Quiz 8

Question 1

The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?

a) A gene from one organism can theoretically be expressed by any other organism.
b) DNA was the first genetic material.
c) The same codons in different organisms translate into the different amino acids.
d) Different organisms have different numbers of different types of amino acids.

Answer 1

a) A gene from one organism can theoretically be expressed by any other organism.

Question 2

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.

Answer 2

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

Question 3

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the..

a) shape of the A and P sites of ribosomes.
b) bonding of the anticodon to the codon.
c) attachment of amino acids to tRNAs.
d) bonding of the anticodon to the codon and the attachment of amino acids to tRNAs

Answer 3

d) bonding of the anticodon to the codon and the attachment of amino acids to tRNAs

Question 4

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 subsitution of the first nucleotide of a GGG codon.

Answer 4

b) a deletion of two nucleotides

Question 5

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) bind to the repressor protein and inactivate it.
d) bind to the repressor protein and activate it.

Answer 5

d) bind to the repressor protein and activate it.

Question 6

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.

Answer 6

b) several transcription factors have bound to the promoter.

Question 7

Which of the following is not true of a codon?

a) It may code for the same amino acid as another codon.
b) It never codes for more than one amino acid.
c) It extends from one end of a tRNA molecule.
d) It is the basic unit of the genetic code.

Answer 7

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

Question 8

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) catalytic, making the tRNA a ribozyme.

Answer 8

a) complementary to the corresponding mRNA codon.

Question 9

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.

Answer 9

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

Question 10

Which component is not directly involved in translation?

a) GTP
b) DNA
c) tRNA
d) ribosomes

Answer 10

b) DNA

Question 11

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

a) a deletion of three nucleotides near the middle of a gene
b) a single nucleotide deletion in the middle of an intron
c) a single nucleotide deletion near the end of the coding sequence
d) a single nucleotide insertion downstream of, and close to, the start of the coding sequence

Answer 11

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

Question 12

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

Answer 12

d) continuous transcription of the operon’s genes

Question 13

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

a) the amino acid inactivates the repressor.
b) the repressor is active in the absence of the amino acid.
c) the amino acid acts as a corepressor.
d) the amino acid turns on transcription of the operon.

Answer 13

c) the amino acid acts as a corepressor.

Question 14

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) proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.
b) none of the proteins in the cell will contain phenylalanine.
c) the ribosome will skip a codon every time a UUU is encountered.
d) the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons.

Answer 14

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

Question 15

Which of the following does not occur in prokaryotic eukaryotic gene expression, but does in eukaryotic gene expression?

a) A poly-A tail is added to the 3’ end of an mRNA and a cap is added to the 5’ end.
b) RNA polymerase binds to the promoter.
c) RNA polymerase requires a primer to elongate the molecule.
d) mRNA, tRNA, and rRNA are transcribed.
e) Transcription can begin as soon as translation has begun even a little.

Answer 15

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

Question 16

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication?

a) The process is extremely fast once it is initiated.
b) The process occurs in the nucleus of a eukaryotic cell.
c) It uses RNA polymerase.
d) The entire template molecule is represented in the product.
e) It makes a new molecule from its 5’ end to its 3’ end.

Answer 16

d) The entire template molecule is represented in the product.

Question 17

A frameshift mutation could result from

a) deletion of three consecutive bases.
b) a base insertion only.
c) a base deletion only.
d) either an insertion or a deletion of a base.
e) a base substitution only.

Answer 17

d) either an insertion or a deletion of a base.

Question 18

The following question refers to this figure of a simple metabolic pathway:

A —enzyme A—> B —enzyme B—> C

A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation?

a) an accumulation of B and no production of A and C
b) an accumulation of A and B and no production of C
c) an accumulation of C and no production of A and B
d) an accumulation of B and C and no production of A
e) an accumulation of A and no production of B and C

Answer 18

e) an accumulation of A and no production of B and C

Question 19

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 has a signal sequence that must be cleaved off before it can enter the ER.
b) Its signal sequence causes it to be encased in a vesicle as soon as it is translated.
c) It must be translated by a ribosome that remains free of attachment to 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 must target it to the ER, from which it goes to the Golgi

Answer 19

e) Its signal sequence must target it to the ER, from which it goes to the Golgi

Question 20

A transcription unit that is 8000 nucleotides long may use 1200 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 are termination exons near the beginning of mRNA.
c) nucleotides break off and are lost during the transcription process.
d) many nucleotides are needed to code for each amino acid.

Answer 20

a) many noncoding stretches of nucleotides are present in mRNA.

