BIO 111- Chapter 13

Why were many of the early experiments on DNA carried out on viruses and bacteria?

(All) They have short generation times. They have relatively small genomes. Their chromosomes have a simpler structure. They can interact with each other.

The sticky end of the DNA restriction fragment shown here will pair with a DNA restriction fragment with the sticky end _____.

-ACGT

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?

-C A B+

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.

1' ... 5'

DNA polymerase adds nucleotides to the __________ of the leading strands and to the __________ of the lagging strands (Okazaki fragments).

3' end; 3' end

Hershey and Chase used _____ to radioactively label the T2 phage's proteins.

35S

Nucleic acids are assembled in the _____ direction.

5' to 3'

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%

In an analysis of the nucleotide composition of DNA, which of the following will be found in a given DNA molecule?

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

Why is it so important to be able to amplify DNA fragments when studying genes?

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

Which of the following sequences in double-stranded DNA is most likely to be recognized as a cutting site for a restriction enzyme?

AAAA TTTT

Which of the following statements concerning the structure of DNA is correct?

Adenine forms two hydrogen bonds with thymine; guanine forms three hydrogen bonds with cytosine.

Some bacteria may be able to respond to environmental stress by increasing the rate at which mutations occur during cell division. How might this be accomplished? Might there be an evolutionary advantage of this ability? Explain

All an increase in the amount of mistakes in DNA replication the movement of mobile genetic elements horizontal gene transfer If the frequency of mutations increases, so does the probability of adaptations to new conditions. Thus, this species is more likely to survive.

Which of the following statements about origins of replication is correct?

All of the listed responses are correct. In both prokaryotes and eukaryotes, replication proceeds in both directions from each origin. In bacteria, the DNA sequence at the origin is recognized by specific proteins that then bind to the origin. Bacterial chromosomes have a single origin, but eukaryotic chromosomes have many origins. The two strands of DNA at the origin are separated, allowing the formation of a replication bubble.

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 nitrogen's. Thus, labeling the nitrogen's would provide a stronger radioactive 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.

In the accompanying image, a nucleotide is indicated by the letter _____.

B

What is the major difference between bacterial chromosomes and eukaryotic chromosomes?

Bacteria have a single circular chromosome, whereas eukaryotes have several linear chromosomes.

A nitrogenous base is indicated by the letter _____.

C

Which of these is(are) pyrimidines?

C, D, E

Duplication of chromosomes occurs during S phase of the cell cycle. Duplication requires the separation of complementary DNA strands to allow for DNA replication. Which of the following statements best explains how weak hydrogen bonds function better in this situation than stronger bonds would?

Complementary DNA strands are separated or "unzipped" for the replication process. Weak hydrogen bonds between complementary strands are easily disrupted during DNA replication because they are not high-energy chemical bonds.

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?

D

Which of these is responsible for catalyzing the formation of an RNA primer?

D

The radioactive isotope 32P labels the T2 phage's _____.

DNA

What are chromosomes made of?

DNA and proteins

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?

DNA contains phosphorus, whereas protein does not

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?

DNA in both daughter cells would be radioactive.

What did Rosalind Franklin's famous photo 51 show?

DNA is a helix

Early, flawed DNA models proposed by Watson and Crick and by Linus Pauling correctly described which property of DNA?

DNA is composed of sugars, phosphates, and bases.

Which of these is a difference between a DNA and an RNA molecule?

DNA is usually double-stranded, whereas RNA is usually single-stranded.

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?

DNA ligase

What enzyme joins Okazaki fragments?

DNA ligase

What catalyzes DNA synthesis?

DNA polymerase

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?

DNA polymerase I

In E. coli, which of the following enzymes removes the RNA primer from the 5' end of the DNA fragment?

DNA polymerase I

Which enzyme in E. coli catalyzes the elongation of a DNA strand in the 5' → 3' direction?

DNA polymerase III

Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?

DNA polymerase can assemble DNA only in the 5' to 3' direction

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 preexisting strand.

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

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

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

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

Select the most accurate statement describing DNA replication complexes.

DNA replication complexes are grouped into factories, which are anchored to the nuclear matrix.

Meselson and Stahl cultured E. coli for several generations in a medium with a heavy isotope of nitrogen, 15N. They transferred the bacteria to a medium with a light isotope of nitrogen, 14 N. After two rounds of DNA replication, half the DNA molecules were light (both strands had 14N) and half were hybrids (15N-14N). What did the researchers conclude from these results?

DNA replication is semiconservative.

During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so?

DNA synthesis can take place only in the 5' to 3' direction.

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?

Descendants of the living cells are also phosphorescent.

