12
40) In an experimental situation, a student researcher inserts an mRNA molecule into a
eukaryotic cell after he has removed its 5' cap and poly(A) tail. Which of the following would
you expect him to find?
A) The mRNA could not exit the nucleus to be translated.
B) The cell recognizes the absence of the tail and polyadenylates the mRNA.
C) The molecule is digested by restriction enzymes in the nucleus.
D) The molecule is digested by exonucleases since it is no longer protected at the 5' end.
E) The molecule attaches to a ribosome and is translated, but more slowly.
Answer: D
Topic: Concept 17.3
Skill: Synthesis/Evaluation
41) A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the
tRNA that binds the mRNA codon is
A) TTT.
B) UUA.
C) UUU.
D) AAA.
E) either UAA or TAA, depending on first base wobble.
Answer: C
Topic: Concept 17.4
Skill: Application/Analysis
42) Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on
specificity in the
A) binding of ribosomes to mRNA.
B) shape of the A and P sites of ribosomes.
C) bonding of the anticodon to the codon.
D) attachment of amino acids to tRNAs.
E) both C and D
Answer: E
Topic: Concept 17.4
Skill: Knowledge/Comprehension
43) A part of an mRNA molecule with the following sequence is being read by a ribosome: 5'
CCG-ACG 3' (mRNA). The following charged transfer RNA molecules (with their anticodons
shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that
a dipeptide can form.
13
Figure 17.3

The dipeptide that will form will be
A) cysteine-alanine.
B) proline-threonine.
C) glycine-cysteine.
D) alanine-alanine.
E) threonine-glycine.

A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to
the growing polypeptide on the other tRNA (#2) in the ribosome already.

60) Where does tRNA #2 move to after this bonding of lysine to the polypeptide?
A) A site
B) P site
C) E site
D) Exit tunnel
E) Directly to the cytosol

A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to
the growing polypeptide on the other tRNA (#2) in the ribosome already.

61) Which component of the complex described enters the exit tunnel through the large subunit
of the ribosome?
A) tRNA with attached lysine (#1)
B) tRNA with polypeptide (#2)
C) tRNA that no longer has attached amino acid
D) newly formed polypeptide
E) initiation and elongation factors

1) In eukaryotic cells, transcription cannot begin until

A) the two DNA strands have completely separated and exposed the promoter.

B) several transcription factors have bound to the promoter.

C) the 5' caps are removed from the mRNA.

D) the DNA introns are removed from the template.

E) DNA nucleases have isolated the transcription unit.

2) Which of the following is not true of a codon?

A) It consists of three nucleotides.

B) It may code for the same amino acid as another codon.

C) It never codes for more than one amino acid.

D) It extends from one end of a tRNA molecule.

E) It is the basic unit of the genetic code.

Answer: A

3) The anticodon of a particular tRNA molecule is

A) complementary to the corresponding mRNA codon.

B) complementary to the corresponding triplet in rRNA.

C) the part of tRNA that bonds to a specific amino acid.

D) changeable, depending on the amino acid that attaches to the tRNA.

E) catalytic, making the tRNA a ribozyme.

Answer: A

4) Which of the following is not true of RNA processing?

A) Exons are cut out before mRNA leaves the nucleus.

B) Nucleotides may be added at both ends of the RNA.

C) Ribozymes may function in RNA splicing.

D) RNA splicing can be catalyzed by spliceosomes.

E) A primary transcript is often much longer than the final RNA molecule that leaves the

nucleus.

Answer: D

5) Using Figure 17.5, identify a 5' 3' sequence of nucleotides in the DNA template strand for

an mRNA coding for the polypeptide sequence Phe-Pro-Lys.

A) 5'-UUUGGGAAA-3'

B) 5'-GAACCCCTT-3'

C) 5'-AAAACCTTT-3'

D) 5'-CTTCGGGAA-3'

E) 5'-AAACCCUUU-3'

Answer: E

6) Which of the following mutations would be most likely to have a harmful effect on an

organism?

