BIOD 210 Module 3: DNA Structure and Replication Exam 2026/2027
UPDATE
1. Which of the following is NOT a component of a DNA nucleotide?
A. A nitrogenous base
B. An amino acid group
C. A pentose sugar
D. A phosphate group
Answer: B
Rationale: A nucleotide consists of a phosphate group, a deoxyribose sugar, and a
nitrogenous base. Amino acids are the building blocks of proteins, not DNA.
2. In the DNA double helix, the two strands are oriented in opposite directions.
This arrangement is known as:
A. Antiparallel
B. Parallel
C. Symmetrical
D. Complementary
Answer: A
Rationale: Antiparallel refers to the 5’ to 3’ orientation of one strand being opposite to the
3’ to 5’ orientation of the other.
,3. Which nitrogenous bases are classified as purines?
A. Cytosine and Thymine
B. Adenine and Thymine
C. Adenine and Guanine
D. Guanine and Cytosine
Answer: C
Rationale: Purines have a double-ring structure and include Adenine (A) and Guanine (G).
4. How many hydrogen bonds form between Adenine and Thymine?
A. 1
B. 3
C. 2
D. 4
Answer: C
Rationale: Adenine and Thymine are held together by two hydrogen bonds, while Guanine
and Cytosine are held by three.
5. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase III
B. Helicase
C. DNA Ligase
D. Primase
Answer: B
Rationale: Helicase breaks the hydrogen bonds between the nitrogenous bases to separate
the two DNA strands.
, 6. What is the primary function of DNA Polymerase III?
A. To seal gaps between DNA fragments
B. To remove RNA primers
C. To add nucleotides to the growing DNA strand
D. To stabilize single-stranded DNA
Answer: C
Rationale: DNA Polymerase III is the main enzyme that synthesizes new DNA by adding
nucleotides in the 5’ to 3’ direction.
7. Which experiment first suggested that DNA, not protein, is the genetic
material?
A. Avery-MacLeod-McCarty experiment
B. Watson and Crick’s model building
C. Mendel’s pea plant experiment
D. Darwin’s finch observation
Answer: A
Rationale: Avery and colleagues demonstrated that DNA was the ‘transforming principle’
in Griffith’s pneumococcus experiment.
8. Okazaki fragments are formed on which part of the replication fork?
A. The leading strand
B. The RNA primer
C. The origin of replication
D. The lagging strand
Answer: D
Rationale: The lagging strand is synthesized discontinuously in short segments called
Okazaki fragments because DNA polymerase can only work in the 5’ to 3’ direction.
UPDATE
1. Which of the following is NOT a component of a DNA nucleotide?
A. A nitrogenous base
B. An amino acid group
C. A pentose sugar
D. A phosphate group
Answer: B
Rationale: A nucleotide consists of a phosphate group, a deoxyribose sugar, and a
nitrogenous base. Amino acids are the building blocks of proteins, not DNA.
2. In the DNA double helix, the two strands are oriented in opposite directions.
This arrangement is known as:
A. Antiparallel
B. Parallel
C. Symmetrical
D. Complementary
Answer: A
Rationale: Antiparallel refers to the 5’ to 3’ orientation of one strand being opposite to the
3’ to 5’ orientation of the other.
,3. Which nitrogenous bases are classified as purines?
A. Cytosine and Thymine
B. Adenine and Thymine
C. Adenine and Guanine
D. Guanine and Cytosine
Answer: C
Rationale: Purines have a double-ring structure and include Adenine (A) and Guanine (G).
4. How many hydrogen bonds form between Adenine and Thymine?
A. 1
B. 3
C. 2
D. 4
Answer: C
Rationale: Adenine and Thymine are held together by two hydrogen bonds, while Guanine
and Cytosine are held by three.
5. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase III
B. Helicase
C. DNA Ligase
D. Primase
Answer: B
Rationale: Helicase breaks the hydrogen bonds between the nitrogenous bases to separate
the two DNA strands.
, 6. What is the primary function of DNA Polymerase III?
A. To seal gaps between DNA fragments
B. To remove RNA primers
C. To add nucleotides to the growing DNA strand
D. To stabilize single-stranded DNA
Answer: C
Rationale: DNA Polymerase III is the main enzyme that synthesizes new DNA by adding
nucleotides in the 5’ to 3’ direction.
7. Which experiment first suggested that DNA, not protein, is the genetic
material?
A. Avery-MacLeod-McCarty experiment
B. Watson and Crick’s model building
C. Mendel’s pea plant experiment
D. Darwin’s finch observation
Answer: A
Rationale: Avery and colleagues demonstrated that DNA was the ‘transforming principle’
in Griffith’s pneumococcus experiment.
8. Okazaki fragments are formed on which part of the replication fork?
A. The leading strand
B. The RNA primer
C. The origin of replication
D. The lagging strand
Answer: D
Rationale: The lagging strand is synthesized discontinuously in short segments called
Okazaki fragments because DNA polymerase can only work in the 5’ to 3’ direction.
