Deck 26: RNA Metabolism

Question 1

"Footprinting," or DNase protection, is a technique used to identify:

A) a region of DNA that has been damaged by mutation.
B) E. coli cells that contain a desired, cloned piece of DNA.
C) the position of a particular gene of a chromosome.
D) the position of internally double-stranded regions in a single-stranded DNA molecule.
E) the specific binding site of a repressor, polymerase, or other protein on the DNA.

Answer 1

E

Question 2

Which factor is NOT known to be involved in initiation by eukaryotic RNA polymerase II?

A) DNA helicase activity
B) DNA polymerase activity
C) formation of an open complex
D) protein binding to specific DNA sequences
E) protein phosphorylation

Answer 2

B

Question 3

The sigma factor of E. coli RNA polymerase:

A) associates with the promoter before binding core enzyme.
B) combines with the core enzyme to confer specific binding to a promoter.
C) is inseparable from the core enzyme.
D) is required for termination of an RNA chain.
E) will catalyze synthesis of RNA from both DNA template strands in the absence of the core enzyme.

Answer 3

B

Question 4

The excision (splicing) of many group I introns requires, in addition to the primary transcript RNA:

A) a cytosine nucleoside or nucleotide and a protein enzyme.
B) a guanine nucleoside or nucleotide (only).
C) a protein enzyme only.
D) a small nuclear RNA and a protein enzyme.
E) ATP, NAD, and a protein enzyme.

Question 5

Which property does NOT apply to RNA polymerase from E. coli (core enzyme alone)?

A) It can extend an RNA chain and initiate a new chain.
B) It is required for the synthesis of mRNA, rRNA, and tRNA in E. coli.
C) It produces an RNA polymer that begins with a 5'-triphosphate.
D) It recognizes specific start signals in DNA.
E) It requires all four ribonucleoside triphosphates and a DNA template.

Question 6

A branched ("lariat") structure is formed during:

A) attachment of a 5' cap to mRNA.
B) attachment of poly(A) tails to mRNA.
C) processing of preribosomal RNA.
D) splicing of all classes of introns.
E) splicing of group II introns.

Question 7

Which statement about E. coli RNA polymerase (core enzyme) is FALSE?

A) In the absence of the $\sigma$ subunit, core polymerase has little specificity for where initiation begins.
B) The core enzyme contains several different subunits.
C) The core enzyme has no polymerizing activity until the $\sigma$ subunit is bound.
D) The RNA chain grows in a 5' $\rightarrow$ 3' direction.
E) The RNA product is complementary to the DNA template.

Question 8

After binding by E. coli RNA polymerase, the CORRECT order of events for transcription initiation is:

A) closed complex formation, open complex formation, promoter clearance, start of RNA synthesis.
B) closed complex formation, open complex formation, start of RNA synthesis, promoter clearance.
C) open complex formation, closed complex formation, start of RNA synthesis, promoter clearance.
D) start of RNA synthesis, closed complex formation, open complex formation, promoter clearance.
E) start of RNA synthesis, open complex formation, closed complex formation, promoter clearance.

Question 9

Which statement is NOT true of the mRNA for calcitonin?

A) Exons are used for polypeptide synthesis.
B) Introns are complementary to their adjacent exons and will form hybrids with them.
C) The mature mRNA is substantially shorter than the corresponding region on the DNA.
D) The mRNA is originally synthesized in the nucleus, but ends up in the cytoplasm.
E) The splicing that yields a mature mRNA occurs at very specific sites in the RNA primary transcript.

Question 10

Which statement about $\rho$ -independent termination of RNA transcription in E. coli is TRUE?

A) The RNA transcript contains self-complementary sequences.
B) There are three conserved A's in the template strand near the end of the transcript.
C) There is a CA-rich sequence near the end of the transcript.
D) The RNA transcript contains self-complementary sequences, and there are three conserved A's in the template strand near the end of the transcript.
E) The RNA transcript contains self-complementary sequences, and there is a CA-rich sequence near the end of the transcript.

