C785 Biochemistry Module 6 Comprehensive Review 2026 |WGU
1. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase III
B. DNA Ligase
C. Helicase
D. Topoisomerase
Answer: C
Rationale: Helicase breaks the hydrogen bonds between the nitrogenous bases to separate
the two strands of DNA.
2. In DNA replication, the leading strand is synthesized in which direction?
A. 5’ to 3’
B. 3’ to 5’
C. Bi-directionally
D. Randomly
Answer: A
Rationale: DNA polymerase can only add nucleotides to the 3’ end of a growing strand,
meaning synthesis always occurs 5’ to 3’.
3. What is the role of Primase in DNA replication?
A. To seal nicks in the sugar-phosphate backbone
B. To synthesize a short RNA primer to provide a 3’-OH group
C. To remove RNA primers
D. To prevent DNA from re-annealing
Answer: B
,Rationale: DNA polymerase requires a pre-existing 3’-OH group to start synthesis, which is
provided by the RNA primer created by Primase.
4. Which of the following describes the semi-conservative model of DNA
replication?
A. Two entirely new DNA molecules are formed
B. The original DNA molecule is preserved and a new one is made
C. Segments of old and new DNA are interspersed in both strands
D. Each new DNA molecule contains one original strand and one new strand
Answer: D
Rationale: Semi-conservative replication means each daughter DNA molecule consists of
one parental strand and one newly synthesized strand.
5. What are Okazaki fragments?
A. Mutated segments of DNA
B. The primers used in PCR
C. Short segments of DNA synthesized on the lagging strand
D. Segments of RNA found in the ribosome
Answer: C
Rationale: Because the lagging strand is antiparallel to the direction of the replication fork,
it must be synthesized in short, discontinuous segments called Okazaki fragments.
6. Which enzyme replaces RNA primers with DNA nucleotides?
A. DNA Polymerase III
B. Ligase
C. RNA Polymerase
D. DNA Polymerase I
Answer: D
Rationale: DNA Polymerase I has exonuclease activity to remove the RNA primer and
replace it with DNA nucleotides.
, 7. Which enzyme facilitates the joining of DNA strands by catalyzing the
formation of a phosphodiester bond?
A. Helicase
B. Primase
C. Telomerase
D. DNA Ligase
Answer: D
Rationale: DNA Ligase ‘glues’ the sugar-phosphate backbones together, specifically
between Okazaki fragments.
8. What is the central dogma of molecular biology?
A. RNA -> DNA -> Protein
B. Protein -> RNA -> DNA
C. DNA -> Protein -> RNA
D. DNA -> RNA -> Protein
Answer: D
Rationale: The central dogma describes the flow of genetic information from DNA
(storage) to RNA (messenger) to Protein (functional product).
9. Transcription occurs in which part of the eukaryotic cell?
A. Cytoplasm
B. Ribosome
C. Mitochondria
D. Nucleus
Answer: D
Rationale: In eukaryotes, DNA is housed in the nucleus, so transcription (DNA to RNA)
must occur there.
1. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase III
B. DNA Ligase
C. Helicase
D. Topoisomerase
Answer: C
Rationale: Helicase breaks the hydrogen bonds between the nitrogenous bases to separate
the two strands of DNA.
2. In DNA replication, the leading strand is synthesized in which direction?
A. 5’ to 3’
B. 3’ to 5’
C. Bi-directionally
D. Randomly
Answer: A
Rationale: DNA polymerase can only add nucleotides to the 3’ end of a growing strand,
meaning synthesis always occurs 5’ to 3’.
3. What is the role of Primase in DNA replication?
A. To seal nicks in the sugar-phosphate backbone
B. To synthesize a short RNA primer to provide a 3’-OH group
C. To remove RNA primers
D. To prevent DNA from re-annealing
Answer: B
,Rationale: DNA polymerase requires a pre-existing 3’-OH group to start synthesis, which is
provided by the RNA primer created by Primase.
4. Which of the following describes the semi-conservative model of DNA
replication?
A. Two entirely new DNA molecules are formed
B. The original DNA molecule is preserved and a new one is made
C. Segments of old and new DNA are interspersed in both strands
D. Each new DNA molecule contains one original strand and one new strand
Answer: D
Rationale: Semi-conservative replication means each daughter DNA molecule consists of
one parental strand and one newly synthesized strand.
5. What are Okazaki fragments?
A. Mutated segments of DNA
B. The primers used in PCR
C. Short segments of DNA synthesized on the lagging strand
D. Segments of RNA found in the ribosome
Answer: C
Rationale: Because the lagging strand is antiparallel to the direction of the replication fork,
it must be synthesized in short, discontinuous segments called Okazaki fragments.
6. Which enzyme replaces RNA primers with DNA nucleotides?
A. DNA Polymerase III
B. Ligase
C. RNA Polymerase
D. DNA Polymerase I
Answer: D
Rationale: DNA Polymerase I has exonuclease activity to remove the RNA primer and
replace it with DNA nucleotides.
, 7. Which enzyme facilitates the joining of DNA strands by catalyzing the
formation of a phosphodiester bond?
A. Helicase
B. Primase
C. Telomerase
D. DNA Ligase
Answer: D
Rationale: DNA Ligase ‘glues’ the sugar-phosphate backbones together, specifically
between Okazaki fragments.
8. What is the central dogma of molecular biology?
A. RNA -> DNA -> Protein
B. Protein -> RNA -> DNA
C. DNA -> Protein -> RNA
D. DNA -> RNA -> Protein
Answer: D
Rationale: The central dogma describes the flow of genetic information from DNA
(storage) to RNA (messenger) to Protein (functional product).
9. Transcription occurs in which part of the eukaryotic cell?
A. Cytoplasm
B. Ribosome
C. Mitochondria
D. Nucleus
Answer: D
Rationale: In eukaryotes, DNA is housed in the nucleus, so transcription (DNA to RNA)
must occur there.
