Test Bank for Genetic Analysis An
Integrated Approach 3rd Edition
Sanders / All Chapters 1 - 20 / Full
Complete
SECTION 1: DNA STRUCTURE, REPLICATION, TRANSCRIPTION, TRANSLATION (Q1–Q26)
1. Which of the following best describes the structure of the DNA double helix as proposed by
Watson and Crick?
A. A left-handed helix with parallel strands
B. A right-handed helix with antiparallel strands
C. A single-stranded helical structure
D. A triple-stranded helical structure
Correct Answer: B
Rationale: Watson and Crick proposed a right-handed double helix with antiparallel strands
(5'→3' and 3'→5'), with bases paired on the inside and sugar-phosphate backbone on the
outside.
2. In the Meselson-Stahl experiment, the observation of a single intermediate-density band
after one generation in ¹⁵N/¹⁴N medium supported which model of replication?
A. Conservative
B. Dispersive
C. Semiconservative
D. Rolling circle
Correct Answer: C
Rationale: A single hybrid band after one generation ruled out conservative replication
(which would produce two bands) and supported semiconservative replication. Dispersive
replication was ruled out after the second generation.
,3. Which enzyme is primarily responsible for unwinding the DNA double helix during
replication in E. coli?
A. DNA polymerase I
B. DNA ligase
C. DNA helicase
D. Topoisomerase I
Correct Answer: C
Rationale: DNA helicase (DnaB in E. coli) unwinds the double helix by breaking hydrogen
bonds between complementary bases. Topoisomerases relieve supercoiling ahead of the
replication fork.
4. Which of the following statements about DNA polymerase III in E. coli is/are TRUE? (Select
all that apply)
A. It has 5'→3' polymerase activity.
B. It has 3'→5' exonuclease activity.
C. It has 5'→3' exonuclease activity.
D. It is the primary enzyme for DNA replication.
Correct Answers: A, B, D
Rationale: DNA polymerase III has 5'→3' polymerase activity and 3'→5' exonuclease
(proofreading) activity, and is the main replicative polymerase. It lacks 5'→3' exonuclease
activity, which is found in DNA polymerase I.
5. The Shine-Dalgarno sequence in prokaryotic mRNA is involved in:
A. Transcription termination
B. Ribosome binding and translation initiation
C. mRNA splicing
D. Polyadenylation
Correct Answer: B
Rationale: The Shine-Dalgarno sequence (AGGAGG) base-pairs with the 16S rRNA of the
small ribosomal subunit to position the ribosome at the start codon.
6. Which of the following is NOT a component of the eukaryotic RNA polymerase II
transcription initiation complex?
,A. TATA-binding protein (TBP)
B. TFIIH
C. Sigma factor
D. TFIIB
Correct Answer: C
Rationale: Sigma factors are used by prokaryotic RNA polymerase for promoter recognition.
Eukaryotic RNA polymerase II uses general transcription factors (TFIIA, B, D, E, F, H) and TBP.
7. Which type of RNA is involved in the process of splicing in eukaryotes?
A. mRNA
B. tRNA
C. snRNA
D. rRNA
Correct Answer: C
Rationale: Small nuclear RNAs (snRNAs) U1, U2, U4, U5, and U6 combine with proteins to
form snRNPs, which make up the spliceosome that catalyzes intron removal.
8. Which of the following describes the role of the 5' cap in eukaryotic mRNA?
A. It signals for transcription termination.
B. It protects mRNA from degradation and aids in ribosome binding.
C. It marks the mRNA for splicing.
D. It encodes the start codon.
Correct Answer: B
Rationale: The 5' 7-methylguanosine cap protects the mRNA from 5'→3' exonuclease
degradation, aids in nuclear export, and is recognized by eIF4E for translation initiation.
9. In the genetic code, how many codons are stop codons?
A. 1
B. 2
C. 3
D. 4
, Correct Answer: C
Rationale: The three stop codons are UAA (ochre), UAG (amber), and UGA (opal). They do
not encode amino acids and signal termination of translation.
10. Which of the following is TRUE regarding the wobble hypothesis?
A. It explains why there are 64 tRNAs.
B. It allows non-standard base pairing at the third codon position.
C. It states that the first codon position is most flexible.
D. It applies only to prokaryotes.
Correct Answer: B
Rationale: The wobble hypothesis (Crick, 1966) states that the third base of a codon can
pair non-standardly with the first base of the anticodon, allowing fewer tRNAs than codons.
11. Which enzyme removes RNA primers during DNA replication in E. coli?
A. DNA polymerase III
B. DNA polymerase I
C. DNA ligase
D. Primase
Correct Answer: B
Rationale: DNA polymerase I has 5'→3' exonuclease activity that removes RNA primers and
replaces them with DNA. DNA ligase then seals the nicks.
12. Which of the following statements about telomeres is/are TRUE? (Select all that apply)
A. They consist of repetitive non-coding sequences.
B. They protect chromosome ends from degradation.
C. They shorten with each cell division in somatic cells.
D. They are synthesized by DNA polymerase III.
Correct Answers: A, B, C
Rationale: Telomeres are repetitive (TTAGGG in humans), protect chromosome ends, and
shorten with each division in most somatic cells. They are synthesized by telomerase, a reverse
transcriptase, not DNA polymerase III.
