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.

genes dictate the production of specific enzymes, and affected individuals have genetic
defects that cause them to lack certain enzymes.

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.

It would have no effect, because tyrosine is also available from the diet.

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

ATP, RNA, and DNA

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.

3' UCA 5'

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.

A gene from an organism can theoretically be expressed by any other organism.

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.

If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually
coded for by UGG only).

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

a triplet in the same reading frame as an upstream AUG

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.

DNA polymerase uses primer, usually made of RNA.

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.

RNA polymerase transcribes through the terminator sequence, causing the polymerase to
separate from the DNA and release the transcript.

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.

A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end.

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 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 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.

It might allow the polymerase to recognize different promoters under certain environmental
conditions.

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

RNA polymerase II

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

several transcription factors

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.

Any mutation in the sequence is selected against.

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 prevents supercoiling of the DNA near the start site.
D) It is the recognition site for ribosomal binding.
E) Its significance has not yet been determined.

It is the recognition site for a specific transcription factor.

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

a bacterial promoter sequence

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

3' to 5' along the template strand

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.

It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~10—35
nucleotides away.

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

an RNA with enzymatic activity

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 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.

many noncoding stretches of nucleotides are present in eukaryotic DNA.

During splicing, which molecular component of the spliceosome catalyzes the excision
reaction?
A) protein
B) DNA
C) RNA
D) lipid
E) sugar

RNA

Alternative RNA splicing
A) is a mechanism for increasing the rate of transcription.
B) can allow the production of proteins of different sizes and functions 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.

can allow the production of proteins of different sizes and functions from a single mRNA.

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 because it is no longer protected at the 5' end.
E) The molecule attaches to a ribosome and is translated, but more slowly.

The molecule is digested by exonucleases because it is no longer protected at the 5' end.

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'

5' UTR E1 E2 E3 E4 UTR 3'

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

to the end of an intron

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

inclusion of I1 in the mRNA

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.

Removal of the 5' UTR also removes the 5' cap, and the mRNA will quickly degrade.

When the spliceosome binds to this transcript, 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) at certain sites along an intron

at certain sites along an intron

Which of the following experimental procedures is most likely to hasten mRNA degradation
in a eukaryotic cell?
A) enzymatic lengthening of the poly-A tail
B) removal of the 5' cap
C) methylation of C nucleotides
D) methylation of histones
E) removal of one or more exons

removal of the 5' cap

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.

UUU

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.

bonding of the anticodon to the codon and the attachment of amino acids to tRNAs.

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.

GTP energizes the formation of the initiation complex, using initiation factors.

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. 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.

proteins in the cell will include lysine instead of phenylalanine at amino acid positions
specified by the codon UUU.

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.

the rules for base pairing between the third base of a codon and tRNA are flexible.

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

the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

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

to translocate polypeptides across the ER membrane

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.

a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.

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 become covalently bound.
D) The anticodon will not bind with the mRNA codon.
E) The aminoacyl-tRNA synthetase will not be formed.

The amino acid methionine will not become covalently bound.

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

polypeptide factors plus GTP

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

an assembled ribosome with a polypeptide attached to the tRNA in the P site