End of Chapter Problems

Question 1

Viruses cause many human infections such as hepatitis, encephalitis, and the “common cold.” Which one of the following is a common trait of all these viruses?
A. They are small, circular DNA molecules that enter bacteria and replicate outside the host genome.
B. Upon infecting eukaryotic cells, they are called phages.
C. All the common cold viruses contain both DNA and RNA genomes
D. In order to reproduce, they must use the infected cell’s DNA, RNA, and protein-synthesizing machinery.
E. Upon becoming infectious, they are called plasmids.

Answer 1

D. In order to reproduce, they must use the infected cell’s DNA, RNA, and protein-synthesizing machinery.

Question 2

Many drugs used to treat cancers inhibit DNA replication, whereas some will inhibit the pathways required to synthesize proteins from certain genes. Which one of the following accurately describes a step leading from DNA replication to the synthesis of a protein?
A. Translation of a gene generates a single-stranded RNA that is complementary to both stands of the DNA
B. Transcription of a gene generates a single-stranded RNA that is complementary to one of the DNA stands
C. tRNA encodes the proteins during translation
D. mRNA encodes the proteins during transcription
E. rRNA encodes the proteins during transcription

Answer 2

B. Transcription of a gene generates a single-stranded RNA that is complementary to one of the DNA strands.

Question 3

Gout is caused by the deposition of urate crystals in the joints and kidneys. Purines are metabolized to uric acid, whereas pyrimidines, when metabolized, do not generate uric acid. Which one of the following should be restricted in the diet of a patient with gout?
A. Cytosine
B. Guanine
C. Thymine
D. Uracil
E. Deoxyribose

Answer 3

B. Guanine

Question 4

A patient has microcytic, hypochromic anemia. In order to ascertain the cause of the anemia, the patient’s hemoglobin was isolated, and it was determined that there was much more beta-chain present alpha chain, indicating an alpha-thalassemia. To determine the genetic basis of the thalassemia, nucleic acids were isolated from the blood of the patient. During the procedure of isolating the nucleic acids, both heat and alkali treatment were required. The alkali heat were included owing to which one of the following?
A. Alkali causes the two strand of DNA and RNA to separate.
B. Heat causes the two strands of DNA and RNA to separate.
C. Alkali cleaves the phosphodiester bonds of DNA and RNA, degrading them to nucleotides.
D. Alkali separates the strands of DNA and degrades the RNA to nucleotides.
E. Alkali separates the strands of RNA and degrades DNA to nucleotides.

Answer 4

D. Alkali separates the strands of DNA and degrades the RNA to nucleotides

Question 5

Targeting certain structural features of eukaryotic mRNA can result in an inhibition of protein synthesis. Which one of the following describes a unique aspect of eukaryotic mRNA?
A. A polyguanosine tail is found at the 3’ -end
B. The 5’ -end begins with a leader sequence that contains an adenine cap.
C. The cap and tail of the mRNA are added posttranscriptionally
D. The leader sequence contains a guanosine cap at the 3’ -end of the mRNA
E. The poly(A) tail is found at the 3’ -end of the mRNA

Answer 5

E. The poly(A) tail is found at the 3’ -end of the mRNA

Question 6

Some chemotherapeutic drugs alter the ability of DNA polymerase to faithfully replicate. For the DNA sequence 5'-ATCGATCGATCGATCG-3', which one of the following represents the sequence and polarity of the complementary strand?
A. 5'-ATCTATCGATCGATCG-3'
B. 3'-ATCGATCGATCGATCG-5'
C. 5'-CGAUCGAUCAUCGAU-3'
D. 5'-CGATCGATCGATCGAT-3'
E. 3'-CGATCGATCGATCGAT-5'

Answer 6

D. 5’-CGATCGATCGATCGAT-3’

Question 7

Certain drugs inhibit bacterial RNA synthesis. If the DNA strand 5'-GCTATGCATCGTGATC GAATTGCGT-3' serves as a template for the synthesis of RNA, which one of the following choices gives the sequence and polarity of the newly synthesized RNA?
A. 5'-ACGCAATTCGATCACGATGCATAGC-3'
B. 5'-UGCGUUAAGCUAGUGCUACGUAUCG-3'
C. 5'-ACGCAAUUCGAUCACGAUGCAUAGC-3'
D. 5'-CGAUACGUAGCACUAGCUUAACGCA-3'
E. 5'-GCTATGCATCGTGATCGAATTGCGT-3'