A) a base-pair substitution

B) a deletion of three nucleotides near the middle of a gene

C) a single nucleotide deletion in the middle of an intron

D) a single nucleotide deletion near the end of the coding sequence

E) a single nucleotide insertion downstream of, and close to, the start of the coding sequence

Answer: B

7) Which component is not directly involved in translation?

A) mRNA

B) DNA

C) tRNA

D) ribosomes

E) GTP

Answer: A

Topic: Concept 18.1

Skill: Knowledge/Comprehension

1) What does the operon model attempt to explain?

A) the coordinated control of gene expression in bacteria

B) bacterial resistance to antibiotics

C) how genes move between homologous regions of DNA

D) the mechanism of viral attachment to a host cell

E) horizontal transmission of plant viruses

Answer: E

Topic: Concept 18.1

Skill: Knowledge/Comprehension

2) The role of a metabolite that controls a repressible operon is to

A) bind to the promoter region and decrease the affinity of RNA polymerase for the promoter.

B) bind to the operator region and block the attachment of RNA polymerase to the promoter.

C) increase the production of inactive repressor proteins.

D) bind to the repressor protein and inactivate it.

E) bind to the repressor protein and activate it.

Answer: E

Topic: Concept 18.1

Skill: Knowledge/Comprehension

3) The tryptophan operon is a repressible operon that is

A) permanently turned on.

B) turned on only when tryptophan is present in the growth medium.

C) turned off only when glucose is present in the growth medium.

D) turned on only when glucose is present in the growth medium.

E) turned off whenever tryptophan is added to the growth medium.

Answer: D

Topic: Concept 18.1

Skill: Knowledge/Comprehension

4) This protein is produced by a regulatory gene:

A) operon

B) inducer

C) promoter

D) repressor

E) corepressor

Answer: C

Topic: Concept 18.1

Skill: Knowledge/Comprehension

5) A mutation in this section of DNA could influence the binding of RNA polymerase to the

DNA:

A) operon

B) inducer

C) promoter

D) repressor

E) corepressor

Answer: E

Topic: Concept 18.1

Skill: Knowledge/Comprehension

6) A lack of this nonprotein molecule would result in the inability of the cell to "turn off" genes:

A) operon

B) inducer

C) promoter

D) repressor

E) corepressor

Answer: B

Topic: Concept 18.1

Skill: Knowledge/Comprehension

7) When this is taken up by the cell, it binds to the repressor so that the repressor no longer binds

to the operator:

A) operon

B) inducer

C) promoter

D) repressor

E) corepressor

Answer: A

Topic: Concept 18.1

Skill: Application/Analysis

8) A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would

result in

A) continuous transcription of the structural gene controlled by that regulator.

B) complete inhibition of transcription of the structural gene controlled by that regulator.

C) irreversible binding of the repressor to the operator.

D) inactivation of RNA polymerase by alteration of its active site.

E) continuous translation of the mRNA because of alteration of its structure.

Answer: D

Topic: Concept 18.1

Skill: Knowledge/Comprehension

9) The lactose operon is likely to be transcribed when

A) there is more glucose in the cell than lactose.

B) the cyclic AMP levels are low.

C) there is glucose but no lactose in the cell.

D) the cyclic AMP and lactose levels are both high within the cell.

E) the cAMP level is high and the lactose level is low.

Answer: B

Topic: Concept 18.1

Skill: Knowledge/Comprehension

10) Transcription of the structural genes in an inducible operon

A) occurs continuously in the cell.

B) starts when the pathway's substrate is present.

C) starts when the pathway's product is present.

D) stops when the pathway's product is present.

E) does not result in the production of enzymes.

Answer: D

Topic: Concept 18.1

Skill: Knowledge/Comprehension

11) How does active CAP induce expression of the genes of the lactose operon?

A) It terminates production of repressor molecules.

B) It degrades the substrate allolactose.

C) It stimulates splicing of the encoded genes.

D) It stimulates the binding of RNA polymerase to the promoter.

E) It binds steroid hormones and controls translation.

Answer: C

Topic: Concept 18.1

Skill: Knowledge/Comprehension

12) For a repressible operon to be transcribed, which of the following must occur?

A) A corepressor must be present.

