In his transformation experiments, what phenomenon did Griffith observe?

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

B) Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.

C) Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.

D) Mice infected with a pathogenic strain of bacteria can spread the infection to other mice.

Answer A

Which of the following statements describes the process of transformation in bacteria?

A) A strand of DNA is created from an RNA molecule.

B) A strand of RNA is created from a DNA molecule.

C) Bacterial cells are infected by a phage DNA molecule.

D) External DNA is taken into a cell, becoming part of the cell's genome.

Answer D

A heat-killed, phosphorescent (light-emitting) strain of bacteria is mixed with a living, non-phosphorescent strain. Further observations of the mixture show that some of the living cells are now phosphorescent. Which of the following observations would provide the best evidence that the ability to phosphoresce is a heritable trait?

A) evidence that DNA was passed from the heat-killed strain to the living strain

B) evidence that protein passed from the heat-killed strain to the living strain

C) especially bright phosphorescence in the living strain

D) phosphorescence in descendants of the living cells

Answer D

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?

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.

Answer B

Which of the following investigators was (were) responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?

A) Alfred Hershey and Martha Chase

B) Oswald Avery, Maclyn McCarty, and Colin MacLeod

C) Erwin Chargaff

D) Matthew Meselson and Franklin Stahl

Answer C

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) 42%

D) 58%

Answer A

Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?

A) 8%

B) 16%

C) 22%

D) 72%

Answer C

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?

A) sequence of bases

B) phosphate-sugar backbones

C) complementary pairing of bases

D) side groups of nitrogenous bases

Answer A

In an analysis of the nucleotide composition of a molecule of DNA, which of the following combinations of base pairs will be found?

A) A = C

B) A = G and C = T

C) A + C = G + T

D) G + C = T + A

Answer C

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

A) There is no radioactive isotope of nitrogen.

B) Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long.

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.

Answer D

Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?

A) protein

B) RNA

C) ribosome

D) DNA

Answer D

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?

A) the 5' phosphate

B) C6

C) the 3' OH

D) a nitrogen from the nitrogen-containing base

Answer C

Which of the following statements accurately describes the differences 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.

Answer B

What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?

A) The double helix structure 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.

Answer B

Suppose you are provided with an actively dividing culture of E. 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.

Answer D

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) Additional proofreading will occur.

B) No replication fork will be formed.

C) Replication will occur via RNA polymerase alone.

D) Replication will require a DNA template from another source.

Answer B

In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?

A) primase

B) DNA ligase

C) DNA polymerase III

D) helicase

Answer C

Which of the following characteristics of eukaryotic telomeres cause them to replicate differently than the rest of the chromosome?

A) the activity of telomerase enzyme

B) DNA polymerase that cannot replicate the leading strand template to its 5' end

C) gaps left at the 5' end of the lagging strand template

D) gaps left at the 3' end of the lagging strand because of the need for a primer

Answer C

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?

A) It adds a single 5' cap structure that resists degradation by nucleases.

B) It causes specific double-strand DNA breaks that result in blunt ends on both strands.

C) It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.

D) It adds numerous GC pairs, which resist hydrolysis and maintain chromosome integrity.

Answer C

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork:

3' C C T A G G C T G C A A T C C 5'

An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

A) 5' G C C T A G G 3'

B) 5' A C G T T A G G 3'

C) 5' A C G U U A G G 3'

D) 5' G C C U A G G 3'

Answer C

In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

A) nuclease, DNA polymerase, RNA primase

B) helicase, DNA polymerase, DNA ligase

C) DNA ligase, nuclease, helicase

D) nuclease, DNA polymerase, DNA ligase

Answer D

In E. coli, what is the function of DNA polymerase III?

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

Answer C

Which of the following statements correctly describes the difference between ATP and the nucleotides used during DNA synthesis?

A) The nucleotides have the sugar deoxyribose; ATP has the sugar ribose.

B) The nucleotides have two phosphate groups; ATP has three phosphate groups.

C) ATP contains three high-energy bonds; the nucleotides have two.

D) ATP is found only in human cells; the nucleotides are found in all animal and plant cells.

Answer A

Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA during DNA replication?

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.

Answer A

Why does a new DNA strand elongate only in the 5' to 3' direction during DNA replication?

A) DNA polymerase begins adding nucleotides at the 5' end of the template.

B) The polarity of the DNA molecule prevents addition of nucleotides at the 3' end.