Question 21

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

a) inactivate their mRNA molecules
b) turn off translation of their mRNA
c) increase the number and responsiveness of their ribosomes
d) alter the sequence of amino acids in certain proteins
e) alter the level of production of various enzymes

Answer 21

e) alter the level of production of various enzymes

Question 22

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. If she moves the operator to the far end of the lac operon (past the terminator sequence), 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 protein will no longer be produced.
c) The genes will be transcribed continuously.
d) The operon will never be transcribed.
e) The repressor will no longer bind to the operator.

Answer 22

c) The genes will be transcribed continuously.

Question 23

Which of the following, when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator?

a) inducer
b) ubiquitin
c) repressor
d) corepressor
e) promoter

Answer 23

a) inducer

Question 24

The tryptophan operon is a repressible operon that is

a) turned on only when glucose is present in the growth medium.
b) turned off whenever tryptophan is added to the growth medium.
c) permanently turned on.
d) turned off only when glucose is present in the growth medium.
e) turned on only when tryptophan is present in the growth medium.

Answer 24

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

Question 25

There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?

a) It makes molecules that bind to one another.
b) It makes a repressor that binds CAP.
c) It cannot make a functional repressor.
d) It cannot bind to the operator.
e) It cannot bind to the inducer.

Answer 25

e) It cannot bind to the inducer.

Question 26

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

a) irreversible binding of the repressor to the operator.
b) continuous transcription of the gene controlled by that regulator.
c) inactivation of RNA polymerase by alteration of its active site.
d) continuous translation of the mRNA because of alteration of its structure.
e) complete inhibition of transcription of the gene controlled by that regulator.

Answer 26

b) continuous transcription of the gene controlled by that regulator.

Question 27

Transcription of the genes in an inducible operon

a) starts when the pathway’s product is present.
b) stops when the pathway’s product is present.
c) does not result in the production of enzymes.
d) occurs continuously in the cell.
e) starts when the pathway’s substrate is present.

Answer 27

e) starts when the pathway’s substrate is present.

Question 28

What is a ribozyme?

a) an enzyme that catalyzes the association between the large and small ribosomal subunits
b) an enzyme that uses RNA as a substrate
c) an enzyme that synthesizes RNA primers during DNA replication
d) an enzyme that synthesizes RNA as part of the transcription process
e) an RNA with enzymatic activity

Answer 28

e) an RNA with enzymatic activity

Question 29

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

a) ribosomes and tRNA
b) the protein product of the promoter
c) aminoacyl synthetase
d) start and stop codons
e) several transcription factors (TFs)

Answer 29

e) several transcription factors (TFs)

Question 30

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

a) RNA polymerase must bind to the promoter, and the repressor must be inactive.
b) RNA polymerase must not occupy the promoter, and the repressor must be inactive.
c) A corepressor must be present.
d) RNA polymerase cannot be present, and the repressor must be inactive.
e) RNA polymerase and the active repressor must be present.

Answer 30

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

Question 31

A lack of which molecule would result in the cell’s inability to “turn off” genes?

a) operon
b) ubiquitin
c) corepressor
d) promoter
e) inducer

Answer 31

c) corepressor

Question 32

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

a) It catalyzes the lengthening of telomeres.
b) It stabilizes the unwound parental DNA.
c) It synthesizes RNA nucleotides to make a primer.
d) It unwinds the parental double helix.
e) It joins Okazaki fragments together.

Answer 32

e) It joins Okazaki fragments together.

Question 33

Which of the following statements is true about protein synthesis in prokaryotes?

a) Translation requires antibiotic activity.
b) Extensive RNA processing is required before prokaryotic transcripts can be translated.
c) Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles.
d) Translation can begin while transcription is still in progress.
e) Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

Answer 33

d) Translation can begin while transcription is still in progress.

Question 34

Alternative RNA splicing

a) can allow the production of proteins of different sizes from a single mRNA.
b) is a mechanism for increasing the rate of transcription.
c) increases the rate of transcription.
d) can allow the production of similar proteins from different RNAs.

Answer 34

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

Question 35

What is the function of the release factor (RF)?

a) It releases the amino acid from its tRNA to allow the amino acid to form a peptide bond.
b) It separates tRNA in the A site from the growing polypeptide.
c) It binds to the stop codon in the A site in place of a tRNA.
d) It releases the ribosome from the ER to allow polypeptides into the cytosol.

Answer 35

c) It binds to the stop codon in the A site in place of a tRNA.