B) RNA polymerase and the active repressor must be present.

C) RNA polymerase must bind to the promoter, and the repressor must be inactive.

D) RNA polymerase cannot be present, and the repressor must be inactive.

E) RNA polymerase must not occupy the promoter, and the repressor must be inactive.

Answer: B

Topic: Concept 18.1

Skill: Knowledge/Comprehension

13) 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?

A) The repressor protein attaches to the regulator.

B) Allolactose binds to the repressor protein.

C) Allolactose binds to the regulator gene.

D) The repressor protein and allolactose bind to RNA polymerase.

E) RNA polymerase attaches to the regulator.

Answer: C

Topic: Concept 18.1

Skill: Synthesis/Evaluation

14) Altering patterns of gene expression in prokaryotes would most likely serve the organism's

survival in which of the following ways?

A) organizing gene expression so that genes are expressed in a given order

B) allowing each gene to be expressed an equal number of times

C) allowing the organism to adjust to changes in environmental conditions

D) allowing young organisms to respond differently from more mature organisms

E) allowing environmental changes to alter the prokaryote's genome

Answer: B                                   

Topic: Concept 18.1

Skill: Knowledge/Comprehension

15) In response to chemical signals, prokaryotes can do which of the following?

A) turn off translation of their mRNA

B) alter the level of production of various enzymes

C) increase the number and responsiveness of their ribosomes

D) inactivate their mRNA molecules

E) alter the sequence of amino acids in certain proteins

Answer: D

Topic: Concept 18.1

Skill: Application/Analysis

16) 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?

A) Three structural genes will no longer be expressed.

B) RNA polymerase will no longer transcribe permease.

C) The operon will no longer be inducible.

D) Beta galactosidase will be produced.

E) The cell will continue to metabolize but more slowly.

Answer: D

Topic: Concept 18.1

Skill: Application/Analysis

17) 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?

A) The inducer will no longer bind to the repressor.

B) The repressor will no longer bind to the operator.

C) The operon will never be transcribed.

D) The structural genes will be transcribed continuously.

E) The repressor protein will no longer be produced

Answer: E

Topic: Concept 18.1

Skill: Application/Analysis

18) 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?

A) The repressor will no longer be made.

B) The repressor will no longer bind to the operator.

C) The repressor will no longer bind to the inducer.

D) The lac operon will be expressed continuously.

E) The lac operon will function normally.

Answer: E

Topic: Concept 18.1

Skill: Synthesis/Evaluation

19) 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?

A) decreased concentration of the lac enzymes

B) increased concentration of the trp enzymes

C) decreased binding of the RNA polymerase to sugar metabolism-related promoters

D) decreased concentration of alternative sugars in the cell

E) increased concentrations of sugars such as arabinose in the cell

Answer: D

Topic: Concept 18.2

Skill: Knowledge/Comprehension

20) Muscle cells and nerve cells in one species of animal owe their differences in structure to

A) having different genes.

B) having different chromosomes.

C) using different genetic codes.

D) having different genes expressed.

E) having unique ribosomes.

Answer: A

Topic: Concept 18.2

Skill: Knowledge/Comprehension

21) Which of the following mechanisms is (are) used to coordinately control the expression of

multiple, related genes in eukaryotic cells?

A) organization of the genes into clusters, with local chromatin structures influencing the

expression of all the genes at once

B) each of the genes sharing a common control element, allowing several activators to turn on

their transcription, regardless of their location in the genome

C) organizing the genes into large operons, allowing them to be transcribed as a single unit

D) a single repressor able to turn off several related genes

E) environmental signals that enter the cell and bind directly to their promoters

Answer: C

Topic: Concept 18.2

Skill: Knowledge/Comprehension

22) If you were to observe the activity of methylated DNA, you would expect it to

A) be replicating nearly continuously.

B) be unwinding in preparation for protein synthesis.

C) have turned off or slowed down the process of transcription.

D) be very actively transcribed and translated.

E) induce protein synthesis by not allowing repressors to bind to it.

Answer: D

Topic: Concept 18.2

Skill: Knowledge/Comprehension

23) Genomic imprinting, DNA methylation, and histone acetylation are all examples of

A) genetic mutation.

