test 1 questions Flashcards
1
Q
1) The difference between a nucleoside and a nucleotide is: A) the presence of uracil. B) a phosphate group. C) a phosphodiester bond. D) a 2' —H group. E) methylated cytosine.
A
B
2
Q
2) Which statement is CORRECT?
A) Both phosphodiester and glycosidic bonds in RNA and DNA are hydrolyzed in acid solution.
B) Both RNA and DNA are hydrolyzed in mild alkaline solution.
C) DNA is more unstable when dehydrated than when in solution
D) RNA is not hydrolyzed in mild alkaline solution.
E) Both A and B
A
A
3
Q
3) Nucleotides are all weak acids.
A
FALSE
4
Q
4) The nucleotide sequence of a polynucleotide chain is called the ________ structure.
A
primary
5
Q
5) Which of the following does NOT describe the secondary structure of DNA as proposed by Watson and Crick?
A) The two strands of the double helix are stabilized by hydrogen-bonding between A and T and between G and C.
B) The two strands of the double helix run in opposite directions.
C) The distance between the 1’ carbons of the deoxyribose units is the same between the A-T and the G-C base pair.
D) The phosphate deoxyribose backbones of the helix are on the outside.
E) The base pairs are stacked on one other with their planes at 180o to the helix axis.
A
E
6
Q
6) An important observation that assisted in the elucidation of the secondary structure of DNA was that the mole percent adenine was almost always the same as the mole percent of thymine. (T/F)
A
TRUE
7
Q
7) The mode of replication of DNA is BEST described as ________.
A
semiconservative
8
Q
8) Which of the following statements about nucleic acid secondary structure is FALSE?
A) The width of the major and minor grooves is more equal in the A-from of DNA than in the B-form.
B) Triple helices and G-quadruplexes can form at specific sequences in DNA.
C) DNA can form cruciform structures at palindromic sequences.
D) The A-form of DNA exists at high humidity, whereas the B-form exists at low humidity.
E) Some nucleic acids can form a zig-zag structure or Z form.
A
D
9
Q
9) Supercoiled DNA has a lower mobility than relaxed DNA with the same number of base pairs when subjected to gel electrophoresis.
A
Answer: FALSE
10
Q
10) Single-stranded RNA molecules can have extensive regions of intramolecular base pairing leading to defined secondary and tertiary structure.
A
Answer: TRUE
11
Q
11) DNA in vivo is normally ________ supercoiled.
A
Answer: negatively
12
Q
12) Calculate the superhelix density of a circular DNA molecule with 210 base pairs and two negative supercoils, assuming that there are 10.5 bp per turn of the double helix.
A
Answer: -0.1
13
Q
13) Calculate the linking number in vivo for a plasmid that is 4200 bp in size if there is normally 1 negative supercoil in every 20 base pairs of a circular DNA. Assume there are 10.5 bp per turn of the double helix.
A
Answer: 190
14
Q
14) Nucleic acids absorb light strongly in the ultraviolet region of the spectrum because they have ________ double-bond systems.
A
Answer: conjugated
15
Q
15) The melting temperature of DNA ________ with increasing G plus C content.
A
Answer: increases
16
Q
16) Expression of genetic information involves first ________ then ________.
A
Answer: transcription, translation
17
Q
17) Restriction endonucleases are useful in gene cloning because:
A) they can cut DNA at specific sequences.
B) they can join DNA molecules that have been cut at specific sequences.
C) they all make cohesive ends when they cut DNA.
D) they all make 5’ phosphate extensions and recessed 3’ OH groups that can be rejoined by DNA ligase.
E) they can both cut and rejoin DNA molecules.
A
Answer: A
18
Q
18) Viral genomes cannot be used as vectors for making recombinant DNA molecules.
A
Answer: FALSE
19
Q
19) Dideoxynucleotide sequence analysis is a template-directed method that makes use of chain terminators that stop DNA synthesis because they lack a 2’OH group.
A
Answer: FALSE
20
Q
20) Which of the following is a feature of X-diffraction?
A) Radiation passing through a structure will be scattered only if the structure contains repeating units.
B) Scattered radiation from repeating units in a structure will be weakened by interference.
C) Scattered radiation from repeating units in a structure will be strengthened by interference.
D) Short spacings in repeating structures will result in short spacings in diffraction patterns.
