C785 Biochemistry Week 6 - Molecular Biology 2026 |WGU
1. Which enzyme is responsible for relieving the torsional strain caused by the
unwinding of the DNA double helix?
A. Helicase
B. Primase
C. DNA Ligase
D. Topoisomerase
Answer: D
Rationale: Topoisomerase (also known as DNA gyrase in bacteria) travels ahead of the
replication fork to relieve supercoiling caused by the unwinding of DNA.
2. In DNA replication, what is the primary role of the lagging strand?
A. To synthesize DNA continuously in the 5’ to 3’ direction
B. To serve as a template for RNA synthesis
C. To synthesize DNA discontinuously in small fragments called Okazaki fragments
D. To provide a starting point for DNA polymerase III
Answer: C
Rationale: Because DNA polymerase can only synthesize in the 5’ to 3’ direction, the
lagging strand must be synthesized away from the replication fork in short Okazaki
fragments.
,3. What type of bond connects the sugar-phosphate backbone of a DNA strand?
A. Hydrogen bond
B. Ionic bond
C. Phosphodiester bond
D. Peptide bond
Answer: C
Rationale: Phosphodiester bonds are strong covalent bonds that connect the 3’ carbon of
one deoxyribose sugar to the 5’ carbon of the next.
4. Which of the following is true regarding the base pairing rules in DNA?
A. Adenine pairs with Uracil via two hydrogen bonds
B. Thymine pairs with Cytosine via two hydrogen bonds
C. Guanine pairs with Cytosine via three hydrogen bonds
D. Adenine pairs with Guanine via three hydrogen bonds
Answer: C
Rationale: Guanine and Cytosine form three hydrogen bonds, while Adenine and Thymine
form two hydrogen bonds in DNA.
5. The process of DNA replication is described as ‘semi-conservative’ because:
A. Both strands of the daughter DNA are entirely new
B. Each new DNA molecule consists of one original strand and one newly synthesized strand
C. Only half of the DNA molecule is replicated at any time
D. The original DNA molecule remains intact and a whole new one is made
Answer: B
Rationale: Semi-conservative replication ensures that each daughter molecule contains
one parental strand and one newly synthesized strand.
, 6. Which enzyme synthesizes the RNA primer needed to initiate DNA
replication?
A. DNA Polymerase I
B. Helicase
C. Primase
D. Telomerase
Answer: C
Rationale: Primase creates a short RNA primer because DNA polymerase cannot start a
new strand from scratch; it requires a 3’-OH group to add nucleotides.
7. What is the function of DNA Ligase in replication?
A. To unwind the double helix
B. To join Okazaki fragments together by forming phosphodiester bonds
C. To add nucleotides to the growing strand
D. To remove RNA primers
Answer: B
Rationale: DNA Ligase acts as ‘glue’ to seal the nicks between fragments on the lagging
strand.
8. Which of the following describes a silent mutation?
A. A mutation that does not change the amino acid sequence of the protein
B. A mutation that changes the amino acid sequence
C. A mutation that results in a premature stop codon
D. A mutation that causes a frame shift
Answer: A
Rationale: Due to the degeneracy of the genetic code, some base changes result in a codon
that still codes for the same amino acid, resulting in no change to the protein.
1. Which enzyme is responsible for relieving the torsional strain caused by the
unwinding of the DNA double helix?
A. Helicase
B. Primase
C. DNA Ligase
D. Topoisomerase
Answer: D
Rationale: Topoisomerase (also known as DNA gyrase in bacteria) travels ahead of the
replication fork to relieve supercoiling caused by the unwinding of DNA.
2. In DNA replication, what is the primary role of the lagging strand?
A. To synthesize DNA continuously in the 5’ to 3’ direction
B. To serve as a template for RNA synthesis
C. To synthesize DNA discontinuously in small fragments called Okazaki fragments
D. To provide a starting point for DNA polymerase III
Answer: C
Rationale: Because DNA polymerase can only synthesize in the 5’ to 3’ direction, the
lagging strand must be synthesized away from the replication fork in short Okazaki
fragments.
,3. What type of bond connects the sugar-phosphate backbone of a DNA strand?
A. Hydrogen bond
B. Ionic bond
C. Phosphodiester bond
D. Peptide bond
Answer: C
Rationale: Phosphodiester bonds are strong covalent bonds that connect the 3’ carbon of
one deoxyribose sugar to the 5’ carbon of the next.
4. Which of the following is true regarding the base pairing rules in DNA?
A. Adenine pairs with Uracil via two hydrogen bonds
B. Thymine pairs with Cytosine via two hydrogen bonds
C. Guanine pairs with Cytosine via three hydrogen bonds
D. Adenine pairs with Guanine via three hydrogen bonds
Answer: C
Rationale: Guanine and Cytosine form three hydrogen bonds, while Adenine and Thymine
form two hydrogen bonds in DNA.
5. The process of DNA replication is described as ‘semi-conservative’ because:
A. Both strands of the daughter DNA are entirely new
B. Each new DNA molecule consists of one original strand and one newly synthesized strand
C. Only half of the DNA molecule is replicated at any time
D. The original DNA molecule remains intact and a whole new one is made
Answer: B
Rationale: Semi-conservative replication ensures that each daughter molecule contains
one parental strand and one newly synthesized strand.
, 6. Which enzyme synthesizes the RNA primer needed to initiate DNA
replication?
A. DNA Polymerase I
B. Helicase
C. Primase
D. Telomerase
Answer: C
Rationale: Primase creates a short RNA primer because DNA polymerase cannot start a
new strand from scratch; it requires a 3’-OH group to add nucleotides.
7. What is the function of DNA Ligase in replication?
A. To unwind the double helix
B. To join Okazaki fragments together by forming phosphodiester bonds
C. To add nucleotides to the growing strand
D. To remove RNA primers
Answer: B
Rationale: DNA Ligase acts as ‘glue’ to seal the nicks between fragments on the lagging
strand.
8. Which of the following describes a silent mutation?
A. A mutation that does not change the amino acid sequence of the protein
B. A mutation that changes the amino acid sequence
C. A mutation that results in a premature stop codon
D. A mutation that causes a frame shift
Answer: A
Rationale: Due to the degeneracy of the genetic code, some base changes result in a codon
that still codes for the same amino acid, resulting in no change to the protein.
