DNA and RNA structure Final Exam Review/ Study
Questions with Correct Verified Answers/ Latest Update
2026 – Rated A+
1. A nucleotide is composed of which three components?
• A. Phosphate, ribose sugar, and nitrogenous base
• B. Phosphate, deoxyribose sugar, and amino acid
• C. Phosphate, sugar, and nitrogenous base
• D. Sugar, nitrogenous base, and protein
Correct Answer: C
Rationale: A nucleotide is composed of three components: a
phosphate group, a pentose sugar (either ribose or deoxyribose),
and a nitrogenous base. The phosphate and sugar form the
backbone of the nucleic acid, while the base carries the genetic
information .
2. Which of the following is NOT found within DNA?
1
, • A. Thymine
• B. Phosphodiester bonds
• C. Complementary base pairing
• D. Amino acids
Correct Answer: D
Rationale: Amino acids are the building blocks of proteins, not
DNA. DNA contains nucleotides with nitrogenous bases (adenine,
thymine, cytosine, guanine), phosphodiester bonds linking
nucleotides, and complementary base pairing between strands .
3. If 30% of the bases within a DNA molecule are adenine, what
is the percentage of thymine?
• A. 20%
• B. 25%
• C. 30%
• D. 35%
2
,Correct Answer: C
Rationale: According to Chargaff's rules, adenine pairs with
thymine in DNA, so the percentage of adenine equals the
percentage of thymine. If adenine is 30%, thymine is also 30%.
Guanine and cytosine would each be 20% .
4. The correct structure of DNA components can be presented as:
• A. Phosphate–base–sugar
• B. Phosphate–sugar–base
• C. Base–phosphate–sugar
• D. Phosphate–sugar–phosphate–base
Correct Answer: B
Rationale: In a nucleotide, the phosphate group is attached to the
5' carbon of the sugar, and the nitrogenous base is attached to the
1' carbon of the sugar. The correct linear representation is
phosphate–sugar–base .
3
, 5. Which of the following is NOT a base of RNA?
• A. Thymine (T)
• B. Adenine (A)
• C. Cytosine (C)
• D. Guanine (G)
Correct Answer: A
Rationale: Thymine is found in DNA, not RNA. RNA contains
adenine (A), cytosine (C), guanine (G), and uracil (U) in place of
thymine. Thymine is replaced by uracil in RNA because uracil is
chemically less stable but sufficient for RNA's temporary
information-carrying role .
6. Which base pairs with adenine in DNA?
• A. Guanine
• B. Cytosine
• C. Thymine
• D. Uracil
4
Questions with Correct Verified Answers/ Latest Update
2026 – Rated A+
1. A nucleotide is composed of which three components?
• A. Phosphate, ribose sugar, and nitrogenous base
• B. Phosphate, deoxyribose sugar, and amino acid
• C. Phosphate, sugar, and nitrogenous base
• D. Sugar, nitrogenous base, and protein
Correct Answer: C
Rationale: A nucleotide is composed of three components: a
phosphate group, a pentose sugar (either ribose or deoxyribose),
and a nitrogenous base. The phosphate and sugar form the
backbone of the nucleic acid, while the base carries the genetic
information .
2. Which of the following is NOT found within DNA?
1
, • A. Thymine
• B. Phosphodiester bonds
• C. Complementary base pairing
• D. Amino acids
Correct Answer: D
Rationale: Amino acids are the building blocks of proteins, not
DNA. DNA contains nucleotides with nitrogenous bases (adenine,
thymine, cytosine, guanine), phosphodiester bonds linking
nucleotides, and complementary base pairing between strands .
3. If 30% of the bases within a DNA molecule are adenine, what
is the percentage of thymine?
• A. 20%
• B. 25%
• C. 30%
• D. 35%
2
,Correct Answer: C
Rationale: According to Chargaff's rules, adenine pairs with
thymine in DNA, so the percentage of adenine equals the
percentage of thymine. If adenine is 30%, thymine is also 30%.
Guanine and cytosine would each be 20% .
4. The correct structure of DNA components can be presented as:
• A. Phosphate–base–sugar
• B. Phosphate–sugar–base
• C. Base–phosphate–sugar
• D. Phosphate–sugar–phosphate–base
Correct Answer: B
Rationale: In a nucleotide, the phosphate group is attached to the
5' carbon of the sugar, and the nitrogenous base is attached to the
1' carbon of the sugar. The correct linear representation is
phosphate–sugar–base .
3
, 5. Which of the following is NOT a base of RNA?
• A. Thymine (T)
• B. Adenine (A)
• C. Cytosine (C)
• D. Guanine (G)
Correct Answer: A
Rationale: Thymine is found in DNA, not RNA. RNA contains
adenine (A), cytosine (C), guanine (G), and uracil (U) in place of
thymine. Thymine is replaced by uracil in RNA because uracil is
chemically less stable but sufficient for RNA's temporary
information-carrying role .
6. Which base pairs with adenine in DNA?
• A. Guanine
• B. Cytosine
• C. Thymine
• D. Uracil
4
