BIOD 101 Module 4 Exam – Essential Biology I (Portage Learning) –
200 Practice Questions with Verified Answers
QUESTIONS 1–200
Topic 1: DNA Structure and Chemistry
1. Which of the following best describes the structure of DNA?
A) A single-stranded molecule composed of nucleotides with ribose sugar
B) A double helix composed of two antiparallel strands held together by hydrogen bonds between
complementary bases
C) A triple-stranded molecule with adenine, guanine, cytosine, and uracil
D) A circular molecule found only in prokaryotic cells
Answer B: A double helix composed of two antiparallel strands held together by hydrogen bonds
between complementary bases
Rationale: DNA is a double helix with two antiparallel strands held together by hydrogen bonds between
complementary bases.
2. What are the four nitrogenous bases found in DNA?
A) Adenine, guanine, cytosine, and uracil
B) Adenine, guanine, cytosine, and thymine
C) Adenine, thymine, cytosine, and uracil
D) Guanine, cytosine, thymine, and uracil
Answer B: Adenine, guanine, cytosine, and thymine
Rationale: DNA contains adenine (A), guanine (G), cytosine (C), and thymine (T). RNA contains uracil (U)
instead of thymine.
3. Which nitrogenous bases are classified as purines?
A) Adenine and thymine
B) Guanine and cytosine
C) Adenine and guanine
,D) Thymine and cytosine
Answer C: Adenine and guanine
Rationale: Purines have a double-ring structure and include adenine (A) and guanine (G). Pyrimidines have
a single-ring structure.
4. Which nitrogenous bases are classified as pyrimidines?
A) Adenine and guanine
B) Thymine and cytosine
C) Adenine and thymine
D) Guanine and cytosine
Answer B: Thymine and cytosine
Rationale: Pyrimidines have a single-ring structure and include thymine (T) and cytosine (C).
5. In DNA, adenine (A) pairs with:
A) Guanine
B) Cytosine
C) Thymine
D) Uracil
Answer C: Thymine
Rationale: Adenine pairs with thymine via two hydrogen bonds in DNA.
6. In DNA, guanine (G) pairs with:
A) Adenine
B) Cytosine
C) Thymine
D) Uracil
Answer B: Cytosine
Rationale: Guanine pairs with cytosine via three hydrogen bonds in DNA.
7. How many hydrogen bonds are formed between adenine and thymine?
A) 1
B) 2
,C) 3
D) 4
Answer B: 2
Rationale: A-T base pairs form two hydrogen bonds; G-C base pairs form three hydrogen bonds.
8. How many hydrogen bonds are formed between guanine and cytosine?
A) 1
B) 2
C) 3
D) 4
Answer C: 3
Rationale: G-C base pairs form three hydrogen bonds, making them stronger than A-T pairs.
9. A nucleoside is composed of:
A) A nitrogenous base plus a phosphate group
B) A nitrogenous base plus a deoxyribose sugar
C) A nitrogenous base plus a deoxyribose sugar plus a phosphate group
D) Two complementary nitrogenous bases held together by hydrogen bonds
Answer B: A nitrogenous base plus a deoxyribose sugar
Rationale: A nucleoside consists of a nitrogenous base linked to deoxyribose sugar; a nucleotide includes a
phosphate group.
10. A nucleotide is composed of:
A) A nitrogenous base plus a deoxyribose sugar
B) A nitrogenous base plus a phosphate group
C) A nitrogenous base plus a deoxyribose sugar plus a phosphate group
D) Two complementary nitrogenous bases held together by hydrogen bonds
Answer C: A nitrogenous base plus a deoxyribose sugar plus a phosphate group
Rationale: A nucleotide consists of a nitrogenous base, a deoxyribose sugar, and a phosphate group.
