Chapter 18: Regulation of Gene Expression

The discovery of many noncoding RNAs is causing scientists to revise the long-held view that __________. a. the vast majority of the human genome consists of "junk" DNA b. only DNA that codes for protein, tRNA, and rRNA is transcribed c. there are only three types of RNA—tRNA, rRNA, and mRNA d. all genes code for proteins e. All of the listed responses are correct.

All of the listed responses are correct. All of the listed "facts" have been challenged by the discovery of a number of types of RNA that do not code for protein.

Which of the following is/are involved in controlling eukaryotic gene expression? a. transcriptional regulation b. DNA packing c. methylation of DNA d. mRNA processing e. All of the listed responses are correct.

All of the listed responses are correct. All of the listed responses do play a role in the regulation of eukaryotic gene expression.

Which of the following statement(s) about feedback inhibition is/are true? a. It allows a cell to adapt quickly to fluctuations in the availability of important substances. b. The end product of the metabolic pathway controls the activity of the first enzyme in the pathway. c. If the end product accumulates in the cell, the whole pathway is shut down. d. It is common in anabolic pathways. e. All of the listed responses are correct.

All of the listed responses are correct. All of these statements about feedback inhibition are true.

Enhancers __________. a. may be located upstream or downstream from the genes they regulate b. increase the rate of transcription c. may be located thousands of base pairs away from the promoter d. are found in eukaryotic genomes e. All of the listed responses are correct.

All of the listed responses are correct. Enhancers increase the rate of transcription and may be located thousands of base pairs away from the promoter, either upstream or downstream.

Post-transcriptional controls of gene expression __________. a. may involve regulation of mRNA splicing b. may involve changes to the rate at which an mRNA is translated c. can include translational controls d. can include changes to mRNA stability e. All of the listed responses are correct.

All of the listed responses are correct. Post-transcriptional control can occur at many steps, including mRNA stability, splicing, and translation.

It is hypothesized that an increase in the number and diversity of noncoding RNA (ncRNA) in the genomes of species has driven the evolution of morphological complexity by way of their influence on gene regulation. Which of the following accurately represents our current understanding of the role that ncRNA is thought to play in gene regulation? a. Some ncRNA can promote the formation of heterochromatin, thereby blocking the expression of genes in the tightly coiled region. b. ncRNAs can re-establish proper patterns of DNA methylation in the genome during gamete formation. c. ncRNAs can fine-tune translation by binding with mRNA via complementary base pairing and promote the degradation of the mRNA strand or block its translation. d. Whereas some ncRNA block the transcription and translation of some genes, others have been observed to activate gene expression. e. All of the listed responses are correct.

All of the listed responses are correct. Recent findings suggest that ncRNAs play a vital role in most aspects of gene regulation in eukaryotic organisms and, in doing so, may have provided the basis for the evolution of a higher degree of complexity of form.

Why is cancer more prevalent in older people? a. Cancer is caused by viruses, and older people are more susceptible to viral infections. b. Cancer lies dormant for many years before causing problems. c. Most cancers are inherited as a recessive allele, so it takes time for the allele to be expressed. d. Cancer involves an accumulation of mutations, and older people have had more time to accumulate mutations in their DNA. e. Cancer involves changes in gene expression, and it takes many years for gene expression to change.

Cancer involves an accumulation of mutations, and older people have had more time to accumulate mutations in their DNA. Older people have simply had more cell divisions, more exposure to environmental carcinogens, and so on. Chance dictates that they have had more opportunities for mutations to occur.

Which of the following best describes the current understanding of the makeup of the human genome? a. Most of the genome consists of protein-coding DNA. b. Most of the genome does not contain meaningful genetic information and is not transcribed. c. Genes for noncoding RNA make up the majority of meaningful genetic information in the human genome. d. A large proportion of DNA consists of genes for ribosomal RNA and transfer RNA, whose transcripts are not translated. e. None of the listed responses is correct.

Genes for noncoding RNA make up the majority of meaningful genetic information in the human genome. Our growing understanding of the human genome is revealing that much of it is transcribed but not translated to form a large repertoire of small and large RNA molecules that play a vital role in gene regulation and likely in other processes that have not yet been discovered.