Question 36

Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation?

a) RNA polymerase
b) inducer
c) cAMP
d) promoter
e) transcription factor

Answer 36

b) inducer

Question 37

The lactose operon is likely to be transcribed when

a) the cyclic AMP levels are low.
b) the cAMP level is high and the lactose level is low.
c) there is more glucose in the cell than lactose.
d) the cyclic AMP and lactose levels are both high within the cell.
e) there is glucose but no lactose in the cell.

Answer 37

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

Question 38

Allolactose, an isomer of lactose, is formed in small amounts from lactose. 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) Allolactose binds to the repressor protein.
b) The repressor protein and allolactose bind to RNA polymerase.
c) The repressor protein attaches to the regulator.
d) Allolactose binds to the regulator gene.

Answer 38

a) Allolactose binds to the repressor protein.

Question 39

If a nucleotide substitution switched a U for a C, such that the codon was read as CGC instead of CGU, what would the effect be?

a) nothing, since both these codons code for arginine
b) a misfolding of the protein
c) an incomplete protein
d) it would initiate a tumour

Answer 39

a) nothing, since both these codons code for arginine

Question 40

The molecule that links the genotype and phenotype of an organism, is (are)

a) receptor complexes.
b) ploidy.
c) mRNA.
d) protein.
e) tRNA.

Answer 40

d) protein.

Question 41

Which of the following statements best describes the termination of transcription in prokaryotes?

a) RNA polymerase transcribes through an intron, and the snRNPs cause the polymerase to let go of the transcript.
b) Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome.
c) RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase.
d) RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.
e) RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.

Answer 41

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

Question 42

If a nucleotide substitution switched an A for a U, such that the codon was read as UAA instead of AAA, what would the effect be?

a) a nonsense mutation
b) a missense mutation
c) it would initiate a tumour
d) a silent mutation
e) no mutation as nucleotides in the first position are interchangeable

Answer 42

a) a nonsense mutation

Question 43

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in

a) a frameshift mutation.
b) a polypeptide missing an amino acid.
c) a nonsense mutation.
d) a nucleotide mismatch.
e) a base-pair substitution.

Answer 43

b) a polypeptide missing an amino acid.

Question 44

The following question refers to this figure of a simple metabolic pathway:

A —enzyme A—> B —enzyme B—> C

If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on which of the following media?

a) minimal medium supplemented with nutrient C only
b) minimal medium supplemented with nutrient A only
c) minimal medium supplemented with nutrient B only
d) minimal medium supplemented with nutrients A and C
e) minimal medium

Answer 44

c) minimal medium supplemented with nutrient B only

Question 45

Which of the following nucleotide triplets best represents a codon?

a) a triplet that has no corresponding amino acid
b) a triplet at the opposite end of tRNA from the attachment site of the amino acid
c) a sequence in tRNA at the 3’ end
d) a triplet separated spatially from other triplets
e) a triplet in the same reading frame as an upstream AUG

Answer 45

e) a triplet in the same reading frame as an upstream AUG

Question 46

The following question refers to this figure of a simple metabolic pathway:

A —enzyme A—> B —enzyme B—> C

If A, B, and C are all required for growth, a strain mutant for the gene encoding enzyme B would be capable of growing on which of the following media?

a) minimal medium supplemented with nutrient C only
b) minimal medium supplemented with nutrient A only
c) minimal medium supplemented with nutrient B only
d) minimal medium supplemented with nutrients A and C
e) minimal medium

Answer 46

a) minimal medium supplemented with nutrient C only

Question 47

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 substitute the N-terminus of the polypeptide for the C-terminus.
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 exchange one stop codon for another stop codon.

Answer 47

d) It might substitute an amino acid in the active site.

Question 48

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 is found in many but not all promoters.
b) Any mutation in the sequence is selected against.
c) The sequence is transcribed at the start of every gene.
d) The sequence does not mutate.
e) The sequence evolves very rapidly.

Answer 48

b) Any mutation in the sequence is selected against.

Question 49

What is the effect of a nonsense mutation in a gene?

a) It prevents introns from being excised.
b) It introduces a premature stop codon into the mRNA.
c) It has no effect on the amino acid sequence of the encoded protein.
d) It alters the reading frame of the mRNA.

Answer 49

b) It introduces a premature stop codon into the mRNA.

Question 50

Which small-scale mutation would be most likely to have a catastrophic effect on the functioning of a protein?

a) a base deletion near the end of the coding sequence, but not in the terminator codon
b) a base deletion near the start of a gene
c) deletion of three bases near the start of the coding sequence, but not in the initiator codon
d) a base substitution
e) a base insertion near the end of the coding sequence, but not in the terminator codon

Answer 50

b) a base deletion near the start of a gene