Biol 309
Test Question Bank
Chromatin Structure & DNA Replication
Multiple Choice
1. Why is an RNA primer necessary for DNA replication?
A. The RNA primer is necessary for the activity of DNA ligase.
B. The RNA primer creates the 5’ and 3’ ends of the strand.
C. DNA polymerase can only add nucleotides to RNA molecules.
D. DNA polymerase can only add nucleotides to an existing strand.
2. Suppose a mutation occurs in a cell such that normal Okazaki fragments were created during
DNA replication but were not linked together into a continuous strand. The gene for which
enzyme would you predict was altered by this mutation?
A. DNA polymerase C. DNA helicase
E. DNA ligase
B. RNA primase
D. ssDNA binding protein
3. The genome of a typical bacterium contains about 5 x 106 base pairs and can be replicated in
about 30 minutes. The human genome is 600X larger (3 x 109 base pairs) and at the rate of a
bacterium would require 300 hours (~12 days) to be replicated; yet the entire human genome can
be replicated with several hours. How is this possible?
A. Eukaryotic DNA is simpler to replicate than prokaryotic DNA.
B. Human DNA polymerases work much faster than those of prokaryotes.
C. The nucleosomes of eukaryotic DNA allow for faster DNA replication.
D. Human DNA contains more origins of replication than prokaryotic DNA.
4. DNA replication is said to be semiconservative because:
A. both RNA and DNA synthesis are involved in the process.
B. part of the telomere is lost during each round of replication.
C. a new double helix contains one old and one new strand.
D. each new strand is complementary, not identical, to its template.
5. What happens after the DNA polymerase laying down a new DNA strand meets up with the
RNA primer of a preceding Okazaki fragment?
A. The other strand is then repliced in the 3 to 5’ direction.
B. The DNA polymerase reverses direction and performs error checking.
C. DNA ligase couples the two fragments together.
D. The RNA primer is removed and is replaced by DNA.
6. A mutation to DNA polymerase that eliminated the 3-to-5 exonuclease activity would
prevent:
A. ligation of the okazaki fragments.
C. removal of the RNA primer.
B. removal of base mismatches.
D. repair of deaminated bases.
Biol 309
Question Bank
Chromatin & DNA
Page 1
7. Imagine a life form in which the orientation of the strands in the DNA double helix was
parallel rather than antiparallel. This life form uses a DNA polymerase with similar properties to
that in normal eukaryotic organisms, thus, we would expect that:
A. DNA replication would be much slower than in normal eukaryotes.
B. DNA replication would occur in the 3’ to 5’ direction on one strand and in a 5’
to 3’ direction on the other.
C. DNA replication would only occur toward one end of a replication bubble.
D. The DNA polymerase would be unable to carry out error-checking.
8. Which one of the following statements correctly describes “telomerase”?
A. This enzyme is active in all dividing cells.
B. Activity of this enzyme is inhibited in many cancerous cells.
C. It creates repetitive DNA at the end of the chromosomes.
D. Telomerase uses the DNA as a template for synthesizing a new strand.
9. The best explanation for why DNA synthesis is discontinuous would be that:
A. DNA polymerase can only move along the DNA strand in one orientation.
B. This allows for efficient error checking of newly synthesized DNA.
C. DNA polymerase must stop periodically to reload more nucleotides.
D. Nucleosomes disrupt the process of DNA synthesis.
10. The experiments of Meselson and Stahl demonstrated the semiconservative mechanism of
DNA replication by showing that when 15N-loaded DNA replicates in the presence of 14N:
A. the new strand of a replicated DNA molecule contains equal amounts of 15N and 14N.
B. after one round of DNA replication, one strand of the DNA molecule contains only
14
N and the other contains only 15N.
C. after several rounds of DNA replication, all of the DNA was converted from the ‘HH’
to the ‘LH’ form.
D. after many rounds of replication, half of DNA has the ‘HH’ density and half has the
‘LL’density.
11. A nucleosome consists of:
A. one of each of the 5 types (H1 – H4) of histone proteins.
B. a cluster of histone proteins that are wrapped around the DNA double helix.
C. the DNA polymerase complex and the Okasaki fragments of approximately 200 bases
in length.
D. clusters of ribosomal large subunits and small subunits bound to the DNA double
helix.
E. two peptides each of histones H2A, H2B, H3 and H4, wrapped by the DNA double
helix.
12. Much of the DNA in a eukaryotic genome is “non-coding”, i.e., it does not carry genetic code
for protein synthesis. Non-coding DNA would be found in all of the following locations,
EXCEPT:
A. in between genes
C. in centromeres
E. in repetitive DNA
B. in telomeres
D. in exons
Biol 309
Question Bank
Chromatin & DNA
Page 2
13.Which one of the following statements about nucleosomes is INCORRECT?