Question 11

Processing of a primary mRNA transcript in a eukaryotic cell does NOT normally involve:

A) attachment of a long poly(A) sequence at the 3' end.
B) conversion of normal bases to modified bases, such as inosine and pseudouridine.
C) excision of intervening sequences (introns).
D) joining of exons.
E) methylation of one or more guanine nucleotides at the 5' end.

Question 12

Which statement about the synthesis of rRNA and tRNA in E. coli is TRUE?

A) Both rRNA and some tRNAs are part of the same primary transcript.
B) Each rRNA sequence (16S, 23S, 5S) is transcribed as a separate primary transcript.
C) Primary tRNA transcripts undergo methylation, but rRNA sequences are not methylated.
D) The tRNA sequences all lie at the 3'end of the rRNA transcripts.
E) There is a single copy of the rRNA genes.

Question 13

Which characteristic does NOT apply to the $\rho$ -terminator in E. coli?

A) The $\rho$ -terminator has an ATP-dependent RNA-DNA helicase activity.
B) The $\rho$ -terminator migrates in the 3'-5' direction along RNA.
C) The $\rho$ -terminator causes RNA polymerase release at a CA-rich sequence near the end of the transcript.
D) ATP is hydrolyzed by the $\rho$ -terminator during the termination process.
E) All of these characteristics apply to the $\rho$ -terminator.

Question 14

Which statement about E. coli RNA polymerase is FALSE?

A) Core enzyme selectively binds promoter regions, but cannot initiate synthesis without a sigma factor.
B) RNA polymerase holoenzyme has several subunits.
C) RNA produced by this enzyme will be completely complementary to the DNA template.
D) The enzyme adds nucleotides to the 3' end of the growing RNA chain.
E) The enzyme cannot synthesize RNA in the absence of DNA.

Question 15

The 5'-terminal cap structure of eukaryotic mRNAs is a(n):

A) 7-methylcytosine joined to the mRNA via a 2',3'-cyclic linkage.
B) 7-methylguanosine joined to the mRNA via a 5' $\rightarrow$ 3' diphosphate linkage.
C) 7-methylguanosine joined to the mRNA via a 5' $\rightarrow$ 5' triphosphate linkage.
D) N⁶-methyladenosine joined to the mRNA via a 5' $\rightarrow$ 5' phosphodiester bond.
E) O⁶-methylguanosine joined to the mRNA via a 5' $\rightarrow$ 5' triphosphate linkage.

Question 16

Splicing of introns in nuclear mRNA primary transcripts requires:

A) a guanine nucleoside or nucleotide.
B) endoribonucleases.
C) polynucleotide phosphorylase.
D) RNA polymerase II.
E) small nuclear ribonucleoproteins (snRNPs).

Question 17

Which statement about E. coli RNA polymerase (core enzyme) is FALSE?

A) It can start new chains de novo or elongate old ones.
B) It has no catalytic activity unless the sigma factor is bound.
C) It uses nucleoside 5'-triphosphates as substrates.
D) Its activity is blocked by rifampicin.
E) Its RNA product will hybridize with the DNA template.

Question 18

Differential RNA processing may result in:

A) a shift in the ratio of mRNA produced from two adjacent genes.
B) attachment of the poly(A) tail to the 5' end of an mRNA.
C) inversion of certain exons in the final mRNA.
D) the production of the same protein from two different genes.
E) the production of two distinct proteins from a single gene.

Question 19

RNA polymerase:

A) binds tightly to a region of DNA thousands of base pairs away from the DNA to be transcribed.
B) can synthesize RNA chains without a primer.
C) has a subunit called $\lambda$
(lambda), which acts as a proofreading ribonuclease.
D) separates DNA strands throughout a long region of DNA (up to thousands of base pairs), then copies one of them.
E) synthesizes RNA chains in the 3' $\rightarrow$ 5' direction.

Question 20

Which process is NOT a known function of TFIIH?

