Ch. 8 HW Questions

Which of these is an evolutionarily ancient defense mechanism that protects a variety of organisms from viral infection?

RNA interference (RNAi)

T or F: Differentiated cells in multicellular organisms require hormonal input to "remember" what type of cell they should be.

false

T or F: In eukaryotes, individual transcription regulators are often involved in controlling the expression of multiple genes. Thus, their interactions with DNA must be weak and relatively non-specific

false

T or F: Once a cell has become specialized to produce the set of proteins that are responsible for its distinctive properties, its gene expression patterns remain fixed

false

T or F: The general transcription factors that assemble at a eukaryotic promoter are different, depending on the specific gene being transcribed by polymerase II

false

What type of molecule triggers RNA interference (RNAi)?

foreign, double-stranded RNA

Using powerful new sequencing technologies, investigators can now catalog every RNA molecule made by a cell and determine at what quantities these RNAs are present. In an experiment, researchers measured the relative quantities of two different mRNAs—one transcribed from gene A, the other from gene B—in two different cell types. Gene B is expressed in both the liver and the brain whereas gene A is expressed in the brain but not in the liver. Which most likely encodes a housekeeping protein?

gene B only

If lactose and glucose are both available to a bacterial cell, which carbon source(s) will be used?

glucose

A housekeeping gene is a gene whose cellular function is

important for processes found in all cell types

MicroRNAs regulate the activity of protein-coding genes by doing which of the following?

inhibiting the translation of mRNAs, promoting the degradation of mRNAs

In bacterial cells, the tryptophan operon encodes the genes needed to synthesize tryptophan. What happens when the concentration of tryptophan inside a cell is high?

it activates the tryptophan repressor, which shuts down expression of the tryptophan operon

A reporter gene is an experimentally engineered regulatory DNA sequence from a gene of interest that has been fused to a gene that encodes a protein that is easily observed experimentally. Why is this approach useful?

it provides information into where and when a gene is expressed

Which of these is NOT a type of noncoding RNA?

mRNA

MicroRNAs block the expression of a specific gene product by binding to the ___________ and inhibiting ___________.

mRNA; translation

Where do transcription regulators usually bind on a DNA double helix?

major groove

Which of the following describes the Lac operon in E. coli when both lactose and glucose are present in the culture medium?

neither CAP nor the Lac repressor is bound to the Lac operon's regulatory DNA, and the Lac operon is not expressed

The figure depicts which of the following mechanisms that cells use to maintain their identity through cell divisions? green circles

positive feedback

Eukaryotic repressor proteins can decrease transcription using which of the following mechanisms?

preventing the assembly of the transcription initiation complex

In eukaryotes, where do transcription regulators bind?

upstream, downstream, or within the genes they control

Researchers assayed the activity of enzyme F in three different types of tissue from the same mouse by determining the amount of enzyme product produced per milligram of tissue per unit time. As shown in the graph below, results indicate more product generation in the liver compared to the kidney and muscle samples. Which of the following factors might explain the different results among the three tissues?

1. differences in the transcription of the gene encoding the enzyme among the tissue types 2. differences in the post-translational modifications of the enzyme among the tissue types 3. differences in the translation of the mRNA encoding the protein among the tissue types

Which of the following describes the Lac operon in E. coli when lactose, but not glucose, is present in the culture medium?

CAP, but not the Lac repressor, is bound to the Lac operon's regulatory DNA, and the Lac operon is expressed

Many transcriptional regulators function together to decide the expression level of a particular gene. This describes the concept of

combinatorial control

T or F: A cell can change the expression of its genes in response to external signals

true

T or F: A single transcription regulator, if expressed in the appropriate precursor cell, can trigger the formation of a specialized cell type or even an entire organ

true

T or F: Intense exercise can change gene expression

true

What is the purpose of the protein coded for by the LacY gene?

LacY codes for permease, which is used to transport lactose into the bacterium

T or F: Master regulators such as Ey in Drosophila are so powerful that they can even activate their regulatory networks outside the normal location.

true

T or F: Small interfering RNAs bind to the same RISC proteins that take up miRNAs

true

Which would be the best method for determining which genes are being transcribed in a particular cell type?

RNA sequencing (RNA seq)

Transplanting the nucleus of an epithelial cell into an egg cell lacking genetic information leads to the formation of

a normally developing embryo

What is an operon?

a set of genes transcribed as a single mRNA from a single promoter

How or where do most transcription regulators bind?

as dimers

What must many activator proteins do before they can interact with DNA?

bind to a metabolite or other small molecule

The image shows cells from the same organism. Which of the following statements is correct regarding these two human cells liver and neuron cell?

both cells contain the same genes, but they are expressed differently

In terms of the Trp operon, where would the Trp operon repressor protein most likely bind?

right before E

What are two types of noncoding regulatory RNAs?

siRNAs and miRNAs

Researchers have created plasmids that only allow expression of inserted genes in response to a metabolite. Researchers can add these plasmids to E. coli cells and increase the expression of the inserted gene by adding the appropriate metabolite to the culture media. Plasmids containing which combination of operator and promoter allow activation of gene expression in response to an added metabolite?

strong promoter, operator recognized by Lac repressor protein

What is the ultimate fate of an mRNA that is targeted by a microRNA (miRNA)?

the mRNA will be destroyed by nucleases

Excess amounts of the amino acid tryptophan result in downregulation of the expression of the enzymes required for its synthesis due to

the repressor binding to the operator

Your friend Sara comes to you because she is having trouble understanding her research results in the lab she has just joined and knows you are studying cell biology. She is trying to study lactose breakdown in E. coli, but she finds β-galactosidase is continuously expressed at high levels and does not respond to normal environmental signals. Which of the following would explain her results?

there is a mutation that significantly changes the sequence of the operator

Which of the following statements is NOT true about the differences between liver cells and kidney cells in the same organism?

they contain different genes

What happens to the miRNAs that are bound in a RISC?

they remain bound to the RISC, where they can target the elimination of multiple mRNAs

Which of the following statements about eukaryotic activator proteins is false?

they stimulate transcriptional initiation by opening up the double helix

Which is the main point of control for regulating gene expression levels?

transcription

Although all of the steps involved in expressing a gene can in principle be regulated, what is the most important stage of control for most genes?

transcription initiation