bio ch 13

16) A mutation is identified in a single-celled eukaryote called a protist in which DNA primase does not assemble RNA primers on the lagging strand during DNA replication. Which of the following statements correctly describes a possible result of this mutation? A) DNA replication will proceed normally. B) The leading strand will not be replicated normally. C) The lagging strand will continue to be replicated normally. D) The lagging strand will not be replicated normally.

? D) The lagging strand will not be replicated normally.

6) Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine? A) 8% B) 16% C) 31% D) 42%

A) 8%

2) What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized? A) DNA polymerase can join new nucleotides only to the 3' end of a preexisting strand. B) Helicases and single-strand binding proteins work at the 5' end. C) The origins of replication occur only at the 5' end. D) DNA ligase works only in the 3' → 5' direction.

A) DNA polymerase can join new nucleotides only to the 3' end of a preexisting strand.

35) Why do histones bind tightly to DNA? A) Histones are positively charged, and DNA is negatively charged. B) Histones are negatively charged, and DNA is positively charged. C) Both histones and DNA are strongly hydrophobic. D) Histones are covalently linked to the DNA.

A) Histones are positively charged, and DNA is negatively charged.

43) Which of the following statements accurately describes why Taq polymerase is used in PCR? A) It is heat stable and can withstand the heating step of PCR. B) Only minute amounts are needed for each cycle of PCR. C) It binds more readily than other polymerases to the primers. D) It has regions that are complementary to the primers.

A) It is heat stable and can withstand the heating step of PCR.

33) If a cell were unable to produce histone proteins, which of the following effects would likely occur? A) The cell's DNA couldn't be packed into its nucleus. B) Spindle fibers would not form during prophase. C) Expression of other genes would compensate for the lack of histones. D) DNA polymerase I would not function properly.

A) The cell's DNA couldn't be packed into its nucleus.

19) Which of the following statements correctly describes how the leading and the lagging strands of DNA formed during DNA replication differ? A) The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction. B) The leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end. C) The lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together. D) The leading strand is synthesized at twice the rate of the lagging strand.

A) The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

40) How does a bacterial cell protect its own DNA from restriction enzymes? A) by adding methyl groups to adenines and cytosines B) by using DNA ligase to seal the bacterial DNA into a closed circle C) by adding histones to protect the double-stranded DNA D) by forming "sticky ends" of bacterial DNA to prevent the enzyme from attaching

A) by adding methyl groups to adenines and cytosines

30) Which of the following sets of materials is required by both eukaryotes and prokaryotes for DNA replication? A) double-stranded DNA, four kinds of DNA nucleotides, primers, origins of replication B) topoisomerases, telomerases, polymerases C) G-C rich regions, polymerases, telomerases D) nucleosomes, four kinds of DNA nucleotides, four kinds of RNA nucleotides

A) double-stranded DNA, four kinds of DNA nucleotides, primers, origins of replication

26) During DNA replication, which of the following enzymes separates the DNA strands during replication? A) helicase B) DNA polymerase III C) ligase D) DNA polymerase I

A) helicase

2) You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent A) leading strands and Okazaki fragments. B) lagging strands and Okazaki fragments. C) Okazaki fragments and RNA primers. D) leading strands and RNA primers.

A) leading strands and Okazaki fragments.

9) The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? A) nuclease, DNA polymerase, DNA ligase B) topoisomerase, primase, DNA polymerase C) topoisomerase, helicase, single-strand binding protein D) DNA ligase, replication fork proteins, adenylyl cyclase

A) nuclease, DNA polymerase, DNA ligase

36) Which of the following lists of structures correctly represents the order of increasingly higher levels of organization of chromatin? A) nucleosome, 30-nm chromatin fiber, looped domain B) looped domain, 30-nm chromatin fiber, nucleosome C) looped domain, nucleosome, 30-nm chromatin fiber D) nucleosome, looped domain, 30-nm chromatin fiber

A) nucleosome, 30-nm chromatin fiber, looped domain

21) What is the function of topoisomerase? A) relieving strain in the DNA ahead of the replication fork B) elongating new DNA at a replication fork by adding nucleotides to the existing chain C) adding methyl groups to bases of DNA D) unwinding of the double helix

A) relieving strain in the DNA ahead of the replication fork

7) Which of the following characteristics of the structure of DNA was determined directly from X-ray diffraction photographs of crystallized DNA? A) the double helical structure B) the length of a given DNA molecule C) the sequence of nucleotides D) the frequency of A versus T nucleotides

