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.
A) Frederick Griffith
B) Alfred Hershey and Martha Chase
C) Oswald Avery, Maclyn McCarty, and Colin MacLeod
D) Erwin Chargaff
E) Matthew Meselson and Franklin Stahl

Erwin Chargaff

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) 31%
D) 42%
E) It cannot be determined from the information provided.

8%

Which of the following can be determined directly from X-ray diffraction photographs of
crystallized DNA?
A) the diameter of the helix
B) the rate of replication
C) the sequence of nucleotides
D) the bond angles of the subunits
E) the frequency of A vs. T nucleotides

the diameter of the helix

8) 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
B) phosphate-sugar backbones
C) complementary pairing of bases
D) side groups of nitrogenous bases
E) different five-carbon sugars

sequence of bases

In an analysis of the nucleotide composition of DNA, which of the following will be found?
A) A = C
B) A = G and C = T
C) A + C = G + T
D) G + C = T + A

A + C = G + T

What is meant by the description "antiparallel" regarding the strands that make up DNA?
A) The twisting nature 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 is positively charged and the other is negatively charged.
E) One strand contains only purines and the other contains only pyrimidines.

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

Replication in prokaryotes differs from replication in eukaryotes for which of the following
reasons?
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.
E) Prokaryotes have telomeres, and eukaryotes do not.

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

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) Radioactive thymine would pair with nonradioactive guanine.
E) DNA in both daughter cells would be radioactive.

DNA in both daughter cells would be radioactive.

An Okazaki fragment has which of the following arrangements?
A) primase, polymerase, ligase
B) 3' RNA nucleotides, DNA nucleotides 5'
C) 5' RNA nucleotides, DNA nucleotides 3'
D) DNA polymerase I, DNA polymerase III
E) 5' ; DNA to 3'

5' RNA nucleotides, DNA nucleotides 3'

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?
A) No proofreading will occur.
B) No replication fork will be formed.
C) The DNA will supercoil.
D) Replication will occur via RNA polymerase alone.
E) Replication will require a DNA template from another source.

No replication fork will be formed.

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?
A) primase
B) DNA ligase
C) DNA polymerase III
D) topoisomerase
E) helicase

DNA polymerase III

At a specific area of a chromosome, the following sequence of nucleotides 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) 3' G C C T A G G 5'
C) 5' A C G T T A G G 3'
D) 5' A C G U U A G G 3'
E) 5' G C C U A G G 3'

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

Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA
strands that are aligned in parallel arrays. How could these arise?
A) replication followed by mitosis
B) replication without separation
C) meiosis followed by mitosis
D) fertilization by multiple sperm
E) special association with histone proteins

replication without separation

To repair a thymine dimer by nucleotide excision repair, in which order do the necessary
enzymes act?
A) exonuclease, DNA polymerase III, RNA primase
B) helicase, DNA polymerase I, DNA ligase
C) DNA ligase, nuclease, helicase
D) DNA polymerase I, DNA polymerase III, DNA ligase
E) endonuclease, DNA polymerase I, DNA ligase

endonuclease, DNA polymerase I, DNA ligase

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
E) to rejoin the two DNA strands (one new and one old) after replication

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

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.
B) the nucleoside triphosphates have two phosphate groups; ATP has three phosphate groups.
C) ATP contains three high-energy bonds; the nucleoside triphosphates have two.
D) ATP is found only in human cells; the nucleoside triphosphates are found in all animal and
plant cells.
E) triphosphate monomers are active in the nucleoside triphosphates, but not in ATP.

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

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.
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.

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.

A new DNA strand elongates only in the 5' to 3' direction because
A) DNA polymerase begins adding nucleotides at the 5' end of the template.
B) Okazaki fragments prevent elongation in the 3' to 5' direction.
C) the polarity of the DNA molecule prevents addition of nucleotides at the 3' end.
D) replication must progress toward the replication fork.
E) DNA polymerase can only add nucleotides to the free 3' end.

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

What is the function of topoisomerase?
A) relieving strain in the DNA ahead of the replication fork
B) elongating new DNA at a replication fork by adding nucleotides to the existing chain
C) adding methyl groups to bases of DNA
D) unwinding of the double helix
E) stabilizing single-stranded DNA at the replication fork

relieving strain in the DNA ahead of the replication fork

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 catalyzes the lengthening of telomeres.
C) It joins Okazaki fragments together.
D) It unwinds the parental double helix.
E) It stabilizes the unwound parental DNA.

It joins Okazaki fragments together.

Which of the following help(s) to hold the DNA strands apart while they are being
replicated?
A) primase
B) ligase
C) DNA polymerase
D) single-strand binding proteins
E) exonuclease

single-strand binding proteins

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This
occurs because their cells are impaired in what way?
A) They cannot replicate DNA.
B) They cannot undergo mitosis.
C) They cannot exchange DNA with other cells.
D) They cannot repair thymine dimers.
E) They do not recombine homologous chromosomes during meiosis.

They cannot repair thymine dimers.

I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase

Which of the enzymes removes the RNA nucleotides from the primer and adds equivalent
DNA nucleotides to the 3' end of Okazaki fragments?
A) I
B) II
C) III
D) IV
E) V
Answer:

IV

I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase

Which of the enzymes separates the DNA strands during replication?
A) I
B) II
C) III
D) IV
E) V

I

I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase

Which of the enzymes covalently connects segments of DNA?
A) I
B) II
C) III
D) IV

III

I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase

Which of the enzymes synthesizes short segments of RNA?
A) I
B) II
C) III
D) IV
E) V

V

Given the damage caused by UV radiation, the kind of gene affected in those with XP is one
whose product is involved with
A) mending of double-strand breaks in the DNA backbone.
B) breakage of cross-strand covalent bonds.
C) the ability to excise single-strand damage and replace it.
D) the removal of double-strand damaged areas.
E) causing affected skin cells to undergo apoptosis.

the ability to excise single-strand damage and replace it.

