Chapter 26 RNA Metabolism
Multiple Choice Questions
1. DNA-dependent synthesis of RNA
Pages: 1022-1023 Difficulty: 2 Ans: B
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 de novo (without a primer).
C) has a subunit called 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' → 5' direction.
2. DNA-dependent synthesis of RNA
Pages: 1024-1025 Difficulty: 2 Ans: B
The sigma factor of E. coli RNA polymerase:
A)
B)
C)
D)
E)
associates with the promoter before binding core enzyme.
combines with the core enzyme to confer specific binding to a promoter.
is inseparable from the core enzyme.
is required for termination of an RNA chain.
will catalyze synthesis of RNA from both DNA template strands in the absence of the
core enzyme.
3. DNA-dependent synthesis of RNA
Pages: 1025-1029 Difficulty: 2 Ans: B
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.
4. DNA-dependent synthesis of RNA
Pages: 1027-1029 Difficulty: 2 Ans: B
Which one of the following statements about E. coli RNA polymerase (core enzyme) is
false?
A)
B)
C)
D)
E)
It can start new chains de novo or elongate old ones.
It has no catalytic activity unless the sigma factor is bound.
It uses nucleoside 5'-triphosphates as substrates.
Its activity is blocked by rifampicin.
Its RNA product will hybridize with the DNA template.
5. RNA processing
Pages: 1033-1034
Difficulty: 1 Ans: B
Processing of a primary mRNA transcript in a eukaryotic cell does not normally involve:
A)
B)
C)
D)
attachment of a long poly(A) sequence at the 3' end.
conversion of normal bases to modified bases, such as inosine and pseudouridine.
excision of intervening sequences (introns).
joining of exons.
6. RNA processing
Page: 1036
Difficulty: 2 Ans: B
The excision (splicing) of many group I introns requires, in addition to the primary transcript
RNA:
A)
B)
C)
D)
E)
a cytosine nucleoside or nucleotide and a protein enzyme.
a guanine nucleoside or nucleotide (only).
a protein enzyme only.
a small nuclear RNA and a protein enzyme.
ATP, NAD, and a protein enzyme.
7. RNA processing
Page: 1036
Difficulty: 2 Ans: E
Splicing of introns in nuclear mRNA primary transcripts requires:
A)
B)
C)
D)
E)
a guanine nucleoside or nucleotide.
endoribonucleases.
polynucleotide phosphorylase.
RNA polymerase II.
small nuclear ribonucleoproteins (snurps).
8. RNA processing
Page: 1040
Difficulty: 2 Ans: B
Which one of the following is not true of the mRNA for ovalbumin?
A)
B)
C)
D)
E)
Exons are used for polypeptide synthesis.
Introns are complementary to their adjacent exons and will form hybrids with them.
The mature mRNA is substantially shorter than the corresponding region on the DNA.
The mRNA is originally synthesized in the nucleus, but ends up in the cytoplasm.
The splicing that yields a mature mRNA occurs at very specific sites in the RNA primary
transcript.
9. RNA processing
Pages: 1046-1047 Difficulty: 2 Ans: C
Which of the following is not usually essential for the catalytic activity of ribozymes?
A)
B)
C)
D)
E)
Correct base pairing
Correct base sequence
Correct interaction with protein
Correct secondary structure
Correct three-dimensional structure
10. RNA-dependent synthesis of RNA and DNA
Page: 1050
Difficulty: 2 Ans: A
The reverse transcriptase of an animal RNA virus catalyzes:
A)
B)
C)
D)
E)
degradation of the RNA strand in a DNA-RNA hybrid.
insertion of the viral genome into a chromosome of the host (animal) cell.
RNA formation in the 3' → 5' direction.
RNA synthesis, but not DNA synthesis.
synthesis of an antisense RNA transcript.
11. RNA-dependent synthesis of RNA and DNA
Page: 1051
Difficulty: 2 Ans: D
Reverse transcriptase:
A)
B)
C)
D)
E)
can utilize only RNA templates.
has a 3'  5' proofreading exonuclease but not a 5'  3' exonuclease.
is activated by AZT.
is encoded by retroviruses.
synthesizes DNA with the same fidelity as a typical DNA polymerase.
12. RNA-dependent synthesis of RNA and DNA
Page: 1051
Difficulty: 2 Ans: C
Compared with DNA polymerase, reverse transcriptase:
A)
B)
C)
D)
introduces no errors into genetic material because it synthesizes RNA, not DNA.
makes fewer errors in synthesizing a complementary polynucleotide.
makes more errors because it lacks the 3' →5' proofreading exonuclease activity.
synthesizes complementary strands in the opposite direction → from 3' →
5'.
