Biology Chapter 16

In a nucleosome, the DNA is wrapped around

C) histones.

Which would you expect of a eukaryotic cell lacking telomerase?

D) a reduction in chromosome length

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?

E) DNA in both daughter cells would be radioactive.

Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

A) 12%

Why do histones bind tightly to DNA?

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

For a couple of decades, biologists knew the nucleus contained DNA and proteins. The prevailing opinion was that the genetic material was proteins, and not DNA. The reason for this belief was that proteins are more complex than DNA. What was the basis of this thinking?

A) Proteins have a greater variety of three-dimensional forms than does DNA.

Why does the DNA double helix have a uniform diameter?

A) Purines pair with pyrimidines.

Which is the most likely interpretation?

A) There are two replication forks going in opposite directions.

Which of the following sets of materials are required by both eukaryotes and prokaryotes for replication?

A) double-stranded DNA, 4 kinds of dNTPs, primers, origins

Which of the following separates the DNA strands during replication?

A) helicase

What kind of chemical bond is found between paired bases of the DNA double helix?

A) hydrogen

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.

The spontaneous loss of amino groups from adenine results in hypoxanthine, an uncommon base, opposite thymine in DNA. What combination of molecules could repair such damage?

A) nuclease, DNA polymerase, DNA ligase

Which of the following represents the order of increasingly higher levels of organization of chromatin?

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

What is the function of topoisomerase?

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

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?

A) sequence of bases

Which of the following can be determined directly from X-ray diffraction photographs of crystallized DNA?

A) the diameter of the helix

The leading and the lagging strands differ in that

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.

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that

A) the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.

Mendel and Morgan did not know about the structure of DNA; however, which of the following of their contributions was (were) necessary to Watson and Crick?

A) the particulate nature of the hereditary material

A typical bacterial chromosome has ~4.6 million nucleotides. This supports approximately how many genes?

B) 4.4 thousand

In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?

B) A + G = C + T

Which of the following best describes the addition of nucleotides to a growing DNA chain?

B) A nucleoside triphosphate is added to the 3ʹ end of the DNA, releasing a molecule of pyrophosphate.

Which of the following investigators was/were responsible for the following discovery? Phage with labeled proteins or DNA was allowed to infect bacteria. It was shown that the DNA, but not the protein, entered the bacterial cells, and was therefore concluded to be the genetic material.

B) Alfred Hershey and Martha Chase

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

B) DNA contains phosphorus, but protein does not.

A biochemist isolates and purifies various molecules needed for DNA replication. When she adds some DNA, 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?

B) DNA ligase

Which of the following statements describes histones?

B) Histone H1 is not present in the nucleosome bead; instead it is involved in the formation of higher-level chromatin structures.

The following scientists made significant contributions to our understanding of the structure and function of DNA. Place the scientistsʹ names in the correct chronological order, starting with the first scientist(s) to make a contribution. I. Avery, McCarty, and MacLeod II. Griffith III. Hershey and Chase IV. Meselson and Stahl V. Watson and Crick

B) II, I, III, V, IV

In his transformation experiments, what did Griffith observe?

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.

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?

B) No replication fork will be formed.

Replication in prokaryotes differs from replication in eukaryotes for which of these reasons?

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

What is meant by the description ʺantiparallelʺ regarding the strands that make up DNA?

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

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

B) The cellʹs DNA couldnʹt be packed into its nucleus.

Studies of nucleosomes have shown that histones (except H1) exist in each nucleosome as two kinds of tetramers: one of 2 H2A molecules and 2 H2B molecules, and the other as 2 H3 and 2 H4 molecules. Which of the following is supported by this data?

B) The two types of tetramers associate to form an octamer.

When T2 phages infect bacteria and make more viruses in the presence of radioactive sulfur, what is the result?

B) The viral proteins will be radioactive.

When DNA is compacted by histones into 10 nm and 30 nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this dynamic activity?

