Campbell Biology in Focus, 2e (Urry)
Chapter 14 Gene Expression: From Gene to Protein
14.1 Multiple-Choice Questions
1) Garrod hypothesized that inherited diseases such as alkaptonuria, the inability to metabolize
the chemical alkapton, occur because
A) metabolic enzymes require vitamin cofactors, and affected individuals have significant
nutritional deficiencies.
B) many metabolic enzymes use DNA as a cofactor, and affected individuals have mutations that
prevent their enzymes from interacting efficiently with DNA.
C) certain metabolic reactions are carried out by ribozymes, and affected individuals lack key
splicing factors.
D) genes dictate the production of specific enzymes, and affected individuals have genetic
defects that cause them to lack certain enzymes.
2) Garrod’s information about the enzyme alteration resulting in alkaptonuria led to further
understanding of these types of metabolic pathways in humans. Phenylketonuria (PKU) occurs
when another enzyme in the pathway is altered or missing, resulting in a failure of phenylalanine
(phe) to be metabolized to another amino acid: tyrosine. Tyrosine is an earlier substrate in the
pathway altered in alkaptonuria. How might PKU affect the presence or absence of alkaptonuria?
A) It would have no effect because PKU occurs several steps away in the pathway.
B) It would have no effect because tyrosine is also available from the diet.
C) Anyone with PKU must also have alkaptonuria.
D) Anyone with PKU is born with a predisposition to later alkaptonuria.
E) Anyone with PKU has mild symptoms of alkaptonuria.
3) The nitrogenous base adenine is found in all members of which of the following groups of
molecules?
A) proteins, triglycerides, and testosterone
B) proteins, ATP, and DNA
C) ATP, RNA, and DNA
D) glucose, ATP, and DNA
E) proteins, carbohydrates, and ATP
4) A particular triplet of bases in the template strand of DNA is 5′-AGT-3′. The corresponding
codon for the mRNA transcribed is
A) 3′-UCA-5′.
B) 3′-UGA-5′.
C) 5′-TCA-3′.
D) 3′-ACU-5′.
E) either UCA or TCA, depending on wobble in the first base.
5) The genetic code is essentially the same for all organisms. Based on this information, one can
logically assume which of the following statements to be correct?
A) A gene from an organism can theoretically be expressed by any other organism.
B) All organisms have experienced convergent evolution.
C) DNA was the first genetic material.
D) The same codons in different organisms translate into the different amino acids.
E) Different organisms have different numbers of different types of amino acids.
6) The “universal” genetic code is now known to have exceptions. Evidence for this can be found
if which of the following is true?
A) if UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually
coded for by UGG only)
B) if one stop codon, such as UGA, is found to have the same effect on translation as another
stop codon, such as UAA
C) if prokaryotic organisms are able to translate a eukaryotic mRNA and produce the same
polypeptide
D) if several codons are found to translate to the same amino acid, such as serine
7) Which of the following descriptions of nucleotide triplets best represents a codon?
A) a triplet separated spatially from other triplets
B) a triplet that has no corresponding amino acid
C) a triplet at the opposite end of tRNA from the attachment site of the amino acid
D) a triplet in the same reading frame as an upstream AUG
E) a sequence in tRNA at the 3′ end
8) Which of the following statements best describes the termination of transcription in
prokaryotes?
A) RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate
with the transcript and cut it free from the polymerase.
B) RNA polymerase transcribes through the terminator sequence, causing the polymerase to
separate from the DNA and release the transcript.
C) RNA polymerase transcribes through an intron, which causes the polymerase to let go of the
transcript.
D) Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the
chromosome.
E) RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing
through the gene and release the mRNA.
9) Which of the following does not occur in prokaryotic gene expression, but does occur in
eukaryotic gene expression?
A) mRNA, tRNA, and rRNA are transcribed.
B) RNA polymerase binds to the promoter.
C) A poly-A tail is added to the 3′ end of an mRNA and a cap is added to the 5′ end.
D) Transcription can begin as soon as translation has begun even a little.
E) RNA polymerase requires a primer to elongate the molecule.
10) RNA polymerase in a prokaryote is composed of several subunits. Most of these subunits are
the same for the transcription of any gene, but one, known as sigma, varies considerably. Which
of the following is the most probable advantage for the organism in having such variability in
RNA polymerase?
