BIOL 2300: Exam 4 Quiz UPDATED ACTUAL Questions and CORRECT
Answers
Question: Several temperature-sensitive mutant strains of E. coli display the following characteristics.
Mutant (a)
Correct Answer: Newly synthesized DNA contains many mismatched base pairs. Mutant (b): Okazaki
fragments accumulate, and DNA synthesis is never completed. Mutant (c): No initiation occurs. Mutant (d):
Synthesis is very slow. Mutant (e): Supercoiled strands remain after replication, which is never completed.:
no DNA repair
Question: Which technique identifies specific areas of a chromosome composed of heterochromatin?
Correct Answer: C-banding
Question: This diagram depicts an origin of replication, with the direction of the movement of the
replication fork indicated. Given the direction of replication and the orientation of the two DNA strands,
which of the following is true? Select the two true statements.
Correct Answer: The top strand (pink) is the leading strand; it is being synthesized continuously. The
bottom strand (blue) is the lagging strand; it is being synthesized discontinuously.
Question: Which of the following are examples of heterochromatin? Select all that apply.
Correct Answer: Barr bodies repetitive DNA telomeric DNA centromeric DNA
Question: Reiji and Tuneko Okazaki conducted a now classic experiment in 1968 in which they discovered
a population of short fragments synthesized during DNA replication. They introduced a short pulse of 3H
-thymidine into a culture of E. coli and extracted DNA from the cells at various intervals. In analyzing the
DNA after centrifugation in denaturing gradients, they noticed that as the interval between the time of 3H
-thymidine introduction and the time of centrifugation increased, the proportion of short strands decreased
and more labeled DNA was found in larger strands. What would account for this observation?
Correct Answer: the ligation of Okazaki fragments by DNA ligase
Question: Meselson and Stahl set out to demonstrate that replication in E. coli takes place in a
semiconservative manner. They first grew cells in a medium containing the heavy isotope of 15N for
several generations. Then they switched the cells to a medium containing common nitrogen (14N). Using
equilibrium centrifugation, what did they determine was the nitrogen composition of the DNA?
Correct Answer: The DNA contained only 14N or a mixture of 15N and 14N.
Question: The DNA contained only 14N or a mixture of 15N and 14N.
Correct Answer: 3000
Question: How did we learn that eukaryotic chromatin exists in the form of repeating nucleosomes, each
consisting of about 200 base pairs and an octamer of histones?
Correct Answer: Endonuclease digestion has shown that DNA fragments are of about 200 base pairs in
length. Electron microscopic, X-ray, and neutron scattering observations revealed the structure of
nucleosomes and their relationship to DNA.
Question: Endonuclease digestion has shown that DNA fragments are of about 200 base pairs in length.
Electron microscopic, X-ray, and neutron scattering observations revealed the structure of nucleosomes and
, their relationship to DNA.
Correct Answer: a) fiber b) nucleosomes c) solenoid d) series of loops e) chromatid
Question: Which activity is not associated with DNA polymerases?
Correct Answer: Ability to initiate DNA synthesis from scratch without a primer
Question: What is the experimental basis for concluding that puffs in polytene chromosomes and loops in
lampbrush chromosomes are areas of intense transcription of RNA?
Correct Answer: Radioactively labeled RNA precursors followed by autoradiography have shown a high
rate of RNA incorporation, indicating intense transcription
Question: Taylor, Woods, and Hughes did an experiment in Vicia faba. They used radioactive
3H-thymidine to label newly synthesized DNA in order to monitor the mechanism of replication. Their
data, seen in Figure 11-5, provided evidence for semi-conservative replication. If replication were
conservative, after one round of replication, which of the following would be true?
Correct Answer: In one sister chromatid, both DNA strands would be labeled. In the other sister
chromatid, both DNA strands would be unlabeled.
Question: Which characteristics of DNA polymerase I raised doubts that its in vivo function is the
synthesis of DNA leading to complete replication?
Correct Answer: mutants resulting in a deficiency of enzyme in some organisms that are still capable of
DNA synthesis
Question: How do we know that in vivo DNA synthesis occurs in the 5′ to 3′ direction?-
Correct Answer: In vitro studies it was indicated that DNA strand elongation occurs by addition of
nucleotides at the 3' end. During chain elongation phosphate can attach only to the 3'- OH group of the
deoxyribose.
Question: What makes up the protein component of a nucleosome?
Correct Answer: two tetramers of histone proteins
Question: All of the following are differences between eukaryotic and prokaryotic DNA replication
EXCEPT__________?
Correct Answer: the ability to form a replication fork
Question: Many of the gene products involved in DNA synthesis were initially defined by studying mutant
E. coli strains that could not synthesize DNA. The dnaE gene encodes the α subunit of DNA polymerase
III. What effect is expected from a mutation in this gene?
Correct Answer: a decreased rate of DNA replication
Question: Which of the following statements is true regarding Okazaki fragments?
Correct Answer: they are short fragments of DNA synthesized from RNA primers on the lagging strand
Question: Cancer can be defined as an abnormal proliferation of cells that defy the normal regulatory
controls observed by normal cells. Recently, histone deacetylation therapies have been attempted in the
treatment of certain cancers (reviewed by Delcuve et al., 2009). Specifically, the FDA has approved histone
deacetylation (HDAC) inhibitors for the treatment of cutaneous T-cell lymphoma. Histone hyperacetylation
(overacetylation) of certain genes is associated with cancer. What is the effect of histone acetylation on
gene expression, and what is the normal function of the genes affected?
