Deck 14: Gene Regulation

Question 1

Repressible genes are usually actively transcribed when:

A) repressor molecules bind to the promoter.
B) the end product of the enzymes encoded by these genes is low.
C) tryptophan accumulates in the cell.
D) quantities of precursor materials are high.
E) there is no other substrate that can be used by the cell.

Answer 1

B

Question 2

The organization of the lac operon, from upstream to downstream sequences, is represented by:

A) repressor gene -> lacZ -> lacY -> lac A
B) lacZ -> lacY -> lac A
C) lacZ -> lacY -> lac A -> operator -> promoter
D) operator -> promoter -> lacZ -> lacY -> lac A
E) promoter -> operator -> lacZ -> lacY -> lac A

Answer 2

E

Question 3

Eukaryotes require more complex methods of gene regulation than prokaryotes because:

A) eukaryotes have more operons than prokaryotes.
B) transcriptional regulation is the only form of gene regulation in eukaryotes.
C) all eukaryotic genes are constitutive.
D) eukaryotes have more genes.
E) individual genes must be regulated differentially in each cell type.

Answer 3

E

Question 4

Gene expression in bacteria is regulated primarily by:

A) controlling the rate of DNA replication.
B) protein modifications.
C) protein degradation.
D) transcriptional control.
E) translational control.

Question 5

An inducible operon is usually controlled by:

A) an inducer molecule that keeps it in the "off" state.
B) an active repressor that keeps it in the "off" state.
C) being active at all times.
D) allolactose.
E) being turned "off," usually by the end product of the pathway.

Question 6

In the tryptophan operon, the repressor actively binds to the operator when:

A) tryptophan binds to an allosteric site on the repressor protein, thereby activating it.
B) tryptophan levels are low.
C) lactose levels are low.
D) there is a great need for proteins.
E) allotryptophan levels are low.

Question 7

A new operon is discovered in bacteria. Transcription of the genes in this operon is blocked by the binding of a protein to DNA sequences upstream of the operon. This is an example of ____ control.

A) positive
B) negative
C) constitutive
D) posttranscriptional
E) inducible

Question 8

In the lac operon, cAMP binds to:

A) lacZ.
B) lacA .
C) lacY .
D) the operator.
E) CAP.

Question 9

An activator protein would have which of the following effects on an operon with a positive control mechanism?

A) Stimulate transcription.
B) Turn off transcription.
C) Stimulate transcription when a coactivator is bound to the allosteric site.
D) Inhibit transcription when a coactivator is bound to the allosteric site.
E) Activator proteins only work on operons under negative control.

Question 10

How does the lactose repressor block transcription of the lactose operon?

A) By "turning off" the lacA intron
B) By degrading the lacZ protein product
C) By binding allosterically to the lacZ gene
D) By slowing the uptake of lactose into the cell
E) By binding to the operator

Question 11

Many genes encode proteins that are always needed by a cell, and therefore are always expressed. Such genes are known as:

A) repressible.
B) promoter.
C) constitutive.
D) inducible.
E) operons.

Question 12

Considering that virtually all cells in any given individual contain the same genetic information, how is it possible to have different cell types with unique functions?

A) Gene expression is regulated such that different cell types produce different proteins.
B) All cells express all proteins encoded in an organism's genes, but turn them on selectively.
C) Gene expression is regulated based on the age of the organism.
D) Only some cell types make protein products, while others do not.
E) Cells lose unneeded genes with each cell division.

Question 13

cAMP levels decrease when __________. This results in __________ of CAP.

A) lactose levels increase; activation
B) lactose levels decrease; inhibition
C) glucose levels increase; inhibition
D) glucose levels decrease; activation
E) glucose levels decrease; inhibition

Question 14

A repressible operon is usually controlled by:

A) an inactive repressor that allows it to be in the "on" state.
B) the supply of the precursor product for the enzymes.
C) an inactive repressor that keeps it in the "off" state.
D) tryptophan.
E) being turned "on," usually by the end product of the pathway.

Question 15

Translational controls regulate the:

A) activity of a protein product.
B) rate at which an mRNA molecule is translated.
C) rate at which an mRNA molecule is synthesized.
D) uptake of nucleic acids into the cell.
E) attachment of phosphate groups to polypeptides.

Question 16

A repressor protein would have which of the following effects on repressible genes with a negative control mechanism?

A) Stimulate transcription in the presence of a corepressor.
B) Turn off transcription in the presence of an inducer.
C) Stimulate transcription in the presence of a coactivator.
D) Turn off transcription in the presence of a corepressor.
E) A repressor protein does not participate in negative control mechanisms.

