C785 Biochemistry - Week 4: Genetics and Molecular Biology 2026
|WGU
1. What type of bond connects the sugar-phosphate backbone of a DNA
molecule?
A. Hydrogen bond
B. Phosphodiester bond
C. Ionic bond
D. Peptide bond
Answer: B
Rationale: Phosphodiester bonds are strong covalent bonds that connect the 3’ carbon of
one sugar molecule to the 5’ carbon of another, forming the backbone of DNA.
2. In a double-stranded DNA molecule, which base pairs with Cytosine and how
many hydrogen bonds are formed?
A. Guanine, 2 hydrogen bonds
B. Adenine, 3 hydrogen bonds
C. Guanine, 3 hydrogen bonds
D. Thymine, 2 hydrogen bonds
Answer: C
Rationale: Guanine pairs with Cytosine via three hydrogen bonds, while Adenine pairs
with Thymine via two hydrogen bonds.
,3. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase
B. DNA Ligase
C. Helicase
D. Primase
Answer: C
Rationale: Helicase breaks the hydrogen bonds between the base pairs to separate the two
strands of the DNA molecule.
4. Which of the following describes the direction of DNA synthesis?
A. 3’ to 5’ direction
B. Randomly in both directions
C. N-terminus to C-terminus
D. 5’ to 3’ direction
Answer: D
Rationale: DNA polymerase can only add new nucleotides to the 3’ hydroxyl group of a
growing strand, meaning synthesis always occurs in the 5’ to 3’ direction.
5. What are Okazaki fragments?
A. Short sequences of RNA used as primers
B. Segments of DNA synthesized on the leading strand
C. Molecules that repair damaged DNA
D. Short segments of DNA synthesized on the lagging strand
Answer: D
Rationale: Because DNA is antiparallel and polymerase only works 5’ to 3’, the lagging
strand is synthesized discontinuously in short pieces called Okazaki fragments.
, 6. Which enzyme joins Okazaki fragments together?
A. Helicase
B. DNA Polymerase I
C. Topoisomerase
D. DNA Ligase
Answer: D
Rationale: DNA Ligase seals the nicks between DNA fragments by creating phosphodiester
bonds, completing the backbone.
7. What is the primary function of DNA Polymerase III in prokaryotes?
A. To remove RNA primers
B. To unwind the DNA helix
C. To proofread and synthesize the new DNA strand
D. To add a poly-A tail to mRNA
Answer: C
Rationale: DNA Polymerase III is the main enzyme involved in replicating the DNA strand
and has proofreading capabilities.
8. Which process converts DNA into mRNA?
A. Translation
B. Transcription
C. Replication
D. Transformation
Answer: B
Rationale: Transcription is the process where a specific segment of DNA is used as a
template to produce a complementary RNA strand.
|WGU
1. What type of bond connects the sugar-phosphate backbone of a DNA
molecule?
A. Hydrogen bond
B. Phosphodiester bond
C. Ionic bond
D. Peptide bond
Answer: B
Rationale: Phosphodiester bonds are strong covalent bonds that connect the 3’ carbon of
one sugar molecule to the 5’ carbon of another, forming the backbone of DNA.
2. In a double-stranded DNA molecule, which base pairs with Cytosine and how
many hydrogen bonds are formed?
A. Guanine, 2 hydrogen bonds
B. Adenine, 3 hydrogen bonds
C. Guanine, 3 hydrogen bonds
D. Thymine, 2 hydrogen bonds
Answer: C
Rationale: Guanine pairs with Cytosine via three hydrogen bonds, while Adenine pairs
with Thymine via two hydrogen bonds.
,3. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase
B. DNA Ligase
C. Helicase
D. Primase
Answer: C
Rationale: Helicase breaks the hydrogen bonds between the base pairs to separate the two
strands of the DNA molecule.
4. Which of the following describes the direction of DNA synthesis?
A. 3’ to 5’ direction
B. Randomly in both directions
C. N-terminus to C-terminus
D. 5’ to 3’ direction
Answer: D
Rationale: DNA polymerase can only add new nucleotides to the 3’ hydroxyl group of a
growing strand, meaning synthesis always occurs in the 5’ to 3’ direction.
5. What are Okazaki fragments?
A. Short sequences of RNA used as primers
B. Segments of DNA synthesized on the leading strand
C. Molecules that repair damaged DNA
D. Short segments of DNA synthesized on the lagging strand
Answer: D
Rationale: Because DNA is antiparallel and polymerase only works 5’ to 3’, the lagging
strand is synthesized discontinuously in short pieces called Okazaki fragments.
, 6. Which enzyme joins Okazaki fragments together?
A. Helicase
B. DNA Polymerase I
C. Topoisomerase
D. DNA Ligase
Answer: D
Rationale: DNA Ligase seals the nicks between DNA fragments by creating phosphodiester
bonds, completing the backbone.
7. What is the primary function of DNA Polymerase III in prokaryotes?
A. To remove RNA primers
B. To unwind the DNA helix
C. To proofread and synthesize the new DNA strand
D. To add a poly-A tail to mRNA
Answer: C
Rationale: DNA Polymerase III is the main enzyme involved in replicating the DNA strand
and has proofreading capabilities.
8. Which process converts DNA into mRNA?
A. Translation
B. Transcription
C. Replication
D. Transformation
Answer: B
Rationale: Transcription is the process where a specific segment of DNA is used as a
template to produce a complementary RNA strand.
