# Chapter 6 Exercises

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## Review questions for Chapter 6

### Multiple Choice

1) Frederick Griffith infected mice with a combination of dead R and live S bacterial strains. What was the outcome, and why did it occur?

1. The mice will live. Transformation was not required.
2. The mice will die. Transformation of genetic material from R to S was required.
3. The mice will live. Transformation of genetic material from S to R was required.
4. The mice will die. Transformation was not required.

2) Why was the alga Acetabularia a good model organism for Joachim Hämmerling to use to identify the location of genetic material?

1. It lacks a nuclear membrane.
2. It self-fertilizes.
3. It is a large, asymmetrical, single cell easy to see with the naked eye.
4. It makes a protein capsid.

3) Which of the following best describes the results from Hershey and Chase’s experiment using bacterial viruses with 35S-labeled proteins or 32P-labeled DNA that are consistent with protein being the molecule responsible for hereditary?

1. After infection with the 35S-labeled viruses and centrifugation, only the pellet would be radioactive.
2. After infection with the 35S-labeled viruses and centrifugation, both the pellet and the supernatant would be radioactive.
3. After infection with the 32P-labeled viruses and centrifugation, only the pellet would be radioactive.
4. After infection with the 32P-labeled viruses and centrifugation, both the pellet and the supernatant would be radioactive.

4) Which method did Morgan and colleagues use to show that hereditary information was carried on chromosomes?

1. statistical predictions of the outcomes of crosses using true-breeding parents
2. correlations between microscopic observations of chromosomal movement and the characteristics of offspring
3. transformation of nonpathogenic bacteria to pathogenic bacteria
4. mutations resulting in distinct defects in metabolic enzymatic pathways

5) According to Beadle and Tatum’s “one gene–one enzyme” hypothesis, which of the following enzymes will eliminate the transformation of hereditary material from pathogenic bacteria to nonpathogenic bacteria?

2. proteinases
3. ribonucleases
4. deoxyribonucleases

1. thymine
2. phosphodiester bonds
3. complementary base pairing
4. amino acids

7) If 30% of the bases within a DNA molecule are adenine, what is the percentage of thymine?

1. 20%
2. 25%
3. 30%
4. 35%

8) Which of the following statements about base pairing in DNA is incorrect?

1. Purines always base pairs with pyrimidines.
3. Base pairs are stabilized by hydrogen bonds.
4. Base pairing occurs at the interior of the double helix.

9) During denaturation of DNA, which of the following happens?

1. Hydrogen bonds between complementary bases break.
2. Phosphodiester bonds break within the sugar-phosphate backbone.
3. Hydrogen bonds within the sugar-phosphate backbone break.
4. Phosphodiester bonds between complementary bases break.

10) Which of the following genes would not likely be encoded on a plasmid?

1. genes encoding toxins that damage host tissue
2. genes encoding antibacterial resistance
3. gene encoding enzymes for glycolysis
4. genes encoding enzymes for the degradation of an unusual substrate

11) Histones are DNA binding proteins that are important for DNA packaging in which of the following?

1. double-stranded and single-stranded DNA viruses
2. archaea and bacteria
3. bacteria and eukaryotes
4. eukaryotes and archaea

12) DNA does all but which of the following?

1. serves as the genetic material passed from parent to offspring
2. remains constant despite changes in environmental conditions
3. provides the instructions for the synthesis of messenger RNA
4. is read by ribosomes during the process of translation

13) According to the central dogma, which of the following represents the flow of genetic information in cells?

1. protein to DNA to RNA
2. DNA to RNA to protein
3. RNA to DNA to protein
4. DNA to protein to RNA

14) Which of the following is the enzyme that replaces the RNA nucleotides in a primer with DNA nucleotides?

1. DNA polymerase III
2. DNA polymerase I
3. primase
4. helicase

15) Which of the following is not involved in the initiation of replication?

1. ligase
2. DNA gyrase
3. single-stranded binding protein
4. primase

16) Which of the following enzymes involved in DNA replication is unique to eukaryotes?

1. helicase
2. DNA polymerase
3. ligase
4. telomerase

17) Which of the following would be synthesized using 5′-CAGTTCGGA-3′ as a template?

1. 3′-AGGCTTGAC-4′
2. 3′-TCCGAACTG-5′
3. 3′-GTCAAGCCT-5′
4. 3′-CAGTTCGGA-5′

18) Which of the following types of RNA codes for a protein?

1. dsRNA
2. mRNA
3. rRNA
4. tRNA

19) A nucleic acid is purified from a mixture. The molecules are relatively small, contain uracil, and most are covalently bound to an amino acid. Which of the following was purified?