Answer 7

C. 5’-ACGCAAUUCGAUCACGAUGCAUAGC-3’

Question 8

Understanding the structure of DNA, and the process of replication, enabled various drugs to be developed that interfered with DNA replication. In DNA, the bond between the deoxyribose sugar and the phosphate is best described by which one of the following?
A. A polar bond
B. An ionic bond
C. A hydrogen bond
D. A covalent bond
E. A van der Waals bond

Answer 8

D. A covalent bond

Question 9

Certain drugs can intercalate between DNA bases and alter the backbone of the DNA. The backbone of a DNA strand is composed of which of the following?
A. Phosphates and sugars
B. Bases and phosphates
C. Nucleotides and sugars
D. Phosphates and nucleosides
E. Sugars and bases

Answer 9

A. Phosphates and sugars

Question 10

Analysis of one strand of a double-stranded piece of DNA displayed 20 mol % A, 25 mol % T, 30 mol % G and 25 mol % C. Which one of the following accurately represents the composition of the complementary strand?
A. A is 25 mol %, T is 20 mol %, G is 25 mol %, and C is 30 mol %
B. [A] is 30 mol %, [T] is 25 mol %, [G] is 20 mol %, and [C] is 25 mol %
C. [U] is 25 mol %, [T] is 20 mol %, [G] is 25 mol %, and [C] is 30 mol %
D. [A] is 25 mol %, [T] is 25 mol %, [G] is 25 mol %, and [C] is 25 mol %
E. The composition of the complementary strand cannot be determined from the data given

Answer 10

A. A is 25 mol %, T is 20 mol %, G is 25 mol %, and C is 30 mol %

Question 11

Similarities between CPSI and CPSII include which one of the following?
A. Carbon source
B. Intracellular location 
C. Nitrogen Source
D. Regulation by N-acetylglutamate
E. Regulation by UMP

Answer 11

A. Carbon Source

Question 12

Gout can result from a reduction in activity of which one of the following enzymes?
A, Glutamine phosphoribosylamidotransferase
B. HGPRT
C. Glucose 6-phosphate dehydrogenase
D. PRPP synthetase
E. Purine nucleoside phosphorylase

Answer 12

B. HGPRT

Question 13

A 2-year-old boy is exhibiting developmental delay and has started to bite his lips and fingers. Orange-colored "sand" is founding his diapers. This child has an inability to metabolize which one of the following molecules?
A. Uric acid
B. Thymine
C. Adenine
D. Uracil
E. Hypoxanthine

Answer 13

E. Hypoxanthine

Question 14

Allopurinol can be used to treat gout because of its ability to inhibit which one of the following reactions?
A. AMP to XMP
B. Xanthine to uric acid
C. Inosine to hypoxanthine
D. IMP to XMP
E. XMP to GMP

Answer 14

B. Xanthine to uric acid

Question 15

The regulation of ribonucleotide reductase is quite complex. Assuming that an enzyme deficiency leads to highly elevated levels of dGTP, what effect would you predict on the reduction of ribonucleotides to deoxyribonucleeotides under these conditions?
A. Elevated levels of dCDP will be produced
B. The formation fo dADP will be favored
C. AMP will begin to be produced
D. Reduced thioredoxin will become rate-limiting, thereby reducing the activity of ribonucleotide reductase.
E. dGTP will bind to the overall activity site and inhibit the functioning of the enzyme

Answer 15

B. The formation of dADP will be favored

Question 16

A patient with von Gierke's disease displays the symptoms of gout. This most likely occurs owing to the overproduction of which one of the following molecules?
A. PRPP
B. Aspartate
C. Glucose
D. NADPH
E. UDP-Glucose