Which of the following accurately characterizes our current understanding of cancer development? a. We now understand that all cancers result from some mutation in the p53 gene. b. Study results suggest that mutations in genes that are transcribed into ncRNA do not likely contribute to cancer development. c. Nearly all cancers are caused by the multistep accumulation of mutations over the life-span of the individual. d. In order for a cell to become fully cancerous, it typically must have at least one active oncogene and the mutation or loss of several tumor-suppressor genes. e. Mutations in a single gene cannot significantly increase susceptibility to cancer.

In order for a cell to become fully cancerous, it typically must have at least one active oncogene and the mutation or loss of several tumor-suppressor genes. Our current understanding suggests that several key changes must occur in the DNA of a cell before it can become cancerous. These changes are brought about by mutations to convert a proto-oncogene to an active oncogene and the loss of tumor-suppressing proteins such as p53.

What is the evolutionary significance of alternative RNA splicing? a. It acts as a defense against viral RNA, helping organisms avoid infection, particularly by cancer-causing viruses. b. It expands the number of proteins that can be coded for by one gene, increasing an organism's ability to produce novel proteins. c. Because it is not specific to a cell type, alternative RNA splicing can make sweeping changes in gene expression, allowing an organism to adapt quickly to new situations. d. It can silence genes, giving cells another way of controlling gene expression. e. The introns that are spliced out can become miRNAs and can recognize and degrade mRNA transcripts.

It expands the number of proteins that can be coded for by one gene, increasing an organism's ability to produce novel proteins. Some genes could produce thousands of different proteins from a primary transcript. In most cases, only a few of the possibilities are actually produced. However, different splicing could give rise to novel proteins, some of which could be advantageous.

This chapter contains a lengthy discussion of the trp operon involved in regulating the synthesis of tryptophan. In the case of E. coli, the bacterium may need to synthesize tryptophan, or its host, a human, may supply all the tryptophan it needs. Why do both bacteria and humans need tryptophan? a. It is one of the 20 amino acids used by all organisms to synthesize proteins. b. It is an important constituent of cell walls in both humans and bacteria. c. It is important in inducing sleep. d. It is an important enzyme in the glycolysis pathway. e. Tryptophan induces the lac operon.

It is one of the 20 amino acids used by all organisms to synthesize proteins. All organisms need tryptophan, but there is no point in wasting resources to synthesize it if it is available in the environment.

Which of the following statements about the DNA in one of your brain cells is true? a. The majority of genes are likely to be transcribed. b. Many genes are grouped into operon-like clusters. c. It is the same as the DNA in one of your heart cells. d. Each gene lies immediately adjacent to an enhancer. e. Most of the DNA codes for protein.

It is the same as the DNA in one of your heart cells.

In what way can cancer be hereditary? a. Proto-oncogenes can be inherited, giving the person a predisposition to developing cancer. b. Tumor-suppressor genes can be inherited, giving the person a predisposition to developing cancer. c. One or two of several mutations necessary for full cancer development can be inherited, giving a person a predisposition to developing cancer. d. A person can inherit cancer cells from one of his/her parents. e. All of the mutations necessary for full cancer development can be inherited, giving a person a predisposition to developing cancer.

One or two of several mutations necessary for full cancer development can be inherited, giving a person a predisposition to developing cancer. Because most cancers involve several mutations, a person who inherits one or more of these mutations will be more susceptible to cancer, but will not necessarily develop it.

Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cells? a. Cells produce proto-oncogenes as they age. b. Proto-oncogenes are genetic "junk." c. Proto-oncogenes are mutant versions of normal genes. d. Proto-oncogenes first arose from viral infections. e. Proto-oncogenes normally help regulate cell division.

Proto-oncogenes normally help regulate cell division.

Which of the following best depicts coordinate control of genes in eukaryotes? a. Different genes for proteins involved in a specific metabolic process typically share the same enhancer regions. b. Although a group of genes involved in a related metabolic process are typically scattered over different chromosomes, their co-activation is achieved by every gene of the group sharing a specific combination of control elements and activator molecules that bind to them. c. Although a group of genes involved in a related metabolic process are typically scattered over different chromosomes, coordinated expression of this group is enhanced by the congregation of loops from different chromosomes in a specific site of the nucleus to form a transcription factory. d. The first and second listed responses are correct. e. The second and third listed responses are correct.

