Campbell’s Biology, 9e (Reece et al.)
Chapter 17 From Gene to Protein
The text for Chapter 17 has remained largely unchanged from the previous edition. However, one-third
of the following questions are new, and considerably more are at the skill level of analysis and
application.
Multiple-Choice Questions
1) Which of the following variations on translation would be most disadvantageous for a cell?
A) translating polypeptides directly from DNA
B) using fewer kinds of tRNA
C) having only one stop codon
D) lengthening the half-life of mRNA
E) having a second codon (besides AUG) as a start codon
2) Garrod hypothesized that “inborn errors of metabolism” such as alkaptonuria occur because
A) metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional
deficiencies.
B) enzymes are made of DNA, and affected individuals lack DNA polymerase.
C) many metabolic enzymes use DNA as a cofactor, and affected individuals have mutations that
prevent their enzymes from interacting efficiently with DNA.
D) certain metabolic reactions are carried out by ribozymes, and affected individuals lack key splicing
factors.
E) genes dictate the production of specific enzymes, and affected individuals have genetic defects that
cause them to lack certain enzymes.
3) Garrod’s information about the enzyme alteration resulting in alkaptonuria led to further elucidation
of the same pathway 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.
4) The nitrogenous base adenine is found in all members of which group?
A) proteins, triglycerides, and testosterone
B) proteins, ATP, and DNA
C) ATP, RNA, and DNA
D) α glucose, ATP, and DNA
E) proteins, carbohydrates, and ATP
5) 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.
6) The genetic code is essentially the same for all organisms. From this, one can logically assume which
of the following?
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.
7) 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 a different effect on translation than 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.
E) If a single mRNA molecule is found to translate to more than one polypeptide when there are two or
more AUG sites.
8) Which of the following 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
9) Which of the following provides some evidence that RNA probably evolved before DNA?
A) RNA polymerase uses DNA as a template.
B) RNA polymerase makes a single-stranded molecule.
C) RNA polymerase does not require localized unwinding of the DNA.
D) DNA polymerase uses primer, usually made of RNA.
E) DNA polymerase has proofreading function.
10) 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, and the snRNPs cause 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.
11) Which of the following does not occur in prokaryotic eukaryotic gene expression, but does 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.
12) 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 of such sigma switching?
A) It might allow the transcription process to vary from one cell to another.
B) It might allow the polymerase to recognize different promoters under certain environmental
conditions.
C) It could allow the polymerase to react differently to each stop codon.
D) It could allow ribosomal subunits to assemble at faster rates.
E) It could alter the rate of translation and of exon splicing.
13) Which of the following is a function of a poly-A signal sequence?
A) It adds the poly-A tail to the 3′ end of the mRNA.
B) It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~10 35 nucleotides
away.
C) It allows the 3′ end of the mRNA to attach to the ribosome.
D) It is a sequence that codes for the hydrolysis of the RNA polymerase.
E) It adds a 7-methylguanosine cap to the 3′ end of the mRNA.
14) In eukaryotes there are several different types of RNA polymerase. Which type is involved in
transcription of mRNA for a globin protein?
A) ligase
B) RNA polymerase I
C) RNA polymerase II
D) RNA polymerase III
E) primase
15) 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 (TFs)
E) aminoacyl synthetase
16) 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.
17) The TATA sequence is found only several nucleotides away from the start site of transcription. This
most probably relates to which of the following?
A) the number of hydrogen bonds between A and T in DNA
B) the triplet nature of the codon
C) the ability of this sequence to bind to the start site
D) the supercoiling of the DNA near the start site
E) the 3-D shape of a DNA molecule
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 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 mRNA.
B) there is redundancy and ambiguity in the genetic code.
C) many nucleotides are needed to code for each amino acid.
D) nucleotides break off and are lost during the transcription process.
E) 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) Alternative RNA splicing
A) is a mechanism for increasing the rate of transcription.
B) can allow the production of proteins of different sizes from a single mRNA.
C) can allow the production of similar proteins from different RNAs.
D) increases the rate of transcription.
E) is due to the presence or absence of particular snRNPs.
22) In the structural organization of many eukaryotic genes, individual exons may be related to which of
the following?
A) the sequence of the intron that immediately precedes each exon
B) the number of polypeptides making up the functional protein
C) the various domains of the polypeptide product
D) the number of restriction enzyme cutting sites
E) the number of start sites for transcription
23) 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.
Use the following model of a eukaryotic transcript to answer the next few questions.