B) chromosomal rearrangements.

C) karyotypes.

D) epigenetic phenomena.

E) translocation.

Answer: E

Topic: Concept 18.2

Skill: Knowledge/Comprehension

24) Approximately what proportion of the DNA in the human genome codes for proteins or

functional RNA?

A) 83%

B) 46%

C) 32%

D) 13%

E) 1.5%

Answer: D

Topic: Concept 18.2

Skill: Knowledge/Comprehension

25) Two potential devices that eukaryotic cells use to regulate transcription are

A) DNA methylation and histone amplification.

B) DNA amplification and histone methylation.

C) DNA acetylation and methylation.

D) DNA methylation and histone acetylation.

E) histone amplification and DNA acetylation.

Answer: A

Topic: Concept 18.2

Skill: Knowledge/Comprehension

26) In both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of

A) transcription.

B) translation.

C) mRNA stability.

D) mRNA splicing.

E) protein stability.

Answer: E

Topic: Concept 18.2

Skill: Knowledge/Comprehension

27) In eukaryotes, transcription is generally associated with

A) euchromatin only.

B) heterochromatin only.

C) very tightly packed DNA only.

D) highly methylated DNA only.

E) both euchromatin and histone acetylation.

Answer: A

Topic: Concept 18.2

Skill: Application/Analysis

28) 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) A transgene integrated into a heterochromatic region of the genome.

B) A transgene integrated into a euchromatic region of the genome.

C) The transgene was mutated during the process of integration into the host cell genome.

D) The host cell lacks the enzymes necessary to express the transgene.

E) A transgene integrated into a region of the genome characterized by high histone acetylation.

Answer: C

Topic: Concept 18.2

Skill: Knowledge/Comprehension

29) During DNA replication,

A) all methylation of the DNA is lost at the first round of replication.

B) DNA polymerase is blocked by methyl groups, and methylated regions of the genome are

therefore left uncopied.

C) 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.

D) methylation of the DNA is maintained because DNA polymerase directly incorporates

methylated nucleotides into the new strand opposite any methylated nucleotides in the template.

E) methylated DNA is copied in the cytoplasm, and unmethylated DNA in the nucleus.

Answer: A

Topic: Concept 18.2

Skill: Knowledge/Comprehension

30) Eukaryotic cells can control gene expression by which of the following mechanisms?

A) histone acetylation of nucleosomes

B) DNA acetylation

C) RNA induced modification of chromatin structure

D) repression of operons

E) induction of operators in the promoter

Answer: B

Topic: Concept 18.2

Skill: Knowledge/Comprehension

31) In eukaryotes, general transcription factors

A) are required for the expression of specific protein-encoding genes.

B) bind to other proteins or to a sequence element within the promoter called the TATA box.

C) inhibit RNA polymerase binding to the promoter and begin transcribing.

D) usually lead to a high level of transcription even without additional specific transcription

factors.

E) bind to sequences just after the start site of transcription.

Answer: C

Topic: Concept 18.2

Skill: Knowledge/Comprehension

32) This binds to a site in the DNA far from the promoter to stimulate transcription:

A) enhancer

B) promoter

C) activator

D) repressor

E) terminator

Answer: D

Topic: Concept 18.2

Skill: Knowledge/Comprehension

33) This can inhibit transcription by blocking the binding of positively acting transcription

factors to the DNA:

A) enhancer

B) promoter

C) activator

D) repressor

E) terminator

Answer: E

Topic: Concept 18.2

Skill: Knowledge/Comprehension

34) This is the site in the DNA located near the end of the final exon, encoding an RNA

sequence that determines the 3' end of the transcript:

A) enhancer

B) promoter

C) activator

D) repressor

E) terminator

Answer: D

Topic: Concept 18.2

Skill: Knowledge/Comprehension

35) Steroid hormones produce their effects in cells by

A) activating key enzymes in metabolic pathways.

B) activating translation of certain mRNAs.

C) promoting the degradation of specific mRNAs.

D) binding to intracellular receptors and promoting transcription of specific genes.