A) It might allow the translation process to vary from one cell to another.
B) It might allow the polymerase to recognize different promoters under certain environmental
conditions.
C) It might allow the polymerase to react differently to each stop codon.
D) It might alter the rate of translation and of exon splicing.
11) In eukaryotes there are several different types of RNA polymerase. Which type is involved in
transcription of mRNA known as pre-mRNA?
A) ligase
B) RNA polymerase I
C) RNA polymerase II
D) RNA polymerase III
12) Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
A) the protein product of the promoter
B) start and stop codons
C) ribosomes and tRNA
D) several transcription factors
E) aminoacyl-tRNA synthetase
13) A part of the promoter, called the TATA box, is said to be highly conserved in evolution.
Which of the following might this illustrate?
A) The sequence evolves very rapidly.
B) The sequence does not mutate.
C) Any mutation in the sequence is selected against.
D) The sequence is found in many but not all promoters.
E) The sequence is transcribed at the start of every gene.
14) Which of the following best describes the significance of the TATA box in eukaryotic
promoters?
A) It is the recognition site for a specific transcription factor.
B) It sets the reading frame of the mRNA.
C) It is the recognition site for ribosomal binding.
D) It signals the end of the nucleotide sequence of the gene.
15) In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what
must be included in addition to the coding exons of the gene?
A) the introns
B) eukaryotic polymerases
C) a bacterial promoter sequence
D) eukaryotic ribosomal subunits
E) eukaryotic tRNAs
16) RNA polymerase moves in which direction along the DNA?
A) 5′ to 3′ along whichever strand it’s on
B) 3′ to 5′ along the template strand
C) 5′ to 3′ along the template strand
D) 5′ to 3′ along the double-stranded DNA
E) 3′ to 5′ along the nontemplate strand
17) Which of the following is a function of a poly-A tail in mRNA?
A) It adds the modified guanine to the 3′ end of the mRNA.
B) It indicates the site of translational termination.
C) It is a sequence that codes for the binding of RNA polymerase to the DNA.
D) It helps protect the mRNA from degradation by hydrolytic enzymes.
18) What is a ribozyme?
A) an enzyme that uses RNA as a substrate
B) an RNA with enzymatic activity
C) an enzyme that catalyzes the association between the large and small ribosomal subunits
D) an enzyme that synthesizes RNA as part of the transcription process
E) an enzyme that synthesizes RNA primers during DNA replication
19) A eukaryotic transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to
make a protein consisting of approximately 400 amino acids. This is best explained by the fact
that
A) many noncoding stretches of nucleotides are present in eukaryotic DNA.
B) there is redundancy in the genetic code.
C) many nucleotides are needed to code for each amino acid.
D) there are termination exons near the beginning of mRNA.
20) During splicing, which molecular component of the spliceosome catalyzes the excision
reaction?
A) protein
B) DNA
C) RNA
D) lipid
E) sugar
21) Which of the following statements correctly describes alternative RNA splicing?
A) It is a mechanism that can increase the rate of transcription.
B) It can allow the production of proteins of different sizes and functions from a single mRNA.
C) It allows the production of similar proteins from different RNAs.
D) It increases the rate of transcription.
22) 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 would not be transported out of the nucleus.
B) The cell recognizes the absence of the tail and adds a new poly-A tail to the mRNA.
C) The molecule is digested by restriction enzymes in the nucleus.
D) The molecule is degraded by hydrolytic enzymes because it is no longer protected at the 5′
end and the 3′ end.
E) The molecule attaches to a ribosome and is translated, but more slowly.
23) Use the following model of a eukaryotic transcript to answer the question. E1-4 refer to the
exons and I1-3 refer to the introns in the pre-mRNA transcript.
5′ UTR E1 I1 E2 I2 E3 I3 E4 UTR 3′
Which components of the previous molecule will also be found in mRNA in the cytosol?
A) 5′ UTR I1 I2 I3 UTR 3′
B) 5′ E1 E2 E3 E4 3′
C) 5′ UTR E1 E2 E3 E4 UTR 3′
D) 5′ I1 I2 I3 3′
E) 5′ E1 I1 E2 I2 E3 I3 E4 3′
24) Use the following model of a eukaryotic transcript to answer the question. E1-4 refer to the
exons and I1-3 refer to the introns in the pre-mRNA transcript.