Integrated Approach 3rd Edition
Sanders / All Chapters 1 - 20 / Full
Complete
SECTION 1: DNA STRUCTURE, REPLICATION, TRANSCRIPTION, TRANSLATION (Q1–Q26)
1. Which of the following best describes the structure of the DNA double helix as proposed by
Watson and Crick?
A. A left-handed helix with parallel strands
B. A right-handed helix with antiparallel strands
C. A single-stranded helical structure
D. A triple-stranded helical structure
Correct Answer: B
Rationale: Watson and Crick proposed a right-handed double helix with antiparallel strands
(5'→3' and 3'→5'), with bases paired on the inside and sugar-phosphate backbone on the
outside.
2. In the Meselson-Stahl experiment, the observation of a single intermediate-density band
after one generation in ¹⁵N/¹⁴N medium supported which model of replication?
A. Conservative
B. Dispersive
C. Semiconservative
D. Rolling circle
Correct Answer: C
Rationale: A single hybrid band after one generation ruled out conservative replication
(which would produce two bands) and supported semiconservative replication. Dispersive
replication was ruled out after the second generation.
,3. Which enzyme is primarily responsible for unwinding the DNA double helix during
replication in E. coli?
A. DNA polymerase I
B. DNA ligase
C. DNA helicase
D. Topoisomerase I
Correct Answer: C
Rationale: DNA helicase (DnaB in E. coli) unwinds the double helix by breaking hydrogen
bonds between complementary bases. Topoisomerases relieve supercoiling ahead of the
replication fork.
4. Which of the following statements about DNA polymerase III in E. coli is/are TRUE? (Select
all that apply)
A. It has 5'→3' polymerase activity.
B. It has 3'→5' exonuclease activity.
C. It has 5'→3' exonuclease activity.
D. It is the primary enzyme for DNA replication.
Correct Answers: A, B, D
Rationale: DNA polymerase III has 5'→3' polymerase activity and 3'→5' exonuclease
(proofreading) activity, and is the main replicative polymerase. It lacks 5'→3' exonuclease
activity, which is found in DNA polymerase I.
5. The Shine-Dalgarno sequence in prokaryotic mRNA is involved in:
A. Transcription termination
B. Ribosome binding and translation initiation
C. mRNA splicing
D. Polyadenylation
Correct Answer: B
Rationale: The Shine-Dalgarno sequence (AGGAGG) base-pairs with the 16S rRNA of the
small ribosomal subunit to position the ribosome at the start codon.
6. Which of the following is NOT a component of the eukaryotic RNA polymerase II
transcription initiation complex?
,A. TATA-binding protein (TBP)
B. TFIIH
C. Sigma factor
D. TFIIB
Correct Answer: C
Rationale: Sigma factors are used by prokaryotic RNA polymerase for promoter recognition.
Eukaryotic RNA polymerase II uses general transcription factors (TFIIA, B, D, E, F, H) and TBP.
7. Which type of RNA is involved in the process of splicing in eukaryotes?
A. mRNA
B. tRNA
C. snRNA
D. rRNA
Correct Answer: C
Rationale: Small nuclear RNAs (snRNAs) U1, U2, U4, U5, and U6 combine with proteins to
form snRNPs, which make up the spliceosome that catalyzes intron removal.
8. Which of the following describes the role of the 5' cap in eukaryotic mRNA?
A. It signals for transcription termination.
B. It protects mRNA from degradation and aids in ribosome binding.
C. It marks the mRNA for splicing.
D. It encodes the start codon.
Correct Answer: B
Rationale: The 5' 7-methylguanosine cap protects the mRNA from 5'→3' exonuclease
degradation, aids in nuclear export, and is recognized by eIF4E for translation initiation.
9. In the genetic code, how many codons are stop codons?
A. 1
B. 2
C. 3
D. 4
, Correct Answer: C
Rationale: The three stop codons are UAA (ochre), UAG (amber), and UGA (opal). They do
not encode amino acids and signal termination of translation.
10. Which of the following is TRUE regarding the wobble hypothesis?
A. It explains why there are 64 tRNAs.
B. It allows non-standard base pairing at the third codon position.
C. It states that the first codon position is most flexible.
D. It applies only to prokaryotes.
Correct Answer: B
Rationale: The wobble hypothesis (Crick, 1966) states that the third base of a codon can
pair non-standardly with the first base of the anticodon, allowing fewer tRNAs than codons.
11. Which enzyme removes RNA primers during DNA replication in E. coli?
A. DNA polymerase III
B. DNA polymerase I
C. DNA ligase
D. Primase
Correct Answer: B
Rationale: DNA polymerase I has 5'→3' exonuclease activity that removes RNA primers and
replaces them with DNA. DNA ligase then seals the nicks.
12. Which of the following statements about telomeres is/are TRUE? (Select all that apply)
A. They consist of repetitive non-coding sequences.
B. They protect chromosome ends from degradation.
C. They shorten with each cell division in somatic cells.
D. They are synthesized by DNA polymerase III.
Correct Answers: A, B, C
Rationale: Telomeres are repetitive (TTAGGG in humans), protect chromosome ends, and
shorten with each division in most somatic cells. They are synthesized by telomerase, a reverse
transcriptase, not DNA polymerase III.