Answer 16

A. PRPP

Question 17

A patient with ornithine transcarbamoylase deficiency exhibits orotic acuduria. This occurs owing to which one of the following?
A. Activation of the regulated step of de novo pyrimidine biosynthesis
B. Bypassing the regulated step of de novo pyrimidine biosynthesis
C. Inhibition of the regulated step of de novo pyrimidine biosynthesis
D. Activation of the CAD complex by carbamoyl phosphate
E. Activation of the UMP synthase complex by carbamoyl phosphate

Answer 17

B. Bypassing the regulated step of do novo pyrimidine biosynthesis

Question 18

Purines and pyrimidines are necessary for the synthesis of DNA. Of the substances that donate atoms to the purine base and pyrimidine ring, which one of the following directly donates atoms to both the purine base and pyrimidine ring?
A. CO2
B. Glycine
C. Carbamoyl phosphate
D. Aspartate 
E. Glutamine

Answer 18

D. Aspartate

Question 19

Which one of the following statements is correct concerning purine and pyrimidine metabolism?
A. Pyrimidines, when degraded, yield uric acid
B. Excess pyrimidine degradation can lead to gout
C. Purines cannot be degraded to generate energy
D. Purines degrade to CO2 and water
E. An excess of urea leads to gout

Answer 19

C. Purines cannot be degraded to generate energy

Question 20

Allopurinol is used to treat gout. The drug is a suicide inhibitor that leads to a reduction in the amount of uric acid produced. Instead of accumulating the uric acid, which other compound would accumulate in the presence of allopurinol?
A. Hypoxanthine
B. Ribose-1-phosphate
C. IMP
D. Guanine
E. Adenine

Answer 20

A. Hypoxanthine

Question 21

A variety of drugs can alter DNA replication in eukaryotic cells. Which one of the following steps could be a target for such a drug?
A. The enzyme family of DNA polymerases, which unwinds parental strands
B. The enzyme family of topoisomerases, which copy each parental strand in the 3’-to-5’ direction
C. The enzyme family of helicases, which copy each parental strand in the 5’-to-3’ direction
D. The finding that both strands of newly synthesized DNA always grow continuously
E. The enzyme DNA ligase, which joins Okazaki fragments

Answer 21

E. The enzyme DNA ligase, which joins Okazaki fragments

Question 22

There are a variety of DNA polymerases in both bacterial and eukaryotic cells. Targeting which one of the following properties of DNA polymerases would result in inhibiting DNA synthesis?
A. The imitation de novo of the synthesis of new DNA strands
B. The formation of phosphodiester bonds through hydrogen bonding
C. The cleavage of released pyrophosphate that provides the energy for the polymerization reaction
D. The dissociation and reassociation of the enzyme with DNA as each nucleotide is added to an existing DNA chain
E. The process of copying a template strand in its 3’-to-5’ direction, producing a new strand in the 5’-to-3’ direction

Answer 22

E. The process of copying a template strand in its 3’-to-5’ direction. producing a new strand in the 5’-to-3’ direction

Question 23

An antibiotic that inhibits bacterial DNA polymerases can damage human mitochondria owing to which one of the following eukaryotic DNA polymerases being most similar to a prokaryotic DNA polymerase.
A. alpha
B. beta
C. gamma
D. delta
E. epsilon

Answer 23

C. gamma

Question 24

A drugs that inhibits DNA replication, but is inactivated by chromosomes containing telomeres, would prove to be a very useful antibiotic. Telomeres can be best described by which one of the following?
A. Telomeres are only present in circular chromosomes
B. Before telomerase action, and after DNA replication, there is a 3’ overhang of the newly synthesized strand
C. Before telomerase action, and after DNA replication, there is a 5’ overhang of the strand being replicated
D. In human DNA, telomeres consist of repeating sequences of TTAGGT
E. Somatic eukaryotic cells do not contain telomeres.

