C785 Biochemistry Module 6 Study Guide Quiz 2026 |WGU
1. Which enzyme is responsible for unwinding the DNA double helix at the
replication fork?
A. Helicase
B. Topoisomerase
C. DNA Polymerase
D. DNA Ligase
Answer: A
Rationale: Helicase breaks the hydrogen bonds between base pairs to separate the two
strands of DNA for replication.
2. In which direction does DNA Polymerase synthesize a new DNA strand?
A. 3’ to 5’
B. N-terminus to C-terminus
C. 5’ to 3’
D. C-terminus to N-terminus
Answer: C
Rationale: DNA Polymerase adds nucleotides only to the 3’ end of a growing strand,
meaning synthesis occurs in the 5’ to 3’ direction.
3. What is the role of Primase in DNA replication?
A. To seal the gaps between Okazaki fragments
B. To prevent the DNA from re-annealing
C. To remove mismatched base pairs
D. To synthesize a short RNA primer to provide a 3’-OH group
Answer: D
,Rationale: DNA Polymerase cannot start a new strand from scratch; Primase provides the
necessary RNA primer.
4. Okazaki fragments are found on which of the following?
A. The leading strand
B. The mRNA transcript
C. The lagging strand
D. The promoter region
Answer: C
Rationale: Because DNA is antiparallel, the lagging strand is synthesized discontinuously
in short segments called Okazaki fragments.
5. Which enzyme is responsible for joining the phosphodiester backbone of DNA
fragments?
A. DNA Ligase
B. RNA Polymerase
C. Exonuclease
D. Helicase
Answer: A
Rationale: DNA Ligase ‘glues’ or seals the nicks in the sugar-phosphate backbone,
particularly between Okazaki fragments.
6. The process of copying a gene’s DNA sequence into a sequence of RNA is
called:
A. Replication
B. Translation
C. Reverse Transcription
D. Transcription
Answer: D
, Rationale: Transcription is the first step of gene expression where DNA is used as a
template to create mRNA.
7. Which nitrogenous base is found in RNA but not in DNA?
A. Thymine
B. Uracil
C. Guanine
D. Adenine
Answer: B
Rationale: RNA uses Uracil (U) instead of Thymine (T), which is found in DNA.
8. Where does transcription occur in a eukaryotic cell?
A. Cytoplasm
B. Ribosome
C. Nucleus
D. Mitochondria
Answer: C
Rationale: In eukaryotes, DNA is contained within the nucleus, so transcription must occur
there before mRNA is exported.
9. What is the primary function of mRNA?
A. To carry amino acids to the ribosome
B. To carry genetic information from DNA to the ribosome
C. To form the structural core of the ribosome
D. To catalyze the formation of peptide bonds
Answer: B
Rationale: Messenger RNA (mRNA) serves as the intermediary ‘message’ that carries
genetic code to the protein-building machinery.
1. Which enzyme is responsible for unwinding the DNA double helix at the
replication fork?
A. Helicase
B. Topoisomerase
C. DNA Polymerase
D. DNA Ligase
Answer: A
Rationale: Helicase breaks the hydrogen bonds between base pairs to separate the two
strands of DNA for replication.
2. In which direction does DNA Polymerase synthesize a new DNA strand?
A. 3’ to 5’
B. N-terminus to C-terminus
C. 5’ to 3’
D. C-terminus to N-terminus
Answer: C
Rationale: DNA Polymerase adds nucleotides only to the 3’ end of a growing strand,
meaning synthesis occurs in the 5’ to 3’ direction.
3. What is the role of Primase in DNA replication?
A. To seal the gaps between Okazaki fragments
B. To prevent the DNA from re-annealing
C. To remove mismatched base pairs
D. To synthesize a short RNA primer to provide a 3’-OH group
Answer: D
,Rationale: DNA Polymerase cannot start a new strand from scratch; Primase provides the
necessary RNA primer.
4. Okazaki fragments are found on which of the following?
A. The leading strand
B. The mRNA transcript
C. The lagging strand
D. The promoter region
Answer: C
Rationale: Because DNA is antiparallel, the lagging strand is synthesized discontinuously
in short segments called Okazaki fragments.
5. Which enzyme is responsible for joining the phosphodiester backbone of DNA
fragments?
A. DNA Ligase
B. RNA Polymerase
C. Exonuclease
D. Helicase
Answer: A
Rationale: DNA Ligase ‘glues’ or seals the nicks in the sugar-phosphate backbone,
particularly between Okazaki fragments.
6. The process of copying a gene’s DNA sequence into a sequence of RNA is
called:
A. Replication
B. Translation
C. Reverse Transcription
D. Transcription
Answer: D
, Rationale: Transcription is the first step of gene expression where DNA is used as a
template to create mRNA.
7. Which nitrogenous base is found in RNA but not in DNA?
A. Thymine
B. Uracil
C. Guanine
D. Adenine
Answer: B
Rationale: RNA uses Uracil (U) instead of Thymine (T), which is found in DNA.
8. Where does transcription occur in a eukaryotic cell?
A. Cytoplasm
B. Ribosome
C. Nucleus
D. Mitochondria
Answer: C
Rationale: In eukaryotes, DNA is contained within the nucleus, so transcription must occur
there before mRNA is exported.
9. What is the primary function of mRNA?
A. To carry amino acids to the ribosome
B. To carry genetic information from DNA to the ribosome
C. To form the structural core of the ribosome
D. To catalyze the formation of peptide bonds
Answer: B
Rationale: Messenger RNA (mRNA) serves as the intermediary ‘message’ that carries
genetic code to the protein-building machinery.