E) The wavelength of radiation used to generate diffraction patterns must be slightly longer than the spacings between the repeating units of the structure.
A
Answer: C
21
Q
1) A bacterial genome is packaged into a nucleoid, which is organized mainly by:
A) interactions with protein.
B) being bound within a nuclear membrane.
C) supercoiling of the DNA.
D) having many attachment points to the cell membrane.
E) being wrapped around histone proteins.
A
Answer: C
22
Q
2) Approximately how much of the human genome has a biological function? A) 90% B) 80% C) 60% D) 50% E) 40%
A
Answer: B
23
Q
3) Heterochromatin is transcriptionally active.
A
Answer: FALSE
24
Q
4) The human genome contains one gene for every protein that can be translated from the mRNA.
A
Answer: FALSE
25
```
5) The linker histone H1 has a high proportion of the following amino acid residue.
A) Leucine
B) Lysine
C) Isoleucine
D) Asparagine
E) Histidine
```
Answer: B
26
6) In eukaryotic cells, chromosomes are organized into a DNA-protein complex known as chromatin.
Answer: TRUE
27
7) The post-translational modifications of histone proteins have functional roles in gene expression.
Answer: TRUE
28
8) The repeating unit of chromatin is known as the ________.
Answer: nucleosome
29
9) Nucleosomal core particles contain ________ bp of DNA wrapped around a histone octamer.
Answer: 146
30
10) If 10.4 bp of DNA represents a linear length of 3.4 nm, how long (in meters) would one copy of the human genome (~3 × 109 bp) be if all of the DNA was placed end to end in a linear fashion?
Answer: 0.98 m
31
11) Restriction-modification systems:
A) exist in all organisms as a protection against foreign DNA invasion.
B) include a site-specific exonuclease to degrade foreign DNA.
C) modify DNA by acetylation.
D) include a DNA methylase and an endonuclease.
E) include three types of endonuclease all of which cleave within a specific DNA target sequence.
Answer: D
32
12) The ________ activity associated with restriction-modification systems is able to flip out the target base from the DNA.
Answer: DNA methylase
33
13) Random variations among human genome sequences can result in gain or loss of ________ endonuclease cleavage sites.
Answer: restriction
34
14) Calculate the number of times a recognition site for a 4 bp restriction endonuclease is likely to occur in the diploid human genome
Answer: 2.4 × 10 7
35
15) Southern blotting and hybridization is a technique that uses specific probes to analyze:
A) restriction fragment length polymorphisms.
B) complex mixtures of any nucleic acid.
C) centromeres or telomeres on condensed chromosomes.
D) DNA fingerprints.
E) both A and D.
Answer: E
36
16) If a PCR reaction starts out with 20 double-stranded DNA targets, how many specific PCR products could be formed after 35 cycles of denaturation, annealing and extension.
Answer: 6.87 × 1011
37
1) Both type I or type II topoisomerases carry out their catalytic activity via a covalent phosphodiester intermediate between a phosphate group on the DNA and a tyrosine hydroxyl group on the enzyme.
Answer: TRUE
38
2) DNA gyrase is able to relax supercoils as well as introduce negative supercoils in DNA.
Answer: TRUE
39
3) The DNA polymerase reaction is a nucleophilic substitution facilitated by:
A) the 3'OH group being a weak nucleophile.
B) the 3'OH group being a strong nucleophile.
C) the pyrophosphate being a good leaving group.
D) the reaction being irreversible.
E) none of the above.
Answer: C
40
4) Which of the following statements about E. coli DNA polymerase I is FALSE?
A) It can copy a circular DNA template but cannot join the ends.
B) It can extend a gapped duplex from a 3'OH group and displace a preexisting 5' end.
C) The 3' exonuclease site is some distance from the polymerase active site.
D) It has 3' exonuclease activity that resides in a small N-terminal fragment that can be cleaved off by limited proteolysis.
E) It has 5' exonuclease activity that resides in a small N-terminal fragment that can be cleaved off by limited proteolysis.
Answer: D
41
5) Which of the following statements about E. coli DNA replication is INCORRECT?
A) The β subunit of DNA polymerase III is the sliding clamp essential for processivity.
B) The clamp-loading complex uses exchange between ADP and ATP to eject the clamp loader and close the clamp.