11. The two strands of DNA are described as antiparallel because:
A) They run in the same direction
, B) One strand runs 5'→3' and the other runs 3'→5'
j j j j j j j j j
C) They are identical in sequence
j j j j j
D) They are held together by covalent bonds
j j j j j j j
Answer B: One strand runs 5'→3' and the other runs 3'→5'
j j j j j j j j j j
Rationale: Antiparallel orientation means the strands run in opposite directions.
j j j j j j j j j
12. The backbone of DNA is composed of:
j j j j j j j
A) Nitrogenous bases
j j
B) Sugar and phosphate groups
j j j j
C) Hydrogen bonds
j j
D) Amino acids
j j
Answer B: Sugar and phosphate groups
j j j j j
Rationale: The sugar-phosphate backbone forms the structural framework of DNA.
j j j j j j j j j
13. Purines contain:
j j
A) 1 carbon-nitrogen ring and 2 nitrogen atoms
j j j j j j j
B) 2 carbon-nitrogen rings and 4 nitrogen atoms
j j j j j j j
C) 1 carbon-nitrogen ring and 4 nitrogen atoms
j j j j j j j
D) 2 carbon-nitrogen rings and 2 nitrogen atoms
j j j j j j j
Answer B: 2 carbon-nitrogen rings and 4 nitrogen atoms
j j j j j j j j
Rationale: Purines (adenine and guanine) have two fused carbon-nitrogen rings.
j j j j j j j j j
14. Pyrimidines contain:
j j
A) 1 carbon-nitrogen ring and 2 nitrogen atoms
j j j j j j j
B) 2 carbon-nitrogen rings and 4 nitrogen atoms
j j j j j j j
C) 1 carbon-nitrogen ring and 4 nitrogen atoms
j j j j j j j
D) 2 carbon-nitrogen rings and 2 nitrogen atoms
j j j j j j j
Answer A: 1 carbon-nitrogen ring and 2 nitrogen atoms
j j j j j j j j
Rationale: Pyrimidines (thymine, cytosine, uracil) have a single carbon-nitrogen ring.
j j j j j j j j j
15. Complete the following DNA strand: 3' ATCG 5' / 5' _____ 3'
j j j j j j j j j j j j
A) TAGC
j
200 Practice Questions with Verified Answers
QUESTIONS 1–200
Topic 1: DNA Structure and Chemistry
1. Which of the following best describes the structure of DNA?
A) A single-stranded molecule composed of nucleotides with ribose sugar
B) A double helix composed of two antiparallel strands held together by hydrogen bonds between
complementary bases
C) A triple-stranded molecule with adenine, guanine, cytosine, and uracil
D) A circular molecule found only in prokaryotic cells
Answer B: A double helix composed of two antiparallel strands held together by hydrogen bonds
between complementary bases
Rationale: DNA is a double helix with two antiparallel strands held together by hydrogen bonds between
complementary bases.
2. What are the four nitrogenous bases found in DNA?
A) Adenine, guanine, cytosine, and uracil
B) Adenine, guanine, cytosine, and thymine
C) Adenine, thymine, cytosine, and uracil
D) Guanine, cytosine, thymine, and uracil
Answer B: Adenine, guanine, cytosine, and thymine
Rationale: DNA contains adenine (A), guanine (G), cytosine (C), and thymine (T). RNA contains uracil (U)
instead of thymine.
3. Which nitrogenous bases are classified as purines?
A) Adenine and thymine
B) Guanine and cytosine
C) Adenine and guanine
,D) Thymine and cytosine
Answer C: Adenine and guanine
Rationale: Purines have a double-ring structure and include adenine (A) and guanine (G). Pyrimidines have
a single-ring structure.
4. Which nitrogenous bases are classified as pyrimidines?
A) Adenine and guanine
B) Thymine and cytosine
C) Adenine and thymine
D) Guanine and cytosine
Answer B: Thymine and cytosine
Rationale: Pyrimidines have a single-ring structure and include thymine (T) and cytosine (C).
5. In DNA, adenine (A) pairs with:
A) Guanine
B) Cytosine
C) Thymine
D) Uracil
Answer C: Thymine
Rationale: Adenine pairs with thymine via two hydrogen bonds in DNA.