Which of the following sets of materials is required by both eukaryotes and prokaryotes for
replication?
A) double-stranded DNA, four kinds of dNTPs, primers, origins of replication
B) topoisomerases, telomerases, polymerases
C) G-C rich regions, polymerases, chromosome nicks
D) nucleosome loosening, four dNTPs, four rNTPs
E) ligase, primers, nucleases

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

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?
A) DNA can wind itself around either of the two kinds of tetramers.
B) The two types of tetramers associate to form an octamer.
C) DNA has to associate with individual histones before they form tetramers.
D) Only H2A can form associations with DNA molecules.
E) The structure of H3 and H4 molecules is not basic like that of the other histones.

The two types of tetramers associate to form an octamer.

In a linear eukaryotic chromatin sample, which of the following strands is looped into
domains by scaffolding?
A) DNA without attached histones
B) DNA with H1 only
C) the 10-nm chromatin fiber
D) the 30-nm chromatin fiber
E) the metaphase chromosome

the 30-nm chromatin fiber

Which of the following statements describes the eukaryotic chromosome?
A) It is composed of DNA alone.
B) The nucleosome is its most basic functional subunit.
C) The number of genes on each chromosome is different in different cell types of an organism.
D) It consists of a single linear molecule of double-stranded DNA plus proteins.
E) Active transcription occurs on heterochromatin but not euchromatin.

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

If a cell were unable to produce histone proteins, which of the following would be a likely
effect?
A) There would be an increase in the amount of "satellite" DNA produced during centrifugation.
B) The cell's DNA couldn't 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.
E) Pseudogenes would be transcribed to compensate for the decreased protein in the cell.

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

Which of the following statements is true 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.
E) The mass of histone in chromatin is approximately nine times the mass of DNA.

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

Why do histones 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.
E) Histones are highly hydrophobic, and DNA is hydrophilic.

Histones are positively charged, and DNA is negatively charged.

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

nucleosome, 30-nm chromatin fiber, looped domain

Which of the following statements describes 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.
E) Only euchromatin is visible under the light microscope.Heterochromatin is highly condensed, whereas euchromatin is less compact.

Heterochromatin is highly condensed, whereas euchromatin is less compact.

Which of the following modifications is least likely to alter the rate at which a DNA
fragment moves through a gel during electrophoresis?
A) altering the nucleotide sequence of the DNA fragment without adding or removing
nucleotides
B) acetylating the cytosine bases within the DNA fragment
C) increasing the length of the DNA fragment
D) decreasing the length of the DNA fragment
E) neutralizing the negative charges within the DNA fragment

altering the nucleotide sequence of the DNA fragment without adding or removing
nucleotides

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
A) insert the fragments cut with restriction enzyme X directly into the plasmid without cutting
the plasmid.
B) cut the plasmid with restriction enzyme X and insert the fragments cut with restriction
enzyme Y into the plasmid.
C) cut the DNA again with restriction enzyme Y and insert these fragments into the plasmid cut
with the same enzyme.
D) cut the plasmid twice with restriction enzyme Y and ligate the two fragments onto the ends of
the DNA fragments cut with restriction enzyme X.
E) cut the plasmid with restriction enzyme X and then insert the gene into the plasmid.

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

How does a bacterial cell protect its own DNA from restriction enzymes?
A) by adding methyl groups to adenines and cytosines
B) by using DNA ligase to seal the bacterial DNA into a closed circle
C) by adding histones to protect the double-stranded DNA
D) by forming "sticky ends" of bacterial DNA to prevent the enzyme from attaching
E) by reinforcing the bacterial DNA structure with covalent phosphodiester bonds

by adding methyl groups to adenines and cytosines

What is the most logical sequence of steps for splicing foreign DNA into a plasmid and
inserting the plasmid into a bacterium?
I. Transform bacteria with a recombinant DNA molecule.
II. Cut the plasmid DNA using restriction enzymes.
III. Extract plasmid DNA from bacterial cells.
IV. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments.
V. Use ligase to seal plasmid DNA to nonplasmid DNA.
A) I, II, IV, III, V
B) II, III, V, IV, I
C) III, II, IV, V, I
D) III, IV, V, I, II
E) IV, V, I, II, III

III, II, IV, V, I

Why is it so important to be able to amplify DNA fragments when studying genes?
A) DNA fragments are too small to use individually.
B) A gene may represent only a millionth of the cell's DNA.
C) Restriction enzymes cut DNA into fragments that are too small.
D) A clone requires multiple copies of each gene per clone.
E) It is important to have multiple copies of DNA in the case of laboratory error.

A gene may represent only a millionth of the cell's DNA.

The reason for using Taq polymerase for PCR is that
A) it is heat stable and can withstand the heating step of PCR.
B) only minute amounts are needed for each cycle of PCR.
C) it binds more readily than other polymerases to the primers.
D) it has regions that are complementary to the primers.
E) it is heat stable, and it binds more readily than other polymerases to the primers.

it is heat stable and can withstand the heating step of PCR.