1. DNA
2. mRNA
3. rRNA
4. tRNA

20) Which of the following types of RNA is known for its catalytic abilities?

1. dsRNA
2. mRNA
3. rRNA
4. tRNA

21) Ribosomes are composed of rRNA and what other component?

1. protein
2. carbohydrates
3. DNA
4. mRNA

22) Which of the following may use RNA as its genome?

1. a bacterium
2. an archaeon
3. a virus
4. a eukaryote

23) During which stage of bacterial transcription is the σ subunit of the RNA polymerase involved?

1. initiation
2. elongation
3. termination
4. splicing

24) Which of the following components is involved in the initiation of transcription?

1. primer
2. origin
3. promoter
4. start codon

25) Which of the following is not a function of the 5’ cap and 3’ poly-A tail of a mature eukaryotic mRNA molecule?

1. to facilitate splicing
3. to aid export of the mature transcript to the cytoplasm
4. to aid ribosome binding to the transcript

26) Mature mRNA from a eukaryote would contain each of these features except which of the following?

1. exon-encoded RNA
2. intron-encoded RNA
3. 5’ cap
4. 3’ poly-A tail

27) Which of the following is the name of the three-base sequence in the mRNA that binds to a tRNA molecule?

1. P site
2. codon
3. anticodon
4. CCA binding site

28) Which component is the last to join the initiation complex during the initiation of translation?

1. the mRNA molecule
2. the small ribosomal subunit
3. the large ribosomal subunit
4. the initiator tRNA

29) During elongation in translation, to which ribosomal site does an incoming charged tRNA molecule bind?

1. A site
2. P site
3. E site
4. B site

30) Which of the following is the amino acid that appears at the N-terminus of all newly translated prokaryotic and eukaryotic polypeptides?

1. tryptophan
2. methionine
3. selenocysteine
4. glycine

31) When the ribosome reaches a nonsense codon, which of the following occurs?

1. a methionine is incorporated
2. the polypeptide is released
3. a peptide bond forms
4. the A site binds to a charged tRNA

32) Which of the following correctly describes the structure of the typical eukaryotic genome?

1. diploid
2. linear
3. singular
4. double stranded

33) Which of the following is typically found as part of the prokaryotic genome?

1. chloroplast DNA
2. linear chromosomes
3. plasmids
4. mitochondrial DNA

34) Serratia marcescens cells produce a red pigment at room temperature. The red color of the colonies is an example of which of the following?

1. genotype
2. phenotype
3. change in DNA base composition

35) Which of the following is a change in the sequence that leads to formation of a stop codon?

1. missense mutation
2. nonsense mutation
3. silent mutation
4. deletion mutation

36) The formation of pyrimidine dimers results from which of the following?

1. spontaneous errors by DNA polymerase
4. exposure to intercalating agents

37) Which of the following is an example of a frameshift mutation?

1. a deletion of a codon
2. missense mutation
3. silent mutation
4. deletion of one nucleotide

38) Which of the following is the type of DNA repair in which thymine dimers are directly broken down by the enzyme photolyase?

1. direct repair
2. nucleotide excision repair
3. mismatch repair

39) Which of the following regarding the Ames test is true?

1. It is used to identify newly formed auxotrophic mutants.
2. It is used to identify mutants with restored biosynthetic activity.
3. It is used to identify spontaneous mutants.
4. It is used to identify mutants lacking photoreactivation activity.

40) Which is the mechanism by which improper excision of a prophage from a bacterial chromosome results in packaging of bacterial genes near the integration site into a phage head?

1. conjugation
2. generalized transduction
3. specialized transduction
4. transformation

41) Which of the following refers to the uptake of naked DNA from the surrounding environment?

1. conjugation
2. generalized transduction
3. specialized transduction
4. transformation

42) The F plasmid is involved in which of the following processes?

1. conjugation
2. transduction
3. transposition
4. transformation

43) Which of the following refers to the mechanism of horizontal gene transfer naturally responsible for the spread of antibiotic resistance genes within a bacterial population?

1. conjugation
2. generalized transduction
3. specialized transduction
4. transformation

44) An operon of genes encoding enzymes in a biosynthetic pathway is likely to be which of the following?

1. inducible
2. repressible
3. constitutive
4. monocistronic

45) An operon encoding genes that are transcribed and translated continuously to provide the cell with constant intermediate levels of the protein products is said to be which of the following?

1. repressible
2. inducible
3. constitutive
4. activated

46) Which of the following conditions leads to maximal expression of the lac operon?