Answer 24

B. Before telomerase action, and after DNA replication, there is a 3’ overhang of the newly synthesized strand

Question 25

Disease caused by defects in DNA repair systems put the patient at risk for developing cancers. DNA repair mechanisms can be best described by which one of the following?
A. Proofreading works as the bases are paired and eliminates all base-pairing errors
B. After replication, no further repairs are possible
C. Genes that produce mRNA have a unique repair system
D. Genes that produce transfer RNA have a unique repair system
E. DNA glycolases recognize distortion of the DNA helix owing to bulky adducts being present on a base within the DNA

Answer 25

C. Genes that produce mRNA have unique repair system

Question 26

The retroviruses, including HIV, use an RNA genome. In order to generate DNA from the genomic RNA, the enzyme reverse transcriptase is required. Reverse transcription differs specifically from DNA Pol delta by which one of the following?
A. Synthesizing DNA in the 5’-to3’ direction
B. Expressing 3’-to-5’ exonuclease activity
C. Using Watson-Crick base-pair rules during DNA synthesis
D. Synthesizing DNA in the 3’to-5’ direction
E. Inserting inosine into a growing DNA chain

Answer 26

B. Expressing 3’-to-5’ exonuclease activity

Question 27

Translocations cause some of the most recognized genetic syndromes in human offspring. A translocation can be best described by which one of the following?
A. They always produce cancer
B. They always produce mental retardation
C. They have to involve the exchange of an entire chromosome
D. They can only occur in the presence of reverse transcriptase
E. They can occur in somatic or stem cells

Answer 27

E. They can occur in somatic or stem cells

Question 28

The large DNA molecules in human chromosomes take more time to replicate than the smaller, circular bacterial chromosomes. If a 1000-kilobase (kb) fragment of DNA has 10  evenly spaced and symmetric replication origins, and DNA polymerase moves at 1 kb per second, how many seconds will it take to produce two daughter molecules?
A. 20
B. 30
C. 40
D. 50
E. 100

Answer 28

D. 50

Question 29

DNA replication is a different process than DNA repair. Mutations in DNA repair enzymes can lead to disease–especially certain forms of cancer. Primase is not required during DNA repair processes because of which one of the following?
A. All of the primate is associated with replication
B. RNA would be highly mutagenic at a repair site
C. Repair DNA polymerase do not require a primer
D. Replicative DNA polymerases do nor require a primer
E.Repair DNA polymerases can use any 3’-OH for elongation

Answer 29

E. Repair DNA polymerase can use any 3’-OH for elongation

Question 30

The key mechanistic failure in patients with XP involves which one of the following?
A. Mutation in the primate gene
B. Inability to excise a section of the UV-damaged DNA
C. Mutation of one of the mismatch repair components
D. Inability to synthesize DNA across the damaged region
E. Loss of proofreading capacity

Answer 30

B. Inability to excise a section of the UV-damaged DNA

Question 31

A gene would need to contain which one of the following templates to generate the short transcript AUCCGUACG?
A. ATCCGTACG
B. CGTACGGAT
C. AUCCGUACG
D. TAGGCATGC
E. GCATGCCTA

Answer 31

B. CGTACGGAT

Question 32

Given that the LD50 of amanitin is 0.1 mg/kg of body weight, and that the average mushroom contains 7mg of amanitin, how many mushrooms must be consumed by Catherine T (50 kg of body weight) to be above the LD50?
A. 1
B. 2
C. 3
D. 4
E. 5

Answer 32

A. 1

Question 33

Mutations in DNA large distances from a structural gene ca lead to over- or underexpression of that gene. Which one of the following eukaryotic DNA control sequences does not need to be in a fixed location and is most responsible for high rates of transcription of particular genes?
A. Promoter
B. Promoter-proximal element
C. Enhancer
D. Operator
E. Splice donor site

Answer 33

C. Enhancer

Question 34

Which one of the following is true of both eukaryotic and prokaryotic gene expression and would therefore not be an effective drug target for drug development
A. After transcription, a 3’-poly(A) tail and a 5’-cap are added to mRNA
B. Translation of mRNA can begin before transcription is complete
C. mRNA is synthesized in the 3’-to-5’ direction
D. RNA polymerase binds at a promoter region upstream of the gene
E. Mature mRNA is always precisely collinear to the gene from which it was transcribed

Answer 34

D. RNA polymerase binds at a promoter region upstream of the gene

Question 35

A family has two children, both of whom have a form of beta-thalassemia. One child is almost nonsymptomatic, whereas the other requires frequent blood transfusions for his disease. The alpha-globulin to beta-globulin ration in the more severely affected child is most likely to be which one of the following?
A. 5:1
B. 2:1
C. 1:1
D. 1:2
E. 1:5