B) methylation and phosphorylation of histone tails

Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA strands that are aligned in parallel arrays. How could these arise?

B) replication without separation

About how many more genes are there in the haploid human genome than in a typical bacterial genome?

C) 1000 X

An Okazaki fragment has which of the following arrangements?

C) 5ʹ RNA nucleotides, DNA nucleotides 3ʹ

In an analysis of the nucleotide composition of DNA, which of the following will be found?

C) A + C = G + T

Which enzyme catalyzes the elongation of a DNA strand in the 5ʹ → 3ʹ direction?

C) DNA polymerase III

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

C) DNA polymerase can join new nucleotides only to the 3ʹ end of a growing strand.

Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?

C) Gaps left at the 5ʹ end of the lagging strand because of the need for a 3ʹ onto which nucleotides can attach

Which of the following statements is true of chromatin?

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

Which of the following investigators was/were responsible for the following discovery? Chemicals from heat-killed S cells were purified. The chemicals were tested for the ability to transform live R cells. The transforming agent was found to be DNA.

C) Oswald Avery, Maclyn McCarty, and Colin MacLeod

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

C) join Okazaki fragments together

Which of the following covalently connects segments of DNA?

C) ligase

In his work with pneumonia-causing bacteria and mice, Griffith found that

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

Chargaffʹs analysis of the relative base composition of DNA was significant because he was able to show that

C) the amount of A is always equivalent to T, and C to G.

What determines the nucleotide sequence of the newly synthesized strand during DNA replication?

C) the nucleotide sequence of the template strand

What is the function of DNA polymerase III?

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

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing ʺheavyʺ nitrogen ( 15N) and then transferred them to a medium containing 14N. Which of the results in Figure 16.1 would be expected after one round of DNA replication in the presence of 14N?

D

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork: 3ʹ C C T A G G C T G C A A T C C 5ʹ An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

D) 5ʹ A C G U U A G G 3ʹ

Which of the following removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3ʹ end of Okazaki fragments?

D) DNA polymerase I

After mixing a heat-killed, phosphorescent strain of bacteria with a living non-phosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observations would provide the best evidence that the ability to fluoresce is a heritable trait?

D) Descendants of the living cells are also phosphorescent.

Which of the following investigators was/were responsible for the following discovery? In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.

D) Erwin Chargaff

In prophase I of meiosis in female Drosophila, studies have shown that there is phosphorylation of an amino acid in the tails of histones. A mutation in flies that interferes with this process results in sterility. Which of the following is the most likely hypothesis?

D) Histone tail phosphorylation prohibits chromosome condensation.

Which of the following statements describes the eukaryotic chromosome?

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

Once the pattern found after one round of replication was observed, Meselson and Stahl could be confident of which of the following conclusions?

D) Replication is not conservative.

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells have which impaired ability?

D) They cannot repair thymine dimers.

The enzyme telomerase solves the problem of replication at the ends of linear chromosomes by which method?

D) adding numerous short DNA sequences such as TTAGGG, which form a hairpin turn

The elongation of the leading strand during DNA synthesis

D) depends on the action of DNA polymerase.

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?

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

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

D) single-strand binding proteins

In a linear eukaryotic chromatin sample, which of the following strands is looped into domains by scaffolding?

D) the 30 nm chromatin fiber

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 signal than labeling the phosphates. Why wonʹt this experiment work?

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

A new DNA strand elongates only in the 5ʹ to 3ʹ direction because

E) DNA polymerase can only add nucleotides to the free 3ʹ end.

What does transformation involve in bacteria?

E) assimilation of external DNA into a cell

To repair a thymine dimmer by nucleotide excision repair, in which order do the necessary enzymes act?

E) endonuclease, DNA polymerase I, DNA ligase

Which of the following synthesizes short segments of RNA?

E) primase

The DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes. What does this most probably reflect?

E) that the critical function of telomeres must be maintained

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 Figure 16.1 would you expect if the DNA was replicated in a conservative manner?

b