A) DNA helicase activity
B) hydrolysis of ATP
C) formation of an open complex
D) termination of transcription
E) nucleotide excision repair

Question 21

The reverse transcriptase of an animal RNA virus catalyzes:

A) degradation of the RNA strand in a DNA-RNA hybrid.
B) insertion of the viral genome into a chromosome of the host (animal) cell.
C) RNA formation in the 3' $\rightarrow$ 5' direction.
D) RNA synthesis, but not DNA synthesis.
E) synthesis of an antisense RNA transcript.

Question 22

Which statement about the reverse transcriptases of retroviruses and the RNA replicases of other single-stranded RNA viruses, such as R17 and influenza virus, is CORRECT?

A) Both enzymes can synthesize either RNA or DNA from an RNA template strand.
B) Both enzymes can utilize DNA in addition to RNA as a template strand.
C) Both enzymes carry the specificity for the RNA of their own virus.
D) Both enzymes have error rates similar to those of cellular RNA polymerases.
E) Both enzymes require host-encoded subunits for their replication function.

Question 23

What metal ion cofactors are required to bind nucleotide triphosphate substrates by E. coli RNA polymerase?

A) Fe²⁺
B) Zn²⁺
C) Mg²⁺
D) Mn²⁺
E) None of these ions is required.

Question 24

Compared with DNA polymerase, reverse transcriptase:

A) does not require a primer to initiate synthesis.
B) introduces no errors into genetic material because it synthesizes RNA, not DNA.
C) makes fewer errors in synthesizing a complementary polynucleotide.
D) makes more errors because it lacks the 3' $\rightarrow$ 5' proofreading exonuclease activity.
E) synthesizes complementary strands in the opposite direction-from 3' $\rightarrow$ 5'.

Question 25

Which statement is NOT true about telomerase?

A) Telomerase is a reverse transcriptase.
B) Telomerase utilizes a tRNA template.
C) The primer for telomerase is the 3'-end of the DNA chromosomes.
D) Telomerase synthesizes DNA in the 5' $\rightarrow$ 3' direction.
E) Telomerase consists of both RNA and protein.

Question 26

Which polymerase does NOT require a template?

A) RNA Pol I
B) RNA Pol II
C) reverse transcriptase
D) polyadenylate polymerase
E) RNA replicase

Question 27

Which statement about mRNA stability is TRUE?

A) Degradation always proceeds in the 5' to 3' direction.
B) Degradation of mRNA by polynucleotide phosphorylase yields 5'-nucleoside monophosphates.
C) In general, bacterial mRNAs have longer half-lives than do eukaryotic mRNAs.
D) Rates of mRNA degradation are always at least 10-fold slower than rates of mRNA synthesis.
E) Secondary structure in mRNA (hairpins, for example) slows the rate of degradation.

Question 28

Which factor is NOT usually essential for the catalytic activity of ribozymes?

A) correct base pairing
B) correct base sequence
C) correct interaction with protein
D) correct secondary structure
E) correct three-dimensional structure

Question 29

Which factor is NOT involved in mRNA processing in vertebrates?

A) 30S pre-rRNA
B) the nucleoleus
C) ribonucleases
D) snoRNAs
E) snoRNPs

Question 30

Which compound is NOT part of miRNA formation?

A) pri-miRNA
B) pre-miRNA
C) Dicer
D) RISC
E) pseudouridine

Question 31

Which statement is TRUE regarding topoisomerases during synthesis of nucleic acids by E. coli RNA polymerase?

A) DNA gyrase is required to relieve supercoils on the DNA exit side of the polymerase.
B) Since no strand cleavage occurs, supercoiling is not a factor in the action of RNA polymerase.
C) Positive supercoils are generated ahead of the transcription bubble.
D) Both the DNA and the RNA product will be supercoiled.
E) None of the statements is true.

Question 32

Which property of the L-19 IVS ribozyme is NOT shared with enzymes that are purely protein?

A) It acts as a true catalyst.
B) It can be competitively inhibited.
C) It displays Michaelis-Menten kinetics.
D) It exploits base pairing with internal guide sequences.
E) It makes use of covalent and metal ion catalysis.