E) promoting the formation of looped domains in certain regions of DNA.

Answer: B

Topic: Concept 18.2

Skill: Application/Analysis

36) 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?

A) increased chromatin condensation

B) decreased chromatin concentration

C) abnormalities of mouse embryos

D) decreased binding of transcription factors

E) inactivation of the selected genes

Answer: A

Topic: Concept 18.2

Skill: Application/Analysis

37) 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?

A) increased chromatin condensation

B) decreased chromatin concentration

C) abnormalities of mouse embryos

D) decreased binding of transcription factors

E) inactivation of the selected genes

Answer: E

Topic: Concept 18.2

Skill: Application/Analysis

38) 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?

A) increased chromatin condensation

B) decreased chromatin concentration

C) abnormalities of mouse embryos

D) decreased binding of transcription factors

E) inactivation of the selected genes

Answer: C

Topic: Concept 18.2

Skill: Application/Analysis

39) 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?

A) increased chromatin condensation

B) decreased chromatin concentration

C) abnormalities of mouse embryos

D) decreased binding of transcription factors

E) inactivation of the selected genes

Answer: D

Topic: Concept 18.2

Skill: Synthesis/Evaluation

40) 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?

A) repressors

B) ATP

C) protein-based hormones

D) other transcription factors

E) tRNA

Answer: C

Topic: Concept 18.2

Skill: Synthesis/Evaluation

41) Gene expression might be altered at the level of post-transcriptional processing in eukaryotes

rather than prokaryotes because of which of the following?

A) Eukaryotic mRNAs get 5' caps and 3' tails.

B) Prokaryotic genes are expressed as mRNA, which is more stable in the cell.

C) Eukaryotic exons may be spliced in alternative patterns.

D) Prokaryotes use ribosomes of different structure and size.

E) Eukaryotic coded polypeptides often require cleaving of signal sequences before localization.

Answer: B

Topic: Concept 18.2

Skill: Synthesis/Evaluation

42) Which of the following experimental procedures is most likely to hasten mRNA degradation

in a eukaryotic cell?

A) enzymatic shortening of the poly(A) tail

B) removal of the 5' cap

C) methylation of C nucleotides

D) memethylation of histones

E) removal of one or more exons

Answer: A

Topic: Concept 18.2

Skill: Synthesis/Evaluation

43) Which of the following is most likely to have a small protein called ubiquitin attached to it?

A) a cyclin that usually acts in G1, now that the cell is in G2

B) a cell surface protein that requires transport from the ER

C) an mRNA that is leaving the nucleus to be translated

D) a regulatory protein that requires sugar residues to be attached

E) an mRNA produced by an egg cell that will be retained until after fertilization

Answer: A

Topic: Concept 18.3

Skill: Knowledge/Comprehension

44) 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

A) RNA interference.

B) RNA obstruction.

C) RNA blocking.

D) RNA targeting.

E) RNA disposal.

Answer: D

Topic: Concept 18.3

Skill: Knowledge/Comprehension

45) 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?

A) "junk" DNA that serves no possible purpose

B) rRNA and tRNA coding sequences

C) DNA that is translated directly without being transcribed

D) non-protein coding DNA that is transcribed into several kinds of small RNAs with biological

function

E) non-protein coding DNA that is transcribed into several kinds of small RNAs without

biological function

Answer: A

Topic: Concept 18.3

Skill: Knowledge/Comprehension

46) Which of the following best describes siRNA?

A) a short double-stranded RNA, one of whose strands can complement and inactivate a

sequence of mRNA

B) a single-stranded RNA that can, where it has internal complementary base pairs, fold into

cloverleaf patterns

C) a double-stranded RNA that is formed by cleavage of hairpin loops in a larger precursor

D) a portion of rRNA that allows it to bind to several ribosomal proteins in forming large or

small subunits

E) a molecule, known as Dicer, that can degrade other mRNA sequences

Answer: C

Topic: Concept 18.3

Skill: Synthesis/Evaluation

47) 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?