Question 17

Bacteria are able to respond quickly to their surroundings, such as in the presence of an abundant food source. This is because:

A) genes for functionally related enzymes are regulated together in operons.
B) genes for functionally related enzymes are always constitutive.
C) genes for functionally related enzymes are always under positive control.
D) efficient protein degradation removes unneeded proteins quickly.
E) all bacterial genes are constitutive.

Question 18

The function of the catabolite activator protein (CAP) is to:

A) increase the affinity of the promoter region for RNA polymerase.
B) decrease RNA polymerase activity.
C) deactivate RNA polymerase after binding to AMP.
D) bind to and activate RNA polymerase directly.
E) block RNA polymerase from accessing the DNA template.

Question 19

A mutation in the IGF2 gene in pigs results in a three-fold increase in the transcriptional activity of this gene in muscle cells; therefore, these pigs are leaner and more muscular. Because this mutation is located in the noncoding region of the IGF2 gene, we can infer that:

A) the IGF2 gene is a prokaryotic gene.
B) the IGF2 gene is present only in muscle cells, but not in adipose (fat) cells.
C) the mutation changes the amino acid sequence of the IGF2 protein.
D) the mutation alters the regulatory region of the IGF2 gene.
E) less IGF2 protein is synthesized in the muscle cells of these pigs.

Question 20

Bacterial enzymes that are part of a rarely used catabolic pathway are usually organized into a(n) __________.

A) inducible operon
B) repressible operon
C) inducible zinc finger
D) repressible leucine zipper
E) constitutive operon

Question 21

If a mutated region on chromosome 15 is inherited from the father, the child will have Prader-Willi syndrome; however, if the same mutated region is inherited from the mother, the child will have Angelman syndrome. This is an example of:

A) epigenetic inheritance.
B) genetic inheritance.
C) gene amplification.
D) eukaryotic operons.
E) repressible genes.

Question 22

The gene that codes for the repressor protein of the E. coli lac operon is constitutive; therefore, the lac operon is typically:

A) turned off.
B) turned on.
C) unaffected by the repressor protein.
D) constitutive.
E) activated by the repressor protein..

Question 23

Translational controls of protein levels in bacteria are governed by the:

A) rate at which small and large subunits of ribosomes assemble.
B) rate at which the cap and tail of pre mRNA are removed.
C) rate at which ribosomes attach to mRNA molecules.
D) concentration of proteins in the cytoplasm.
E) rate at which sugars are incorporated into the cell.

Question 24

DNA sequences called ____ increase the rate of RNA synthesis after initiation of transcription.

A) promoters
B) TATA boxes
C) silencers
D) enhancers
E) regulators

Question 25

An operon is defined as:

A) a group of structural genes, with no regulatory sequences.
B) regulatory sequences upstream of a structural gene.
C) a group of related structural genes, plus their associated regulatory sequences.
D) one structural gene plus one regulatory gene.
E) a group of unrelated structural genes, plus their associated regulatory sequences.

Question 26

Figure 14-1 Refer to the accompanying figure. The area of the tryptophan operon labeled as 3 is the:

A) promoter.
B) repressor gene.
C) ribosome.
D) RNA polymerase.
E) operator.

Question 27

In an inducible operon, the ____ is the molecular switch that controls gene expression, while the ____ is the DNA region where RNA polymerase binds to begin transcription.

A) repressor; inducer
B) inducer; repressor
C) operator; promoter
D) promoter; operator
E) lactose; promoter

Question 28

Temporal gene regulation refers to which of the following circumstances?

A) Certain genes are induced only at a particular point in the organism's life cycle.
B) Certain genes are induced only in specific tissues.
C) Heat-shock genes are induced during periods of temperature stress.
D) "Housekeeping" genes are induced in response to a viral infection.
E) Molecular chaperones are synthesized after heavy-metal ingestion.

Question 29

Transcriptional activation of the lac operon requires both high lactose and low glucose conditions because:

A) RNA polymerase requires CAP in order to bind to the lac operon promoter, even in the absence of the repressor.
B) glucose normally activates the lac operon repressor.
C) RNA polymerase is inactive in the presence of high glucose concentrations.
D) high glucose concentrations stimulate CAP activity.
E) glucose and lactose compete for binding to, and inactivation of, the lac operon repressor.

Question 30

A TATA box is seen in ____ cells and is the site where ____.