A) the double helical structure

5) A eukaryotic gene has "sticky ends" produced by the restriction endonuclease EcoRI. The gene is added to a mixture containing EcoRI and a bacterial plasmid that carries two genes conferring resistance to the antibiotics ampicillin and tetracycline. The plasmid has one recognition site for EcoRI located in the tetracycline resistance gene. This mixture is incubated for several hours, exposed to DNA ligase, and then added to bacteria growing in nutrient broth. The bacteria are allowed to grow overnight and are streaked on a plate using a technique that produces isolated colonies that are clones of the original. Samples of these colonies are then grown in four different media: nutrient broth plus ampicillin, nutrient broth plus tetracycline, nutrient broth plus ampicillin and tetracycline, and nutrient broth without antibiotics. Bacteria that do not take up any plasmids would grow on which media? A) the nutrient broth only B) the nutrient broth and the tetracycline broth C) the nutrient broth and the ampicillin broth D) the tetracycline broth and the ampicillin broth

A) the nutrient broth only

8) Which of the following characteristics of the structure of DNA allows it to carry a large amount of hereditary information? A) the sequence of bases B) phosphate-sugar backbones C) complementary pairing of bases D) different five-carbon sugars

A) the sequence of bases

4) The segment of DNA shown in the figure above has restriction sites I and II, which create restriction fragments A, B, and C. Which of the gels produced by electrophoresis shown below best represents the separation and identity of these fragments? A) B) C) D)

B)

3) In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules? A) A = G B) A + G = C + T C) A + T = G + C D) A = C

B) A + G = C + T

42) Why is it so important to be able to amplify DNA fragments when studying genes? A) DNA fragments are too small to use individually. B) A gene may represent only a very small portion of the cell's DNA. C) Restriction enzymes cut DNA into fragments that are too small. D) A clone requires multiple copies of each gene per clone.

B) A gene may represent only a very small portion of the cell's DNA.

4) In trying to determine whether DNA or protein was the genetic material, Hershey and Chase made use of which of the following facts about these two types of molecules? A) DNA contains sulfur, whereas protein does not. B) DNA contains phosphorus, whereas protein does not. C) DNA contains nitrogen, whereas protein does not. D) DNA contains purines, whereas protein includes pyrimidines.

B) DNA contains phosphorus, whereas protein does not.

8) A student isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. After adding some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has the student probably left out of the mixture? A) DNA polymerase B) DNA ligase C) Okazaki fragments D) primase

B) DNA ligase

25) During DNA replication in E. coli, which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments? A) helicase B) DNA polymerase III C) ligase D) DNA polymerase I

B) DNA polymerase III

34) Which of the following statements correctly describes one characteristic of histones? A) Each nucleosome consists of two histones. B) Each nucleosome consists of eight histones. C) The carboxyl end of each histone extends outward from the nucleosome and is called a "histone tail." D) Histones are found in mammals but not in other eukaryotes.

B) Each nucleosome consists of eight histones.

6) Which of the following sequences in double-stranded DNA is most likely to be recognized as a cutting site for a restriction enzyme? A) AAGG TTCC B) GGCC CCGG C) ACCA TGGT D) AAAA TTTT

B) GGCC CCGG

1) In his transformation experiments, which of the following results did Griffith observe? A) Mutant mice were resistant to bacterial infections. B) Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form. C) Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic. D) Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.

B) Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.

11) Which of the following statements describes one difference between DNA replication in prokaryotes and DNA replication in eukaryotes? A) Prokaryotic chromosomes have histones, whereas eukaryotic chromosomes do not. B) Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many. C) The rate of elongation during DNA replication is slower in prokaryotes than in eukaryotes. D) Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not.

B) Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.

10) What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA? A) The twisting nature of DNA creates nonparallel strands. B) The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. C) Base pairings create unequal spacing between the two DNA strands. D) One strand contains only purines and the other contains only pyrimidines.

B) The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

14) In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation? A) No proofreading will occur. B) The DNA strands at the origin of replication will separate, but replication will not progress. C) The DNA will supercoil. D) DNA polymerase I will not function correctly.

B) The DNA strands at the origin of replication will separate, but replication will not progress.

