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BIOD 210 Genetics Final Exam Actual
Exam 2026/2027 | Portage Learning |
Questions and 100% Verified Answers |
Pass Guaranteed - A+ Graded
Section 1: DNA Structure and Replication
Questions 1-12
Question 1
Which experiment definitively proved that DNA (not protein) is the genetic material by using
radioactive isotopes to label bacteriophage components?
A. Griffith's transformation experiment
B. Avery-MacLeod-McCarty experiment
C. Hershey-Chase experiment [CORRECT]
D. Meselson-Stahl experiment
Correct Answer: C
Rationale: The Hershey-Chase experiment (1952) used radioactive ³²P to label DNA and ³⁵S to
label protein in T2 bacteriophages. After infection, only ³²P (DNA) entered bacterial cells,
proving DNA is the genetic material. Griffith's experiment (A) showed transformation but didn't
identify DNA as the transforming principle. Avery et al. (B) identified DNA as the transforming
principle but used biochemical extraction, not radioactive labeling. Meselson-Stahl (D)
demonstrated semiconservative replication.
Question 2
According to Chargaff's rules, if a DNA sample contains 22% guanine, what percentage of
adenine would it contain?
A. 22%
B. 28% [CORRECT]
C. 44%
,2
D. 78%
Correct Answer: B
Rationale: Chargaff's rules state that %A = %T and %G = %C, and %A + %T + %G + %C =
100%. If G = 22%, then C = 22%. G + C = 44%. Therefore A + T = 56%, and A = T = 28%.
Option A incorrectly assumes A = G. Option C is G+C content. Option D incorrectly calculates
100% - 22%.
Question 3
During DNA replication, which enzyme creates a short RNA primer to provide a 3'-OH group for
DNA polymerase to begin synthesis?
A. DNA polymerase I
B. DNA polymerase III
C. Primase [CORRECT]
D. Helicase
Correct Answer: C
Rationale: Primase (an RNA polymerase) synthesizes short RNA primers (5-10 nucleotides) that
provide the necessary 3'-OH group for DNA polymerase III to initiate DNA synthesis. DNA
polymerase I (A) removes RNA primers and fills gaps. DNA polymerase III (B) is the main
replicative polymerase but cannot initiate synthesis de novo. Helicase (D) unwinds the DNA
double helix.
Question 4
Which enzyme is responsible for relieving the torsional stress (supercoiling) ahead of the
replication fork?
A. DNA polymerase
B. Helicase
C. Topoisomerase [CORRECT]
D. Ligase
Correct Answer: C
Rationale: Topoisomerase (specifically DNA gyrase in prokaryotes) cuts and rejoins DNA
strands to relieve supercoiling tension ahead of the replication fork. DNA polymerase (A)
synthesizes DNA. Helicase (B) unwinds the double helix. Ligase (D) joins Okazaki fragments.
Without topoisomerase, the DNA would become too tightly wound for replication to proceed.
,3
Question 5
In eukaryotic DNA replication, the enzyme that extends telomeres in germ cells and stem cells is:
A. DNA polymerase α
B. DNA polymerase δ
C. Telomerase [CORRECT]
D. Reverse transcriptase
Correct Answer: C
Rationale: Telomerase is a reverse transcriptase that adds repetitive DNA sequences (TTAGGG
in humans) to the 3' ends of telomeres, compensating for the end replication problem. DNA
polymerases α (A) and δ (B) are involved in normal DNA synthesis but cannot fully replicate
chromosome ends. While telomerase is a reverse transcriptase (D), this answer is too general and
doesn't specify the telomere-specific enzyme.
Question 6
Which statement correctly describes semiconservative replication?
A. Each daughter DNA molecule contains one original strand and one newly synthesized strand
[CORRECT]
B. Each daughter DNA molecule contains two original strands
C. Each daughter DNA molecule contains two newly synthesized strands
D. Parental DNA remains intact while new DNA is synthesized separately
Correct Answer: A
Rationale: Semiconservative replication (demonstrated by Meselson-Stahl, 1958) produces
daughter DNA molecules each containing one parental strand and one newly synthesized strand.
Option B describes conservative replication (disproven). Option C describes dispersive
replication (also disproven). Option D is biologically impossible as DNA replication requires
template strands.
