CHEM 210 Module 6 Exam: Nucleotides, DNA, Replication, and
Transcription 2026/2027 UPDATE
1. Which of the following components is NOT found in a nucleotide?
A. A nitrogenous base
B. A five-carbon sugar
C. A phosphate group
D. A hexose sugar
Answer: D
Rationale: Nucleotides consist of a nitrogenous base, a pentose (five-carbon) sugar, and at
least one phosphate group. Hexose sugars are six-carbon sugars like glucose.
2. Which nitrogenous bases are classified as purines?
A. Guanine and Cytosine
B. Cytosine and Thymine
C. Adenine and Thymine
D. Adenine and Guanine
Answer: D
Rationale: Purines consist of a double-ring structure and include Adenine (A) and Guanine
(G).
,3. What is the structural difference between ribose and deoxyribose?
A. Ribose has an -OH group at the C2 position, while deoxyribose has an -H.
B. Deoxyribose has an -OH group at the C3 position, while ribose has an -H.
C. Ribose contains six carbons, while deoxyribose contains five.
D. There is no structural difference; they are isomers.
Answer: A
Rationale: Deoxyribose lacks the oxygen atom at the C2 position, hence the name ‘deoxy’.
4. Which bond links the phosphate group of one nucleotide to the sugar of the
next in a DNA strand?
A. Hydrogen bond
B. Glycosidic bond
C. Phosphodiester bond
D. Peptide bond
Answer: C
Rationale: A phosphodiester bond connects the 3’ hydroxyl group of one sugar to the 5’
phosphate group of the adjacent sugar.
5. In a DNA double helix, how many hydrogen bonds form between Guanine
and Cytosine?
A. One
B. Two
C. Three
D. Four
Answer: C
Rationale: G-C base pairs are held together by three hydrogen bonds, making them more
stable than A-T pairs.
, 6. What does it mean that DNA strands are ‘antiparallel’?
A. One strand runs 5’ to 3’ while the other runs 3’ to 5’.
B. They run in the same 5’ to 3’ direction.
C. They are composed of different sugars.
D. They do not form a helical structure.
Answer: A
Rationale: Antiparallel orientation means the two strands of the DNA double helix run in
opposite directions relative to their carbon numbering.
7. According to Chargaff’s rules, if a DNA sample contains 20% Adenine, what is
the percentage of Guanine?
A. 20%
B. 40%
C. 30%
D. 80%
Answer: C
Rationale: If A=20%, then T=20% (Total 40%). The remaining 60% must be split equally
between G and C, so G=30%.
8. Which form of DNA is a left-handed helix?
A. A-DNA
B. Z-DNA
C. B-DNA
D. C-DNA
Answer: B
Rationale: Z-DNA is a left-handed helical form of DNA that occurs in specific sequences or
under high salt conditions.
Transcription 2026/2027 UPDATE
1. Which of the following components is NOT found in a nucleotide?
A. A nitrogenous base
B. A five-carbon sugar
C. A phosphate group
D. A hexose sugar
Answer: D
Rationale: Nucleotides consist of a nitrogenous base, a pentose (five-carbon) sugar, and at
least one phosphate group. Hexose sugars are six-carbon sugars like glucose.
2. Which nitrogenous bases are classified as purines?
A. Guanine and Cytosine
B. Cytosine and Thymine
C. Adenine and Thymine
D. Adenine and Guanine
Answer: D
Rationale: Purines consist of a double-ring structure and include Adenine (A) and Guanine
(G).
,3. What is the structural difference between ribose and deoxyribose?
A. Ribose has an -OH group at the C2 position, while deoxyribose has an -H.
B. Deoxyribose has an -OH group at the C3 position, while ribose has an -H.
C. Ribose contains six carbons, while deoxyribose contains five.
D. There is no structural difference; they are isomers.
Answer: A
Rationale: Deoxyribose lacks the oxygen atom at the C2 position, hence the name ‘deoxy’.
4. Which bond links the phosphate group of one nucleotide to the sugar of the
next in a DNA strand?
A. Hydrogen bond
B. Glycosidic bond
C. Phosphodiester bond
D. Peptide bond
Answer: C
Rationale: A phosphodiester bond connects the 3’ hydroxyl group of one sugar to the 5’
phosphate group of the adjacent sugar.
5. In a DNA double helix, how many hydrogen bonds form between Guanine
and Cytosine?
A. One
B. Two
C. Three
D. Four
Answer: C
Rationale: G-C base pairs are held together by three hydrogen bonds, making them more
stable than A-T pairs.
, 6. What does it mean that DNA strands are ‘antiparallel’?
A. One strand runs 5’ to 3’ while the other runs 3’ to 5’.
B. They run in the same 5’ to 3’ direction.
C. They are composed of different sugars.
D. They do not form a helical structure.
Answer: A
Rationale: Antiparallel orientation means the two strands of the DNA double helix run in
opposite directions relative to their carbon numbering.
7. According to Chargaff’s rules, if a DNA sample contains 20% Adenine, what is
the percentage of Guanine?
A. 20%
B. 40%
C. 30%
D. 80%
Answer: C
Rationale: If A=20%, then T=20% (Total 40%). The remaining 60% must be split equally
between G and C, so G=30%.
8. Which form of DNA is a left-handed helix?
A. A-DNA
B. Z-DNA
C. B-DNA
D. C-DNA
Answer: B
Rationale: Z-DNA is a left-handed helical form of DNA that occurs in specific sequences or
under high salt conditions.
