BIOL 101 Week 7 Quiz V2 | BIOL 101 Principles of
Biology | Actual Q&A with Rationale (BIOL101
Week 7 Quiz) | Liberty University
1. Which enzyme is primarily responsible for unwinding the DNA double helix at the
replication fork?
A. DNA Ligase
B. Helicase
C. Primase
D. DNA Polymerase III
Correct Answer: B
Explanation: Helicase is the specific enzyme that disrupts the hydrogen bonds between
nitrogenous bases to separate the two strands. This unwinding action creates a replication
fork, which serves as the site for DNA synthesis. Without this activity, the DNA molecule
would remain in its stable double-helix form, preventing other enzymes from accessing the
genetic code.
2. In DNA replication, which strand is synthesized continuously in the direction of the
replication fork?
A. Leading strand
B. Lagging strand
,C. Template strand
D. Okazaki strand
Correct Answer: A
Explanation: The leading strand is synthesized in the 5’ to 3’ direction, moving toward the
unwinding replication fork. Because DNA polymerase can only add nucleotides to the 3’
end, this strand requires only one primer for continuous synthesis. In contrast, the lagging
strand is synthesized in short segments away from the fork.
3. Which of the following describes the semiconservative model of DNA replication?
A. The original DNA molecule is completely preserved, and a new double helix is created.
B. The original DNA molecule is broken into fragments and dispersed throughout new
strands.
C. Both strands of the double helix are synthesized from scratch without using a template.
D. Each new DNA molecule consists of one original parent strand and one newly
synthesized strand.
Correct Answer: D
Explanation: The semiconservative model, confirmed by Meselson and Stahl, dictates that
each parental strand serves as a template for a new complementary strand. Following
replication, each daughter DNA molecule contains one conserved old strand and one new
strand. This mechanism ensures high fidelity in the transmission of genetic information
across generations.
, 4. What is the role of DNA Ligase during the replication of the lagging strand?
A. It synthesizes RNA primers to initiate DNA synthesis.
B. It unwinds the DNA double helix to provide single-strand templates.
C. It joins Okazaki fragments by forming phosphodiester bonds between them.
D. It adds nucleotides to the growing DNA chain.
Correct Answer: C
Explanation: DNA Ligase functions as a molecular glue that connects fragments of DNA.
During lagging strand synthesis, DNA polymerase I replaces RNA primers with DNA,
leaving nicks in the sugar-phosphate backbone. Ligase seals these gaps to ensure the
continuity of the DNA strand.
5. According to Chargaff’s rules, if a DNA sample contains 20% Adenine, what is the
percentage of Guanine?
A. 20%
B. 30%
C. 40%
D. 80%
Correct Answer: B
Explanation: Chargaff’s rules state that the amount of Adenine equals Thymine, and
Guanine equals Cytosine. If Adenine is 20%, then Thymine must also be 20%, totaling 40%
Biology | Actual Q&A with Rationale (BIOL101
Week 7 Quiz) | Liberty University
1. Which enzyme is primarily responsible for unwinding the DNA double helix at the
replication fork?
A. DNA Ligase
B. Helicase
C. Primase
D. DNA Polymerase III
Correct Answer: B
Explanation: Helicase is the specific enzyme that disrupts the hydrogen bonds between
nitrogenous bases to separate the two strands. This unwinding action creates a replication
fork, which serves as the site for DNA synthesis. Without this activity, the DNA molecule
would remain in its stable double-helix form, preventing other enzymes from accessing the
genetic code.
2. In DNA replication, which strand is synthesized continuously in the direction of the
replication fork?
A. Leading strand
B. Lagging strand
,C. Template strand
D. Okazaki strand
Correct Answer: A
Explanation: The leading strand is synthesized in the 5’ to 3’ direction, moving toward the
unwinding replication fork. Because DNA polymerase can only add nucleotides to the 3’
end, this strand requires only one primer for continuous synthesis. In contrast, the lagging
strand is synthesized in short segments away from the fork.
3. Which of the following describes the semiconservative model of DNA replication?
A. The original DNA molecule is completely preserved, and a new double helix is created.
B. The original DNA molecule is broken into fragments and dispersed throughout new
strands.
C. Both strands of the double helix are synthesized from scratch without using a template.
D. Each new DNA molecule consists of one original parent strand and one newly
synthesized strand.
Correct Answer: D
Explanation: The semiconservative model, confirmed by Meselson and Stahl, dictates that
each parental strand serves as a template for a new complementary strand. Following
replication, each daughter DNA molecule contains one conserved old strand and one new
strand. This mechanism ensures high fidelity in the transmission of genetic information
across generations.
, 4. What is the role of DNA Ligase during the replication of the lagging strand?
A. It synthesizes RNA primers to initiate DNA synthesis.
B. It unwinds the DNA double helix to provide single-strand templates.
C. It joins Okazaki fragments by forming phosphodiester bonds between them.
D. It adds nucleotides to the growing DNA chain.
Correct Answer: C
Explanation: DNA Ligase functions as a molecular glue that connects fragments of DNA.
During lagging strand synthesis, DNA polymerase I replaces RNA primers with DNA,
leaving nicks in the sugar-phosphate backbone. Ligase seals these gaps to ensure the
continuity of the DNA strand.
5. According to Chargaff’s rules, if a DNA sample contains 20% Adenine, what is the
percentage of Guanine?
A. 20%
B. 30%
C. 40%
D. 80%
Correct Answer: B
Explanation: Chargaff’s rules state that the amount of Adenine equals Thymine, and
Guanine equals Cytosine. If Adenine is 20%, then Thymine must also be 20%, totaling 40%