A) prokaryotic; RNA polymerase binds
B) eukaryotic; DNA ligase cleaves introns
C) eukaryotic; RNA polymerase binds
D) both prokaryotic and eukaryotic; transcription factors bind
E) prokaryotic; a repressor protein binds

Question 31

The rate of eukaryotic transcription after initiation is increased by:

A) upstream promoter elements.
B) the order of gene arrangement in operons.
C) the action of catabolite activator proteins.
D) how fast 5' caps and 3' tails can be added to pre-mRNA.
E) enhancers.

Question 32

How is enzyme activity regulated by feedback inhibition?

A) The end product of the metabolic pathway inactivates the first enzyme in the pathway.
B) The end product of the metabolic pathway inactivates the last enzyme in the pathway.
C) The end product of the metabolic pathway induces the first enzyme in the pathway.
D) The end product of the metabolic pathway degrades the first enzyme in the pathway.
E) The end product of the metabolic pathway degrades the last enzyme in the pathway.

Question 33

In Jacob and Monad's analysis of mutant E. coli strains in their study of the lac operon, the absence of the β -galactosidase enzyme, but presence of the lactose permease and galactosidase transacetylase enzymes, indicated that the mutation occurred in the _____ of the lac operon.

A) regulatory region
B) lacZ gene
C) lacA gene
D) lacY gene
E) heterochromatin

Question 34

Feedback inhibition is an example of:

A) translational control.
B) transcriptional control.
C) posttranslational control.
D) a repressible system.
E) constitutive control

Question 35

Figure 14-1 The promoter in the accompanying figure is labeled as ____.

A) 6
B) 3
C) 1
D) 2
E) 7

Question 36

Lactose induces the transcription of the lactose operon by:

A) binding to the allosteric site of the repressor after being converted to allolactose.
B) stimulating lactose metabolism in the cell.
C) first being converted to glucose, then binding to the repressor.
D) binding to the allosteric site of RNA polymerase.
E) inhibiting the activity of CAP.

Question 37

Inducible genes are usually actively transcribed when:

A) an inducer inactivates the repressor.
B) repressor molecules bind to the promoter.
C) lactose is absent from the cell.
D) expression of repressor genes is turned off.
E) energy is not needed by the cell.

Question 38

The function of upstream promoter elements in eukaryotes, such as enhancers and silencers, is to:

A) serve as binding sites for RNA polymerase.
B) regulate the efficiency of transcription initiation.
C) regulate RNA polymerase binding to the TATA box.
D) encode enhancer and silencer proteins.
E) add methyl groups to genes.

Question 39

Figure 14-1 Refer to the accompanying figure. The structure labeled as 7 in the figure of the tryptophan operon is a(n):

A) active repressor protein.
B) inactive repressor protein.
C) active RNA polymerase.
D) inactive RNA polymerase.
E) ribosome.

Question 40

Under high tryptophan conditions, tryptophan binds to and activates the repressor protein, thereby blocking transcription of the trp operon. This is an example of:

A) protein degradation.
B) negative control of inducible genes.
C) negative control of repressible genes
D) positive control of inducible genes.
E) positive control of repressible genes.

Question 41

Enzymes that alter another protein or enzyme's activity by attaching a phosphate group are called:

A) kinases.
B) phosphatases.
C) phosphators.
D) transcription factors.
E) coenzymes.

Question 42

Eukaryotic transcription factors are best described as:

A) regulators of transcription initiation of operons.
B) containing only a regulatory domain.
C) containing only a DNA binding domain.
D) containing a DNA binding domain plus one or more regulatory domains.
E) imprinted genes.

Question 43

Explain the respective advantages associated with operons being inducible (e.g., the lactose operon) or repressible (e.g., the tryptophan operon).

Question 44

A cell may meet the demand for large quantities of a specific protein by:

A) blocking transcription of the gene that encodes the protein.
B) decreasing the half-life of the mRNA that specifies the protein.
C) adding methyl groups to the gene that encodes the protein.
D) gene amplification
E) inhibition of DNA synthesis

Question 45

Transcription factors that increase the rate of transcription by binding a target in the general transcriptional machinery and an enhancer are known specifically as:

A) activator proteins.
B) leucine zipper proteins.
C) helix-turn-helix proteins.
D) zinc finger proteins.
E) lnc RNAs

Question 46

Constitutive genes code for proteins that are needed for survival.
__________________

Question 47

When the intracellular level of lactose drops, the repressor protein binds to the operator of the lac operon and shuts down translation of the lac structural genes.
__________________

Question 48

Some transcription factors, such as leucine zipper proteins, form homodimers or heterodimers. How does this increase the complexity of available strategies of gene regulation?

