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

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 Figure 13.1 would
you expect if the DNA was replicated in a conservative manner?
A) A
B) B
C) C
D) D
E) E

B

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 semi-conservative.
B) Replication is not dispersive.
C) Replication is not semi-conservative.
D) Replication is not conservative.
E) Replication is neither dispersive nor conservative.

Replication is not conservative

In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes,
dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine). After several minutes, the
DNA is switched to nonradioactive medium and is then viewed by electron microscopy and
autoradiography. Figure 13.2 represents the results. It shows a replication bubble, and the dots
represent radioactive material. Which of the following is the most likely interpretation of the
results?
A) There are two replication forks going in opposite directions.
B) Thymidine is being added only where the DNA strands are farthest apart.
C) Thymidine is being added only at the very beginning of replication.
D) Replication proceeds in one direction only.

There are two replication forks going in opposite directions

Which enzyme was used to produce the molecule in Figure 13.3?
A) ligase
B) transcriptase
C) a restriction enzyme
D) RNA polymerase
E) DNA polymerase

a restriction enzyme

The segment of DNA shown in Figure 13.4 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?

CAB

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 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) Avery et al. have already concluded that this experiment showed inconclusive results.
D) Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra
neutrons; therefore, they are more radioactive.
E) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not
distinguish between DNA and proteins.

Amino Acids (and thus proteins) also have nitrogen atoms: thus, the radioactivity would not distinguish between DNA and proteins

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.
E) RNA primers and mitochondrial DNA.

leading strands and Okazaki fragments

Bacteria that contain the plasmid, but not the eukaryotic gene, would grow
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.
E) in the nutrient broth without antibiotics only.

in all four types of broth

Bacteria containing a plasmid into which the eukaryotic gene has integrated would grow
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 all four types of broth.
E) in the ampicillin broth and the nutrient broth.

in the ampicillin broth and the nutrient broth

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
E) all three broths

the nutrient broth only

Why might they be conducting such an experiment?
A) to find the location of this gene in the human genome
B) to prepare to isolate the chromosome on which the gene of interest is found
C) to find which of the students has which alleles
D) to collect population data that can be used to assess natural selection
E) to collect population data that can be used to study genetic drift

to find which of the students has which alleles

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) The students with three fragments are said to have "fragile sites."
E) Each of these students is heterozygous for this gene.

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

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.
E) bacteriophages injected DNA into bacteria

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

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 growing strand.
D) DNA ligase works only in the 3' → 5' direction.
E) Polymerase can work on only one strand at a time.

DNA polymerase can join new nucleotides only to the 3' end of a growing strand

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 + T
D) A = C
E) G = T

A + G = C + T

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.
E) does not require a template strand.

depends on the action of DNA polymerase

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

histones

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
E) one low-density band

one low-density and one intermediate density band