BioChem 210 Module 7 Exam: Molecular Genetics 2026 Geneva
College
1. What are the three components of a nucleotide?
A. Glucose, phosphate group, and nitrogenous base
B. Pentose sugar, sulfate group, and nitrogenous base
C. Pentose sugar, phosphate group, and nitrogenous base
D. Amino acid, phosphate group, and pentose sugar
Answer: C
Rationale: Nucleotides consist of a five-carbon (pentose) sugar, a phosphate group, and a
nitrogenous base.
2. Which nitrogenous bases are classified as purines?
A. Cytosine and Guanine
B. Adenine and Thymine
C. Cytosine and Uracil
D. Adenine and Guanine
Answer: D
Rationale: Purines (Adenine and Guanine) have a double-ring structure, while pyrimidines
have a single ring.
,3. In a DNA double helix, which base pairs with Cytosine through three
hydrogen bonds?
A. Adenine
B. Thymine
C. Guanine
D. Uracil
Answer: C
Rationale: According to Chargaff’s rules, Guanine always pairs with Cytosine via three
hydrogen bonds.
4. What type of bond links the sugar of one nucleotide to the phosphate of the
next in a DNA strand?
A. Phosphodiester bond
B. Hydrogen bond
C. Peptide bond
D. Ionic bond
Answer: A
Rationale: The DNA backbone is formed by phosphodiester bonds between the 3’ hydroxyl
group and 5’ phosphate group.
5. 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 base pairs to separate the two
strands of DNA.
, 6. In which direction is a new DNA strand always synthesized?
A. 5’ to 3’
B. 3’ to 5’
C. N-terminus to C-terminus
D. Left to right
Answer: A
Rationale: DNA polymerases can only add nucleotides to the 3’ end of a growing strand,
meaning synthesis occurs 5’ to 3’.
7. What are the short segments of DNA synthesized on the lagging strand
called?
A. Introns
B. Exons
C. Okazaki fragments
D. Primers
Answer: C
Rationale: The lagging strand is synthesized discontinuously in short pieces called Okazaki
fragments.
8. Which enzyme joins Okazaki fragments together?
A. DNA Polymerase I
B. Topoisomerase
C. DNA Ligase
D. RNA Polymerase
Answer: C
Rationale: DNA ligase seals the nicks between DNA fragments by creating phosphodiester
bonds.
College
1. What are the three components of a nucleotide?
A. Glucose, phosphate group, and nitrogenous base
B. Pentose sugar, sulfate group, and nitrogenous base
C. Pentose sugar, phosphate group, and nitrogenous base
D. Amino acid, phosphate group, and pentose sugar
Answer: C
Rationale: Nucleotides consist of a five-carbon (pentose) sugar, a phosphate group, and a
nitrogenous base.
2. Which nitrogenous bases are classified as purines?
A. Cytosine and Guanine
B. Adenine and Thymine
C. Cytosine and Uracil
D. Adenine and Guanine
Answer: D
Rationale: Purines (Adenine and Guanine) have a double-ring structure, while pyrimidines
have a single ring.
,3. In a DNA double helix, which base pairs with Cytosine through three
hydrogen bonds?
A. Adenine
B. Thymine
C. Guanine
D. Uracil
Answer: C
Rationale: According to Chargaff’s rules, Guanine always pairs with Cytosine via three
hydrogen bonds.
4. What type of bond links the sugar of one nucleotide to the phosphate of the
next in a DNA strand?
A. Phosphodiester bond
B. Hydrogen bond
C. Peptide bond
D. Ionic bond
Answer: A
Rationale: The DNA backbone is formed by phosphodiester bonds between the 3’ hydroxyl
group and 5’ phosphate group.
5. 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 base pairs to separate the two
strands of DNA.
, 6. In which direction is a new DNA strand always synthesized?
A. 5’ to 3’
B. 3’ to 5’
C. N-terminus to C-terminus
D. Left to right
Answer: A
Rationale: DNA polymerases can only add nucleotides to the 3’ end of a growing strand,
meaning synthesis occurs 5’ to 3’.
7. What are the short segments of DNA synthesized on the lagging strand
called?
A. Introns
B. Exons
C. Okazaki fragments
D. Primers
Answer: C
Rationale: The lagging strand is synthesized discontinuously in short pieces called Okazaki
fragments.
8. Which enzyme joins Okazaki fragments together?
A. DNA Polymerase I
B. Topoisomerase
C. DNA Ligase
D. RNA Polymerase
Answer: C
Rationale: DNA ligase seals the nicks between DNA fragments by creating phosphodiester
bonds.