Which of these DNA molecules is the shortest?

E (The shorter the DNA molecule, the farther it moves.)

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 statements correctly describes one characteristic of histones?

Each nucleosome consists of eight histones.

What is the most logical sequence of steps for splicing foreign DNA into a plasmid and inserting the plasmid into a bacterium?

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.

Who conducted the X-ray diffraction studies that were key to the discovery of the structure of DNA?

Franklin

Who demonstrated that DNA is the genetic material of the T2 phage?

Hershey and Chase

Which of the following statements correctly describes one difference between heterochromatin and euchromatin?

Heterochromatin is highly condensed, whereas euchromatin is less compact.

Why do histones bind tightly to DNA?

Histones are positively charged, and DNA is negatively charged.

Nucleotides are added to a growing DNA strand as nucleoside triphosphates. What is the significance of this fact?

Hydrolysis of the two phosphate groups (P-Pi) and DNA polymerization are a coupled exergonic reaction.

Which of the following statements correctly describes one characteristic of DNA replication in eukaryotes?

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

Which of the following statements best describes the eukaryotic chromosome?

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

Which of the following is true of DNA during interphase?

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

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

It joins Okazaki fragments together

What is the function of helicase in DNA replication?

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

In the early 1950s, many researchers were racing to describe the structure of DNA using different approaches. Which of the following statements is true?

Jim Watson and Francis Crick built theoretical models, incorporating current knowledge about chemical bonding and X-ray data.

In his transformation experiments, which of the following results 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.

Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?

Phosphate groups

Which of the following enzymes creates a primer for DNA polymerase?

Primase

Which of the following statements about DNA synthesis is true?

Primers are short sequences that allow the initiation of DNA synthesis.

Which of the following statements describes one difference between DNA replication in prokaryotes and DNA replication in eukaryotes?

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

The synthesis of a new strand begins with the synthesis of a(n) _____.

RNA primer complementary to a preexisting DNA strand

Which of the following components is required for DNA replication?

RNA primers

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 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?

Replication is not conservative.

Once the DNA at the replication fork is unwound by helicases, what prevents the two strands from coming back together to re-form a double helix?

Single-strand binding proteins bind the unwound DNA and prevent the double helix from re-forming.

One strand of a double-stranded DNA molecule has the base sequence 5'-ATAGGT-3'. The complementary base sequence on the other strand of DNA will be 3'-__________-5'.

TATCCA

What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA?

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

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?

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

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

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

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?

The lagging strand will not be replicated normally.

Which of the following statements correctly describes how the leading and the lagging strands of DNA formed during DNA replication differ?

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.

DNA is a self-replicating molecule. What accounts for this important property of DNA?

The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C

Which of the following statements correctly describes one of Chargaff's rules regarding DNA?

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

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.

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?

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

Which of the following statements about Okazaki fragments in E. coli is true?

They are formed on the lagging strand of DNA.

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. What function is impaired in their cells?

They cannot repair thymine dimers.

Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?

Topoisomerase

Which of the following statements most accurately describes transformation in bacteria?

Transformation is the assimilation of external DNA into a cell.

True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions.

True

Archaeologists unearthed a human skull with a small dried fragment of the scalp still attached. They extracted a tiny amount of DNA from the scalp tissue. How could they obtain sufficient DNA for an analysis of the ancient human's genes?

Use the polymerase chain reaction.

Which of the following lists is in order from the entity with the smallest genome to the entity with the largest genome?

Virus, bacteria, eukaryote

Who is credited with discovering the structure of the DNA double helix?

Watson and Crick

What technique was most helpful to Watson and Crick in developing their model for the structure of DNA?

X-ray crystallography

Which type of enzyme was used to produce the DNA molecule in the figure above? Which type of enzyme was used to produce the DNA molecule in the figure above? RNA polymerasea restriction enzymeDNA polymeraseligase

a restriction enzyme

In recombinant DNA experiments, what is used to cut pieces of DNA and what joins the resulting fragments to form recombinant DNA?

a restriction enzyme ... DNA ligase

In DNA, the two purines are __________, and the two pyrimidines are __________.

adenine and guanine; cytosine and thymine

The role of DNA polymerases in DNA replication is to __________.

attach free nucleotides to the new DNA strand

How does a bacterial cell protect its own DNA from restriction enzymes?

by adding methyl groups to adenines and cytosines

The incorporation of an incorrect base into a DNA molecule during replication __________.

can be repaired by the mismatch repair system

In the 1950s, when Watson and Crick were working on their model of DNA, which concepts were well accepted by the scientific community?