6) A group of six students has taken samples of their own cheek cells, purified the DNA, and used a restriction enzyme known to cut at zero, one, or two sites in a particular gene of interest. Analysis of the data obtained shows that two students each have two fragments, two students each have three fragments, and two students each have one only. What does this demonstrate? A) Each pair of students has a different gene for this function. B) The two students who have two fragments have one restriction site in this region. C) The two students who have two fragments have two restriction sites within this gene. D) Each of these students is heterozygous for this gene.

B) The two students who have two fragments have one restriction site in this region.

3) Which type of enzyme was used to produce the DNA molecule in the figure above? A) ligase B) a restriction enzyme C) RNA polymerase D) DNA polymerase

B) a restriction enzyme

9) In an analysis of the nucleotide composition of DNA, which of the following will be found in a given DNA molecule? A) A = C B) A = G and C = T C) A + C = G + T D) G + C = T + A

C) A + C = G + T

15) Which enzyme in E. coli catalyzes the elongation of a DNA strand in the 5' → 3' direction? A) primase B) DNA ligase C) DNA polymerase III D) topoisomerase

C) DNA polymerase III

41) What is the most logical sequence of steps for splicing foreign DNA into a plasmid and inserting the plasmid into a bacterium? A) Transform bacteria with a recombinant DNA molecule. Cut the plasmid DNA using restriction enzymes. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments. Extract plasmid DNA from bacterial cells. Use ligase to seal plasmid DNA to nonplasmid DNA. B) Cut the plasmid DNA using restriction enzymes. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments. Use ligase to seal plasmid DNA to nonplasmid DNA. Extract plasmid DNA from bacterial cells. Transform bacteria with a recombinant DNA molecule. C) Extract plasmid DNA from bacterial cells. Cut the plasmid DNA using restriction enzymes. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments. Use ligase to seal plasmid DNA to nonplasmid DNA. Transform bacteria with a recombinant DNA molecule. D) Extract plasmid DNA from bacterial cells. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments. Use ligase to seal plasmid DNA to nonplasmid DNA. Transform bacteria with a recombinant DNA molecule. Cut the plasmid DNA using restriction enzymes.

C) Extract plasmid DNA from bacterial cells. Cut the plasmid DNA using restriction enzymes. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments. Use ligase to seal plasmid DNA to nonplasmid DNA. Transform bacteria with a recombinant DNA molecule.

37) Which of the following statements correctly describes one difference between heterochromatin and euchromatin? A) Heterochromatin is composed of DNA, whereas euchromatin is made of DNA and RNA. B) Heterochromatin is found in the cytoplasm while euchromatin is found in the nucleus. C) Heterochromatin is highly condensed, whereas euchromatin is less compact. D) Euchromatin is not transcribed, whereas heterochromatin is transcribed.

C) Heterochromatin is highly condensed, whereas euchromatin is less compact.

13) Which of the following statements correctly describes one characteristic of DNA replication in eukaryotes? A) In the leading strand, DNA is replicated in short pieces called Okazaki fragments, which are then joined together at the end of the process. B) DNA is replicated in the 3' to 5' direction in the leading strand. C) In the lagging strand, DNA is replicated in short pieces called Okazaki fragments, which are then joined together at the end of the process. D) Helicase joins the Okazaki fragments together in the lagging strand.

C) In the lagging strand, DNA is replicated in short pieces called Okazaki fragments, which are then joined together at the end of the process.

22) What is the role of DNA ligase in the elongation of the lagging strand during DNA replication? A) It synthesizes RNA nucleotides to make a primer. B) It catalyzes the lengthening of telomeres. C) It joins Okazaki fragments together. D) It unwinds the parental double helix.

C) It joins Okazaki fragments together.

39) Assume that you are trying to insert a gene into a plasmid. Someone gives you a preparation of genomic DNA that has been cut with restriction enzyme X. The gene you wish to insert has sites on both ends for cutting by restriction enzyme Y. You have a plasmid with a single site for Y but not for X. Your strategy should be to A) insert the fragments cut with restriction enzyme X directly into the plasmid without cutting the plasmid. B) cut the plasmid with restriction enzyme X, and insert the fragments cut with restriction enzyme Y into the plasmid. C) cut the DNA again with restriction enzyme Y, and insert these fragments into the plasmid cut with the same enzyme. D) cut the plasmid twice with restriction enzyme Y, and ligate the two fragments onto the ends of the DNA fragments cut with restriction enzyme X.