Answers
Question: Several temperature-sensitive mutant strains of E. coli display the following characteristics.
Mutant (a)
Correct Answer: Newly synthesized DNA contains many mismatched base pairs. Mutant (b): Okazaki
fragments accumulate, and DNA synthesis is never completed. Mutant (c): No initiation occurs. Mutant (d):
Synthesis is very slow. Mutant (e): Supercoiled strands remain after replication, which is never completed.:
no DNA repair
Question: Which technique identifies specific areas of a chromosome composed of heterochromatin?
Correct Answer: C-banding
Question: This diagram depicts an origin of replication, with the direction of the movement of the
replication fork indicated. Given the direction of replication and the orientation of the two DNA strands,
which of the following is true? Select the two true statements.
Correct Answer: The top strand (pink) is the leading strand; it is being synthesized continuously. The
bottom strand (blue) is the lagging strand; it is being synthesized discontinuously.
Question: Which of the following are examples of heterochromatin? Select all that apply.
Correct Answer: Barr bodies repetitive DNA telomeric DNA centromeric DNA
Question: Reiji and Tuneko Okazaki conducted a now classic experiment in 1968 in which they discovered
a population of short fragments synthesized during DNA replication. They introduced a short pulse of 3H
-thymidine into a culture of E. coli and extracted DNA from the cells at various intervals. In analyzing the
DNA after centrifugation in denaturing gradients, they noticed that as the interval between the time of 3H
-thymidine introduction and the time of centrifugation increased, the proportion of short strands decreased
and more labeled DNA was found in larger strands. What would account for this observation?
Correct Answer: the ligation of Okazaki fragments by DNA ligase
Question: Meselson and Stahl set out to demonstrate that replication in E. coli takes place in a
semiconservative manner. They first grew cells in a medium containing the heavy isotope of 15N for
several generations. Then they switched the cells to a medium containing common nitrogen (14N). Using
equilibrium centrifugation, what did they determine was the nitrogen composition of the DNA?
Correct Answer: The DNA contained only 14N or a mixture of 15N and 14N.
Question: The DNA contained only 14N or a mixture of 15N and 14N.
Correct Answer: 3000
Question: How did we learn that eukaryotic chromatin exists in the form of repeating nucleosomes, each
consisting of about 200 base pairs and an octamer of histones?
Correct Answer: Endonuclease digestion has shown that DNA fragments are of about 200 base pairs in
length. Electron microscopic, X-ray, and neutron scattering observations revealed the structure of
nucleosomes and their relationship to DNA.
Question: Endonuclease digestion has shown that DNA fragments are of about 200 base pairs in length.
Electron microscopic, X-ray, and neutron scattering observations revealed the structure of nucleosomes and
, their relationship to DNA.
Correct Answer: a) fiber b) nucleosomes c) solenoid d) series of loops e) chromatid
Question: Which activity is not associated with DNA polymerases?
Correct Answer: Ability to initiate DNA synthesis from scratch without a primer
Question: What is the experimental basis for concluding that puffs in polytene chromosomes and loops in
lampbrush chromosomes are areas of intense transcription of RNA?
Correct Answer: Radioactively labeled RNA precursors followed by autoradiography have shown a high
rate of RNA incorporation, indicating intense transcription
Question: Taylor, Woods, and Hughes did an experiment in Vicia faba. They used radioactive
3H-thymidine to label newly synthesized DNA in order to monitor the mechanism of replication. Their
data, seen in Figure 11-5, provided evidence for semi-conservative replication. If replication were
conservative, after one round of replication, which of the following would be true?
Correct Answer: In one sister chromatid, both DNA strands would be labeled. In the other sister
chromatid, both DNA strands would be unlabeled.
Question: Which characteristics of DNA polymerase I raised doubts that its in vivo function is the
synthesis of DNA leading to complete replication?
Correct Answer: mutants resulting in a deficiency of enzyme in some organisms that are still capable of
DNA synthesis
Question: How do we know that in vivo DNA synthesis occurs in the 5′ to 3′ direction?-
Correct Answer: In vitro studies it was indicated that DNA strand elongation occurs by addition of
nucleotides at the 3' end. During chain elongation phosphate can attach only to the 3'- OH group of the
deoxyribose.
Question: What makes up the protein component of a nucleosome?
Correct Answer: two tetramers of histone proteins
Question: All of the following are differences between eukaryotic and prokaryotic DNA replication
EXCEPT__________?
Correct Answer: the ability to form a replication fork
Question: Many of the gene products involved in DNA synthesis were initially defined by studying mutant
E. coli strains that could not synthesize DNA. The dnaE gene encodes the α subunit of DNA polymerase
III. What effect is expected from a mutation in this gene?
Correct Answer: a decreased rate of DNA replication
Question: Which of the following statements is true regarding Okazaki fragments?
Correct Answer: they are short fragments of DNA synthesized from RNA primers on the lagging strand
Question: Cancer can be defined as an abnormal proliferation of cells that defy the normal regulatory
controls observed by normal cells. Recently, histone deacetylation therapies have been attempted in the
treatment of certain cancers (reviewed by Delcuve et al., 2009). Specifically, the FDA has approved histone
deacetylation (HDAC) inhibitors for the treatment of cutaneous T-cell lymphoma. Histone hyperacetylation
(overacetylation) of certain genes is associated with cancer. What is the effect of histone acetylation on
gene expression, and what is the normal function of the genes affected?