The second and third listed responses are correct. Coordinate control of genes involved in a specific cellular process but scattered over different chromosomes is facilitated by: 1) a specific combination of control elements and activator molecules being shared by every gene of a dispersed group and 2) the congregation of the dispersed genes on different chromosomes into transcription factories within the nucleus.

A high rate of gene transcription in eukaryotic cells is usually dependent on __________. a. the binding of general transcription factors to the TATA box within the promoter of a gene b. the coordinated control of genes within operons c. specific binding of activator molecules to enhancers d. protein-protein interactions that are promoted by the activation domains of activator proteins e. The third and fourth listed responses are correct.

The third and fourth listed responses are correct. Specific binding of activator molecules to enhancers and the protein-protein interactions that are promoted by the activation domains of activator proteins equate to elevated rates of gene transcription.

What is the role of proteasomes? a. They inject double-stranded RNA into a cell, turning off a gene with the same sequence. b. They are segments of noncoding DNA that help regulate transcription by binding certain proteins. c. They are giant protein complexes that recognize ubiquitin and degrade the tagged proteins. d. They encode for products that help prevent uncontrolled cell growth. e. None of the listed responses is correct.

They are giant protein complexes that recognize ubiquitin and degrade the tagged proteins. Mutations that make cell cycle proteins impervious to proteasome degradation can lead to cancer.

Oncogene

a gene found in viral or cellular genomes that is involved in triggering molecular events that can lead to cancer

Ras Gene

a gene that codes for Ras, a G protein that relays a growth signal from a growth factor receptor on the plasma membrane to a cascade of protein kinases, ultimately resulting in stimulation of the cell cycle

Regulatory Gene

a gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes

Egg-Polarity Gene

a gene that helps control the orientation (polarity) of the egg; also called a maternal effect gene

Maternal Effect Gene

a gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the offspring's genotype; maternal effect genes, also called egg-polarity genes, were first identified in Drosophila melanogaster

Tumor-Suppressor Gene

a gene whose protein product inhibits cell division, thereby preventing the uncontrolled cell growth that contributes to cancer

Bicoid

a maternal effect gene that codes for a protein responsible for specifying the anterior end in Drosophila melanogaster

Cytoplasmic Determinant

a maternal substance, such as a protein or RNA, that when placed into an egg influences the course of early development by regulating the expression of genes that affect the developmental fate of cells

RNA Interference (RNAi)

a mechanism for silencing the expression of specific genes; in RNAi, double-stranded RNA molecules that match the sequence of a particular gene are processed into siRNAs that either block translation or trigger the degradation of the gene's messenger RNA; this happens naturally in some cells, and can be carried out in laboratory experiments as well

Instead of developing a head and a tail, an abnormal Drosophila embryo develops two tails. This is most likely due to __________. a. apoptosis b. destruction of the RNA polymerase molecules responsible for the transcription of genes that encode head-related proteins c. a failure involving post-transcriptional modification of mRNA d. a mutation in an operon e. a mutation in a maternal effect gene

a mutation in a maternal effect gene Some maternal effect genes provide positional information in the developing embryo. Mutations in these genes can cause abnormal development.

Embryonic Lethal

a mutation with a phenotype leading to death of an embryo or larva

Proto-Oncogene

a normal cellular gene that has the potential to become an oncogene

Induction

a process in which a group of cells or tissues influences the development of another group through close-range interactions

activator

a protein that binds to DNA and stimulates gene transcription. In prokaryotes, activators bind in or near the promoter; in eukaryotes, activators generally bind to control elements in enhancers

Repressor

a protein that inhibits gene transcription; in prokaryotes, repressors bind to the DNA in or near the promoter; in eukaryotes, repressors may bind to control elements within enhancers, to activators, or to other proteins in a way that blocks activators from binding to DNA

Enhancer

a segment of eukaryotic DNA containing multiple control elements, usually located far from the gene whose transcription it regulates

Control Element

a segment of noncoding DNA that helps regulate transcription of a gene by serving as a binding site for a transcription factor; multiple control elements are present in a eukaryotic gene's enhancer