C) Single-stranded DNA-binding protein promotes denaturation of DNA by lowering the melting temperature.
D) Helicases are multimeric proteins that bind preferentially to one strand and rely on ATP-hydrolysis to unwind the duplex.
E) Topoisomerases are responsible for relieving torsional stress ahead of the replication fork generated by unwinding the duplex.
Answer: B
42
6) The specificity of DNA polymerase activity is determined by the shapes of the substrate molecules as well as their ________ capacity.
Answer: hydrogen-bonding
43
7) Evidence supporting E.coli DNA polymerase III having the major role in nucleotide incorporation during replication includes:
A) DNA polymerase III has a high Vmax.
B) There are ten or fewer molecules of enzyme per cell.
C) Replication is blocked at high temperatures in temperature sensitive mutants with a thermolabile form of DNA polymerase III.
D) A point mutation can inactivate DNA pol III and inhibit replication.
E) All of the above.
Answer: E
44
8) E. coli DNA polymerase III makes extensive contacts with the ________ in duplex DNA.
Answer: minor groove
45
9) A null mutant in the ________ activity of DNA polymerase I will be defective in DNA replication because it will be unable to carry out primer removal.
Answer: 5'-exonuclease OR 5'-exonucleolytic
46
10) Okazaki fragments are initiated with ________ primers by a primase enzyme.
Answer: RNA, or ribonucleic acid
47
11) DNA ligase can join Okazaki fragments after activation by ________ of a lysine residue in the active site.
Answer: adenylation
48
12) E. coli DNA polymerase I in vitro requires a template and primer, which must always be separate nucleic acids.
Answer: FALSE
49
13) The individual proteins of the E. coli replisome complex dissociate and reassociate in a dynamic manner.
Answer: TRUE
50
14) The replicative E. coli DNA polymerase is a symmetrical dimer, with each part of the dimer being responsible for replicating one strand of the DNA duplex.
Answer: FALSE
51
15) Which of the following is NOT a requirement of E. coli DNA ligase?
A) A nick in the DNA strand must have a 3' OH group.
B) A nick in the DNA strand must have a 5' phosphate group.
C) The nucleotides being linked must be adjacent in the duplex structure.
D) The nucleotides being linked must be properly based-paired.
E) ATP
Answer: E
52
16) Which of the following statement about eukaryotic DNA replication is INCORRECT?
A) Only one DNA polymerase is required to propagate a replication fork.
B) The same polymerase in humans is involved in proofreading and primer removal as well as lagging strand elongation.
C) The main DNA polymerase that elongates the leading strand has an intrinsic processivity factor.
D) Eukaryotes require two enzymes to remove RNA primers.
E) Chromatin must be dismantled in advance of replication forks and reassembled on daughter strands after the fork has passed through.
Answer: A
53
17) The initiation of DNA replication in E. coli can occur anywhere on the genome that has repeat sequence elements and requires the interaction of DnaA proteins that results in stretching and bending of DNA causing tension that leads to local unwinding.
Answer: FALSE
54
18) Eukaryotes solve the problem of replicating the ends of their linear chromosomes by:
A) terminal redundancy whereby each end of the chromosome is duplicated allowing recombination.
B) using a protein as a primer.
C) by covalently linking the two strands at each end of the linear chromosome to form a circle.
D) enzyme activity that uses an RNA template and reverse transcription in a series of repeat cycles.
E) all of the above.
Answer: D
55
19) Replication of linear genomes is problematic because primer removal at the ________ leaves a gap in the duplex.
Answer: 5'-end
56
20) Fidelity of DNA replication is determined solely by the 3' exonucleolytic proofreading activity of the DNA polymerase.
Answer: FALSE
57
21) A single-stranded RNA virus makes a DNA copy of itself by the use of a viral multifunctional enzyme called ________.
Answer: reverse transcriptase
58
```
1) O6-methylguanine has a high probability of base pairing with thymine to result in a post replication mutation from a GC base pair to:
A) TA.
B) AT.
C) CG.
D) GT.
E) TC.
```
Answer: B
59
2) The only function of Uracil-DNA N-glycosylase is to remove dUMP residues in DNA that have been arisen by deamination of cytosine.
Answer: FALSE
60
```
3) Which of the following types of DNA damage cannot be repaired by base excision repair?