Question 49

Leucine zipper proteins regulate transcription by:

A) forming dimers with zinc finger transcription factors.
B) changing the chromatin structure to heterochromatin
C) blocking DNA regulatory elements.
D) binding to and activating DNA regulatory elements such as enhancers and silencers.
E) degrading RNA polymerase.

Question 50

_____ are densely staining, highly compacted, and transcriptionally inactive regions of chromatin.

A) Homochromatin
B) Heterochromatin
C) Histone-dependent chromatin
D) Primary chromatin
E) Euchromatin

Question 51

Genes in euchromatic regions are:

A) transcriptionally inactive.
B) duplicated
C) transcriptionally active.
D) repressed.
E) unregulated.

Question 52

Methylated DNA sequences typically contain ____ genes.

A) transcriptionally active
B) transcriptionally inactive
C) constitutive
D) housekeeping
E) alternatively spliced

Question 53

Identify two ways in which posttranscriptional gene regulation occurs in eukaryotes and briefly explain each.

Question 54

Proteolytic processing of eukaryotic proteins involves:

A) removal of a portion of the polypeptide chain from an inactive protein precursor.
B) the addition of one or more functional groups to a precursor protein.
C) the removal of one or more functional groups from a precursor protein.
D) removal of histones.
E) removing the cap and tail of a newly synthesized protein.

Question 55

Eukaryotic transcription factors:

A) are known as CAPs.
B) may be activators or repressors of transcription.
C) are inducers.
D) are corepressors.
E) are also known as enhancers.

Question 56

Some eukaryotic DNA sequences act as introns in the cells of some tissues and exons in the cells of other tissues. This is an example of ____, and allows for ____.

A) positive control; feedback inhibition
B) gene amplification; the regulation of the rate of transcription
C) alternative splicing; the formation of different types of closely related proteins
D) DNA methylation; the formation of different types of closely related proteins
E) DNA replication; heterodimer formation

Question 57

In female mammals, most of the inactive X chromosome becomes:

A) associated with histones.
B) transcriptionally active.
C) euchromatin.
D) replicated.
E) heterochromatin.

Question 58

Why is it important that a few β -galactosidase molecules be present in E. coli even if these cells have been growing on a lactose-free medium?

Question 59

In an operon, the switch that controls mRNA synthesis is the promotor , which is a sequence of bases upstream from the first structural gene.
__________________

Question 60

Long coding RNAs (lnc RNAs) are characterized by:

A) the presence of introns.
B) the lack of a polyA tail.
C) their roles in regulating transcription.
D) being less than 100 bases in length.
E) binding to zinc finger transcription factors.

Question 61

Acetyl groups attached to histone tails generally indicate that the genes associated with this nucleosome will be transcriptionally inactive .

Question 62

Processing of prokaryotic mRNA molecules, such as splicing and polyadenylation, allows for greater posttranscriptional regulation.

Question 63

Eukaryotes have inducible genes that respond to environmental stimuli.
__________________

Question 66

Repressible genes typically regulate gene expression of enzymes involved in anabolic pathways.
__________________

Question 67

Sketch the main elements of an inducible operon, such as the lactose operon, and explain the functions of the operator and promoter regions.

Question 68

Proteolytic processing, chemical modification, and protein degradation are all methods of posttranslational regulation mechanism.

Question 69

Explain how epigenetic inheritance (for example, DNA methylation) can result in different phenotypes observed in identical twins (who have identical DNA sequences).

Question 70

The binding of active CAP to the lac operon promoter decreases the rate of transcription of the lac operon.
__________________

Question 71

Mutations in the TATA box increase the rate of transcription.
__________________

Question 72

DNA methylation suppresses gene expression in eukaryotes.
____________________

Question 73

miRNA-protein complexes regulate gene expression by binding to a target mRNA and preventing translation.

Question 74

The leucine zipper has a unique structure compared to the other transcription factors because it is a(n) dimer . __________________

Question 75

Genomic imprinting is an example of epigenetics.
__________________

Question 76

The general transcriptional machinery is composed of the regulatory proteins bound to the promoter of a eukaryotic gene.

Question 77

Outline the various methods of gene regulation in eukaryotic cells. Include chromatin, transcriptional, posttranscriptional, translational, and posttranslational levels of regulation.