Corepressor

a small molecule that binds to a bacterial repressor protein and changes the protein's shape, allowing it to bind to the operator and switch an operon off

MicroRNA (miRNA)

a small, single-stranded RNA molecule, generated from a double-stranded RNA precursor; the miRNA associates with one or more proteins in a complex that can degrade or prevent translation of an mRNA with a complementary sequence

Inducer

a specific small molecule that binds to a bacterial repressor protein and changes the repressor's shape so that it cannot bind to an operator, thus switching an operon on

Morphogen

a substance, such as Bicoid protein in Drosophila, that provides positional information in the form of a concentration gradient along an embryonic axis

P53 Gene

a tumor-suppressor gene that codes for a specific transcription factor that promotes the synthesis of proteins that inhibit the cell cycle

Alternative RNA Splicing

a type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

Operon

a unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a coordinately regulated cluster of genes whose products function in a common pathway

Histogram

a variant of a bar graph that is made for numeric data by first grouping, or "binning," the variable plotted on the x-axis into intervals of equal width; the "bins" may be integers or ranges of numbers; the height of each bar shows the percent or number of experimental subjects whose characteristics can be described by one of the intervals plotted on the x-axis

You have inserted the gene for human growth factor into the E. coli lactose operon, replacing the structural genes with the gene for human growth factor. What substance must you add to your culture of bacteria to cause them to produce human growth factor for you? a. operator protein b. transcription factors c. repressor protein d. allolactose e. human growth factor

allolactose Allolactose will bind to the repressor protein, inactivating it, and allowing transcription of the genes in the operon, including human growth factor.

Although the number of genes in the human genome is surprisingly low compared to less complex organisms, the number of possible products from those genes is greatly amplified by __________. a. each gene being activated by a unique combination of control elements and activator molecules b. coordinate control of genes on different chromosomes c. alternate arrangements of exons from a primary transcript d. differential activation of genes in different cell types e. the congregation in specific sites in the nucleus of genes involved in related metabolic processes, but on different chromosomes

alternate arrangements of exons from a primary transcript It is now thought that 75 to 100% of genes with multiple exons in the human genome undergo some degree of alternate splicing, thereby greatly increasing the number of possible human proteins and helping to account for the complex morphology in the human form.

In prokaryotic genomes, groups of functionally related genes along with their promoters and operators are found together in __________. a. an operon b. an enhancer c. a regulatory gene d. a repressor e. a transcription factor

an operon Putting these related sequences together helps prokaryotes keep related genes under coordinate control.

Homeotic Gene

any of the master regulatory genes that control placement and spatial organization of body parts in animals, plants, and fungi by controlling the developmental fate of groups of cells

Cytoplasmic determinants __________. a. are coded for by maternal genes b. act by binding to a plasma protein receptor that then initiates a signal-transduction pathway c. are coded for by embryonic genes d. are carried to the ovum by the sperm e. are coded for by paternal genes

are coded for by maternal genes Cytoplasmic determinants are stored in egg cells by the mother before fertilization. Mutations in the mother's genes can lead to defects such as a fly embryo having two heads.

Most human cancers are __________. a. caused by the accumulation of somatic mutations b. caused by radiation c. caused by viruses d. inherited from both parents, like an autosomal recessive allele e. inherited from one parent, like an autosomal dominant allele

caused by the accumulation of somatic mutations Most human cancers result from the accumulation of multiple mutations in a single somatic cell that then loses control over its rate of growth and cell division.

A scientist clones a regulatory gene that is involved in controlling the expression of other genes, and discovers that the regulatory gene encodes an enzyme that acetylates histones. It is likely that this enzyme regulates gene expression by __________. a. causing tighter packing of the chromatin at the target gene, thereby enhancing transcription b. causing looser packing of the chromatin at the target gene, thereby inhibiting transcription c. causing looser packing of the chromatin at the target gene, thereby enhancing transcription d. causing tighter packing of the chromatin at the target gene, thereby inhibiting translation e. causing tighter packing of the chromatin at the target gene, thereby inhibiting transcription

causing looser packing of the chromatin at the target gene, thereby enhancing transcription Acetylation promotes a more open chromatin structure, making DNA more accessible for transcription.