C) Replication must progress toward the replication fork.

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

Answer D

What is the function of the enzyme topoisomerase in DNA replication?

A) relieving strain in the DNA ahead of the replication fork caused by the untwisting of the double helix

B) elongating new DNA at a replication fork by adding nucleotides to the existing chain

C) reattaching the hydrogen bonds between the base pairs in the double helix

D) building RNA primers using the parental DNA strand as a template

Answer A

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 joins Okazaki fragments together.

C) It unwinds the parental double helix.

D) It stabilizes the unwound parental DNA.

Answer B

Which of the following types of molecules help to hold the DNA strands apart while they are being replicated?

A) primase

B) ligase

C) DNA polymerase

D) single-strand DNA binding proteins

Answer D

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight, and mutations to the DNA in their skin cells are left uncorrected. Why are the mutations not corrected in individuals with this disorder?

A) The disorder makes cells unable to replicate DNA.

B) The disorder causes mitosis to stop during metaphase.

C) The disorder makes cells unable to form chromosomes.

D) The disorder causes cells to be unable to repair thymine dimers

Answer D

Which of the following characteristics would you expect of a eukaryotic organism that lacks the enzyme telomerase?

A) a high probability of somatic cells becoming cancerous

B) an inability to produce Okazaki fragments

C) an inability to repair thymine dimers

D) a reduction in chromosome length in gametes

Answer D

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 (non-radioactive). Which of the results in the figure would be expected after one round of DNA replication in the presence of 14N?

A) A

B) B

C) C

D) D

Answer D

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in the figure would you expect if the DNA was replicated in a conservative manner?

A) A

B) B

C) C

D) D

Answer B

After the first replication was observed in their experiments testing the nature of DNA replication, Meselson and Stahl could be confident of which of the following conclusions?

A) Replication is semi-conservative.

B) Replication is not dispersive.

C) Replication is not conservative.

D) Replication is neither dispersive nor conservative.

Answer C

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). Which two classes of DNA do these different samples 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

Answer A

Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine, and cytosine forms hydrogen bonds with guanine. What is the significance of the structural arrangement?

A) It allows variable width of the double helix.

B) It permits complementary base pairing.

C) It determines the tertiary structure of a DNA molecule.

D) It determines the type of protein produced.

Answer B

Semiconservative replication involves a template. What is the template?

A) single-stranded binding proteins

B) DNA polymerase

C) one strand of the DNA molecule

D) an RNA molecule

Answer C

In DNA replication, the resulting daughter molecules contain one strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?

A) DNA replication is semiconservative.

B) DNA replication is conservative.

C) DNA replication is not conservative.

D) RNA synthesis is conservative.

Answer A

Who performed classic experiments that supported the semiconservative model of DNA replication?

A) Watson and Crick

B) Meselson and Stahl

C) Hershey and Chase

D) Franklin and Wilkins

Answer B

DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed during DNA replication?

A) ribozymes

B) DNA polymerase

C) ATP

D) RNA primers

Answer B

Referring to the figure, what bases will be added to the primer as DNA replication proceeds?

A) 5′ C, A, G, C, A, G, A 3′

B) 3′ T, C, T, G, C, T, G 5′

C) 5′ A, G, A, C, G, A, C 3′

D) 3′ G, T, C, G, T, C, T 5′

Answer C

Which of the following statements correctly describes the difference between the leading strand and the lagging strand in DNA replication?

A) The leading strand is synthesized in the 3' → 5' direction in a discontinuous fashion, while the lagging strand is synthesized in the 5' → 3' direction in a continuous fashion.

B) The leading strand is synthesized continuously in the 5' → 3' direction, while the lagging strand is synthesized discontinuously in the 5' → 3' direction.

C) The leading strand requires an RNA primer, whereas the lagging strand does not.

D) There are different DNA polymerases involved in elongation of the leading strand and the lagging strand.

Answer B

What are telomeres?

A) the structures that hold two sister chromatids together

B) enzymes that elongate the DNA strand during replication

C) the sites of origin of DNA replication

D) the ends of linear chromosomes

Answer D

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?

A) Telomerase will speed up the rate of cell proliferation.

B) Telomerase eliminates telomere shortening and retards aging.

C) Telomerase shortens telomeres, which delays cellular aging.

D) Telomerase would have no effect on cellular aging.