6. In DNA, guanine (G) pairs with:
A) Adenine
B) Cytosine
C) Thymine
D) Uracil
Answer B: Cytosine
Rationale: Guanine pairs with cytosine via three hydrogen bonds in DNA.
7. How many hydrogen bonds are formed between adenine and thymine?
A) 1
B) 2
,C) 3
D) 4
Answer B: 2
Rationale: A-T base pairs form two hydrogen bonds; G-C base pairs form three hydrogen bonds.
8. How many hydrogen bonds are formed between guanine and cytosine?
A) 1
B) 2
C) 3
D) 4
Answer C: 3
Rationale: G-C base pairs form three hydrogen bonds, making them stronger than A-T pairs.
9. A nucleoside is composed of:
A) A nitrogenous base plus a phosphate group
B) A nitrogenous base plus a deoxyribose sugar
C) A nitrogenous base plus a deoxyribose sugar plus a phosphate group
D) Two complementary nitrogenous bases held together by hydrogen bonds
Answer B: A nitrogenous base plus a deoxyribose sugar
Rationale: A nucleoside consists of a nitrogenous base linked to deoxyribose sugar; a nucleotide includes a
phosphate group.
10. A nucleotide is composed of:
A) A nitrogenous base plus a deoxyribose sugar
B) A nitrogenous base plus a phosphate group
C) A nitrogenous base plus a deoxyribose sugar plus a phosphate group
D) Two complementary nitrogenous bases held together by hydrogen bonds
Answer C: A nitrogenous base plus a deoxyribose sugar plus a phosphate group
Rationale: A nucleotide consists of a nitrogenous base, a deoxyribose sugar, and a phosphate group.
11. The two strands of DNA are described as antiparallel because:
A) They run in the same direction
, B) One strand runs 5'→3' and the other runs 3'→5'
j j j j j j j j j
C) They are identical in sequence
j j j j j
D) They are held together by covalent bonds
j j j j j j j
Answer B: One strand runs 5'→3' and the other runs 3'→5'
j j j j j j j j j j
Rationale: Antiparallel orientation means the strands run in opposite directions.
j j j j j j j j j
12. The backbone of DNA is composed of:
j j j j j j j
A) Nitrogenous bases
j j
B) Sugar and phosphate groups
j j j j
C) Hydrogen bonds
j j
D) Amino acids
j j
Answer B: Sugar and phosphate groups
j j j j j
Rationale: The sugar-phosphate backbone forms the structural framework of DNA.
j j j j j j j j j
13. Purines contain:
j j
A) 1 carbon-nitrogen ring and 2 nitrogen atoms
j j j j j j j
B) 2 carbon-nitrogen rings and 4 nitrogen atoms
j j j j j j j
C) 1 carbon-nitrogen ring and 4 nitrogen atoms
j j j j j j j
D) 2 carbon-nitrogen rings and 2 nitrogen atoms
j j j j j j j
Answer B: 2 carbon-nitrogen rings and 4 nitrogen atoms
j j j j j j j j
Rationale: Purines (adenine and guanine) have two fused carbon-nitrogen rings.
j j j j j j j j j
14. Pyrimidines contain:
j j
A) 1 carbon-nitrogen ring and 2 nitrogen atoms
j j j j j j j
B) 2 carbon-nitrogen rings and 4 nitrogen atoms
j j j j j j j
C) 1 carbon-nitrogen ring and 4 nitrogen atoms
j j j j j j j
D) 2 carbon-nitrogen rings and 2 nitrogen atoms
j j j j j j j
Answer A: 1 carbon-nitrogen ring and 2 nitrogen atoms
j j j j j j j j
Rationale: Pyrimidines (thymine, cytosine, uracil) have a single carbon-nitrogen ring.
j j j j j j j j j
15. Complete the following DNA strand: 3' ATCG 5' / 5' _____ 3'
j j j j j j j j j j j j
A) TAGC
j
