C785 Biochemistry Module 3: DNA, RNA, and Gene Expression 2026
|WGU
1. Which of the following components is not found in a DNA nucleotide?
A. Deoxyribose sugar
B. Phosphate group
C. Uracil
D. Nitrogenous base
Answer: C
Rationale: Uracil is a nitrogenous base found in RNA nucleotides, whereas DNA uses
Thymine instead.
2. In a DNA double helix, which type of bond holds the nitrogenous bases of the
two strands together?
A. Ionic bonds
B. Covalent bonds
C. Hydrogen bonds
D. Phosphodiester bonds
Answer: C
Rationale: Hydrogen bonds form between complementary nitrogenous bases (A-T and C-
G) to hold the two strands of DNA together.
,3. If a DNA sample contains 20% Adenine, what percentage of Cytosine would
you expect it to contain?
A. 30%
B. 20%
C. 40%
D. 80%
Answer: A
Rationale: According to Chargaff’s rules, A=T (20% each, total 40%). The remaining 60%
must be split equally between C and G, so C=30%.
4. During DNA replication, which enzyme is responsible for unwinding the DNA
double helix?
A. DNA Polymerase
B. DNA Ligase
C. Topoisomerase
D. Helicase
Answer: D
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases to separate the DNA strands.
5. In which direction is a new DNA strand synthesized?
A. 3’ to 5’
B. 5’ to 3’
C. 5’ to 5’
D. 3’ to 3’
Answer: B
Rationale: DNA polymerase can only add new nucleotides to the 3’ hydroxyl end of a
growing strand, meaning synthesis occurs in the 5’ to 3’ direction.
, 6. What is the role of DNA Ligase during replication?
A. To join Okazaki fragments together
B. To stabilize single strands
C. To add RNA primers
D. To proofread the new strand
Answer: A
Rationale: DNA Ligase ‘glues’ the sugar-phosphate backbones of DNA fragments, such as
Okazaki fragments on the lagging strand, together.
7. Which enzyme relieves the torsional strain (overwinding) ahead of the
replication fork?
A. Primase
B. Topoisomerase
C. DNA Polymerase I
D. Single-strand binding protein
Answer: B
Rationale: Topoisomerase (or DNA Gyrase) cuts and reseals the DNA backbone to prevent
overwinding as helicase separates the strands.
8. What are the short segments of DNA synthesized on the lagging strand
called?
A. Introns
B. Okazaki fragments
C. Exons
D. Codons
Answer: B
Rationale: Because the lagging strand is oriented 3’ to 5’, DNA must be synthesized in
short, discontinuous bursts called Okazaki fragments.
|WGU
1. Which of the following components is not found in a DNA nucleotide?
A. Deoxyribose sugar
B. Phosphate group
C. Uracil
D. Nitrogenous base
Answer: C
Rationale: Uracil is a nitrogenous base found in RNA nucleotides, whereas DNA uses
Thymine instead.
2. In a DNA double helix, which type of bond holds the nitrogenous bases of the
two strands together?
A. Ionic bonds
B. Covalent bonds
C. Hydrogen bonds
D. Phosphodiester bonds
Answer: C
Rationale: Hydrogen bonds form between complementary nitrogenous bases (A-T and C-
G) to hold the two strands of DNA together.
,3. If a DNA sample contains 20% Adenine, what percentage of Cytosine would
you expect it to contain?
A. 30%
B. 20%
C. 40%
D. 80%
Answer: A
Rationale: According to Chargaff’s rules, A=T (20% each, total 40%). The remaining 60%
must be split equally between C and G, so C=30%.
4. During DNA replication, which enzyme is responsible for unwinding the DNA
double helix?
A. DNA Polymerase
B. DNA Ligase
C. Topoisomerase
D. Helicase
Answer: D
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases to separate the DNA strands.
5. In which direction is a new DNA strand synthesized?
A. 3’ to 5’
B. 5’ to 3’
C. 5’ to 5’
D. 3’ to 3’
Answer: B
Rationale: DNA polymerase can only add new nucleotides to the 3’ hydroxyl end of a
growing strand, meaning synthesis occurs in the 5’ to 3’ direction.
, 6. What is the role of DNA Ligase during replication?
A. To join Okazaki fragments together
B. To stabilize single strands
C. To add RNA primers
D. To proofread the new strand
Answer: A
Rationale: DNA Ligase ‘glues’ the sugar-phosphate backbones of DNA fragments, such as
Okazaki fragments on the lagging strand, together.
7. Which enzyme relieves the torsional strain (overwinding) ahead of the
replication fork?
A. Primase
B. Topoisomerase
C. DNA Polymerase I
D. Single-strand binding protein
Answer: B
Rationale: Topoisomerase (or DNA Gyrase) cuts and reseals the DNA backbone to prevent
overwinding as helicase separates the strands.
8. What are the short segments of DNA synthesized on the lagging strand
called?
A. Introns
B. Okazaki fragments
C. Exons
D. Codons
Answer: B
Rationale: Because the lagging strand is oriented 3’ to 5’, DNA must be synthesized in
short, discontinuous bursts called Okazaki fragments.