5′ UTR E1 I1 E2 I2 E3 I3 E4 UTR 3′
Where on a pre-mRNA transcript does a spliceosome bind?
A) to the exons
B) to the 5′ UTR
C) to the 3′ UTR
D) to each end of an intron
25) Use the following model of a eukaryotic transcript to answer the question. E1-4 refer to the
exons and I1-3 refer to the introns in the pre-mRNA transcript.
5′ UTR E1 I1 E2 I2 E3 I3 E4 UTR 3′
Suppose that exposure to a chemical mutagen results in a change in the sequence that alters the 5′
end of intron 1 (I1). Which of the following results might occur?
A) loss of the gene product
B) loss of E1
C) premature stop to the mRNA
D) inclusion of I1 in the mRNA
26) Use the following model of a eukaryotic transcript to answer the question. E1-4 refer to the
exons and I1-3 refer to the introns in the pre-mRNA transcript.
5′ UTR E1 I1 E2 I2 E3 I3 E4 UTR 3′
Suppose that an induced mutation removes most of the 5′ end of the 5′ UTR. What might be the
result of this removal?
A) Removal of the 5′ UTR has no effect because the exons remain intact.
B) Removal of the 5′ UTR also removes the 5′ cap, so the mRNA may be quickly degraded by
hydrolytic enzymes.
C) The 3′ UTR will duplicate and one copy will replace the 5′ end.
D) The first exon will not be read because I1 will now serve as the UTR.
27) When the spliceosome binds to a pre-mRNA transcript, where does it typically attach?
A) to the exons
B) to the 5′ UTR
C) to the 3′ UTR
D) at certain sequences along an intron
28) Which of the following experimental procedures is most likely to speed up mRNA
degradation in a eukaryotic cell?
A) lengthening of the poly-A tail
B) removal of the 5′ cap
C) removal of C nucleotides
D) removal of one or more exons
29) 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.
30) Accuracy in the translation of mRNA into the sequence of amino acids in a polypeptide
depends on specificity in which of the following?
A) binding of ribosomes to mRNA
B) shape of the A and P sites of ribosomes
C) attachment of amino acids to tRNAs
D) bonding of the anticodon to the codon and the attachment of amino acids to tRNAs
31) What is the function of GTP in translation?
A) GTP provides the energy for the formation of the initiation complex, using initiation factors.
B) GTP is hydrolyzed to provide phosphate groups for tRNA binding.
C) GTP is hydrolyzed to provide energy for breaking peptide bonds.
D) GTP supplies phosphates and energy to make ATP from ADP.
32) A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to
tRNAs with the anticodon AAA instead of the normal phenylalanine. What would be a potential
consequence for a cell in which this happens? Remember that phenylalanine may be encoded by
multiple codons.
A) None of the proteins in the cell will contain phenylalanine.
B) Proteins in the cell will include lysine instead of phenylalanine at amino acid positions
specified by the codon UUU.
C) The cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-
specifying anticodons.
D) The ribosome will skip a codon every time a UUU is encountered.
33) There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best
explained by the fact that
A) some tRNAs have anticodons that recognize four or more different codons.
B) the rules for base pairing between the third base of a codon and tRNA are flexible.
C) many codons are never used, so the tRNAs that recognize them are dispensable.
D) the DNA codes for all 61 tRNAs, but some are then destroyed.
E) competitive exclusion forces some tRNAs to be destroyed by nucleases.
34) Which of the following events in translation is the first to occur in eukaryotes?
A) elongation of the polypeptide
B) base pairing of activated methionine-tRNA to AUG of the messenger RNA
C) binding of the larger ribosomal subunit to smaller ribosomal subunits
D) covalent bonding between the first two amino acids
E) the small subunit of the ribosome recognizing and attaching to the 5′ cap of mRNA
35) Which of the following statements correctly describes the function of a signal peptide?
A) It directs an mRNA molecule into the Golgi apparatus.
B) It causes RNA polymerase to bind DNA and initiate transcription.
C) It terminates translation of the messenger RNA.
D) It assists in the translocation of polypeptides across the ER membrane.
E) It leads the initiation of transcription.
36) When translating secretory or membrane proteins, ribosomes are directed to the ER
membrane by
A) a specific characteristic of the ribosome itself, which distinguishes free ribosomes from bound
ribosomes.