Answer 35

A. 5:1

Question 36

Certain drugs can be used as antibiotics because they affect bacterial RNA polymerases but not eukaryotic RNA polymerases. RNA polymerase is a key enzyme in the process of transcription, which can be best described by which one of the following?
A. The single-stranded RNA produced is identical to one of the strands of double-stranded DNA
B. The single-stranded RNA produced is identical to both of the strands of double-stranded DNA
C. Eukaryotic genes are transcribed in the cytosol by three different RNA polymerases
D. RNA polymerase cannot initiate new strand synthesis and must have a primer
E. Eukaryotic genes are transcribed in the nucleus by three different DNA polymerases

Answer 36

A. The single-stranded RNA produced is identical to one of the strands of double-stranded DNA

Question 37

Eukaryotic cells contain multiple RNA polymerases, which makes it difficult to block all RNA synthesis with one drug targeted to a specific polymerase. Which one of the following best describes properties of eukaryotic RNA polymerases?
A. Polymerase I produces most of the rRNA
B. Polymerase II produces most of the tRNA
C. Polymerase III produces most of the mRNA
D. All three RNA polymerases have the same mechanism of action and bind to the same promoter sequence on DNA
E. Enhancers identify the start point for transcription for all three polymerase.

Answer 37

A. Polymerase I produces most of the rRNA

Question 38

The production of mRNA in eukaryotic cells requires a large number of steps, and drugs targeted to any of these steps could block mRNA production. Which one of the following accurately describes a part of the process of producing mRNA from a eukaryotic gene?
A. The sense strand of DNA is the strand used by RNA polymerase during transcription
B. The antisense DNA strand is identical to the RNA transcript except that the DNA strand contains thymine and the RNA strand contains uracil
C. The first RNA form produced contains both intron and exon sequences
D. Mature mRNA contains a cap the the 5’- and, a poly(A) tail at the 3’-end, introns, and exons
E. During processing in the nucleus of a precursor mRNA, introns and eons are shuffled in a sequence to produce the mature mRNA

Answer 38

C. The first RNA form produced contains both intron and exon sequences

Question 39

Genetic abnormalities in DNA are transcribed into mRNA. This error then causes tRNA to use an incorrectly coded amino acid to produce a protein, which may then malfunction because of the alteration in primary structure of the synthesized protein. The tRNAs used for protein synthesis can be best described by which one of the following?
A. A specific tRNA can code for multiple different amino acids
B. tRNA contains a codon site that binds with an anticodon of mRNA
C. tRNA contains one specific binding site for both the sequence of three nucleotides in mRNA and the encoded amino acid
D. One of the loops of tRNA contains the anticodon
E. The D loop contains the anticodon

Answer 39

D. One of the loops of tRNA contains the anticodon

Question 40

A researcher wants to develop an antibiotic that targets histones and introns in bacteria, and she has applied for a grant. Why would the grant’s physician/biochemist advisor against funding this grant application?
A. The proposed antibiotic would have no effect on bacteria but could harm human cells
B. The proposed antibiotic would negatively affect both bacteria and human cells
C. The proposed antibiotic would have no effect on either bacteria or human cells
D. Bacteria have histones but do not have introns
E. Bacteria have introns but do not have histones

Answer 40

A. The proposed antibiotic would have mo effect on bacteria but could harm human cells.

Question 41

Antibiotics can target differences in processing of the genetic code between bacteria and humans. In the readout of the genetic code in prokaryotes, which one of the following processes acts before any of the others?
A. tRNA alignment with mRNA
B. Termination of transcription
C. Movement of the ribosome from one codon to the next
D. Recruitment of termination factors to the A site
E. Export of mRNA from the nucleus

Answer 41

A. tRNA alignment with mRNA

Question 42

Genetic mutations can be simulated in laboratory situations. tRNA charged with cysteine can be chemically treated so that the amino acid changes its identity to alanine. If some of this charged tRNA is added to a protein-synthesizing extract that contains all the normal components required for translation, which of the following statements represents the most likely outcome after adding an mRNA that has both Cys and Ala codons in the normal reading frame?
A. Cysteine would be added each time the alanine codon was translated
B. Alanine would be added each time the cysteine codon was translated
C. The protein would have a deficiency of cysteine residues
D. The protein would have a deficiency of alanine residues
E. The protein would be entirely normal