A) Depurination
B) Cytosine deamination
C) Thymine dimer
D) Single-strand break
E) Base oxidation
```
Answer: C
61
4) Nucleotide excision repair:
A) involves a multisubunit enzyme.
B) preferentially repairs genes that are being actively transcribed.
C) involves making nicks on either side of a DNA lesion.
D) uses helicase, polymerase and ligase to repair the DNA.
E) all of the above.
Answer: E
62
5) Photoreactivation using DNA photolyase is responsible for direct repair of thymine dimers in all organisms.
Answer: FALSE
63
6) ________ and bulky adducts on DNA can be repaired using the nucleotide excision repair process.
Answer: Thymine dimers
64
7) The direct DNA repair enzymes DNA photolyase and O6-alkyguanine alkytransferase are unusual in that they are ________ after one catalytic cycle.
Answer: inactivated
65
8) Base excision repair starts with cleavage of the ________ between the damaged base and the deoxyribose.
Answer: glycosidic bond
66
```
9) Which of the following enzyme activities is NOT used in base excision repair?
A) Glycosylase
B) Apyriminidic endonuclease
C) Deoxyribose-5'-phosphatase
D) DNA polymerase
E) Helicase
```
Answer: E
67
10) The SOS response to DNA damage in bacteria is error-prone because:
A) it uses DNA polymerase that lacks 5' exonuclease activity.
B) it is an inducible system.
C) the polymerases used lack 3' exonuclease activity.
D) more than one polymerase can be used to repair the damage.
E) it is stimulated by ultraviolet light that causes mutations.
Answer: C
68
11) Transcription-coupled repair usually repairs the template strand.
Answer: TRUE
69
```
12) The dam methylase has a role in which of the following DNA repair systems?
A) Base-excision repair
B) Nucleotide excision repair
C) Non-homologous end-joining
D) Mismatch repair
E) Homologous recombination
```
Answer: D
70
```
13) Strand-displacement in homologous recombination in E. coli is facilitated by:
A) the RecBCD complex.
B) ss-binding protein.
C) RecA.
D) RuvC.
E) the chi structure.
```
Answer: C
71
14) Which of the following mechanisms is NOT involved in the generation of antibody diversity?
A) Recombination with excision of DNA between a V gene sequence and a J sequence
B) Splicing out of RNA sequences between a J region and a C region
C) Somatic hypermutation
D) Non-homologous end joining and DNA repair
E) Transposition
Answer: E
72
15) Bacteria cannot use homologous recombination for DNA repair as they only have a single copy of their genome.
Answer: FALSE
73
16) Site-specific recombination generally requires longer homologous sequences than does homologous recombination.
Answer: FALSE
74
17) Homologous recombination occurs by nicking followed by strand invasion, ligation then branch migration.
Answer: TRUE
75
18) The λ genome is inserted into the E. coli genome in the lysogenic pathway by the use of ________ recombination.
Answer: site-specific
76
```
19) Which of the following is a feature of bacterial transposition?
A) Homologous recombination
B) DNA synthesis
C) Target site duplication
D) Deletions or inversions
E) All of the above
```
Answer: E
77
20) Gene amplification occurring as a result of specific metabolic stress will always be reversed once the stress has been removed.
Answer: FALSE
78
21) The movement of transposable genetic elements within a genome is essentially ________.
Answer: random
79
22) Retroviruses are characterized by the presence of ________ that flank the viral structural genes.
Answer: long terminal repeats
80
23) One mechanism that could result in gene duplication involves ________ sister-chromatid exchange.
Answer: unequal
81
1) RNA polymerase transcribes all DNA sequences at an equal rate.
Answer: FALSE
82
2) Which of the following is FALSE when comparing DNA pol III and RNA polymerase?
A) There are many more copies of RNA polymerase in the cell.
B) DNA pol III is much more processive.
C) RNA polymerase makes more errors.
D) RNA polymerase has a much slower kcat.
E) RNA polymerase does not need a primer.
Answer: B
83
3) Which of the following statements about E. coli RNA polymerase is INCORRECT?
A) It has five different subunits.
B) The σ subunit can be dissociated easily from the rest of the enzyme.
C) The σ subunit is responsible for accurate determination of transcription start sites.
D) Without the σ subunit the enzyme has no RNA polymerase activity.
