3B Chapter 18 Questions


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What does the operon model attempt to explain?
A) the coordinated control of gene expression in bacteria
The role of a metabolite that controls a repressible operon is to
bind to the repressor protein and activate it.
The tryptophan operon is a repressible operon that is
turned off whenever tryptophan is added to the growth medium.
This protein is produced by a regulatory gene:
A mutation in this section of DNA could influence the binding of RNA polymerase to the
A lack of this nonprotein molecule would result in the inability of the cell to ʺturn offʺ
When this is taken up by the cell, it binds to the repressor so that the repressor no longer
binds to the operator:
A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell
would result in
continuous transcription of the structural gene controlled by that regulator.
The lactose operon is likely to be transcribed when
the cyclic AMP and lactose levels are both high within the cell.
Transcription of the structural genes in an inducible operon
starts when the pathwayʹs substrate is present.
How does active CAP induce expression of the genes of the lactose operon?
It stimulates the binding of RNA polymerase to the promoter.
For a repressible operon to be transcribed, which of the following must occur?
RNA polymerase must bind to the promoter, and the repressor must be inactive.
Allolactose induces the synthesis of the enzyme lactase. An E. coli cell is presented for the
first time with the sugar lactose (containing allolactose) as a potential food source. Which of
the following occurs when the lactose enters the cell?
Allolactose binds to the repressor protein.
Altering patterns of gene expression in prokaryotes would most likely serve the organismʹs
survival in which of the following ways?
allowing the organism to adjust to changes in environmental conditions
In response to chemical signals, prokaryotes can do which of the following?
alter the level of production of various enzymes
Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences
within a prokaryotic genome.

