chp 16

The elongation of the leading strand during DNA synthesis

depends on the action of DNA polymerase.

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?

dna

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

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

In a nucleosome, the DNA is wrapped around

histones

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

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

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?

nuclease, DNA polymerase, DNA ligase

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

nucleosome, 30-nm chromatin fiber, looped domain

What process repairs damage to a preexisting double helix?

nucleotide excision repair

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?

one low-density and one intermediate-density band

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?

phosphorescence in descendants of the living cells

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?

sequence of bases

Semiconservative replication involves a template. What is the template?

single strand of DNA molecule

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

single-strand DNA binding proteins

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

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

What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?

telomeres

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?

the 3' OH

What are telomeres?

the ends of linear chromosomes

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

A + C = G + T

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

A + G = C + T

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?

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

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?

B. 15n and 14n

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

Cells age and begin to lose function.

What are chromosomes made of?

DNA and proteins

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

DNA contains phosphorus, whereas protein does not.

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?

DNA in both daughter cells would be radioactive.

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?

DNA ligase

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

DNA polymerase III

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

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

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

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

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?

DNA replication is semiconservative.

DNA replication is said to be semiconservative. What does this mean?

Each new double helix consists of one old and one new strand.

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?

Erwin Chargaff

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

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

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

Heterochromatin is highly condensed, whereas euchromatin is less compact.

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

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

Which of the following molecular characteristics cause histones to bind tightly to DNA?

Histones are positively charged, and DNA is negatively charged.

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

Histones are positively charged.

Which of the following is true of DNA during interphase?

It exists as chromatin and is less condensed than mitotic chromosomes.

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

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

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

It joins Okazaki fragments together.

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?

It permits complementary base pairing.

What is the function of helicase in DNA replication?

It untwists the double helix and separates the two DNA strands.

In his transformation experiments, what phenomenon did Griffith observe?

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 of replication. Which of the following events would you expect to occur as a result of this mutation?

No replication fork will be formed.

Which of the following statements accurately describes the differences between DNA replication in prokaryotes and DNA replication in eukaryotes?

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

In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding?

Radioactively labeled phosphorus was present inside the infected bacteria.

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?

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

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

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

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

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

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

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

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

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.

Griffith's experiments with S. pneumoniae were significant because they showed that traits could be transferred from one organism to another. What else did he find that was significant?

The transferred traits were heritable.

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

a reduction in chromosome length in gametes

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?

22%

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?

8%