E) The σ subunit has a role in regulation of transcription.
Answer: D
84
4) Which of the following is NOT correct when considering the initiation of transcription in E. coli?
A) The σ subunit of RNA polymerase makes strong contacts with the -10 region of promoters.
B) Only the -10 region of the promoter is required.
C) DNA melting near the transcription start site is essential for promoter recognition.
D) The phosphodiester bonds that are formed are not stable until about 10 nucleotides have been incorporated.
E) The RNA polymerase contacts about 50 bp of DNA.
Answer: B
85
5) Alignment of conserved sequences in promoters recognized by E. coli RNA polymerase revealed two ________ sequences upstream of the transcribed region, which are separated by similar lengths of DNA.
Answer: consensus
86
6) In bacteria, mRNA, tRNA and rRNA are all transcribed by the same RNA polymerase.
Answer: TRUE
87
7) Rho-dependent termination of transcription makes use of a hexameric protein, which has RNA-DNA helicase activity.
Answer: TRUE
88
8) Most ________ of transcription in prokaryotes is based on a weakened interaction due to ________ base pairing between the template and the transcript as well as a stable stem loop structure in the nascent transcript which eliminates base pairing between the template and transcript upstream of the AU interaction.
Answer: termination, AU
89
9) In eukaryotes RNA polymerase I transcribes all of the ribosomal RNA components.
Answer: FALSE
90
10) The different sensitivities to the toxin ________ revealed that eukaryotes have three distinct RNA polymerases for synthesis of mRNA, rRNA and small RNAs including tRNA and the 5S species of rRNA.
Answer: α-amanitin
91
11) All the tRNA genes are transcribed by ________ in eukaryotes.
Answer: RNA polymerase III
92
12) Which of the following statements is FALSE?
A) RNA polymerase II is responsible for the transcription of genes encoding protein-coding sequences only.
B) Many promoters recognized by RNA polymerase II contain regulatory elements several kbp upstream of the initiation site.
C) TFIIB has a role in converting a closed-promoter into an open-promoter complex.
D) The C-terminal domain of the largest subunit of RNA pol II undergoes extensive phosphorylation prior to transcription elongation.
E) A multiprotein complex is involved in communication between upstream control elements and proteins bound at the promoter.
Answer: A
93
13) After promoter clearance by RNA polymerase II:
A) all associated factors remain bound to the polymerase for elongation.
B) a subset of factors remain at the promoter region.
C) no further elongation factors are acquired by the polymerase.
D) no further chromatin remodeling is required.
E) transcription continues until the polymerase reaches the poly (A) tail.
Answer: B
94
14) In eukaryotes genes encoding enzymes for metabolic pathways often exist as operons of several genes with a single regulatory region to provide coordinate regulation of all genes required for the pathway.
Answer: FALSE
95
15) Eukaryotic transcription normally takes place on a chromatin template at nuclease-accessible sites.
Answer: TRUE
96
16) In eukaryotes a set of ________ function in a comparable manner to the σ subunit of E. coli RNA polymerase.
Answer: transcription factors
97
17) High levels of histone ________ correlate with high levels of transcriptional activity.
Answer: acetylation
98
18) Degradation of bacterial mRNAs occurs:
A) from the 3' end.
B) largely by the activity of non-specific nucleases.
C) from the 5' end.
D) relatively slowly.
E) from both 3' and 5' ends at the same time.
Answer: C
99
19) Which of the following types of post-transcriptional processing does NOT occur for bacterial tRNAs?
A) Exonuclease cleavage
B) Endonuclease cleavage
C) Non-template directed addition of bases
D) Methylation of bases
E) Addition of a phosphate group to the 5' end
Answer: E
100
20) In bacteria post-transcriptional processing of pre-rRNA species can yield mature tRNAs.
Answer: TRUE
101
21) All processing of eukaryotic mRNAs takes place in the nucleus after transcription has been completed.
Answer: FALSE
102
22) The 5' cap added to eukaryotic mRNA serves to stabilize the mRNA and assists in the efficiency of ________.
Answer: translation
103
23) Alternative splicing can:
A) be tissue-specific.
B) produce proteins with different functions from the same gene.
C) contribute to temporal control of gene expression.
D) produce mRNAs that are nonfunctional.
E) all of the above.