B) a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.
C) moving through a specialized channel of the nucleus.
D) a chemical signal given off by the ER.
E) a signal sequence of RNA that precedes the start codon of the message.
37) An experimenter has altered the 3′ end of the tRNA corresponding to the amino acid
methionine in such a way as to remove the 3′ AC. Which of the following statements correctly
describes the most likely result of this change?
A) tRNA will not form a cloverleaf.
B) The nearby stem end will pair improperly.
C) The amino acid methionine will not be covalently bound to the altered tRNA.
D) The anticodon will not bind with the mRNA codon.
E) The aminoacyl-tRNA synthetase will not be formed.
38) The process of translation in both prokaryotes and eukaryotes requires tRNAs, amino acids,
and ribosomal subunits. Which of the following components must also be present for translation
to proceed?
A) protein factors and ATP
B) protein factors and GTP
C) polymerases and GTP
D) signal peptides plus release factor
39) When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the
A site. If the translation reaction were to be experimentally stopped at this point, which of the
following sets of structures would you be able to isolate from the cell?
A) an assembled ribosome with a polypeptide attached to the tRNA in the P site
B) separated ribosomal subunits, a polypeptide, and free tRNA
C) an assembled ribosome with a separated polypeptide
D) separated ribosomal subunits with a polypeptide attached to the tRNA
40) What is the function of the release factor in translation?
A) It separates tRNA in the A site from the growing polypeptide.
B) It binds to the stop codon in the A site in place of a tRNA.
C) It releases the amino acid from its tRNA to allow the amino acid to form a peptide bond.
D) It releases the ribosome from the ER to allow polypeptides into the cytosol.
41) Suppose that an error in transcription alters the formation of a single tRNA molecule in a
cell. The altered tRNA still attaches to the same amino acid (Phe), but its anticodon loop has the
sequence AAU, which binds to the mRNA codon UUA (usually specifying the amino acid
leucine, Leu). What will be the effect on the translation of polypeptides in this cell?
A) The altered tRNA will cause this mRNA to make only nonfunctioning product.
B) The tRNA-Leu will not be able to enter the ribosome to bind to the UUA codon.
C) One altered tRNA molecule will have little effect because it will compete with many
“normal” ones.
D) The altered tRNA will result in an amino acid variant in all copies of the protein.
42) What must happen to a newly made polypeptide before it can be secreted from a cell?
A) It must be translated by a ribosome that remains free of attachment to the ER.
B) Its signal sequence must target it to the ER, after which it goes to the Golgi.
C) Its signal sequence must be cleaved off before the polypeptide can enter the ER.
D) Its signal sequence must target it to the plasma membrane, where it causes exocytosis.
E) Its signal sequence must cause it to be encased in a vesicle as soon as it is translated.
43) In what way might a point mutation in DNA make a difference in the function of a protein?
A) It might result in a chromosomal translocation.
B) It might exchange one stop codon for another stop codon.
C) It might exchange one serine codon for a different serine codon.
D) It might substitute a different amino acid in the active site.
E) It might substitute the N-terminus of the polypeptide for the C-terminus.
44) In the 1920s, Hermann Muller discovered that X-rays caused genetic changes in Drosophila.
In a related series of experiments in the 1940s, other scientists discovered that other types of
chemicals have a similar effect. A new chemical food additive is developed by a cereal
manufacturer. Why is it necessary to test for its ability to cause mutation?
A) We worry that it might cause mutation in cereal grain plants.
B) We want to make sure that it does not emit radiation.
C) We want to be sure that it increases the rate of mutation sufficiently.
D) We want to prevent any chance that it might cause mutations.
45) Which of the following types of mutation, resulting in an error in the mRNA just after the 3ʹ
AUG start codon, is likely to have the most serious effect on the polypeptide product?
A) a deletion of a codon
B) a deletion of two nucleotides
C) a substitution of the third nucleotide in an ACC codon
D) a substitution of the first nucleotide of a GGG codon
E) an insertion of a codon
46) What is the effect of a nucleotide-pair substitution that results in a nonsense mutation in a
gene?
A) It changes an amino acid in the encoded protein.
B) It has no effect on the amino acid sequence of the encoded protein.
C) It introduces a premature stop codon into the mRNA.
D) It alters the reading frame of the mRNA.