14-17 MULTIPLE CHOICE

29. In a nucleosome, the DNA is wrapped around a. polymerase molecules. b. ribosomes. c. histones. d. a thymine dimer. e. satellite DNA

C

88. Which of the following characteristics, structures, or processes is common to both bacteria and viruses? a. metabolism b. ribosomes c. genetic material composed of nucleic acid d. cell division e. independent existence

C

32. A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is a. 3' UCA 5'. b. 3' UGA 5'. c. 5' TCA 3'. d. 3'ACU 5'. e. either UCA or TCA, depending on wobble in the first base.

A

37. RNA polymerase moves in which direction along the DNA? a. 3' 5' along the template strand b. 3' 5' along the coding (sense) strand c. 5' 3' along the template strand d. 3' 5' along the coding strand e. 5' 3' along the double-stranded DNA

A

77. Which of the following molecules make up the viral envelope? a. glycoproteins b. proteosugars c. carbopeptides d. peptidocarbs e. carboproteins

A

78. Most human-infecting viruses are maintained in the human population only. However, a zoonosis is a disease that is transmitted from other vertebrates to humans, at least sporadically, without requiring viral mutation. Which of the following is the best example of a zoonosis? a. rabies b. herpesvirus c. smallpox d. HIV e. hepatitis virus

A

81. What is the name given to viruses that are single-stranded RNA that acts as a template for DNA synthesis? a. retroviruses b. proviruses c. viroids d. bacteriophages e. lytic phages

A

85. What are prions? a. misfolded versions of normal brain protein b. tiny molecules of RNA that infect plants c. viral DNA that has had to attach itself to the host genome d. viruses that invade bacteria e. a mobile segment of DNA

A

48. A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form. The dipeptide that will form will be a. cysteine-alanine. b. proline-threonine. c. glycine-cysteine. d. alanine-alanine. e. threonine-glycine.

B

82. What is the function of reverse transcriptase in retroviruses? a. It hydrolyzes the host cell's DNA. b. It uses viral RNA as a template for DNA synthesis. c. It converts host cell RNA into viral DNA. d. It translates viral RNA into proteins. e. It uses viral RNA as a template for making complementary RNA strands.

B

87. RNA viruses require their own supply of certain enzymes because a. host cells rapidly destroy the viruses. b. host cells lack enzymes that can replicate the viral genome. c. these enzymes translate viral mRNA into proteins. d. these enzymes penetrate host cell membranes. e. these enzymes cannot be made in host cells

B

35. A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences in the coding strand of the DNA could code for this peptide? a. 3' UUU-CCC-AAA-GGG-UUU-CCC b. 3' AUG-AAA-GGG-TTT-CCC-AAA-GGG c. 5' TTT-CCC-AAA-GGG-TTT-CCC d. 5' GGG-AAA-TTT-AAA-CCC-ACT-GGG e. 5' ACT-TAC-CAT-AAA-CAT-TAC-UGA

C

40. A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which might this illustrate? a. The sequence evolves very rapidly. b. The sequence does not mutate. c. Any mutation in the sequence is selected against. d. The sequence is found in many but not all promoters. e. The sequence is transcribed at the start of every gene

C

41. Which of the following help(s) to stabilize mRNA by inhibiting its degradation? a. TATA box b. spliceosomes c. 5' cap and poly (A) tail d. introns e. RNA polymerase

C

42. What is a ribozyme? a. an enzyme that uses RNA as a substrate b. an RNA with enzymatic activity c. an enzyme that catalyzes the association between the large and small ribosomal subunits d. an enzyme that synthesizes RNA as part of the transcription process e. an enzyme that synthesizes RNA primers during DNA replication

C

46. Which of the following is (are) true of snRNPs? a. They are made up of both DNA and RNA. b. They bind to splice sites at each end of the exon. c. They join together to form a large structure called the spliceosome. d. They act only in the cytosol. e. They attach introns to exons in the correct order

C

47. A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is a. TTT. b. UUA. c. UUU. d. AAA. e. either UAA or TAA, depending on first base wobble.

C

49. What is the most abundant type of RNA? a. mRNA b. tRNA c. rRNA d. pre-mRNA e. hnRNA

C

60. Of the following, which is the most current description of a gene? a. a unit of heredity that causes formation of a phenotypic characteristic b. a DNA subunit that codes for a single complete protein c. a DNA sequence that is expressed to form a functional product: either RNA or polypeptide d. a DNA—RNA sequence combination that results in an enzymatic product e. a discrete unit of hereditary information that consists of a sequence of amino acids

C

68. This binds to a site in the DNA far from the promoter to stimulate transcription: a. enhancer b. promoter c. activator d. repressor e. terminator

C

80. Which of the following terms describes bacteriophage DNA that has become integrated into the host cell chromosome? a. intemperate bacteriophages b. transposons c. prophages d. T-even phages e. plasmids