Answer: E
104
24) Splicing of mRNA occurs in spliceosomes and chemically is a series of ________ reactions.
Answer: transesterification
105
25) DNA microarrays can be used for gene ________ profiling, starting with RNA and using the enzyme ________ to synthesize cDNA and simultaneously incorporate nucleotides labeled with fluorescent dyes.
Answer: expression, reverse transcriptase
106
26) Which of the following is the first step in chromatin immunoprecipitation?
A) Extraction of chromatin from cells
B) Cross-linking with formaldehyde
C) Shearing by sonication
D) Addition of antibodies to recognize proteins that bind to DNA
E) PCR to amplify the target sites
Answer: B
107
1) Which of the following statements about initiation of translation in bacteria is FALSE?
A) fMet-tRNAfMet is the only charged tRNA that can bind to the 30S subunit on its own.
B) The formyl group is transferred to Met-tRNAfMet from 10-formyl-tetrahydrofolate.
C) Three initiation factor proteins are required to bind the mRNA and the initiator tRNA to the 30S ribosome.
D) Pairing between mRNA and rRNA places the initiation codon next to the P site in the ribosome.
E) The complete 70S initiation complex ready to receive a second charged tRNA is assembled without any GTP hydrolysis.
Answer: E
108
2) Which of the following statements about translation elongation in bacteria is TRUE?
A) Charged amino acids are escorted to the A site of the ribosome by an initiation factor.
B) The growing polypeptide chain is moved from the A site to the P site before peptide bond formation.
C) GTP hydrolysis occurs after moving the aminoacyl-tRNA into the A site and before peptide bond formation.
D) The entire peptidyl-tRNA is translocated from the P site to the A site during peptide bond formation.
E) The uncharged tRNA leaves from the E site as the ribosome moves one codon in the 5' direction.
Answer: C
109
3) Termination of translation requires GTP hydrolysis and direct interaction of a release factor with a termination codon.
Answer: TRUE
110
4) Translation is an RNA-directed process whereby amino acids are specified by ________ on the mRNA, which are complementary to ________ on aminoacyl tRNAs.
Answer: codons, anticodons
111
5) An ________ is a sequence within an mRNA that is bounded by stop and start codons that can be continuously translated.
Answer: open reading frame
112
6) In the secondary structure of ribosomal RNA, the regions of self-complementarity are highly ________.
Answer: conserved
113
7) The anticodon ends of tRNAs contact the ________ subunit and the acceptor ends contact the ________ subunit of the ribosome.
Answer: small, large
114
8) Termination of translation occurs when a stop codon is translocated into the ________ site of the ribosome.
Answer: A
115
9) Which of the following BEST explains the "wobble" hypothesis proposed by Francis Crick?
A) The genetic code is degenerate in that most amino acids have more than one codon.
B) The genetic code is ambiguous in that each codon can specify more than one amino acid.
C) The anticodon can pair with any part of the corresponding codon.
D) The 5' base of the anticodon can make non Watson-Crick hydrogen bonds with several different bases at the 3' position of the codon.
E) Inosine can pair up with A, U, or C.
Answer: D
116
10) Which of the following statements is FALSE?
A) There does not need to be as many different tRNA types as there are codons.
B) The modified bases in the tRNAs are added during transcription.
C) The amino acid is attached at the 3' terminus of the tRNA.
D) The 3D structures of all tRNA molecules are such that they fit equally well into the ribosome.
E) tRNA exhibits unusual base pairing including single bases pairing with two others.
Answer: B
117
11) The genetic code is universal for all organisms and organelles.
Answer: FALSE
118
12) Aminoacyl-tRNA synthetases do not contribute to the fidelity of translation.
Answer: FALSE
119
13) Peptide bond formation requires GTP hydrolysis.
Answer: FALSE
120
14) Differences between eukaryote and prokaryote translation include the 40S ribosome recognizing the ________ rather than a Shine-Dalgarno sequence and the N-terminal amino acid is ________.
Answer: 7-methylguanine cap, methionine
121
15) The bacterial Shine-Dalgarno sequence aligns the mRNA with the 16S rRNA to start translation at the correct position.
Answer: TRUE
122
16) Antibiotics that inhibit translation are useful because:
A) the translational machinery of eukaryotes is sufficiently different to that of bacteria.
B) microorganisms can develop resistance to other antibiotics.