Question 7
The leading strand is synthesized continuously while the lagging strand is synthesized
discontinuously because:
A. DNA polymerase can only synthesize in the 5' to 3' direction [CORRECT]
B. DNA polymerase can only synthesize in the 3' to 5' direction
, 4
C. Helicase unwinds DNA in only one direction
D. The replication fork moves asymmetrically
Correct Answer: A
Rationale: DNA polymerases can only add nucleotides to the 3'-OH end, synthesizing 5'→3'. At
the replication fork, the two template strands are antiparallel, so one strand (leading) can be
synthesized continuously 5'→3' toward the fork, while the other (lagging) must be synthesized
5'→3' away from the fork in short segments (Okazaki fragments). Option B is false—no known
DNA polymerase synthesizes 3'→5'. Options C and D are incorrect explanations.
Question 8
How many hydrogen bonds form between adenine and thymine, and between guanine and
cytosine, respectively?
A. 2 and 3 [CORRECT]
B. 3 and 2
C. 2 and 2
D. 3 and 3
Correct Answer: A
Rationale: A-T base pairs form 2 hydrogen bonds, while G-C base pairs form 3 hydrogen bonds.
This difference affects DNA stability (higher G-C content = higher melting temperature) and
explains why DNA with more G-C content is more stable. Options B, C, and D reverse or
incorrectly state the bonding patterns.
Question 9
Which of the following is a key difference between prokaryotic and eukaryotic DNA replication?
A. Prokaryotes use DNA polymerase; eukaryotes use RNA polymerase
B. Prokaryotes have multiple origins of replication; eukaryotes have a single origin
C. Prokaryotic DNA replication occurs in the cytoplasm; eukaryotic replication occurs in the
nucleus [CORRECT]
D. Prokaryotes use semiconservative replication; eukaryotes use conservative replication
Correct Answer: C
Rationale: Prokaryotic DNA replication occurs in the cytoplasm (no membrane-bound nucleus),
while eukaryotic replication occurs in the nucleus. Both use DNA polymerases (A is false).
BIOD 210 Genetics Final Exam Actual
Exam 2026/2027 | Portage Learning |
Questions and 100% Verified Answers |
Pass Guaranteed - A+ Graded
Section 1: DNA Structure and Replication
Questions 1-12
Question 1
Which experiment definitively proved that DNA (not protein) is the genetic material by using
radioactive isotopes to label bacteriophage components?
A. Griffith's transformation experiment
B. Avery-MacLeod-McCarty experiment
C. Hershey-Chase experiment [CORRECT]
D. Meselson-Stahl experiment
Correct Answer: C
Rationale: The Hershey-Chase experiment (1952) used radioactive ³²P to label DNA and ³⁵S to
label protein in T2 bacteriophages. After infection, only ³²P (DNA) entered bacterial cells,
proving DNA is the genetic material. Griffith's experiment (A) showed transformation but didn't
identify DNA as the transforming principle. Avery et al. (B) identified DNA as the transforming
principle but used biochemical extraction, not radioactive labeling. Meselson-Stahl (D)
demonstrated semiconservative replication.
Question 2
According to Chargaff's rules, if a DNA sample contains 22% guanine, what percentage of
adenine would it contain?
A. 22%
B. 28% [CORRECT]
C. 44%
,2
D. 78%
Correct Answer: B
Rationale: Chargaff's rules state that %A = %T and %G = %C, and %A + %T + %G + %C =
100%. If G = 22%, then C = 22%. G + C = 44%. Therefore A + T = 56%, and A = T = 28%.
Option A incorrectly assumes A = G. Option C is G+C content. Option D incorrectly calculates
100% - 22%.
Question 3
During DNA replication, which enzyme creates a short RNA primer to provide a 3'-OH group for
DNA polymerase to begin synthesis?
A. DNA polymerase I
B. DNA polymerase III
C. Primase [CORRECT]
D. Helicase
Correct Answer: C
Rationale: Primase (an RNA polymerase) synthesizes short RNA primers (5-10 nucleotides) that
provide the necessary 3'-OH group for DNA polymerase III to initiate DNA synthesis. DNA
polymerase I (A) removes RNA primers and fills gaps. DNA polymerase III (B) is the main
replicative polymerase but cannot initiate synthesis de novo. Helicase (D) unwinds the DNA
double helix.