A) exploring a way to turn on the expression of pseudogenes

B) targeting siRNAs to disable the expression of an allele associated with autosomal recessive

disease

C) targeting siRNAs to disable the expression of an allele associated with autosomal dominant

disease

D) creating knock-out organisms that can be useful for pharmaceutical drug design

E) looking for a way to prevent viral DNA from causing infection in humans

Answer: D

Topic: Concept 18.3

Skill: Knowledge/Comprehension

48) Which of the following describes the function of an enzyme known as Dicer?

A) It degrades single-stranded DNA.

B) It degrades single-stranded mRNA.

C) It degrades mRNA with no poly(A) tail.

D) It trims small double-stranded RNAs into molecules that can block translation.

E) It chops up single-stranded DNAs from infecting viruses.

Answer: C

Topic: Concept 18.3

Skill: Synthesis/Evaluation

49) 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?

A) The usual mRNAs transcribed from centromeric DNA will be missing from the cells.

B) Tetrads will no longer be able to form during meiosis I.

C) Centromeres will be euchromatic rather than heterochromatic and the cells will soon die in

culture.

D) The cells will no longer be able to resist bacterial contamination.

E) The DNA of the centromeres will no longer be able to replicate.

Answer: E

Topic: Concept 18.3

Skill: Synthesis/Evaluation

50) 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?

A) As RNAs have evolved since that time, they have taken on new functions.

B) Watson and Crick described DNA but did not predict any function for RNA.

C) The functions of small RNAs could not be approached until the entire human genome was

sequenced.

D) Ethical considerations prevented scientists from exploring this material until recently.

E) Changes in technology as well as our ability to determine how much of the DNA is expressed

have now made this possible.

Answer: D

1) If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then the

A) amino acid inactivates the repressor.

B) enzymes produced are called inducible enzymes.

C) repressor is active in the absence of the amino acid.

D) amino acid acts as a corepressor.

E) amino acid turns on transcription of the operon.

2) Muscle cells differ from nerve cells mainly because they

A) express different genes.

B) contain different genes.

C) use different genetic codes.

D) have unique ribosomes.

E) have different chromosomes.

Answer: D

3) 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) reduced transcription of the operon's genes

C) buildup of a substrate for the pathway controlled by the operon

D) continuous transcription of the operon's genes

E) overproduction of catabolite activator protein (CAP)

4) The functioning of enhancers is an example of

A) transcriptional control of gene expression.

B) a post-transcriptional mechanism for editing mRNA.

C) the stimulation of translation by initiation factors.

D) post-translational control that activates certain proteins.

E) a eukaryotic equivalent of prokaryotic promoter functioning.

Answer: C

5) 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) is transcribed in the early embryo.

B) normally leads to formation of tail structures.

C) normally leads to formation of head structures.

D) is a protein present in all head structures.

E) leads to programmed cell death.

6) Which of the following statements about the DNA in one of your brain cells is true?

A) Most of the DNA codes for protein.

B) The majority of genes are likely to be transcribed.

C) Each gene lies immediately adjacent to an enhancer.

D) Many genes are grouped into operon-like clusters.

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

7) Cell differentiation always involves the

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

B) movement of cells.

C) transcription of the myoD gene.

D) selective loss of certain genes from the genome.

E) cell's sensitivity to environmental cues such as light or heat.

Answer: C

8) Which of the following is an example of post-transcriptional control of gene expression?

A) the addition of methyl groups to cytosine bases of DNA

B) the binding of transcription factors to a promoter

C) the removal of introns and splicing together of exons

D) gene amplification during a stage in development

E) the folding of DNA to form heterochromatin

Answer: B

9) Within a cell, the amount of protein made using a given mRNA molecule depends partly on

A) the degree of DNA methylation.

B) the rate at which the mRNA is degraded.

C) the presence of certain transcription factors.

D) the number of introns present in the mRNA.

E) the types of ribosomes present in the cytoplasm.

Answer: B

10) 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) Proto-oncogenes first arose from viral infections.

B) Proto-oncogenes normally help regulate cell division.

C) Proto-oncogenes are genetic "junk."

D) Proto-oncogenes are mutant versions of normal genes.

E) Cells produce proto-oncogenes as they age.