C) cut the DNA again with restriction enzyme Y, and insert these fragments into the plasmid cut with the same enzyme.

5) In a nucleosome, the DNA is wrapped around A) polymerase molecules. B) ribosomes. C) histones. D) a thymine dimer.

C) histones.

38) Which of the following modifications is most likely to alter the rate at which a DNA fragment moves through a gel during electrophoresis? A) altering the nucleotide sequence of the DNA fragment without adding or removing nucleotides B) radioactively labeling the cytosine bases within the DNA fragment C) increasing the length of the DNA fragment D) leaving the length of the DNA fragment the same

C) increasing the length of the DNA fragment

27) During DNA replication, which of the following enzymes covalently connects segments of DNA? A) helicase B) DNA polymerase III C) ligase D) DNA polymerase I

C) ligase

29) Which of the following mechanisms removes nucleotides that are paired incorrectly during DNA replication? A) nucleotide excision repair B) chromosomal breakage repair C) mismatch repair D) telomerase activity

C) mismatch repair

1) In his work with pneumonia-causing bacteria and mice, Griffith found that A) the protein coat from pathogenic cells was able to transform nonpathogenic cells. B) heat-killed pathogenic cells caused pneumonia. C) some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. D) the polysaccharide coat of bacteria caused pneumonia.

C) some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic.

18) What is the function of DNA polymerase III in replication in E. coli? A) to unwind the DNA helix during replication B) to seal together the broken ends of DNA strands C) to add nucleotides to the 3' end of a growing DNA strand D) to degrade damaged DNA molecules

C) to add nucleotides to the 3' end of a growing DNA strand

1) For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger radioactive signal than labeling the phosphates. Why won't this experiment work? A) There is no radioactive isotope of nitrogen. B) The phosphate in normal DNA is naturally radioactive. C) Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive. D) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

D) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

1) In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (15N) and then transferred them to a medium containing 14N, which is a nonradioactive form of nitrogen. They then extracted DNA from the bacteria and centrifuged it to separate the DNA of different densities. Which of the results in figure above would be expected after one round of DNA replication in the presence of 14N? A) A B) B C) C D) D

D) D

12) Suppose you are provided with an actively dividing culture of Escherichia coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? A) One of the daughter cells, but not the other, would have radioactive DNA. B) Neither of the two daughter cells would be radioactive. C) All four bases of the DNA would be radioactive. D) DNA in both daughter cells would be radioactive.

D) DNA in both daughter cells would be radioactive.

28) In E. coli, which of the following enzymes removes the RNA primer from the 5' end of the DNA fragment? A) helicase B) DNA polymerase III C) ligase D) DNA polymerase I

D) DNA polymerase I

20) Why does a new DNA strand elongate only in the 5' to 3' direction in replication? A) DNA polymerase begins adding nucleotides at the 5' end of the template. B) Okazaki fragments prevent elongation in the 3' to 5' direction. C) Replication must progress toward the replication fork. D) DNA polymerase can only add nucleotides to the free 3' end.

D) DNA polymerase can only add nucleotides to the free 3' end.

3) After mixing a heat-killed, phosphorescent (light-emitting) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observation(s) would provide the best evidence that the ability to phosphoresce is a heritable trait? A) DNA passed from the heat-killed strain to the living strain. B) Protein passed from the heat-killed strain to the living strain. C) The phosphorescence in the living strain is especially bright. D) Descendants of the living cells are also phosphorescent.

D) Descendants of the living cells are also phosphorescent.

32) Which of the following statements best describes the eukaryotic chromosome? A) It is composed of DNA alone. B) The nucleosome is its most basic functional subunit. C) The number of genes on each chromosome is different in different cell types of an organism. D) It consists of a single linear molecule of double-stranded DNA plus proteins.

D) It consists of a single linear molecule of double-stranded DNA plus proteins.

2) In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (15N) and then transferred them to a medium containing 14N, which is a less radioactive form of nitrogen. They then extracted DNA from the bacteria and centrifuged it to separate the DNA of different densities. Once the pattern found after one round of replication was observed, Meselson and Stahl could be confident of which of the following conclusions? A) Replication is semiconservative. B) Replication is not dispersive. C) Replication is not semiconservative. D) Replication is not conservative.

D) Replication is not conservative.