C) antibiotic resistance genes are often carried on plasmids rather than the bacterial chromosome.
D) different antibiotics can inhibit different steps of translation.
E) they do not cross the cell membrane in higher animals.
Answer: A
123
17) Which of the following applies only to prokaryotic proteins?
A) Secreted proteins have signal sequences in their N-terminal regions.
B) Some proteins are covalently modified after translation.
C) Hydrophilic proteins are able to either traverse or become embedded in hydrophobic membranes.
D) Some proteins are synthesized on polyribosomes.
E) Translation is coupled to transcription.
Answer: E
124
18) Which of the following BEST describes the transport of nuclear proteins across the nuclear membrane?
A) Simple diffusion
B) An N-terminal targeting sequence that is cleaved during transport
C) A targeting sequence that interacts with a carrier protein
D) Vesicular transport followed by delivery via fusion with the nuclear membrane
E) Co-translational transport using ribosomes attached to the membrane
Answer: C
125
```
19) Which of the following does NOT apply to proteins synthesized on the rough endoplasmic reticulum?
A) Signal recognition particle
B) Vesicular transport
C) Signal sequence cleavage
D) Continuous translation
E) Docking protein
```
Answer: D
126
20) Glycosylated proteins are synthesized on rough endoplasmic reticulum.
Answer: TRUE
127
21) Nuclear encoded proteins destined for ________, chloroplasts or nuclei are synthesized in the cytoplasm.
Answer: mitochondria
128
22) The fusion of vesicles, from the Golgi complex, with specific membranes is facilitated by ________ protein pairs called t-SNARES and v-SNARES on membranes as well as cytosolic fusion proteins.
Answer: complementary
129
1) Which of the following BEST describes transcriptional regulation of the lac operon in E. coli?
A) On in the presence of lactose
B) On in the presence of lactose and presence of glucose
C) Off in the presence of glucose
D) On in the absence of lactose and presence of glucose
E) On in the presence of lactose and absence of glucose
Answer: E
130
2) A partial diploid containing a wild type allele for lacI and a lacI mutant that was unable to bind the inducer would:
A) always show low levels of β-galactosidase gene expression.
B) show normal induction in the presence of an inducer.
C) express β-galactosidase at all times.
D) only show normal induction in the presence of an inducer in the absence of glucose.
E) show induction in the presence of an inducer in the presence of glucose.
Answer: A
131
3) Which of the following is INCORRECT when considering the lac repressor?
A) It is tetramer of two dimers.
B) Binding to the operator site is cooperative.
C) Binding of each dimer is to different regions of the operator.
D) Binding of inducer forces the DNA-binding helices apart so they cannot contact the DNA-binding sites.
E) It is an allosteric protein.
Answer: B
132
4) Which of the following BEST describes catabolite repression of the lac operon?
A) The operon is transcriptionally inactive in the absence of lactose.
B) The operon is transcriptionally inactivated by a repressor protein, which binds to glucose.
C) The operon is transcriptionally active when an activator protein binds to the promoter in the absence of glucose.
D) Glucose is the preferred energy source for E. coli.
E) The operon is repressed by its protein products.
Answer: C
133
5) A partial diploid containing a wild type allele for lacO and a lacO mutant that was unable to bind to the lac repressor would always express β-galactosidase.
Answer: TRUE
134
6) Catabolite or glucose repression of the lac operon is a regulatory system, which depends on the levels of cAMP in the cell.
Answer: TRUE
135
7) The λ repressor can act as a transcriptional activator as well as a repressor.
Answer: TRUE
136
8) The physiological inducer of the lac operon is ________.
Answer: allolactose
137
9) ________ mutants of the lac operon express β-galactosidase at high levels in the absence of an inducer, while ________ mutants of the lac operon express only very low levels of β-galactosidase even in the presence of inducer.
Answer: Constitutive, noninducible
138
10) The affinity of the lac repressor for DNA ________ markedly when the inducer binds to the lac repressor.
Answer: decreases
139
11) Conformational changes in the cAMP receptor protein upon binding to cAMP trigger ________ of the lac operon in the presence of lactose.
Answer: activation
140
12) The λ repressor is inactivated by proteolytic cleavage stimulated by the ________ protein.