A bacterium can make the amino acid glycine or absorb it from its surroundings. A biochemist finds that glycine binds to a repressor protein and causes the repressor to bind to the bacterial chromosome, turning off an operon. If it is like other similar operons, the presence of glycine will result in the __________. a. inhibition of bacterial cell division b. production of the repressor protein c. breakdown of glycine d. cessation of the synthesis of glycine e. formation of sex pili

cessation of the synthesis of glycine Because synthesis of glycine requires energy and raw materials, it does not make sense to synthesize it when it is available in the environment.

Which of the following statements is NOT associated with epigenetic inheritance? a. removal of acetyl groups from histones b. DNA phosphorylation c. histone acetylation d. chemical mutagens e. DNA methylation

chemical mutagens By definition, chemical mutagens are chemical agents that can cause an inheritable change in the nucleotide sequence of an organism's DNA. All the other answers are examples of changes made to DNA other than the nucleotide sequence that can affect gene expression and are inheritable.

What would occur if the repressor of an inducible operon were mutated so it could not bind the operator? a. irreversible binding of the repressor to the promoter b. continuous transcription of the operon's genes c. reduced transcription of the operon's genes d. buildup of a substrate for the pathway controlled by the operon e. overproduction of catabolite activator protein (CAP)

continuous transcription of the operon's genes

In eukaryotes, DNA packing seems to affect gene expression primarily by __________. a. allowing unpacked genes to be eliminated from the genome b. protecting DNA from mutations c. controlling access to DNA d. enhancing the recombination of genes e. positioning related genes near each other

controlling access to DNA For example, the genes of tightly packed heterochromatin are usually not transcribed, presumably because RNA polymerase and other necessary proteins can't make contact with the DNA.

Gene expression in bacteria is regulated primarily by __________. a. transcription factors encoded for by mitochondrial DNA b. selectively breaking down the proteins encoded by the genes c. controlling the transcription of genes into mRNA d. controlling the translation of mRNA to produce polypeptides e. controlling gene packing and unpacking

controlling the transcription of genes into mRNA In prokaryotes, most gene expression is regulated by controlling transcription.

Cyclic AMP (cAMP)

cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells; it is also a regulator of some bacterial operons

A cancer cell __________. a. is typically more than 10 times larger than a normal cell b. requires less nutrients than a normal cell c. does not respond to the chemical signals that control cell division d. usually does not contain a nucleus e. All of the listed responses are correct.

does not respond to the chemical signals that control cell division Cancer is a set of diseases in which cells escape from the control mechanisms that normally limit their rate of division.

In a eukaryote, transcription factors called activators may stimulate gene expression by binding to DNA sites called __________. a. operons b. promoters c. silencers d. histones e. enhancers

enhancers Enhancers are sites within the DNA where activators bind, increasing the rate of transcription.

Muscle cells differ from nerve cells mainly because they a. express different genes. b. use different genetic codes. c. have unique ribosomes. d. have different chromosomes. e. contain different genes.

express different genes.

The expression of a gene located in a tightly coiled region of DNA can be promoted by __________. a. methylation of histone tails b. the arrival of the RNA polymerase c. removal of acetyl groups from histones d. histone acetylation e. demethylation of DNA

histone acetylation Addition of acetyl groups to the amino acid lysine in the histone tails neutralizes the positive charge of this amino acid so that the histone tails no longer bind to neighboring nucleosomes, thus giving the chromatin a looser structure.

The control of gene expression is more complex in multicellular eukaryotes than in prokaryotes because __________. a. prokaryotes are restricted to stable environments b. eukaryotic cells are much smaller c. many genes of eukaryotes provide information for making polypeptides d. in a multicellular eukaryote, different cells are specialized for different functions e. eukaryotic chromosomes have fewer nucleotides; therefore, each nucleotide sequence must do several jobs

in a multicellular eukaryote, different cells are specialized for different functions Also, eukaryotic cells are more complex than prokaryotic cells.

Operator

in bacterial and phage DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach; the binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon

Cells can influence each other's development by a process known as __________. a. transduction b. induction c. apoptosis d. differentiation e. determination

induction Induction occurs when cell signals from one cell affect the development of nearby cells.