If she moves the promoter for the lac operon to the region between the beta galactosidase
gene and the permease gene, which of the following would be likely?
Beta galactosidase will be produced.
If she moves the operator to the far end of the operon (past the transacetylase gene), which
of the following would likely occur when the cell is exposed to lactose?
The structural genes will be transcribed continuously.
If she moves the repressor gene (lac I), along with its promoter, to a position at some
several thousand base pairs away from its normal position, which will you expect to occur?
The lac operon will function normally.
If glucose is available in the environment of E. coli, the cell responds with very low
concentration of cAMP. When the cAMP increases in concentration, it binds to CAP. Which
of the following would you expect would then be a measurable effect?
increased concentrations of sugars such as arabinose in the cell
Muscle cells and nerve cells in one species of animal owe their differences in structure to
having different genes expressed.
Which of the following mechanisms is (are) used to coordinately control the expression of
multiple, related genes in eukaryotic cells?
organization of the genes into clusters, with local chromatin structures influencing the
expression of all the genes at once
If you were to observe the activity of methylated DNA, you would expect it to
have turned off or slowed down the process of transcription.
Genomic imprinting, DNA methylation, and histone acetylation are all examples of
epigenetic phenomena.
Approximately what proportion of the DNA in the human genome codes for proteins or
functional RNA?
Two potential devices that eukaryotic cells use to regulate transcription are
DNA methylation and histone acetylation.
In both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of
In eukaryotes, transcription is generally associated with
both euchromatin and histone acetylation.
A geneticist introduces a transgene into yeast cells and isolates five independent cell lines
in which the transgene has integrated into the yeast genome. In four of the lines, the
transgene is expressed strongly, but in the fifth there is no expression at all. Which is a
likely explanation for the lack of transgene expression in the fifth cell line?
A transgene integrated into a heterochromatic region of the genome.
During DNA replication,
methylation of the DNA is maintained because methylation enzymes act at DNA sites
where one strand is already methylated and thus correctly methylates daughter
strands after replication.
Eukaryotic cells can control gene expression by which of the following mechanisms?
histone acetylation of nucleosomes
In eukaryotes, general transcription factors
bind to other proteins or to a sequence element within the promoter called the TATA
This binds to a site in the DNA far from the promoter to stimulate transcription:
This can inhibit transcription by blocking the binding of positively acting transcription
factors to the DNA:
This is the site in the DNA located near the end of the final exon, encoding an RNA
sequence that determines the 3ʹ end of the transcript:
Steroid hormones produce their effects in cells by
binding to intracellular receptors and promoting transcription of specific genes.
A researcher found a method she could use to manipulate and quantify phosphorylation
and methylation in embryonic cells in culture. In one set of experiments using this
procedure in Drosophila, she was readily successful in increasing phosphorylation of amino
acids adjacent to methylated amino acids in histone tails. Which of the following results
would she most likely see?
decreased chromatin concentration
A researcher found a method she could use to manipulate and quantify phosphorylation
and methylation in embryonic cells in culture. In one set of experiments she succeeded in
decreasing methylation of histone tails. Which of the following results would she most
likely see?
increased chromatin condensation
A researcher found a method she could use to manipulate and quantify phosphorylation
and methylation in embryonic cells in culture. One of her colleagues suggested she try
increased methylation of C nucleotides in a mammalian system. Which of the following
results would she most likely see?
inactivation of the selected genes
A researcher found a method she could use to manipulate and quantify phosphorylation
and methylation in embryonic cells in culture. She tried decreasing the amount of
methylation enzymes in the embryonic stem cells and then allowed the cells to further
differentiate. Which of the following results would she most likely see?
abnormalities of mouse embryos
Transcription factors in eukaryotes usually have DNA binding domains as well as other
domains also specific for binding. In general, which of the following would you expect
many of them to be able to bind?
other transcription factors
Gene expression might be altered at the level of post-transcriptional processing in
eukaryotes rather than prokaryotes because of which of the following?
Eukaryotic exons may be spliced in alternative patterns.
Which of the following experimental procedures is most likely to hasten mRNA
degradation in a eukaryotic cell?
removal of the 5ʹ cap
Which of the following is most likely to have a small protein called ubiquitin attached to it?
a cyclin that usually acts in G1, now that the cell is in G2
The phenomenon in which RNA molecules in a cell are destroyed if they have a sequence
complementary to an introduced double-stranded RNA is called
RNA interference.
At the beginning of this century there was a general announcement regarding the
sequencing of the human genome and the genomes of many other multicellular eukaryotes.
There was surprise expressed by many that the number of protein-coding sequences is
much smaller than they had expected. Which of the following accounts for most of the rest?
non-protein coding DNA that is transcribed into several kinds of small RNAs with
biological function
Which of the following best describes siRNA?
a short double-stranded RNA, one of whose strands can complement and inactivate a
sequence of mRNA
One of the hopes for use of recent knowledge gained about non-coding RNAs lies with the
possibilities for their use in medicine. Of the following scenarios for future research, which
would you expect to gain most from RNAs?
targeting siRNAs to disable the expression of an allele associated with autosomal
dominant disease
Which of the following describes the function of an enzyme known as Dicer?
It trims small double-stranded RNAs into molecules that can block translation.
In a series of experiments, the enzyme Dicer has been inactivated in cells from various
vertebrates, and the centromere is abnormally formed from chromatin. Which of the
following is most likely to occur?
Centromeres will be euchromatic rather than heterochromatic and the cells will soon
die in culture.
Since Watson and Crick described DNA in 1953, which of the following might best explain
why the function of small RNAs is still being explained?
Changes in technology as well as our ability to determine how much of the DNA is
expressed have now made this possible.
A researcher has arrived at a method to prevent gene expression from Drosophila embryonic genes. The
following questions assume that he is using this method.

The researcher in question measures the amount of new polypeptide production in
embryos from 2—8 hours following fertilization and the results show a steady and
significant rise in polypeptide concentration over that time. The researcher concludes that
the resulting new polypeptides are due to translation of maternal mRNAs.
The researcher continues to study the reactions of the embryo to these new proteins and
you hypothesize that he is most likely to see which of the following (while embryonic genes
are still not being expressed)?
Spatial axes (anterior → posterior, etc.) begin to be determined.
The researcher measures the concentration of the polypeptides from different regions in the
early embryo and finds the following pattern (darker shading = greater concentration):]]

