Biochem: Chapter 26 RNA Metabolism

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' → 5' direction. D) RNA synthesis, but not DNA synthesis. E) synthesis of an antisense RNA transcript.

A

Which of the following statements 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.

A

Which of the following statements 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 into 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.

A

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.

B

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.

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 λ (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.

B

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.

B

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.

B

Which of the following 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

B

Which one of the following is not true of the mRNA for ovalbumin? 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.

B

Which one of the following statements 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.

B

Which one of the following statements about eukaryotic RNA polymerases is correct? A) All three eukaryotic RNA polymerases recognize the same promoters as prokaryotic polymerases. B) None of the eukaryotic RNA polymerases recognizes prokaryotic promoters. C) Only eukaryotic RNA polymerase I recognizes prokaryotic promoters. D) Only eukaryotic RNA polymerase II recognizes prokaryotic promoters. E) Only eukaryotic RNA polymerase III recognizes prokaryotic promoters.

B

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.

C

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.

C

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' → 3' diphosphate linkage. C) 7-methylguanosine joined to the mRNA via a 5' → 5' triphosphate linkage. D) N6-methyladenosine joined to the mRNA via a 5' → 5' phosphodiester bond. E) O6-methylguanosine joined to the mRNA via a 5' → 5' triphosphate linkage.

C

Which of the following 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

C

Which of the following statements about E. coli RNA polymerase (core enzyme) is false? A) In the absence of the σ 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 σ subunit is bound. D) The RNA chain grows in a 5' → 3' direction. E) The RNA product is complementary to the DNA template.

C

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' → 5' proofreading exonuclease activity. E) synthesizes complementary strands in the opposite directionfrom 3' → 5'.

D

RNA polymerase from E. coli (core enzyme alone) has all of the following properties except that it: A) can extend an RNA chain and initiate a new chain. B) is required for the synthesis of mRNA, rRNA, and tRNA in E. coli. C) produces an RNA polymer that begins with a 5'-triphosphate. D) recognizes specific start signals in DNA. E) requires all four ribonucleoside triphosphates and a DNA template.

D

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

D

Which one of the following properties 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.

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.

D

"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.

E

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.

E

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.

E

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 (snurps).

E

Which one of the following statements 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 ared always at least 10-fold slower than rates of mRNA synthesis. E) Secondary structure in mRNA (hairpins, for example) slows the rate of degradation.

E