1. lactose present, glucose absent
2. lactose present, glucose present
3. lactose absent, glucose absent
4. lactose absent, glucose present

47) Which of the following is a type of regulation of gene expression unique to eukaryotes?

1. attenuation
2. use of alternate σ factor
3. chemical modification of histones
4. alarmones

### Fill-in-the-Blanks

48) The process of making an RNA copy of a gene is called ________.

49) A cell’s ________ remains constant whereas its phenotype changes in response to environmental influences.

50) The enzyme responsible for relaxing supercoiled DNA to allow for the initiation of replication is called ________.

51) Unidirectional replication of a circular DNA molecule like a plasmid that involves nicking one DNA strand and displacing it while synthesizing a new strand is called ________.

52) A ________ mRNA is one that codes for multiple polypeptides.

53) The protein complex responsible for removing intron-encoded RNA sequences from primary transcripts in eukaryotes is called the ________.

54) The third position within a codon, in which changes often result in the incorporation of the same amino acid into the growing polypeptide, is called the ________.

55) The enzyme that adds an amino acid to a tRNA molecule is called ________.

56) A chemical mutagen that is structurally similar to a nucleotide but has different base-pairing rules is called a ________.

57) The enzyme used in light repair to split thymine dimers is called ________.

58) The phenotype of an organism that is most commonly observed in nature is called the ________.

59) A small DNA molecule that has the ability to independently excise from one location in a larger DNA molecule and integrate into the DNA elsewhere is called a ________.

60) ________ is a group of mechanisms that allow for the introduction of genetic material from one organism to another organism within the same generation.

61) The DNA sequence, to which repressors may bind, that lies between the promoter and the first structural gene is called the ________.

62) The prevention of expression of operons encoding substrate use pathways for substrates other than glucose when glucose is present is called _______.

63) The element ____________ is unique to nucleic acids compared with other macromolecules.

64) In the late 1800s and early 1900s, the macromolecule thought to be responsible for heredity was ______________.

65) The end of a nucleic acid strand with a free phosphate group is called the ________.

66) Plasmids are typically transferred among members of a bacterial community by ________ gene transfer.

67) Why do bacteria and viruses make good model systems for various genetic studies?

68) Why was nucleic acid disregarded for so long as the molecule responsible for the transmission of hereditary information?

69) Bacteriophages inject their genetic material into host cells, whereas animal viruses enter host cells completely. Why was it important to use a bacteriophage in the Hershey–Chase experiment rather than an animal virus?

70) What is the role of phosphodiester bonds within the sugar-phosphate backbone of DNA?

71) What is meant by the term “antiparallel?”

72) Why is DNA with a high GC content more difficult to denature than that with a low GC content?

73) What are the differences between DNA nucleotides and RNA nucleotides?

74) How is the information stored within the base sequence of DNA used to determine a cell’s properties?

75) How do complementary base pairs contribute to intramolecular base pairing within an RNA molecule?

76) If an antisense RNA has the sequence 5ʹAUUCGAAUGC3ʹ, what is the sequence of the mRNA to which it will bind? Be sure to label the 5ʹ and 3ʹ ends of the molecule you draw.

77) Why does double-stranded RNA (dsRNA) stimulate RNA interference?

78) What are some differences in chromosomal structures between prokaryotes and eukaryotes?

79) How do prokaryotes and eukaryotes manage to fit their lengthy DNA inside of cells? Why is this necessary?

80) What are some functions of noncoding DNA?

81) In the chromatin of eukaryotic cells, which regions of the chromosome would you expect to be more compact: the regions that contain genes being actively copied into RNA or those that contain inactive genes?

82) Can two observably different cells have the same genotype? Explain.

83) Why is primase required for DNA replication?

84) What is the role of single-stranded binding protein in DNA replication?

85) Below is a DNA sequence. Envision that this is a section of a DNA molecule that has separated in preparation for replication, so you are only seeing one DNA strand. Construct the complementary DNA sequence (indicating 5’ and 3’ ends).

DNA sequence: 3’-T A C T G A C T G A C G A T C-5’

86) What is the purpose of RNA processing in eukaryotes? Why don’t prokaryotes require similar processing?

87) Below is a DNA sequence. Envision that this is a section of a DNA molecule that has separated in preparation for transcription, so you are only seeing the antisense strand. Construct the mRNA sequence transcribed from this template.

Antisense DNA strand: 3’-T A C T G A C T G A C G A T C-5’

89) Why does translation terminate when the ribosome reaches a stop codon? What happens?

90) How does the process of translation differ between prokaryotes and eukaryotes?