Question 33

Which statement is TRUE regarding the RNA product synthesized by E. coli RNA polymerase?

A) Its sequence is identical to that of the template strand.
B) Its sequence is identical to that of the non-template strand.
C) It is able to form a duplex with the template strand.
D) It is able to form a duplex with the nontemplate strand
E) None of the statements is true.

Question 34

What acts as the nucleophile in the mechanism of nucleotide addition by RNA polymerase?

A) the 5' phosphate of an incoming nucleotide
B) a water molecule
C) a 5' hydroxyl of the template DNA
D) a 3' hydroxyl from the RNA being extended
E) an aspartate in the active site

Question 35

AZT (3'-azido-2',3'-dideoxythymidine), used to treat HIV infection, acts in HIV-infected cells by:

A) blocking ATP production.
B) blocking deoxynucleotide synthesis.
C) inhibiting reverse transcriptase.
D) inhibiting RNA polymerase II.
E) inhibiting RNA processing.

Question 36

Reverse transcriptase:

A) can utilize only RNA templates.
B) has a 3' $\rightarrow$ 5' proofreading exonuclease but not a 5' $\rightarrow$ 3' exonuclease.
C) is activated by AZT.
D) is encoded by retroviruses.
E) synthesizes DNA with the same fidelity as a typical DNA polymerase.

Question 37

E. coli RNA polymerase (RNAP) has no 3' to 5' exonuclease activity. Which statement BEST explains why this is not a required activity for this enzyme?

A) RNAP makes fewer errors in NTP addition, so this activity is unnecessary.
B) RNAP does not need to degrade nucleic acids ahead of the transcription bubble.
C) Errors in transcription will have no impact on the function of the RNA product.
D) Multiple RNA products are created and turnover rapidly, so errors have less impact.
E) None of the statements explains why this is not a required activity.

Question 38

Which compound is NOT a posttranscriptional modification in mRNA or tRNA?

A) 4-thiouridine
B) pseudouridine
C) dihydrouridine
D) ribouridine
E) ribothymidine

Question 39

What statement is TRUE regarding synthesis of nucleic acids by E. coli RNA polymerase?

A) The RNA/DNA hybrid assumes a B-form DNA conformation.
B) The RNA/DNA hybrid is antiparallel.
C) The RNA/DNA hybrid is between 10 and 20 base pairs long.
D) Unwinding the DNA duplex creates negative supercoils in the template DNA.
E) None of the statements is true.

Question 40

Aptamers are:

A) double-stranded RNA products of nuclease action on hairpin RNAs.
B) repeat sequence elements at the ends of transposons.
C) small RNA molecules selected for tight binding to specific molecular targets.
D) the RNA primers required for retroviral replication.
E) the short tandem repeat units found in telomeres.

Question 41

In eukaryotes, RNA polymerase II:

A) is a multisubunit protein with subunits that are homologous to E. coli RNAP.
B) is associated with transcription of mRNA and rRNA.
C) is found in chloroplasts and mitochondria.
D) includes a small protein subunit that is phosphorylated during elongation.
E) All of the answers are correct.

Question 42

Which statement is TRUE regarding E. coli RNAP?

A) The dissociation constant (K_d) for promoter DNA and the core enzyme is smaller than that for promoter DNA and the associated holoenzyme.
B) The dissociation constant (K_d) for non-promoter sequences and the RNAP holoenzyme is larger than the K_d for the core enzyme and nonpromoter DNA.
C) The dissociation constant (K_d) for promoter sequences and the RNAP holoenzyme is the same as the K_d for the core enzyme and nonpromoter DNA.
D) All of the statements are true.
E) None of the statements is true.

Question 43

Which structure is NOT a folded RNA structure?

A) tRNA
B) a riboswitch
C) a group II intron
D) U2 snRNA
E) All of these are folded RNA structures.

Question 44

Which statement CORRECTLY describes a difference between prokaryotic and eukaryotic mRNA transcription?