13. RNA-dependent synthesis of RNA and DNA
Page: 1056
Difficulty: 3 Ans: D
Which one of the following statements 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.Short Answer
Questions
14. DNA-dependent synthesis of RNA
Pages: 1022-1023 Difficulty: 2
Write the sequence of the messenger RNA molecule synthesized from a DNA template
strand (non-coding) having the sequence:
(5')ATCGTACCGTTA(3')
Ans: (3')UAGCAUGGCAAU(5'). Also acceptable is (5')UAACGGUACGAU(3').
Short Answers
15. DNA-dependent synthesis of RNA
Pages: 1021-1024 Difficulty: 2
List one basic property that distinguishes RNA polymerases from DNA polymerases, and list
one basic property they share.
Ans: Among the distinguishing characteristics: RNA polymerase does not require a primer,
but DNA polymerase does; RNA polymerase lacks the 3' → 5' proofreading exonuclease
activity present in DNA polymerase. Among the shared properties: both enzymes use
nucleoside triphosphates as substrates, require Mg 2+, produce an antiparallel complement to
the template, and synthesize nucleic acids in the direction 5' → 3'.
16. DNA-dependent synthesis of RNA
Pages: 1022-1023 Difficulty: 2
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?
Ans:
17. DNA-dependent synthesis of RNA
Page: 1025
Difficulty: 2
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+C base pairs. In no
more than a few sentences, speculate on why this might be the case.
Ans: Because A=T base pairs are stabilized by only two hydrogen bonds (compared with
three for G+C pairs), double-stranded regions rich in A+T pairs are easier for RNA
polymerase to bind and unwind in preparation for the transcription of one of the DNA
strands.
18. DNA-dependent synthesis of RNA
Pages: 1025-1029 Difficulty: 2
Describe the sequence of events in the initiation of transcription by E. coli RNA polymerase.
Ans: The core enzyme plus sigma subunit, called holoenzyme, binds to the promoter region
forming a closed complex (i.e., in which the DNA double helix is not unwound). This is
converted to an open complex by the unwinding of a short region of the promoter. Synthesis
of the RNA chain begins within the complex. The complex then moves along the DNA away
from the promoter region and the sigma subunit dissociates.
19. RNA processing
Pages: 1035, 1039-1040 Difficulty: 2
Describe in words (not using structures) the important features of the structures present on
the 5' and 3' ends of mature (processed) eukaryotic mRNAs.
Ans: At the 5' end there is a cap consisting of a guanosine joined to the 5'-terminal
nucleotide through a 5' to 5' triphosphate group. This guanine nucleotide is methylated on N7. The next two nucleotides in the chain are also sometimes methylated on their 2'-OH
groups. At the 3' end is the poly(A) tail consisting of a run of 80–250 adenylate residues.
20. RNA processing
Pages: 1036-1038 Difficulty: 2
Describe the mechanistic difference that distinguishes the splicing of group I introns from
that of group II introns.
Ans: In the group I introns, the initial break in the RNA chain is induced by a free guanine
nucleoside. In group II introns, the attacking species is a nucleotide that is part of the intron
itself.
21. RNA processing
Pages: 1045-1048 Difficulty: 2
Define ribozymes.
Ans: Ribozymes are enzymes that consist in part or entirely of RNA.
22. RNA-dependent synthesis of RNA and DNA
Pages: 1022, 1050-1051 Difficulty: 2
Compare transcription and reverse transcription in terms of the following characteristics:
(a) direction of polynucleotide synthesis
(b) nature of template
(c) nature of primer
(d) incorporated nucleotides
Ans:
(a) direction of polynucleotide synthesis
(b) nature of template
(c) nature of primer
(d) incorporated nucleotides
23. RNA-dependent synthesis of RNA and DNA
Page: 1051
Difficulty: 2
Reverse Transcription
Transcription
5' → 3'
RNA or DNA
RNA
dNTPs
5' →3'
DNA
none
NTPs
Describe all of the known catalytic activities of reverse transcriptase.
Ans: Reverse transcriptase can (1) synthesize DNA complementary to an RNA template; (2)
degrade the RNA strand of the resulting RNA-DNA hybrid; and (3) synthesize DNA
complementary to the resulting single-stranded DNA.