Answer: RecA
141
13) The helix-turn-helix is a common protein motif that is able to interact with DNA in the major grooves by both electrostatic and specific interactions between amino acids of the helix and the bases of the DNA.
Answer: TRUE
142
14) Which of the following BEST describes the SOS response?
A) DNA damage by UV light causes a λ lysogen to be induced to the lytic life cycle.
B) It is an error prone DNA repair system.
C) Activation of RecA by sensing DNA damage and single-stranded DNA.
D) Coordinated activation of a set of unlinked genes whose protein products will collectively help the cell to respond to environmental damage.
E) Transcriptional depression by proteolytic cleavage of the LexA repressor.
Answer: D
143
15) Which of the following BEST describes attenuation of the trp operon?
A) The ribosome will stall at adjacent trp codons if tryptophan levels in the cell are low.
B) High levels of tryptophan result in continued translation by the ribosome.
C) A transcription termination sequence forms in the leader mRNA because the ribosome reaches a translation stop codon if tryptophan levels are high.
D) The structural genes are not expressed if tryptophan levels in the cell are high.
E) Regulation of trp operon expression by transcriptional repression by the trp repressor when tryptophan levels in the cell are high.
Answer: C
144
16) A set of linked genes regulated by a common mechanism is called a regulon.
Answer: TRUE
145
17) The trp operon is transcribed when the trp repressor is bound to tryptophan.
Answer: FALSE
146
18) The greater complexity of humans compared to worms and flies is due to:
A) a greater number of genes.
B) higher levels of alternative splicing.
C) a much greater number of transcription factors.
D) chromatin structure.
E) combinatorial regulation by a greater number of transcription factors.
Answer: E
147
19) Nucleosomes very close to the transcription start site in eukaryotes tend to have a high proportion of the histone variants H3.3 and H2A.Z.
Answer: TRUE
148
20) All chromatin remodelling complexes are associated with activation of transcription.
Answer: FALSE
149
21) Nucleosome remodeling complexes use ________ to drive changes in chromatin structure.
Answer: ATP hydrolysis
150
22) Which of the following is NOT part of initiation of transcription in eukaryotes?
A) Phosphorylation of Ser-5 in the heptad repeats in the C-terminal domain of RNA polymerase II by TF-IIH.
B) Unwinding of the DNA template by TF-IIH
C) Non-specific interactions of general transcription factors at promoters
D) Phosphorylation of Ser-2 in the heptad repeats in the C-terminal domain of RNA polymerase II by P-TEFb.
E) The binding of upstream regulatory proteins
Answer: D
151
23) In eukaryotes RNA polymerase is only bound at promoters that are carrying out active transcription.
Answer: FALSE
152
24) Chromatin modifications that tend to inhibit transcription include:
A) methylation at lysine 9 or 27 of histone H3.
B) methylation at lysine 4 of histone H3.
C) ubiquitylation at lysine 119 of histone H3.
D) A, B, and C.
E) A and C.
Answer: E
153
```
25) DNA methylation in eukaryotes:
A) is part of the epigenetic process.
B) occurs only on cytosine residues.
C) is maintained by specific DNA methyl transferases.
D) is inhibited by 5'-azacytidine.
E) all of the above.
```
Answer: E
154
26) Transcriptionally active chromatin usually contains ________ histones, while ________ is normally inhibitory to transcription.
Answer: acetylated, methylation
155
27) ATPase domains of chromatin remodelers associated with transcriptionally active chromatin can contain a bromodomain that interacts specifically with ________ lysines or a chromodomain that interacts specifically with ________ histones.
Answer: acetylated, methylated
156
28) Epigenetics is the heritable transmission of gene ________ patterns that does not involve a change in the DNA base sequence.
Answer: expression
157
```
29) miRNAs are used in gene regulation to:
A) block translation.
B) target mRNA for degradation.
C) cause ribosomes to stall.
D) promote degradation of polyA tails.
E) all of the above.
```
Answer: E
158
30) RNA interference can be a mechanism of defense against viral infection as well as for regulation of gene expression.
Answer: TRUE
159
31) ________ are alternative mRNA structures that are produced by binding of a ________ which is often a product of a specific metabolic pathway.
Answer: Riboswitches, ligand
160
32) ________ of specific RNA nucleotides in a process known as RNA editing is a mechanism of altering the protein product encoded by some genes in mammals.
Answer: Deamination