Answer 42

C. The protein would have a deficiency of cysteine residues

Question 43

Human and bacterial DNA differ in the organization of genetic information. A series of eukaryotic gene sequences (coding sequences) is given below. Based on this portion of the sequence, which gene could produce a protein that contains 300 amino acids and has a phenylalanine residue near its N terminus? The phenylalanine codons (5'-to-3') are UUU and UUC?
A. 5'-CCATGCCATTTGCATCA-3'
B. 5'-CCATGCCATTTGCATGA-3'
C. 5'-CCATGCCAATTTGCATC-3'
D. 5'-CCATCCCATTTGCATGA-3'
E. 5'-CCATCCCATTTGCATCA-3'

Answer 43

A. 5’-CCATGCCATTTGCATCA-3’

Question 44

A drug is being designed to block eukaryotic translation. Which of the following would be an appropriate target for the drug?

Answer 44

See book for table

Answer: F.

Question 45

A gene has undergone a mutation in which a certain codon has been altered, through a single nucleotide change, into a Phe codon. Which one of the following amino acids could the original codon code for?
A. Pro
B. Leu
C. Gly
D. Asn
E. Arg
F. Trp

Answer 45

B. Leu

Question 46

A mutation in a gene has led to the generation of a nonsense codon in the corresponding protein. If this is caused by a single nucleotide change, the original codon may have coded for which one of the following?
A. Gly
B. Pro
C. Phe
D. Asn
E. Trp

Answer 46

E. Trp

Question 47

Which type of mutation leads to sickle cell anemia?
A. Silent
B. Nonsense
C. Insertion
D. Deletion
E. Missense

Answer 47

E. Missense

Question 48

The creation of a stop codon in DNA often leads to a deleterious condition. If a mutation in DNA caused a stop codon TAG to be created on the coding strand between the TATA box and the transcription initiation site, what would be the most likely outcome?
A. No effect
B. Loss of transcription
C. Loss of translation
D. A shorter protein
E. A mistake in splicing

Answer 48

A. No effect

Question 49

A temperature-sensitive variant of E. coli was discovered which had a complete loss of protein synthetic ability after about five generations of growth at the non permissive temperature. Analysis of the components required for protein synthesis indicated that mRNA synthesis (transcription) still occurred at the non permissive temperature, and the mRNA produced had normal half-lives. The transcription of rRNA and tRNA was also normal as was ribosome structure. A potential protein in which loss of activity at the non permissive temperature would lead to these findings is which one of the following.
A. A spliceosome protein 
B. A tRNA-modifying enzyme
C. The capping protein 
D. Poly(A) polymerase
E. A nuclear mRNA export protein

Answer 49

B. A tRNA-modifying enzyme

Question 50

A new patient, recently admitted to the hospital, has contracted diphtheria. A family history indicates that the patient had never been vaccinated against this pathogen. Protein synthesis in the patient’s cells is inhibited owing to which of the following?
A. An inhibition of RNA polymerase II activity
B. An inhibition of peptidyltransferase activity
C. An inhibition of the assembly of the translation-initiation complex
D. An inhibition of the translocation step of protein synthesis
E. An inhibition of the termination of protein synthesis

Answer 50

D. An inhibition of the translocation step of protein synthesis

Question 51

Bacteria can coordinately express several genes simultaneously. Which one of the following explains why several different proteins can be synthesized from a typical prokaryotic mRNA?
A. Any of the three reading frames can be used.
B. There is redundancy in the choice of codon/tRNA interactions
C. The gene contains several operator sequences from which to initiate translation
D. Alternative splicing events are commonly found
E. Many RNAs are organized in a series of consecutive translational cistrons