5) Which of the following statements correctly describes one of Chargaff's rules regarding DNA? A) The percentages of adenine and cytosine are roughly equal, as are the percentages of guanine and thymine in the DNA of a given species. B) DNA has a double helical structure. C) DNA base composition does not vary between species. D) The percentages of adenine and thymine are roughly equal, as are the percentages of guanine and cytosine in the DNA of a given species.

D) The percentages of adenine and thymine are roughly equal, as are the percentages of guanine and cytosine in the DNA of a given species.

24) Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. What function is impaired in their cells? A) They cannot replicate DNA. B) They cannot undergo mitosis. C) They cannot exchange DNA with other cells. D) They cannot repair thymine dimers.

D) They cannot repair thymine dimers.

2) Which of the following statements most accurately describes transformation in bacteria? A) Transformation is the creation of a strand of DNA from an RNA molecule. B) Transformation is the creation of a strand of RNA from a DNA molecule. C) Transformation is the infection of cells by a phage DNA molecule. D) Transformation is the assimilation of external DNA into a cell.

D) Transformation is the assimilation of external DNA into a cell.

4) The elongation of the leading strand during DNA synthesis A) progresses away from the replication fork. B) occurs in the 3' → 5' direction. C) produces Okazaki fragments. D) depends on the action of DNA polymerase.

D) depends on the action of DNA polymerase.

3) A eukaryotic gene has "sticky ends" produced by the restriction endonuclease EcoRI. The gene is added to a mixture containing EcoRI and a bacterial plasmid that carries two genes conferring resistance to the antibiotics ampicillin and tetracycline. The plasmid has one recognition site for EcoRI located in the tetracycline resistance gene. This mixture is incubated for several hours, exposed to DNA ligase, and then added to bacteria growing in nutrient broth. The bacteria are allowed to grow overnight and are streaked on a plate using a technique that produces isolated colonies that are clones of the original. Samples of these colonies are then grown in four different media: nutrient broth plus ampicillin, nutrient broth plus tetracycline, nutrient broth plus ampicillin and tetracycline, and nutrient broth without antibiotics. Bacteria that contain the plasmid, but not the eukaryotic gene, would grow in which of the following conditions? A) in the nutrient broth plus ampicillin, but not in the broth containing tetracycline B) only in the broth containing both antibiotics C) in the broth containing tetracycline, but not in the broth containing ampicillin D) in all four types of broth

D) in all four types of broth

4) A eukaryotic gene has "sticky ends" produced by the restriction endonuclease EcoRI. The gene is added to a mixture containing EcoRI and a bacterial plasmid that carries two genes conferring resistance to the antibiotics ampicillin and tetracycline. The plasmid has one recognition site for EcoRI located in the tetracycline resistance gene. This mixture is incubated for several hours, exposed to DNA ligase, and then added to bacteria growing in nutrient broth. The bacteria are allowed to grow overnight and are streaked on a plate using a technique that produces isolated colonies that are clones of the original. Samples of these colonies are then grown in four different media: nutrient broth plus ampicillin, nutrient broth plus tetracycline, nutrient broth plus ampicillin and tetracycline, and nutrient broth without antibiotics. Bacteria containing a plasmid into which the eukaryotic gene has been inserted would grow in which of the following conditions? A) in the nutrient broth only B) in the nutrient broth and the tetracycline broth only C) in the nutrient broth, the ampicillin broth, and the tetracycline broth D) in the ampicillin broth and the nutrient broth

D) in the ampicillin broth and the nutrient broth

17) In which order do the necessary enzymes act to repair a thymine dimer by nucleotide excision repair? A) nuclease, DNA polymerase, RNA primase B) helicase, DNA polymerase, DNA ligase C) DNA ligase, nuclease, helicase D) nuclease, DNA polymerase, DNA ligase

D) nuclease, DNA polymerase, DNA ligase

7) E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment? A) one high-density and one low-density band B) one intermediate-density band C) one high-density and one intermediate-density band D) one low-density and one intermediate-density band

D) one low-density and one intermediate-density band

23) Which of the following molecule(s) help(s) to hold the DNA strands apart while they are being replicated? A) primase B) ligase C) DNA polymerase D) single-strand binding proteins

D) single-strand binding proteins

31) In a linear eukaryotic chromatin sample, which of the following strands is looped into nucleosomes? A) DNA without attached histones B) RNA primers C) the 10-nm chromatin fiber D) the 30-nm chromatin fiber

D) the 30-nm chromatin fiber