A) Prokaryotic transcripts are often translated cotranscriptionally, while eukaryotic transcripts are not.
B) Prokaryotic transcripts are often edited, while eukaryotic transcripts are not.
C) Prokaryotic transcripts often include multiple protein-coding sequences, while eukaryotic transcripts do not.
D) Prokaryotic transcripts are often translated cotranscriptionally, while eukaryotic transcripts are not, and prokaryotic transcripts are often edited, while eukaryotic transcripts are not .
E) Prokaryotic transcripts are often translated cotranscriptionally, while eukaryotic transcripts are not, and prokaryotic transcripts often include multiple protein-coding sequences, while eukaryotic transcripts do not.

Question 45

Which process is involved in generating the different forms of the apoB gene product in liver and intestines?

A) alternative 5' splice-site choice
B) alternative 3' splice-site choice
C) a C $\rightarrow$ U deamination
D) All of these processes are involved.
E) None of these processes is involved.

Question 46

Which groups act as nucleophiles in the splicing of group I introns?

A) 2' OH groups only
B) 3' OH groups only
C) 5´ OH groups only
D) both 2' and 5'OH groups
E) both 3'and 5' OH groups

Question 47

Which statement is FALSE with respect to different $\sigma$ (sigma) subunits in bacterial RNA polymerase?

A) Specific amino acids in $\sigma$ subunits will interact with the polymerase.
B) $\sigma$ subunits will specifically interact with DNA sequences spanning approximately three turns of the helix.
C) $\sigma$ subunits interact with both DNA and the RNA polymerase in the elongation form.
D) Multiple $\sigma$ subunits exist in E. coli.
E) The binding of NusA is competitive with the binding of $\sigma$ subunits in E. coli.

Question 48

In order for RNA polymerase II to create a transcript, what is NOT necessary?

A) magnesium
B) dNTPs
C) topoisomerases
D) zinc
E) All of these are necessary.

Question 49

Synthesis and maturation of tRNA does NOT require which process?

A) transcription of a gene
B) RNaseD cleavage
C) RNaseP cleavage
D) addition of CCA to the 5' end of the molecule
E) methylation of specific bases

Question 50

Which eukaryotic transcription factor has helicase activity?

A) TFIIA
B) TFIIB
C) TFIIF
D) TFIIH
E) TBP

Question 51

Which statement does NOT describe the CAP structure of mRNA?

A) The CAP structure contains two phosphoanhydride bonds.
B) The CAP is added to an existing 5'triphosphate nucleotide.
C) The CAP structure may include multiple methylations.
D) The CAP structure is added after addition of the poly(A) structure.
E) The CAP interacts with both the ribosome and the carboxyterminal domain of RNA Pol II.

Question 52

Which statement is FALSE regarding transcription at RNA polymerase II promoters?

A) Transcription requires binding of TBP to the -10 promoter element.
B) TFIIB binds TBP and recruits TFIIF that directs RNA polymerase II to the promoter.
C) TFIIH unwinds the DNA and phosphorylates the CTD of RNA polymerase II.
D) TFIIH subunits contribute to a nucleotide-excision repair process.
E) During the elongation phase, elongation factors suppress RNA polymerase II pausing and coordinate protein-protein interactions.

Question 53

Which item(s) can be described as a ribozyme(s)?

A) group I introns
B) RNase P
C) group II introns
D) both group I and group II introns but not RNase P
E) Group I introns, group II introns, and RNase P can all be described as ribozymes.

Question 54

Which process is NOT part of the processing of the 30S pre-rRNA transcript?

A) addition of a poly(A) tail
B) methylation of bases
C) conversion of uridine to pseudoiuridine
D) conversion of uridine to dihydrouridine
E) hydrolysis by RNase P

Question 55

Which statement is TRUE regarding the TATA box in transcription?

A) It is involved in binding the $\sigma$ subunit in E. coli transcription.
B) It is found at position -10 relative to the transcription start site.
C) It is a site for assembly of the preinitiation complex.
D) It is a site for binding of repressor proteins.
E) All of the statements are true.