A. the nucleosome core is wrapped by the DNA double helix.
B. the nucleosome core contains an octet of 8 histone proteins.
C. there are two copies of each histone protein in the nucleosome core.
D. Four copies of histone H1 are present in the nucleosome core.
E. Binding between nucleosomes cause chromosomes to supercoil during mitosis.
14. The type of mutation most commonly associated with exposure to UV light is:
A. thymine dimerization
C. a base deamination
B. depurinization
D. a base deletion
15. DNA repair enzymes preferentially replace mismatched bases on the newly transcribed
strand. If bases in a mismatched pair were replaced at random, what would be the effect on
DNA mutation rates?
A. Essentially no change, since base pair mismatch is an example of a ‘silent’
mutation.
B. A significant reduction in mutation rate, since replacing either base will create
proper base pairing.
C. Essentially no change, because the mismatch would be repaired during the next
round of cell division.
D. Mutation rates would increase, because 50% of the time the wrong base pair
would result.
True or false
1. Single-stranded binding proteins attach after DNA helicase separates the double helix.
2. Formation of a leading strand but not a lagging strand does not require a primer.
3. DNA Ligase is the enzyme that links together Okazaki fragments.
4. Plasmid DNA replicates independent of the host chromosomes.
5. DNA replication always begins with the synthesis of an RNA primer.
6. RNA primers are removed and replaced with DNA before DNA ligase links together the new
DNA strands.
7. Nucleosomes are present in both eukaryotes and prokaryotes.
Biol 309
Question Bank
Chromatin & DNA
Page 3
Fill in, etc
1. Telomerase adds new bases to the ____ end of a DNA strand. The base sequence created by
the telomerase is a repetitive sequence for which each repeat has a length of approximately
______ bases (add number). The template for this sequence exists on a _______ molecule held in
the ________________ enzyme. After the DNA strand is extended with the addition of the
telomere repeats, the _______________ enzyme creates a complementary strand.
2. A sequence such as ‘ATGG’ repeated several million times is an example of
__________________________ DNA, and would be typical of DNA found in the
__________________________ region of a chromosome
4. The experiments of Meselson and Stahl demonstrated the semiconservative mechanism of
DNA replication by studying the density of DNA of cells that were first grown in the presence of
15
N and then in presence of 14N :
(Draw DNA bands in appropriate relative positions and labeled as DD, LL or DL)
A. How did the 15N-Loaded DNA
originally appear in the
density gradient
How did the DNA appear in gradients after growth
in the presence of 14N for:
1 cell division
several cell divisions
B. Why does some of the DNA form a ‘HL’ band?
C. After how rounds of cell division are required to show definitively that DNA replication is
semiconservative? Explain.
5. The structure shown to the right is a ______________________
and the labeled components are
A. ____________________
B. ____________________
C. ____________________
Name the 4 histones that make up ‘C’: __________________
Which histone is particularly important in regulating DNA
Biol 309
Question Bank
Chromatin & DNA
Page 4
remodeling? _____ How is it regulated?
6. Explain how telomerase and DNA polymerase operate together to lengthen the chromosomes.
Label the 3’ and 5’ ends of the strands, and modify this diagram to show where DNA polymerase
and telomerase will lengthen the strands
7. Label the various proteins and
components of the DNA replication
complex shown in this diagram.
Identify the function of each.
8. What is the sequence (1 to 6) in which these proteins function during DNA replication
____ RNA primase
____ DNA helicase
____ DNA ligase
____ Initiator proteins
____ DNA polymerase
____ RNA ribonuclease
9. Retroviruses, such as HIV, create a DNA molecule using RNA as a template, with an enzyme
called reverse transcriptase. The HIV DNA molecule is then inserted into a human chromosome,
where it is replicated by DNA polymerase each time the cell divides. Treatment of AIDS is
compounded by the high mutation rates of HIV. During which step would you expect the most
mutations to enter the HIV genome: during replication by reverse transcriptase or by DNA
polymerase? Explain.
Biol 309
Question Bank
Chromatin & DNA
Page 5
10. Match each of the following DNA repair mechanisms with the correct description
Mechanism
___ DNA Polymerase proofreading
___ Homologous recombination
___ Double strand end-joining
___ Post-replication excision repair
___ S-phase mismatch repair
Description
A. might repair a base depurination
B. fix a mismatch that evades DNA polymerase
C. occurs during DNA replication
D. repairs a double strand break
E. repair results in a short deleteion
11. Use this figure to
complete the
following questions:
A. Place arrow heads at the ends of the newly synthesized DNA strands to indicate the
direction of DNA synthesis.
B. Place an ‘X’ in the diagram to show where the origin of replication was.
C. At the ends of the original strands, label the 5’ and 3’ ends.
D. On each strand, number the lagging Okasaki fragments (1, 2 and 3) to show the order
in which they were produced, 1 being first.
E. Label the ‘leading’ strands.
Biol 309
Question Bank
Chromatin & DNA
Page 6