Epigenetic Inheritance

inheritance of traits transmitted by mechanisms that do not involve the nucleotide sequence

Cell differentiation is first observable when __________. a. patterns of mitosis change in different cells b. the genome of a particular cell changes c. a cell appears different under the microscope d. mRNAs for tissue-specific proteins appear in a cell e. apoptosis occurs

mRNAs for tissue-specific proteins appear in a cell Even before a cell's structure begins to change, differentiation is heralded by the appearance of these mRNAs in the cell.

Positional Information

molecular cues that control pattern formation in an animal or plant embryonic structure by indicating a cell's location relative to the organism's body axes; these cues elicit a response by genes that regulate development

Specific cells that appear undifferentiated under the microscope but are already fated to become muscle cells are called __________. a. muscle cells b. myoblasts c. bicoids d. myosins e. embryonic cells

myoblasts Under certain conditions precursor cells undergo changes in gene expression that commit them to becoming muscle cells. Once this differentiation has occurred, the cells are called myoblasts.

Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene a. normally leads to formation of tail structures. b. is transcribed in the early embryo. c. leads to programmed cell death. d. normally leads to formation of head structures. e. is a protein present in all head structures.

normally leads to formation of head structures.

What determines how long a particular mRNA molecule will persist in a eukaryotic cell? a. the number of introns removed during processing b. the number of exons removed during processing c. nucleotide sequences in the 3′ untranslated region of the mRNA d. the presence of proteasomes in the cytoplasm e. the length of the 5′ cap

nucleotide sequences in the 3′ untranslated region of the mRNA Nucleotide sequences in the untranslated region at the 3′ end of the molecule seem to be crucial in determining how long-lived a particular mRNA is.

Small Interfering RNA (siRNA)

one of multiple small, single-stranded RNA molecules generated by cellular machinery from a long, linear, double-stranded RNA molecule; the siRNA associates with one or more proteins in a complex that can degrade or prevent translation of an mRNA with a complementary sequence

MicroRNAs and small interfering RNAs both function similarly in "silencing" genes. What are two ways in which they may act? a. cut up mRNAs using the Dicer enzyme and bind to complementary DNA sequences to prevent transcription b. promote the degradation of mRNA and inhibit RNA splicing c. promote the degradation of mRNA and bind to complementary mRNA sequences to prevent translation d. cut up mRNAs using the Dicer enzyme and bind to complementary mRNA sequences to prevent translation e. inhibit RNA splicing and bind to complementary DNA sequences to prevent transcription

promote the degradation of mRNA and bind to complementary mRNA sequences to prevent translation miRNAs and siRNAs act in both of these ways to prevent a transcribed gene from being translated into protein. In addition to their normal roles in cells, researchers see these RNAs as useful tools in studying the function of genes by being able to silence them.

What two genes are often mutated in colon cancer? a. BRCA1 and BRCA2 b. ras and p53 c. APC and myoD d. ras and myoD e. p21 and p53

ras and p53 ras, an oncogene, and p53, a tumor-suppressor gene, are often found to be mutated in colon cancers.

In general, operons that encode the enzymes of a biosynthetic (anabolic) pathway (such as the trp operon) are __________, and those encoding the enzymes of a catabolic pathway (such as the lac operon) are __________. a. inducible ... repressible b. permanently on ... permanently off c. permanently off ... permanently on d. easily mutated ... resistant to mutations e. repressible ... inducible

repressible ... inducible Anabolic pathways are generally on unless their product is not needed. Catabolic pathways need to adjust to the available substrate.

In some cases, DNA methylation and removal of acetyl groups from histones (i.e., deacetylation) combine to __________. a. remove genomic imprinting b. form a transcription factor c. silence certain genes d. form an enhancer e. turn certain genes on

silence certain genes Both DNA methylation and histone deacetylation tend to repress transcription.

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of causing cancer and birth defects in animals and humans. It apparently acts by entering cells and binding to specific proteins, which then enter the nucleus and alter the pattern of gene expression. Therefore, dioxin acts by mimicking the action of __________. a. enhancers b. histones c. steroid hormones d. DNA polymerase e. proteins of the mitochondria

steroid hormones Steroid hormones enter cells, bind to specific receptors, and enter the nucleus to affect transcription.