Question 56

Which statement is FALSE regarding the TATA-binding protein (TBP)?

A) It is a general transcription factor in eukaryotic transcription.
B) This protein stays associated with the RNA polymerase during elongation.
C) This protein interacts with TBP-associated factors in TFIID.
D) All of the statements are false.
E) None of the statements is false.

Question 57

In eukaryotic splicing, U1-snRNP:

A) is made entirely of RNA.
B) is a component of the active splicesosome.
C) is complementary to the 5' splice site for the intron.
D) becomes covalently attached to a lariat intermediate.
E) dissociates from the spliceosomal complex after lariat formation.

Question 58

Which process is associated with the carboxy-terminal domain (CTD) of RNA polymerase II in eukaryotes?

A) formation of spliceosomes
B) attachment of the 5' cap to mRNA
C) polyadenylation of the 3' end of mRNA
D) phosphorylation and dephosphorylation
E) All of the answers are correct.

Question 59

Which statement is CORRECT with respect to $\rho$ (rho)-dependent termination of RNA synthesis?

A) Self-complementary GC sequences act as signals for transcriptional termination.
B) Formation of a hairpin structure disrupts DNA duplex formation and facilitates dissociation of the transcript.
C) ATP is hydrolyzed as part of the termination process.
D) Transcripts are terminated at specific residues in the sequence.
E) Transcripts terminate immediately at rut sites.

Question 60

Which step is NOT a part of the synthesis of a 5' mRNA cap?

A) conversion of a 5'triphosphate into a 5F1' diphosphate
B) formation of a 5' to 5'phosphodiester bond
C) methylation of 2' OH groups
D) transfer of a GMP group onto a nucleic acid
E) All of these steps are part of 5' cap synthesis.

Question 61

The specific sequences that E. coli RNA polymerase usually binds to in E. coli DNA before initiating transcription generally contain more A=T base pairs than G $\equiv$ C base pairs. In no more than a few sentences, speculate on why this might be the case.

Question 62

AZT is one drug used as an HIV inhibitor. How does its structure differ from thymidine?

A) The aromatic ring in AZT is not methylated at the 5 position.
B) An azido group is present at C-2' in AZT.
C) An azido group is present at C-3' in AZT.
D) The 5' OH is methylated in AZT.
E) The aromatic ring is amidated at the 4 position.

Question 63

Describe the sequence of events in the initiation of transcription by E. coli RNA polymerase.

Question 64

Which statement is FALSE regarding telomerase?

A) This enzyme requires a DNA component as a cofactor.
B) This enzyme is a DNA polymerase.
C) This enzyme extends the 3' end of a linear nucleic acid structure.
D) This enzyme uses dGTP and dTTP as substrates.
E) This enzyme synthesizes nucleic acids in a 5'to 3'direction.

Question 65

Which process is part of the original central dogma?

A) RNA-dependent RNA synthesis
B) the process catalyzed by RNA polymerase II
C) RNA editing processes
D) RNA-dependent DNA synthesis
E) None of these is part of the original central dogma.

Question 66

Below, an RNA molecule is being transcribed from a strand of DNA. Indicate the 5' and 3' ends of the RNA molecule and of the strand of DNA that is complementary to the RNA molecule. In which direction is synthesis occurring?

Question 67

RNA replicase carries out what function?

A) DNA-dependent DNA synthesis
B) RNA-dependent DNA synthesis
C) DNA-dependent RNA synthesis
D) RNA-dependent RNA synthesis
E) None of the answers is correct.

Question 68

Consider the following small hypothetical gene. The DNA bases corresponding to the first and last mRNA nucleotides are indicated by a "+" and a "*," respectively. Give the sequence(s) of the mRNA strand(s) produced by this gene.

Question 69

List one basic property that distinguishes RNA polymerases from DNA polymerases, and list one basic property they share.

Question 70

Which activity is NOT associated with retrovirus reverse transcriptases?

