C785 Biochemistry Module 3: DNA and Genetics 2026 |WGU
1. Which of the following components is NOT part of a DNA nucleotide?
A. Phosphate group
B. Deoxyribose sugar
C. Nitrogenous base
D. Uracil
Answer: D
Rationale: Uracil is found in RNA, not DNA. DNA contains Adenine, Thymine, Cytosine, and
Guanine.
2. What type of bond connects the sugar-phosphate backbone of a DNA
molecule?
A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond
D. Ionic bond
Answer: B
Rationale: Phosphodiester bonds are covalent bonds that link the 3’ carbon of one sugar to
the 5’ phosphate of the next.
,3. In a double-stranded DNA molecule, how many hydrogen bonds form
between Guanine and Cytosine?
A. Three
B. Two
C. One
D. Four
Answer: A
Rationale: G-C pairs share three hydrogen bonds, while A-T pairs share two, making G-C
pairs more stable.
4. The DNA double helix is described as ‘antiparallel’. What does this mean?
A. The strands run in opposite directions (5’ to 3’ and 3’ to 5’)
B. The strands are identical in sequence
C. One strand is made of RNA and the other is DNA
D. The bases are located on the outside of the helix
Answer: A
Rationale: Antiparallel means the two strands run in opposite directions relative to their
carbon numbering.
5. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase
B. Primase
C. Ligase
D. Helicase
Answer: D
Rationale: Helicase breaks the hydrogen bonds between bases to unzip the double helix.
, 6. What is the primary function of DNA Polymerase III during replication?
A. To unzip the DNA
B. To synthesize new DNA strands by adding nucleotides
C. To join Okazaki fragments
D. To remove RNA primers
Answer: B
Rationale: DNA Polymerase III is the main enzyme that adds nucleotides to the growing
DNA strand in the 5’ to 3’ direction.
7. Why are Okazaki fragments formed on the lagging strand?
A. Because DNA polymerase can only synthesize in the 5’ to 3’ direction
B. Because the lagging strand is shorter than the leading strand
C. Because there is no RNA primer on the lagging strand
D. Because helicase only works in one direction
Answer: A
Rationale: Since DNA is antiparallel and polymerase only adds to the 3’ end, the lagging
strand must be made in short segments as the fork opens.
8. Which enzyme seals the gaps between DNA fragments (like Okazaki
fragments) to create a continuous strand?
A. Topoisomerase
B. RNA Polymerase
C. Ligase
D. Primase
Answer: C
Rationale: DNA Ligase ‘glues’ the sugar-phosphate backbone together where nicks exist.
1. Which of the following components is NOT part of a DNA nucleotide?
A. Phosphate group
B. Deoxyribose sugar
C. Nitrogenous base
D. Uracil
Answer: D
Rationale: Uracil is found in RNA, not DNA. DNA contains Adenine, Thymine, Cytosine, and
Guanine.
2. What type of bond connects the sugar-phosphate backbone of a DNA
molecule?
A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond
D. Ionic bond
Answer: B
Rationale: Phosphodiester bonds are covalent bonds that link the 3’ carbon of one sugar to
the 5’ phosphate of the next.
,3. In a double-stranded DNA molecule, how many hydrogen bonds form
between Guanine and Cytosine?
A. Three
B. Two
C. One
D. Four
Answer: A
Rationale: G-C pairs share three hydrogen bonds, while A-T pairs share two, making G-C
pairs more stable.
4. The DNA double helix is described as ‘antiparallel’. What does this mean?
A. The strands run in opposite directions (5’ to 3’ and 3’ to 5’)
B. The strands are identical in sequence
C. One strand is made of RNA and the other is DNA
D. The bases are located on the outside of the helix
Answer: A
Rationale: Antiparallel means the two strands run in opposite directions relative to their
carbon numbering.
5. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase
B. Primase
C. Ligase
D. Helicase
Answer: D
Rationale: Helicase breaks the hydrogen bonds between bases to unzip the double helix.
, 6. What is the primary function of DNA Polymerase III during replication?
A. To unzip the DNA
B. To synthesize new DNA strands by adding nucleotides
C. To join Okazaki fragments
D. To remove RNA primers
Answer: B
Rationale: DNA Polymerase III is the main enzyme that adds nucleotides to the growing
DNA strand in the 5’ to 3’ direction.
7. Why are Okazaki fragments formed on the lagging strand?
A. Because DNA polymerase can only synthesize in the 5’ to 3’ direction
B. Because the lagging strand is shorter than the leading strand
C. Because there is no RNA primer on the lagging strand
D. Because helicase only works in one direction
Answer: A
Rationale: Since DNA is antiparallel and polymerase only adds to the 3’ end, the lagging
strand must be made in short segments as the fork opens.
8. Which enzyme seals the gaps between DNA fragments (like Okazaki
fragments) to create a continuous strand?
A. Topoisomerase
B. RNA Polymerase
C. Ligase
D. Primase
Answer: C
Rationale: DNA Ligase ‘glues’ the sugar-phosphate backbone together where nicks exist.
