C785 Biochemistry Week 5 Study Guide Quiz 2026 – WGU
1. Which component of a nucleotide is responsible for the ‘acidic’ nature of
nucleic acids?
A. The phosphate group
B. The nitrogenous base
C. The deoxyribose sugar
D. The hydrogen bonds
Answer: A
Rationale: The phosphate group in a nucleotide is acidic because it can donate protons,
giving nucleic acids a negative charge at physiological pH.
2. In a double-stranded DNA molecule, which base pairing rule is consistently
followed?
A. A pairs with G; C pairs with T
B. A pairs with C; G pairs with T
C. A pairs with T; G pairs with C
D. A pairs with U; G pairs with C
Answer: C
Rationale: According to Chargaff’s rules and Watson-Crick base pairing, Adenine pairs
with Thymine via two hydrogen bonds, and Guanine pairs with Cytosine via three
hydrogen bonds.
,3. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. Helicase
B. DNA Ligase
C. DNA Polymerase III
D. Topoisomerase
Answer: A
Rationale: Helicase uses ATP to break the hydrogen bonds between the nitrogenous bases,
effectively ‘unzipping’ the DNA double helix.
4. During DNA replication, the ‘leading strand’ is synthesized in which direction?
A. 5’ to 3’ continuously
B. 3’ to 5’ continuously
C. 3’ to 5’ in Okazaki fragments
D. 5’ to 3’ in Okazaki fragments
Answer: A
Rationale: DNA polymerase can only add nucleotides to the 3’ end of a growing strand, so
synthesis always occurs in the 5’ to 3’ direction. The leading strand follows the replication
fork continuously.
5. What is the function of DNA Ligase?
A. To join Okazaki fragments on the lagging strand
B. To proofread the new DNA strand
C. To synthesize RNA primers
D. To stabilize single-stranded DNA
Answer: A
Rationale: DNA Ligase catalyzes the formation of phosphodiester bonds between DNA
fragments, specifically sealing nicks between Okazaki fragments on the lagging strand.
, 6. Which of the following describes the ‘Central Dogma’ of molecular biology?
A. RNA -> DNA -> Protein
B. DNA -> RNA -> Protein
C. Protein -> RNA -> DNA
D. DNA -> Protein -> RNA
Answer: B
Rationale: The Central Dogma states that genetic information flows from DNA
(replication) to RNA (transcription) and then to protein (translation).
7. How does RNA differ from DNA?
A. RNA contains thymine instead of uracil
B. RNA is always triple-stranded
C. RNA contains a 2’-OH group on its ribose sugar
D. RNA uses deoxyribose sugar
Answer: C
Rationale: RNA contains ribose sugar which has a hydroxyl group at the 2’ carbon,
whereas DNA contains deoxyribose (missing that oxygen).
8. Which enzyme catalyzes the synthesis of mRNA from a DNA template?
A. RNA Polymerase
B. Reverse Transcriptase
C. DNA Polymerase I
D. RNA Primase
Answer: A
Rationale: RNA Polymerase binds to the promoter region of DNA and synthesizes a
complementary mRNA strand in the 5’ to 3’ direction.
1. Which component of a nucleotide is responsible for the ‘acidic’ nature of
nucleic acids?
A. The phosphate group
B. The nitrogenous base
C. The deoxyribose sugar
D. The hydrogen bonds
Answer: A
Rationale: The phosphate group in a nucleotide is acidic because it can donate protons,
giving nucleic acids a negative charge at physiological pH.
2. In a double-stranded DNA molecule, which base pairing rule is consistently
followed?
A. A pairs with G; C pairs with T
B. A pairs with C; G pairs with T
C. A pairs with T; G pairs with C
D. A pairs with U; G pairs with C
Answer: C
Rationale: According to Chargaff’s rules and Watson-Crick base pairing, Adenine pairs
with Thymine via two hydrogen bonds, and Guanine pairs with Cytosine via three
hydrogen bonds.
,3. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. Helicase
B. DNA Ligase
C. DNA Polymerase III
D. Topoisomerase
Answer: A
Rationale: Helicase uses ATP to break the hydrogen bonds between the nitrogenous bases,
effectively ‘unzipping’ the DNA double helix.
4. During DNA replication, the ‘leading strand’ is synthesized in which direction?
A. 5’ to 3’ continuously
B. 3’ to 5’ continuously
C. 3’ to 5’ in Okazaki fragments
D. 5’ to 3’ in Okazaki fragments
Answer: A
Rationale: DNA polymerase can only add nucleotides to the 3’ end of a growing strand, so
synthesis always occurs in the 5’ to 3’ direction. The leading strand follows the replication
fork continuously.
5. What is the function of DNA Ligase?
A. To join Okazaki fragments on the lagging strand
B. To proofread the new DNA strand
C. To synthesize RNA primers
D. To stabilize single-stranded DNA
Answer: A
Rationale: DNA Ligase catalyzes the formation of phosphodiester bonds between DNA
fragments, specifically sealing nicks between Okazaki fragments on the lagging strand.
, 6. Which of the following describes the ‘Central Dogma’ of molecular biology?
A. RNA -> DNA -> Protein
B. DNA -> RNA -> Protein
C. Protein -> RNA -> DNA
D. DNA -> Protein -> RNA
Answer: B
Rationale: The Central Dogma states that genetic information flows from DNA
(replication) to RNA (transcription) and then to protein (translation).
7. How does RNA differ from DNA?
A. RNA contains thymine instead of uracil
B. RNA is always triple-stranded
C. RNA contains a 2’-OH group on its ribose sugar
D. RNA uses deoxyribose sugar
Answer: C
Rationale: RNA contains ribose sugar which has a hydroxyl group at the 2’ carbon,
whereas DNA contains deoxyribose (missing that oxygen).
8. Which enzyme catalyzes the synthesis of mRNA from a DNA template?
A. RNA Polymerase
B. Reverse Transcriptase
C. DNA Polymerase I
D. RNA Primase
Answer: A
Rationale: RNA Polymerase binds to the promoter region of DNA and synthesizes a
complementary mRNA strand in the 5’ to 3’ direction.
