a/an

activator

Function of _____________can be modulated by binding of small effector molecules, protein-protein interactions, or covalent modifications.

activators and repressors

In the absence of lactose, the lac repressor is

active and can bind to the operator

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.

Small RNA gene regulation

bind to an mRNA, resulting in destruction of the mRNA or blockage of translation.

Small RNAs, typically 22 nucleotides long, that function in post-transcriptional regulation of gene activity are produced

by digestion of double-stranded RNA into smaller pieces.

When in a complex with ________, the CAP protein binds to the CAP site and ________ the expression of the lac operon.

cAMP; switches on

DNA is associated with proteins to form ________

chromatin.

The idea that gene regulation involves multiple factors is called

combinatorial control.

Removal of acetyl groups from histones results in a/an ______ in gene expression.

decrease

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

five

Cancer results from cells that divide when they should not. A hallmark of cancer is high levels of DNA methylation in cell genomes. Methylation of which genes is MOST likely to lead to cancerous cell formation?

genes that prevent cell division

The lac operon is expressed when

glucose is low and lactose is present.

An activator can increase transcription by attracting a _______ to the region.

histone acetyltransferase

In the absence of tryptophan, the trp repressor is

inactive and cannot bind to the operator

Addition of (-COCH3) groups to histone amino terminal tails results in a/an ______ in gene expression.

increase

When a transcription factor interacts with DNA,

it forms noncovalent bonds with functional groups on the nitrogenous bases.

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

lacO

Which region associated with the lac operon is not involved in the binding of RNA polymerase?

lacZ

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

lacl

When glucose is present

low; CAP does not bind to the activator binding site, and transcription ofthe operon is turned off

Modification of bases in DNA, usually resulting in inhibition of transcription, results from

methylation

What would probably NOT increase the accessibility of the DNA for gene transcription?

methylation of DNA

A ______ is composed of DNA wrapped around an octamer of histone proteins.

nucleosome

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

Combinatorial control of gene expression does not involve

polycistronic RNA.

RNA polymerase binds to the

promoter

A protein that binds to DNA and blocks activation of a small number of genes is a/an

repressor

What protein would not interact with a coactivator?

repressors

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)

Which of the following statements about basal transcription factors is TRUE?

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

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

transcription initiation.

When both glucose and lactose are present,

transcription is turned off

What level of regulation do eukaryotes possess that prokaryotes do not?

transport of RNA out of the nucleus

In the presence of tryptophan, tryptophan binds to the

trp repressor.

The assembly of transcription factors begins

upstream from the transcription start site

What is the MOST important reason a cell would have translational control over the regulation of gene expression?

At the translational level, protein synthesis can be turned on and off quickly to respond to the needs of the cell.

The lac repressor

Binds to the operator and prevents transcription