Answer B

Which of the following types of cells are affected most by telomere shortening?

A) only prokaryotic cells

B) only eukaryotic cells

C) cells in prokaryotes and eukaryotes

D) only animal cells

Answer B

Which of the following effects might be caused by reduced or very little active telomerase activity?

A) Cells may become cancerous.

B) Telomere lengthens in germ cells.

C) Cells age and begin to lose function.

D) Cells maintain normal functioning.

Answer C

Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results?

A) The single-strand binding proteins were malfunctioning during DNA replication.

B) There were one or more base pair mismatches in the RNA primer.

C) The proofreading mechanism of DNA polymerase was not working properly.

D) The DNA polymerase was unable to add bases to the 3′ end of the growing nucleic acid chain.

Answer C

In a healthy eukaryotic cell, the rate of DNA repair is typically equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?

A) The cell can be transformed into a cancerous cell.

B) RNA may be used instead of DNA as inheritance material.

C) DNA replication will proceed more quickly.

D) DNA replication will continue by a new mechanism.

Answer A

Which of the following statements accurately describes the structure of a eukaryotic chromosome?

A) It is composed of a single strand of DNA.

B) It is constructed as a series of nucleosomes wrapped around two DNA molecules.

C) It has different numbers of genes in different cell types of an organism.

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

Answer D

If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?

A) There would be an increase in the amount of DNA produced during replication.

B) The cell's DNA could not be packed into its nucleus.

C) Spindle fibers would not form during prophase.

D) Amplification of other genes would compensate for the lack of histones.

Answer B

Which of the following statements accurately describes one characteristic of histones?

A) Each nucleosome consists of two molecules of histone H1.

B) Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.

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 animals or in plants or fungi.

Answer B

Which of the following molecular characteristics cause histones to 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.

Answer A

Which of the following lists 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) nucleosome, looped domain, 30-nm chromatin fiber

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

Answer A

Which of the following statements correctly describes the structure of chromatin?

A) Heterochromatin is composed of DNA, whereas euchromatin is made of DNA and RNA.

B) Both heterochromatin and euchromatin are found in the cytoplasm.

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

D) Euchromatin is not transcribed, whereas heterochromatin is transcribed.

Answer C

Which of the following structural characteristics is most critical for the association between histones and DNA?

A) Histones are small proteins.

B) Histones are highly conserved (that is, histones are very similar in every eukaryote).

C) There are at least five different histone proteins in every eukaryote.

D) Histones are positively charged.

Answer D

In DNA replication in E. coli, the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following results would you expect?

A) Replication would only occur on the leading strand.

B) Replication would only occur on the lagging strand.

C) Replication would not occur on either the leading or lagging strand.

D) Replication would not be affected as the enzyme primase in involved with RNA synthesis.

Answer C

Hershey and Chase used a DNA-based virus for their work. How might the results have been different if they had used an RNA virus?

A) With an RNA virus, radioactive protein would have been in the final pellet.

B) With an RNA virus, radioactive RNA would have been in the final pellet.

C) With an RNA virus, neither sample would have had a radioactive pellet.

D) With an RNA virus, the protein shell would have been radioactive in both samples.

Answer B

The lagging strand is characterized by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki fragments gave evidence for which of the following ideas?

A) DNA polymerase is an enzyme that synthesizes leading and lagging strands during replication only in one direction.

B) DNA is a polymer consisting of four monomers: adenine, thymine, guanine, and cytosine.

C) DNA is the genetic material.

D) Bacterial replication is fundamentally different from eukaryotic replication. The key should not be way longer than the distractors.

Answer A

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.

Answer C

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

A) The origins of replication occur only at the 5′ end.

B) Helicases and single-strand binding proteins work at the 5′ end.

C) DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel.

D) DNA ligase works only in the 3′ → 5′ direction.

Answer C

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

Answer B

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.

Answer D

In a nucleosome, the DNA is wrapped around

A) histones.

B) ribosomes.

C) polymerase molecules.

D) a thymine dimer.

Answer A

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

Answer D

A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds 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 she probably left out of the mixture?

A) DNA polymerase

B) DNA ligase

C) Okazaki fragments

D) primase

Answer B

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) telomerase, primase, DNA polymerase

C) telomerase, helicase, single-strand binding protein

D) DNA ligase, replication fork proteins, adenylyl cyclase

Answer A