5′ UTR E1 I1 E2 I2 E3 I3 E4 UTR 3′
24) 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′
25) When the spliceosome binds to elements of this structure, where can it attach?
A) to the exons
B) to the 5′ UTR
C) to the 3′ UTR
D) to an adjacent intron and exon
E) to the end of an intron
26) Which of the following is a useful feature of introns for this model?
A) They are translated into small polypeptides.
B) They become parts of snRNPs.
C) Each intron has enzymatic properties.
D) Introns allow exon shuffling.
E) Introns protect exon structure.
27) Suppose that exposure to a chemical mutagen results in a change in the sequence that alters the 5′
end of intron 1 (I1). What 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
E) exclusion of E2
28) Suppose that an induced mutation removes most of the 5′ end of the 5′ UTR. What might result?
A) Removal of the 5′ UTR has no effect because the exons are still maintained.
B) Removal of the 5′ UTR also removes the 5′ cap and the mRNA will quickly degrade.
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.
E) Removal of the 5′ UTR will result in the strand not binding to tRNAs.
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 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) 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 energizes the formation of the initiation complex, using initiation factors.
B) GTP hydrolyzes to provide phosphate groups for tRNA binding.
C) GTP hydrolyzes to provide energy for making peptide bonds.
D) GTP supplies phosphates and energy to make ATP from ADP.
E) GTP separates the small and large subunits of the ribosome at the stop codon.
32) A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the
anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that
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.
E) none of the options will occur; the cell will recognize the error and destroy the tRNA.
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 is the first event to take place in translation 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 recognizes and attaches to the 5′ cap of mRNA
35) Which of the following is a function of a signal peptide?
A) to direct an mRNA molecule into the cisternal space of the ER
B) to bind RNA polymerase to DNA and initiate transcription
C) to terminate translation of the messenger RNA
D) to translocate polypeptides across the ER membrane
E) to signal 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 hypotheses describes the most likely result?
A) tRNA will not form a cloverleaf.
B) The nearby stem end will pair improperly.
C) The amino acid methionine will not bind.
D) The anticodon will not bind with the mRNA codon.
E) The aminoacylsynthetase will not be formed.
38) The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids,
ribosomal subunits, and which of the following?
A) polypeptide factors plus ATP
B) polypeptide factors plus GTP
C) polymerases plus GTP
D) SRP plus chaperones
E) 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 would
you be able to isolate?
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
E) a cell with fewer ribosomes
40) What is the function of the release factor (RF)?
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 supplies a source of energy for termination of translation.
E) It releases the ribosome from the ER to allow polypeptides into the cytosol.
41) When the function of the newly made polypeptide is to be secreted from the cell where it has been
made, what must occur?
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, from which it goes to the Golgi.
C) It has a signal sequence that must be cleaved off before it can enter the ER.
D) It has a signal sequence that targets it to the cell’s plasma membrane where it causes exocytosis.
E) Its signal sequence causes it to be encased in a vesicle as soon as it is translated.
42) Suppose that a mutation alters the formation of a tRNA such that it still attaches to the same amino
acid (phe) but its anticodon loop has the sequence AAU that binds to the mRNA codon UUA (that
usually specifies leucine leu).
A) The modified tRNA will cause this mRNA to make only nonfunctioning product.
B) The tRNA-leu will not be able to enter the site of the ribosome to bind to the UUA.
C) One mutated tRNA molecule will be relatively inconsequential because it will compete with many
“normal” ones.
D) The tRNA will be so unstable that it will not participate in translation.
E) The mutated tRNA will result in an amino acid variant in all copies of the protein.
43) Why might a point mutation in DNA make a difference in the level of protein’s activity?
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 an amino acid in the active site.
E) It might substitute the N-terminus of the polypeptide for the C-terminus.
44) In the 1920s Muller discovered that X-rays caused mutation in Drosophila. In a related series of
experiments in the 1940s, Charlotte Auerbach discovered that chemicals–she used nitrogen mustards–
have a similar effect. A new chemical food additive is developed by a cereal manufacturer. Why do we
test for its ability to induce 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 increase in mutation frequency.
E) We worry about its ability to cause infection.
45) Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start
of translation, 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 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.
E) It prevents introns from being excised.
47) A frameshift mutation could result from
A) a base insertion only.
B) a base deletion only.
C) a base substitution only.
D) deletion of three consecutive bases.
E) either an insertion or a deletion of a base.