BIOL180 Practice Exam 5 DNA, RNA,
and Protein Synthesis Questions And
Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. Which molecule stores the hereditary information in most living
organisms?
A. Protein
B. RNA
C. Lipid
D. DNA
Answer: D. DNA
Rationale: DNA is the primary hereditary material in cellular
organisms. Its nucleotide sequence contains the information needed to
specify RNA molecules and proteins and to transmit genetic
information from one generation to the next.
2. What are the three components of a DNA nucleotide?
A. Phosphate group, deoxyribose sugar, and nitrogenous base
B. Phosphate group, ribose sugar, and amino acid
C. Glycerol, fatty acid, and phosphate group
D. Ribose sugar, amino acid, and nitrogenous base
Answer: A. Phosphate group, deoxyribose sugar, and nitrogenous
base
,Rationale: Each DNA nucleotide consists of a phosphate group, the
five-carbon sugar deoxyribose, and one nitrogenous base. The bases in
DNA are adenine, thymine, cytosine, and guanine.
3. Which nitrogenous bases are classified as purines?
A. Cytosine and thymine
B. Adenine and guanine
C. Adenine and thymine
D. Guanine and cytosine
Answer: B. Adenine and guanine
Rationale: Adenine and guanine are purines, which have two fused
nitrogen-containing rings. Cytosine, thymine, and uracil are
pyrimidines and contain a single ring.
4. Which nitrogenous base is found in DNA but normally not in
RNA?
A. Adenine
B. Cytosine
C. Thymine
D. Guanine
Answer: C. Thymine
Rationale: DNA contains adenine, thymine, cytosine, and guanine.
RNA generally contains uracil instead of thymine. Thus, thymine is
the characteristic pyrimidine found in DNA.
5. Which nitrogenous base pairs with adenine in DNA?
A. Guanine
B. Cytosine
,C. Uracil
D. Thymine
Answer: D. Thymine
Rationale: In double-stranded DNA, adenine forms hydrogen bonds
with thymine. This complementary base pairing is essential for
accurate DNA replication and maintenance of genetic information.
6. What type of bond connects complementary nitrogenous bases
between the two DNA strands?
A. Hydrogen bond
B. Peptide bond
C. Ionic bond
D. Phosphodiester bond
Answer: A. Hydrogen bond
Rationale: Complementary bases on opposite DNA strands are held
together by hydrogen bonds. Adenine-thymine pairs form two
hydrogen bonds, while guanine-cytosine pairs form three.
7. Which bond links adjacent nucleotides within a single DNA
strand?
A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond
D. Disulfide bond
Answer: B. Phosphodiester bond
Rationale: Phosphodiester bonds connect the phosphate group of one
nucleotide to the sugar of the next nucleotide. These bonds create the
strong covalent sugar-phosphate backbone of DNA.
, 8. The two strands of DNA are described as antiparallel because they:
A. contain different types of nucleotides
B. have completely unrelated sequences
C. run in opposite 5′-to-3′ directions
D. contain different sugars
Answer: C. run in opposite 5′-to-3′ directions
Rationale: One DNA strand runs from 5′ to 3′, while the
complementary strand runs from 3′ to 5′. This antiparallel
arrangement is important because DNA polymerase synthesizes new
DNA only in the 5′-to-3′ direction.
9. Which enzyme unwinds the DNA double helix during replication?
A. DNA ligase
B. RNA polymerase
C. Helicase
D. Primase
Answer: C. Helicase
Rationale: Helicase breaks the hydrogen bonds between
complementary bases and separates the two DNA strands. This creates
the replication fork where DNA synthesis can occur.
10. What is the primary function of DNA polymerase during
DNA replication?
A. Unwind the DNA
B. Add nucleotides to a growing DNA strand
C. Remove all RNA from the cell
D. Join amino acids together
Answer: B. Add nucleotides to a growing DNA strand
and Protein Synthesis Questions And
Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which molecule stores the hereditary information in most living
organisms?
A. Protein
B. RNA
C. Lipid
D. DNA
Answer: D. DNA
Rationale: DNA is the primary hereditary material in cellular
organisms. Its nucleotide sequence contains the information needed to
specify RNA molecules and proteins and to transmit genetic
information from one generation to the next.
2. What are the three components of a DNA nucleotide?
A. Phosphate group, deoxyribose sugar, and nitrogenous base
B. Phosphate group, ribose sugar, and amino acid
C. Glycerol, fatty acid, and phosphate group
D. Ribose sugar, amino acid, and nitrogenous base
Answer: A. Phosphate group, deoxyribose sugar, and nitrogenous
base
,Rationale: Each DNA nucleotide consists of a phosphate group, the
five-carbon sugar deoxyribose, and one nitrogenous base. The bases in
DNA are adenine, thymine, cytosine, and guanine.
3. Which nitrogenous bases are classified as purines?
A. Cytosine and thymine
B. Adenine and guanine
C. Adenine and thymine
D. Guanine and cytosine
Answer: B. Adenine and guanine
Rationale: Adenine and guanine are purines, which have two fused
nitrogen-containing rings. Cytosine, thymine, and uracil are
pyrimidines and contain a single ring.
4. Which nitrogenous base is found in DNA but normally not in
RNA?
A. Adenine
B. Cytosine
C. Thymine
D. Guanine
Answer: C. Thymine
Rationale: DNA contains adenine, thymine, cytosine, and guanine.
RNA generally contains uracil instead of thymine. Thus, thymine is
the characteristic pyrimidine found in DNA.
5. Which nitrogenous base pairs with adenine in DNA?
A. Guanine
B. Cytosine
,C. Uracil
D. Thymine
Answer: D. Thymine
Rationale: In double-stranded DNA, adenine forms hydrogen bonds
with thymine. This complementary base pairing is essential for
accurate DNA replication and maintenance of genetic information.
6. What type of bond connects complementary nitrogenous bases
between the two DNA strands?
A. Hydrogen bond
B. Peptide bond
C. Ionic bond
D. Phosphodiester bond
Answer: A. Hydrogen bond
Rationale: Complementary bases on opposite DNA strands are held
together by hydrogen bonds. Adenine-thymine pairs form two
hydrogen bonds, while guanine-cytosine pairs form three.
7. Which bond links adjacent nucleotides within a single DNA
strand?
A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond
D. Disulfide bond
Answer: B. Phosphodiester bond
Rationale: Phosphodiester bonds connect the phosphate group of one
nucleotide to the sugar of the next nucleotide. These bonds create the
strong covalent sugar-phosphate backbone of DNA.
, 8. The two strands of DNA are described as antiparallel because they:
A. contain different types of nucleotides
B. have completely unrelated sequences
C. run in opposite 5′-to-3′ directions
D. contain different sugars
Answer: C. run in opposite 5′-to-3′ directions
Rationale: One DNA strand runs from 5′ to 3′, while the
complementary strand runs from 3′ to 5′. This antiparallel
arrangement is important because DNA polymerase synthesizes new
DNA only in the 5′-to-3′ direction.
9. Which enzyme unwinds the DNA double helix during replication?
A. DNA ligase
B. RNA polymerase
C. Helicase
D. Primase
Answer: C. Helicase
Rationale: Helicase breaks the hydrogen bonds between
complementary bases and separates the two DNA strands. This creates
the replication fork where DNA synthesis can occur.
10. What is the primary function of DNA polymerase during
DNA replication?
A. Unwind the DNA
B. Add nucleotides to a growing DNA strand
C. Remove all RNA from the cell
D. Join amino acids together
Answer: B. Add nucleotides to a growing DNA strand