Which of the following would be his most logical assumption?
The substance is produced in region 1 and diffuses toward region
You are given an experimental problem involving control of a geneʹs expression in the
embryo of a particular species. One of your first questions is whether the geneʹs expression
is controlled at the level of transcription or translation. Which of the following might best
give you an answer?
You measure the quantity of the appropriate pre-mRNA in various cell types and
find they are all the same.
In humans, the embryonic and fetal forms of hemoglobin have a higher affinity for oxygen
than that of adults. This is due to
nonidentical genes that produce different versions of globins during development.
The process of cellular differentiation is a direct result of
differential gene expression.
The fact that plants can be cloned from somatic cells demonstrates that
differentiated cells retain all the genes of the zygote.
A cell that remains entirely flexible in its developmental possibilities is said to be
Differentiation of cells is not easily reversible because it involves
frameshift mutations and inversions.
In animals, embryonic stem cells differ from adult stem cells in that
embryonic stem cells are totipotent, and adult stem cells are pluripotent.
Which of the following statements is true about stem cells?
Stem cells can differentiate into specialized cells.
What is considered to be the first evidence of differentiation in the cells of an embryo?
the occurrence of mRNAs for the production of tissue-specific proteins
In most cases, differentiation is controlled at which level?
Which of the following serve as sources of developmental information?
cytoplasmic determinants such as mRNAs and proteins produced before fertilization
The MyoD protein
is a transcription factor that binds to and activates the transcription of muscle-related
The gene for which protein would most likely be expressed as a result of MyoD activity?
The general process that leads to the differentiation of cells is called
Your brother has just purchased a new plastic model airplane. He places all the parts on the
table in approximately the positions in which they will be located when the model is
complete. His actions are analogous to which process in development?
pattern formation
Which of the following is established prior to fertilization in Drosophila eggs?
the anterior-posterior and dorsal-ventral axes
One of the human leukemias, called CML (chronic myelogenous leukemia) is associated
with a chromosomal translocation between chromosomes 9 and 22 in somatic cells of bone
marrow. Which of the following allows CML to provide further evidence of this multi-step
nature of cancer?
The translocation requires breaks in both chromosomes 9 and 22, followed by fusion
between the reciprocal pieces.
The product of the bicoid gene in Drosophila provides essential information about
the anterior-posterior axis.
In colorectal cancer, several genes must be mutated in order to make a cell a cancer cell,
supporting Knudsenʹs hypothesis. Which of the following kinds of genes would you expect
to be mutated?
genes involved in control of the cell cycle
If a Drosophila female has a homozygous mutation for a maternal effect gene,
all of her offspring will show the mutant phenotype, regardless of their genotype.
If there are two children born from the same parents, and child one inherits a
predisposition to retinoblastoma (one of the mutations) and child two does not, but both
children develop the retinoblastoma, which of the following would you expect?
an earlier age of onset in child one
Mutations in these genes lead to transformations in the identity of entire body parts:
homeotic genes
One hereditary disease in humans, called xeroderma pigmentosum (XP), makes
homozygous individuals exceptionally susceptible to UV-induced mutation damage in the
cells of exposed tissue, especially skin. Without extraordinary avoidance of sunlight
exposure, patients soon succumb to numerous skin cancers. Which of the following best
describes this phenomenon?
inherited inability to repair UV-induced mutation
These genes are expressed by the mother, and their products are deposited into the
developing egg:
egg-polarity genes
Which of the following can contribute to the development of cancer?

A) random spontaneous mutations
B) mutations caused by X-rays
C) transposition
D) chromosome translocations
E) all of the above
E) all of the above
These genes map out the basic subdivisions along the anterior-posterior axis of the
Drosophila embryo:
segmentation genes
A genetic test to detect predisposition to cancer would likely examine the APC gene for
involvement in which type(s) of cancer?
colorectal only
These genes form gradients and help establish the axes and other features of an embryo:
Forms of the ras protein found in tumors usually cause which of the following?
growth factor signaling to be hyperactive
Gap genes and pair-rule genes fall into this category:
segmentation genes
The cancer-causing forms of the Ras protein are involved in which of the following
relaying a signal from a growth factor receptor
The product of the bicoid gene in Drosophila could be considered a(n)
cytoplasmic determinant.
The incidence of cancer increases dramatically in older humans because
the longer we live, the more mutations we accumulate.
The bicoid gene product is normally localized to the anterior end of the embryo. If large
amounts of the product were injected into the posterior end as well, which of the following
would occur?
Anterior structures would form in both sides of the embryo.
Tumor suppressor genes
can encode proteins that promote DNA repair or cell-cell adhesion.
Which of the following is characteristic of the product of the p53 gene?
It is an activator for other genes.
What do gap genes, pair-rule genes, segment polarity genes, and homeotic genes all have
in common?
Their products act as transcription factors.
Which of the following statements describes proto-oncogenes?
They can code for proteins associated with cell growth.