Answer 51

E. Many RNAs are organized in a series of consecutive translational cistrons

Question 52

E. coli will only express genes for lactose metabolism when lactose is present in the growth medium. In E. coli, under high-lactose, high-glucose conditions, which one of the following could lead to maximal transcription activation of the lac operon?
A. A mutation in the lac I gene ( which encodes the repressor)
B. A mutation in the CRP-binding site leading to an enhanced binding
C. A mutation in the operator sequence
D. A mutation leading to enhanced cAMP levels
E. A mutation leading to lower binding of repressor

Answer 52

D. A mutation leading to enhanced cAMP levels

Question 53

Expression of the lactose operon in E. coli can be quite complex. A mutation in the lac I (repressor) gene of a noninducible strain of E. coli resulted in an inability to synthesize any of the proteins of the lac operon. Which one of the following provides a rational explanation?
A. The repressor has lost its affinity for the inducer
B. The repressor has lost its affinity for the operator
C. A trans-acting factor can no longer bind to the promoter
D. The CAP protein is no longer being made
E. Lactose feedback inhibition becomes constitutive

Answer 53

A. The repressor has lost its affinity for the inducer

Question 54

Many transcription factors, which act as dimers, bind to palindromic sequences in their target DNA. Which one of the following double-stranded DNA sequences shows perfect dyad symmetry (the same sequence of bases on both strands?
A. GAACTGCTAGTCGC
B. GGCATCGCGATGCC
C. TAATCGGAACCAAT
D. GCAGATTTTAGACG
E. TGACCGGTGACCGG

Answer 54

B. GGCATCGCGATGCC

Question 55

Transcription factors can be activated in several ways as well as inhibited under certain conditions. Which one of the following describes a common theme in the structure of DNA-binding proteins?
A. The presence of a specific helix that lies across the major or minor groove of DNA
B. The ability to recognize RNA molecules with the same sequence
C. The ability to form multiple hydrogen bonds between the protein peptide backbone and the DNA phosphodiester backbone
D. The presence of zinc
E. The ability to form dimers with disulfide linkages

Answer 55

A. The presence of a specific helix that lies across the major or minor groove of DNA

Question 56

Altered eukaryotic DNA can lead to mutations; however, the alteration in DNA does not necessarily have to be within an exon. Which one of the following best represents an epigenetic alteration in DNA which could lead to altered gene regulation?
A. Deamination of C to U in DNA
B. Deamination of A to I in DNA
C. Methylation of C residues in DNA
D. Substitution of an A for a G in DNA
E. A simple base deletion in the DNA

Answer 56

C. Methylation of C residues in DNA

Question 57

An altered response to hormones can occur if the receptor contains a mutation. A nuclear receptor has a mutation in its transactivation domain, such that it can no longer bind to other transcription factors. Which one of the following is most likely to occur when this receptor binds its cognate ligand?
A. Inability to bind to DNA
B. Enhanced ability to bind to DNA
C. Enhanced transcription of hormone-responsive genes
D. Enhanced dimerization of hormone receptors
E. Reduced transcription of hormone-responsive genes

Answer 57

E. Reduced transcription of hormone-responsive genes

Question 58

A patient presents with a beta-thalessemia. Such a disorder could result from a mutation located in which of the following?

Answer 58

See book for table

Answer: B.

Question 59

In response to foreign organisms, humans produce a variety of antibodies that can bind to the organism. In the production of human antibodies, which one of the following can causes the production of different proteins form a single gene?
A. Pretranscription of hnRNA
B. Removal of introns from hnRNA
C. Addition of a cap to the 5’-end of hnRNA
D. Addition of a cap to the 3’-end of hnRNA
E. Alternative sites for synthesizing the poly(A) tail

Answer 59

E. Alternative sites for synthesizing the poly(A) tail

Question 60

A eukaryotic cell line grows normally at 30˚C, but at 42˚C, its growth rate is reduced owing to iron toxicity. At the elevated temperature, the cell displays elevated free intracellular iron levels, coupled with high levels of transferrin receptor. Ferritin levels within the cell are extremely low at the elevated temperature. The results can be explained by a single-nucelotide mutation in which one of the following proteins?
A. Transferrin
B. Ferritin
C. Transferrin receptor
D. IRE-BP
E. RNA polymerase

Answer 60

D. IRE-BP