In the human genome, oncogenes __________. a. promote cell adhesion b. enhance DNA repair c. suppress tumors d. slow cell division e. stimulate cell division

stimulate cell division Oncogenes stimulate cell division.

In an inducible operon, the inducer is often the __________ in the pathway being regulated; the inducer binds to the __________, which then becomes __________. a. substrate ... repressor ... active b. substrate ... corepressor ... inactive c. substrate ... repressor ... inactive d. end product ... corepressor ... inactive e. end product ... repressor ... inactive

substrate ... repressor ... inactive The presence of the substrate turns the operon on by binding to the repressor and inactivating it.

If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then a. the amino acid inactivates the repressor. b. the repressor is active in the absence of the amino acid. c. the amino acid acts as a corepressor. d. the enzymes produced are called inducible enzymes. e. the amino acid turns on transcription of the operon.

the amino acid acts as a corepressor.

Histone Acetylation

the attachment of acetyl groups to certain amino acids of histone proteins

Pattern Formation

the development of a multicellular organism's spatial organization, the arrangement of organs and tissues in their characteristic places in three-dimensional space

Morphogenesis

the development of the form of an organism and its structures

Differential Gene Expression

the expression of different sets of genes by cells with the same genome

What gene has been called the "guardian angel of the genome"? a. the myoD gene b. the BRCA1 gene c. the p53 gene d. the ras gene e. the p21 gene

the p53 gene The p53 gene can activate several genes involved in DNA repair, halting of the cell cycle, or initiation of apoptosis.

DNA Methylation

the presence of methyl groups on the DNA bases (usually cytosine) of plants, animals, and fungi; (The term also refers to the process of adding methyl groups to DNA bases.)

Differentiation

the process by which a cell or group of cells becomes specialized in structure and function

Cell differentiation always involves a. the transcription of the myoD gene. b. the cell's sensitivity to environmental cues, such as light or heat. c. the movement of cells. d. the selective loss of certain genes from the genome. e. the production of tissue-specific proteins, such as muscle actin.

the production of tissue-specific proteins, such as muscle actin.

Determination

the progressive restriction of developmental potential in which the possible fate of each cell becomes more limited as an embryo develops; at the end of determination, a cell is committed to its fate

Within a cell, the amount of protein made using a given mRNA molecule depends partly on a. the degree of DNA methylation. b. the presence of certain transcription factors. c. the types of ribosomes present in the cytoplasm. d. the number of introns present in the mRNA. e. the rate at which the mRNA is degraded.

the rate at which the mRNA is degraded.

Which of the following is an example of post-transcriptional control of gene expression? a. gene amplification contributing to cancer b. the removal of introns and alternative splicing of exons c. the addition of methyl groups to cytosine bases of DNA d. the binding of transcription factors to a promoter e. the folding of DNA to form heterochromatin

the removal of introns and alternative splicing of exons

Both repressible and inducible operons control gene expression at the level of __________. a. transcription b. translation c. post-transcriptional processing d. post-translational processing e. DNA packing

transcription The repressors that attach to operators act to block transcription.

The functioning of enhancers is an example of a. post-translational control that activates certain proteins. b. a eukaryotic equivalent of prokaryotic promoter functioning. c. transcriptional control of gene expression. d. a post-transcriptional mechanism to regulate mRNA. e. the stimulation of translation by initiation factors.

transcriptional control of gene expression.

The BRCA1 and BRCA2 genes are thought to be what type of genes? a. tumor-suppressor genes b. viral genes c. transcription factor genes d. oncogenes e. proto-oncogenes

tumor-suppressor genes They are thought to be tumor-suppressor genes because the wild-type alleles protect against breast cancer.

MyoD promotes muscle cell development by __________. a. enhancing apoptosis of non-muscle cells b. increasing the translation of muscle-related genes c. stimulating a receptor on the surface of muscle cells, thus activating a signal-transduction pathway that promotes muscle development d. stimulating the production of muscle-specific splicing variants of certain mRNAs e. turning on the expression of multiple muscle-related genes

turning on the expression of multiple muscle-related genes MyoD is a protein that acts as a transcription factor to turn on many genes involved in muscle cell development, including the gene that codes for MyoD.