91) What is meant by the genetic code being nearly universal?

93) Below is an antisense DNA sequence. Translate the mRNA molecule synthesized using the genetic code, recording the resulting amino acid sequence, indicating the N and C termini.

Antisense DNA strand: 3’-T A C T G A C T G A C G A T C-5’

94) Why is it more likely that insertions or deletions will be more detrimental to a cell than point mutations?

95) Briefly describe two ways in which chromosomal DNA from a donor cell may be transferred to a recipient cell during the process of conjugation.

96) Describe what happens when a nonsense mutation is introduced into the gene encoding transposase within a transposon.

97) What are two ways that bacteria can influence the transcription of multiple different operons simultaneously in response to a particular environmental condition?

### Critical Thinking

98) In the first figure from this chapter, if the nuclei were contained within the stalks of Acetabularia, what types of caps would you expect from the pictured grafts?

99) Why are Hershey and Chase credited with identifying DNA as the carrier of heredity even though DNA had been discovered many years before?

100) A certain DNA sample is found to have a makeup consisting of 22% thymine. Use Chargaff’s rules to fill in the percentages for the other three nitrogenous bases.

101) In considering the structure of the DNA double helix, how would you expect the structure to differ if there was base pairing between two purines? Between two pyrimidines?

102) Identify the location of mRNA, rRNA, and tRNA in the figure.

103) Why does it make sense that tRNA and rRNA molecules are more stable than mRNA molecules?

104) A new type of bacteriophage has been isolated and you are in charge of characterizing its genome. The base composition of the bacteriophage is A (15%), C (20%), T (35%), and G (30%). What can you conclude about the genome of the virus?

105) A pure culture of an unknown bacterium was streaked onto plates of a variety of media. You notice that the colony morphology is strikingly different on plates of minimal media with glucose compared to that seen on trypticase soy agar plates. How can you explain these differences in colony morphology?

106) Why was it important that Meselson and Stahl continue their experiment to at least two rounds of replication after isotopic labeling of the starting DNA with 15N, instead of stopping the experiment after only one round of replication?

107) If deoxyribonucleotides that lack the 3’-OH groups are added during the replication process, what do you expect will occur?

108) Predict the effect of an alteration in the sequence of nucleotides in the –35 region of a bacterial promoter.

109) Label the following in the figure: ribosomal E, P, and A sites; mRNA; codons; anticodons; growing polypeptide; incoming amino acid; direction of translocation; small ribosomal unit; large ribosomal unit.

110) Prior to the elucidation of the genetic code, prominent scientists, including Francis Crick, had predicted that each mRNA codon, coding for one of the 20 amino acids, needed to be at least three nucleotides long. Why is it not possible for codons to be any shorter?

111) Below are several DNA sequences that are mutated compared with the wild-type sequence: 3’-T A C T G A C T G A C G A T C-5’. Envision that each is a section of a DNA molecule that has separated in preparation for transcription, so you are only seeing the template strand. Construct the complementary DNA sequences (indicating 5’ and 3’ ends) for each mutated DNA sequence, then transcribe (indicating 5’ and 3’ ends) the template strands, and translate the mRNA molecules using the genetic code, recording the resulting amino acid sequence (indicating the N and C termini). What type of mutation is each?

each?

 Mutated DNA Template Strand #1: 3’-T A C T G T C T G A C G A T C-5’ Complementary DNA sequence: mRNA sequence transcribed from template: Amino acid sequence of peptide: Type of mutation: Mutated DNA Template Strand #2: 3’-T A C G G A C T G A C G A T C-5’ Complementary DNA sequence: mRNA sequence transcribed from template: Amino acid sequence of peptide: Type of mutation: Mutated DNA Template Strand #3: 3’-T A C T G A C T G A C T A T C-5’ Complementary DNA sequence: mRNA sequence transcribed from template: Amino acid sequence of peptide: Type of mutation: Mutated DNA Template Strand #4: 3’-T A C G A C T G A C T A T C-5’ Complementary DNA sequence: mRNA sequence transcribed from template: Amino acid sequence of peptide: Type of mutation:

112) Why do you think the Ames test is preferable to the use of animal models to screen chemical compounds for mutagenicity?

113) The following figure is from Monod’s original work on diauxic growth showing the growth of E. coli in the simultaneous presence of xylose and glucose as the only carbon sources. Explain what is happening at points A–D with respect to the carbon source being used for growth, and explain whether the xylose-use operon is being expressed (and why). Note that expression of the enzymes required for xylose use is regulated in a manner similar to the expression of the enzymes required for lactose use.

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