C

34. What amino acid sequence will be generated, based on the following mRNA codon sequence? 5' AUG-UCU-UCG-UUA-UCC-UUG 3' a. met-arg-glu-arg-glu-arg b. met-glu-arg-arg-gln-leu c. met-ser-leu-ser-leu-ser d. met-ser-ser-leu-ser-leu e. met-leu-phe-arg-glu-glu

D

39. Transcription in eukaryotes requires which of the following in addition to RNA polymerase? a. the protein product of the promoter b. start and stop codons c. ribosomes and tRNA d. several transcription factors (TFs) e. aminoacyl synthetase

D

44. Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes a. union with ribosomes. b. fusion into circular forms known as plasmids. c. linkage to histone molecules. d. excision of introns. e. fusion with other newly transcribed mRNA

D

69. This can inhibit transcription by blocking the binding of positively acting transcription factors to the DNA: a. enhancer b. promoter c. activator d. repressor e. terminator

D

76. Viral genomes vary greatly in size and may include from four genes to several hundred genes. Which of the following viral features is most apt to correlate with the size of the genome? a. size of the viral capsomeres b. RNA versus DNA genome c. double versus single strand genomes d. size and shape of the capsid e. glycoproteins of the envelope

D

79. Which of the following is characteristic of the lytic cycle? a. Many bacterial cells containing viral DNA are produced. b. Viral DNA is incorporated into the host genome. c. The viral genome replicates without destroying the host. d. A large number of phages is released at a time. e. The virus-host relationship usually lasts for generations.

D

33. A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be a. 5' TTG-CTA-CAG-TAG 3'. b. 3' AAC-GAC-GUC-AUA 5'. c. 5' AUG-CTG-CAG-TAT 3'. d. 3' AAA-AAT-ATA-ACA 5'. e. 3' AAA-GAA-TAA-CAA 5'.

E

36. What is the sequence of a peptide based on the following mRNA sequence? 5' . . . UUUUCUUAUUGUCUU 3' a. leu-cys-tyr-ser-phe b. cyc-phe-tyr-cys-leu c. phe-leu-ile-met-val d. leu-pro-asp-lys-gly e. phe-ser-tyr-cys-leu

E

70. This is the site in the DNA located near the end of the final exon, encoding an RNA sequence that determines the 3' end of the transcript: a. enhancer b. promoter c. activator d. repressor e. terminator

E

86. Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host? a. It is able to spread to a large number of new hosts quickly because the new hosts have no immunological memory of them. b. The new virus replicates quickly and undergoes rapid adaptation to a series of divergent hosts. c. A change in environmental conditions such as weather patterns quickly forces the new virus to invade new areas. d. Sporadic outbreaks will be followed almost immediately by a widespread pandemic. e. The newly emerging virus will die out rather quickly or will mutate to be far less lethal.

E

61. What does the operon model attempt to explain? a. the coordinated control of gene expression in bacteria b. bacterial resistance to antibiotics c. how genes move between homologous regions of DNA d. the mechanism of viral attachment to a host cell e. horizontal transmission of plant viruses

A

66. In both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of a. transcription. b. translation. c. mRNA stability. d. mRNA splicing. e. protein stability

A

43. What are the coding segments of a stretch of eukaryotic DNA called? a. introns b. exons c. codons d. replicons e. transposons

B

50. Choose the answer that has these events of protein synthesis in the proper sequence. 1. An aminoacyl-tRNA binds to the A site. 2. A peptide bond forms between the new amino acid and a polypeptide chain. 3. tRNA leaves the P site, and the P site remains vacant. 4. A small ribosomal subunit binds with mRNA. 5. tRNA translocates to the P site. a. 1, 3, 2, 4, 5 b. 4, 1, 2, 5, 3 c. 5, 4, 3, 2, 1 d. 4, 1, 3, 2, 5 e. 2, 4, 5, 1, 3

B

58. Which point mutation would be most likely to have a catastrophic effect on the functioning of a protein? a. a base substitution b. a base deletion near the start of a gene c. a base deletion near the end of the coding sequence, but not in the terminator codon d. deletion of three bases near the start of the coding sequence, but not in the initiator codon e. a base insertion near the end of the coding sequence, but not in the terminator codon

B

65. The lactose operon is likely to be transcribed when a. there is more glucose in the cell than lactose. b. the cyclic AMP levels are low. c. there is glucose but no lactose in the cell. d. the cyclic AMP and lactose levels are both high within the cell. e. the cAMP level is high and the lactose level is low.

D

57. A frameshift mutation could result from a. a base insertion only. b. a base deletion only. c. a base substitution only. d. deletion of three consecutive bases. e. either an insertion or a deletion of a base

E

62. The tryptophan operon is a repressible operon that is a. permanently turned on. b. turned on only when tryptophan is present in the growth medium. c. turned off only when glucose is present in the growth medium. d. turned on only when glucose is present in the growth medium. e. turned off whenever tryptophan is added to the growth medium.

E