A) RNA-dependent DNA synthesis
B) synthesis of RNA primers
C) RNA degradation
D) DNA-dependent DNA synthesis
E) All of these are associated with reverse transcriptase.

Question 71

Write the sequence of the messenger RNA molecule synthesized from a DNA template strand having the sequence:
(5')ATCGTACCGTTA(3')

Question 72

For each of the following statements, indicate with a P if the statement applies only to prokaryotes, an E if the statement applies only to eukaryotes, and an E and P if the statement applies to both eukaryotes and prokaryotes.
___ RNA synthesis is blocked by actinomycin D.
___ A single RNA polymerase transcribes genes that encode mRNAs, tRNAs, and rRNA.
___ Transcription of mRNA is blocked by $\alpha$ -amanitin.
___ Sigma ( $\sigma$ ) subunit detaches from RNA polymerase shortly after transcription has initiated.
___ The 5' end of the mature mRNA begins with a triphosphate.
___ The primary mRNA transcript is inactive.
___ Termination of transcription requires the protein $\rho$ factor.

Question 73

In a $\rho$ -independent terminator, there is a palindrome rich in G $\equiv$ C base pairs, followed by 8-10 uridine residues. Explain how each of the following changes might affect terminator function: (a) substitution of cytidines for the 8-10 uridines; (b) mutations in the palindrome that decrease its G $\equiv$ C content; (c) elimination of half of the palindromic sequence.

Question 74

What do retrovirus reverse transcriptases use to initiate DNA synthesis?

A) They can synthesize DNA without a primer.
B) They require the action of cellular primase.
C) They contain a primase activity.
D) They use a tRNA molecule as a primer.
E) None of these is used by reverse transcriptases in initiation of DNA synthesis.

Question 75

What statement is NOT true regarding retroviral reverse transcriptase and eukaryotic DNA polymerase $\delta$ ?

A) Both enzymes require nucleic acid templates.
B) Both enzymes include proof-reading functions.
C) Both enzymes use dNTPs as substrates for synthesis.
D) Both enzymes require metal cofactors.
E) All of the statements are true.

Question 76

AZT is one drug used as an HIV inhibitor. How does it specifically inhibit viral replication?

A) AZT is not taken up by human cells.
B) AZT binds to human polymerases with lower affinity than to viral reverse transcriptase.
C) AZT cannot be phosphorylated to a triphosphate.
D) AZT only inhibits active transcription and not DNA replication.
E) AZT inhibits viral assembly and packing.

Question 77

Which statement does NOT indicate how retrotransposons and retroviruses are similar to each other?

A) Both contain long terminal repeated sequences.
B) Both are able to produce RNA products from their DNA.
C) Both contain reverse transcriptase coding regions.
D) Both contain envelope protein coding sequences.
E) Both integrate into a host genome.

Question 78

Retroviral genomes tend to mutate at a very high rate. What statement BEST explains this observation?

A) The RNA genome is highly susceptible to chemical damage.
B) Specific enzymes in cells will modify the genome as a protection against infection.
C) RNA phosphodiester bonds will tend to hydrolyze spontaneously.
D) The virus changes the sequence to prevent antibody binding to the viral genome.
E) Reverse transcriptase lacks a 3' to 5'exonuclease activity.

Question 79

Which statement does NOT accurately describe a difference between RNA synthesis by polynucleotide phosphorylase and RNAP?

A) RNAP is a bacterial enzyme, while polynucleotide phosphorylase is not.
B) RNAP requires a template, while polynucleotide phosphorylase does not.
C) RNAP produces a specific product, while polynucleotide phosphorylase does not.
D) RNAP uses nucleotide triphosphates as substrates, while polynucleotide phosphorylase uses nucleotide diphosphates.
E) RNAP synthesizes RNA, while polynucleotide phosphorylase can synthesize or degrade RNA.

Question 80

Compare and contrast $\rho$ -dependent and $\rho$ -independent termination of transcription in prokaryotes.