Question 4
Which enzyme is responsible for relieving the torsional stress (supercoiling) ahead of the
replication fork?
A. DNA polymerase
B. Helicase
C. Topoisomerase [CORRECT]
D. Ligase
Correct Answer: C
Rationale: Topoisomerase (specifically DNA gyrase in prokaryotes) cuts and rejoins DNA
strands to relieve supercoiling tension ahead of the replication fork. DNA polymerase (A)
synthesizes DNA. Helicase (B) unwinds the double helix. Ligase (D) joins Okazaki fragments.
Without topoisomerase, the DNA would become too tightly wound for replication to proceed.
,3
Question 5
In eukaryotic DNA replication, the enzyme that extends telomeres in germ cells and stem cells is:
A. DNA polymerase α
B. DNA polymerase δ
C. Telomerase [CORRECT]
D. Reverse transcriptase
Correct Answer: C
Rationale: Telomerase is a reverse transcriptase that adds repetitive DNA sequences (TTAGGG
in humans) to the 3' ends of telomeres, compensating for the end replication problem. DNA
polymerases α (A) and δ (B) are involved in normal DNA synthesis but cannot fully replicate
chromosome ends. While telomerase is a reverse transcriptase (D), this answer is too general and
doesn't specify the telomere-specific enzyme.
Question 6
Which statement correctly describes semiconservative replication?
A. Each daughter DNA molecule contains one original strand and one newly synthesized strand
[CORRECT]
B. Each daughter DNA molecule contains two original strands
C. Each daughter DNA molecule contains two newly synthesized strands
D. Parental DNA remains intact while new DNA is synthesized separately
Correct Answer: A
Rationale: Semiconservative replication (demonstrated by Meselson-Stahl, 1958) produces
daughter DNA molecules each containing one parental strand and one newly synthesized strand.
Option B describes conservative replication (disproven). Option C describes dispersive
replication (also disproven). Option D is biologically impossible as DNA replication requires
template strands.
Question 7
The leading strand is synthesized continuously while the lagging strand is synthesized
discontinuously because:
A. DNA polymerase can only synthesize in the 5' to 3' direction [CORRECT]
B. DNA polymerase can only synthesize in the 3' to 5' direction
, 4
C. Helicase unwinds DNA in only one direction
D. The replication fork moves asymmetrically
Correct Answer: A
Rationale: DNA polymerases can only add nucleotides to the 3'-OH end, synthesizing 5'→3'. At
the replication fork, the two template strands are antiparallel, so one strand (leading) can be
synthesized continuously 5'→3' toward the fork, while the other (lagging) must be synthesized
5'→3' away from the fork in short segments (Okazaki fragments). Option B is false—no known
DNA polymerase synthesizes 3'→5'. Options C and D are incorrect explanations.
Question 8
How many hydrogen bonds form between adenine and thymine, and between guanine and
cytosine, respectively?
A. 2 and 3 [CORRECT]
B. 3 and 2
C. 2 and 2
D. 3 and 3
Correct Answer: A
Rationale: A-T base pairs form 2 hydrogen bonds, while G-C base pairs form 3 hydrogen bonds.
This difference affects DNA stability (higher G-C content = higher melting temperature) and
explains why DNA with more G-C content is more stable. Options B, C, and D reverse or
incorrectly state the bonding patterns.
Question 9
Which of the following is a key difference between prokaryotic and eukaryotic DNA replication?
A. Prokaryotes use DNA polymerase; eukaryotes use RNA polymerase
B. Prokaryotes have multiple origins of replication; eukaryotes have a single origin
C. Prokaryotic DNA replication occurs in the cytoplasm; eukaryotic replication occurs in the
nucleus [CORRECT]
D. Prokaryotes use semiconservative replication; eukaryotes use conservative replication
Correct Answer: C
Rationale: Prokaryotic DNA replication occurs in the cytoplasm (no membrane-bound nucleus),
while eukaryotic replication occurs in the nucleus. Both use DNA polymerases (A is false).