chromosomes are made up of protein and nucleic acid; genes are located on chromosomes; chromosomes are found in the nucleus

The bonds or interactions that hold together adjacent nucleotides in the sugar-phosphate backbone of DNA are

covalent bonds

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

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

The elongation of the leading strand during DNA synthesis

depends on the action of DNA polymerase

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

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

After DNA replication is completed, _____.

each new DNA double helix consists of one old DNA strand and one new DNA strand

Which of the following functions in the regulation of gene expression?

euchromatin

During Griffith's experiments with Streptococcus pneumoniae in mice, material from __________ bacteria transformed __________ bacteria.

heat-killed virulent; living nonvirulent

During DNA replication, which of the following enzymes separates the DNA strands during replication?

helicase

The first step in the replication of DNA is catalyzed by _____.

helicase

In a nucleosome, the DNA is wrapped around __________.

histones

The bonds or interactions that hold together complementary bases from opposite strands of DNA are

hydrogen bonds

Bacteria that contain the plasmid, but not the eukaryotic gene, would grow in which of the following conditions?

in all four types of broth

Bacteria containing a plasmid into which the eukaryotic gene has been inserted would grow in which of the following conditions?

in the ampicillin broth and the nutrient broth

Which of the following modifications is most likely to alter the rate at which a DNA fragment moves through a gel during electrophoresis?

increasing the length of the DNA fragment

Which of the following is an example of "recombinant DNA technology"?

introducing a human gene into a bacterial plasmid

After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.

labeled DNA ... DNA

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

leading strands and Okazaki fragments.

Gel electrophoresis separates DNA fragments on the basis of what characteristic?

length

During DNA replication, which of the following enzymes covalently connects segments of DNA?

ligase

Short segments of newly synthesized DNA are joined into a continuous strand by _____.

ligase

Which of the following mechanisms removes nucleotides that are paired incorrectly during DNA replication?

mismatch repair

The rate of elongation of a DNA strand in prokaryotes is __________ the rate in eukaryotes.

much faster than

In gel electrophoresis DNA molecules migrate from _____ to _____ ends of the gel.

negative, positive

What are the chemical components of a DNA molecule?

nitrogenous bases; phosphate groups; sugars

In nucleotide excision repair, damaged DNA is excised by what enzyme(s)?

nuclease

In which order do the necessary enzymes act to repair a thymine dimer by nucleotide excision repair?

nuclease, DNA polymerase, DNA ligase

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 of structures correctly represents the order of increasingly higher levels of organization of chromatin?

nucleosome, 30-nm chromatin fiber, looped domain

The "beads on a string" seen in interphase chromatin are __________.

nucleosomes

This is an image of a(n) _____.

nucleotide

What process repairs damage to a preexisting double helix?

nucleotide excision repair

The overall error rate in a completed DNA molecule is approximately___________.

one error per 10,000,000,000 nucleotides

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

The two strands of a DNA double helix are antiparallel. This means that __________.

one strand runs in the 5' to 3' direction and the other runs in the 3' to 5' direction

The letter A indicates a _____.

phosphate group

What is the function of topoisomerase?

relieving strain in the DNA ahead of the replication fork

The experiments of Meselson and Stahl showed that DNA

replicates in a semiconservative fashion

The action of helicase creates _____.

replication forks and replication bubbles

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

single-strand 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

The unpaired nucleotides produced by the action of restriction enzymes are referred to as _____.

sticky ends

You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____.

sugar with two, and not three, oxygen atoms

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

telomeres

An old DNA strand is used as a _____ for the assembly of a new DNA strand

template

Bacteria that do not take up any plasmids would grow on which media?

the nutrient broth only

A scientist assembles a bacteriophage with the protein coat of phage T2 and the DNA of phage T4. If this composite phage were allowed to infect a bacterium, the phages produced in the host cell would have __________.

the protein and DNA of T4

Chargaff found that in DNA samples,___________.

the ratio of A to T is close to 1:1 and the ratio of G to C is close to 1:1

Which of the following characteristics of the structure of DNA allows it to carry a large amount of hereditary information?

the sequence of bases

Which of these nitrogenous bases is found in DNA but not in RNA?

thymine

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine

What is the function of DNA polymerase III in replication in E. coli?

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

The unwinding of DNA at the replication fork causes twisting and strain in the DNA ahead of the fork, which is relieved by an enzyme called___________.

topoisomerase

The bonds or interactions between stacked nucleotide units that help hold the DNA molecule together are

van der Waals interactions

Avery and his colleagues' 1944 experiment showed that DNA __________.

was the substance that transformed that bacteria in Griffith's experiment