BIOD 102 Biology II Module 1 Exam
Portage Learning (2026/2027)
Section 1: DNA Structure & Replication
Section 2: Transcription & RNA Processing
Section 3: Translation & Protein Synthesis
Section 4: Gene Regulation & Mutations
Q1: Which of the following correctly lists the three components of a DNA nucleotide?
A. Ribose sugar, phosphate group, nitrogenous base
B. Deoxyribose sugar, amino acid, nitrogenous base
C. Deoxyribose sugar, phosphate group, nitrogenous base [CORRECT]
D. Ribose sugar, sulfate group, nitrogenous base
Correct Answer: C
Rationale: A DNA nucleotide consists of a deoxyribose sugar (lacking an oxygen at the 2'
carbon), a phosphate group, and a nitrogenous base. Ribose is found in RNA, and amino acids
are the building blocks of proteins, not nucleic acids.
Q2: According to Chargaff's rules, if a sample of double-stranded DNA contains 15% adenine,
what percentage of the DNA is guanine?
A. 15%
B. 30%
C. 35% [CORRECT]
D. 70%
Correct Answer: C
.
,Rationale: Chargaff's rules state that adenine (A) pairs with thymine (T), and cytosine (C) pairs
with guanine (G). If there is 15% A, there must be 15% T, totaling 30%. The remaining 70%
must be split equally between C and G, meaning G makes up 35%.
Q3: The two strands of a DNA double helix are described as antiparallel. What does this mean?
A. They run in the same direction, from 5' to 3'.
B. They twist in opposite directions around the histones.
C. One strand runs from 5' to 3', while the other runs from 3' to 5'. [CORRECT]
D. The nitrogenous bases point in opposite directions.
Correct Answer: C
Rationale: Antiparallel orientation means that the sugar-phosphate backbones of the two DNA
strands are aligned in opposite chemical directions; if one strand runs 5' to 3', the complementary
strand runs 3' to 5'.
Q4: The Meselson-Stahl experiment demonstrated that DNA replication is:
A. Conservative
B. Dispersive
C. Non-conservative
D. Semi-conservative [CORRECT]
Correct Answer: D
Rationale: The Meselson-Stahl experiment used heavy and light nitrogen isotopes to prove that
after replication, each new DNA molecule consists of one original (parental) strand and one
newly synthesized strand, supporting the semi-conservative model.
Q5: What is the primary function of the enzyme helicase during DNA replication?
A. Adding new nucleotides to the growing DNA strand
B. Unwinding the double helix by breaking hydrogen bonds between base pairs [CORRECT]
C. Sealing gaps between Okazaki fragments
D. Synthesizing a short RNA primer
.
, Correct Answer: B
Rationale: Helicase acts like a zipper to break the hydrogen bonds between complementary
nitrogenous bases, unwinding the DNA double helix so that each strand can serve as a template
for replication.
Q6: DNA polymerase can only add nucleotides in which direction?
A. 3' to 5'
B. 5' to 3' [CORRECT]
C. Both 3' to 5' and 5' to 3' simultaneously
D. Randomly in either direction depending on the base
Correct Answer: B
Rationale: DNA polymerase has an active site that only accommodates the 3'-OH group of the
growing strand, meaning it can only catalyze the formation of a phosphodiester bond by adding
new nucleotides to the 3' end.
Q7: Which enzyme is responsible for synthesizing a short RNA sequence complementary to the
DNA template to initiate replication?
A. DNA polymerase III
B. Ligase
C. Primase [CORRECT]
D. Topoisomerase
Correct Answer: C
Rationale: DNA polymerase cannot initiate synthesis on a bare template; primase is an RNA
polymerase that lays down a short RNA primer, providing the necessary 3'-OH group for DNA
polymerase to begin adding DNA nucleotides.
Q8: On the lagging strand, what is the function of DNA ligase?
A. To relieve tension caused by unwinding ahead of the replication fork
B. To join the sugar-phosphate backbones of Okazaki fragments [CORRECT]
.
Portage Learning (2026/2027)
Section 1: DNA Structure & Replication
Section 2: Transcription & RNA Processing
Section 3: Translation & Protein Synthesis
Section 4: Gene Regulation & Mutations
Q1: Which of the following correctly lists the three components of a DNA nucleotide?
A. Ribose sugar, phosphate group, nitrogenous base
B. Deoxyribose sugar, amino acid, nitrogenous base
C. Deoxyribose sugar, phosphate group, nitrogenous base [CORRECT]
D. Ribose sugar, sulfate group, nitrogenous base
Correct Answer: C
Rationale: A DNA nucleotide consists of a deoxyribose sugar (lacking an oxygen at the 2'
carbon), a phosphate group, and a nitrogenous base. Ribose is found in RNA, and amino acids
are the building blocks of proteins, not nucleic acids.
Q2: According to Chargaff's rules, if a sample of double-stranded DNA contains 15% adenine,
what percentage of the DNA is guanine?
A. 15%
B. 30%
C. 35% [CORRECT]
D. 70%
Correct Answer: C
.
,Rationale: Chargaff's rules state that adenine (A) pairs with thymine (T), and cytosine (C) pairs
with guanine (G). If there is 15% A, there must be 15% T, totaling 30%. The remaining 70%
must be split equally between C and G, meaning G makes up 35%.
Q3: The two strands of a DNA double helix are described as antiparallel. What does this mean?
A. They run in the same direction, from 5' to 3'.
B. They twist in opposite directions around the histones.
C. One strand runs from 5' to 3', while the other runs from 3' to 5'. [CORRECT]
D. The nitrogenous bases point in opposite directions.
Correct Answer: C
Rationale: Antiparallel orientation means that the sugar-phosphate backbones of the two DNA
strands are aligned in opposite chemical directions; if one strand runs 5' to 3', the complementary
strand runs 3' to 5'.
Q4: The Meselson-Stahl experiment demonstrated that DNA replication is:
A. Conservative
B. Dispersive
C. Non-conservative
D. Semi-conservative [CORRECT]
Correct Answer: D
Rationale: The Meselson-Stahl experiment used heavy and light nitrogen isotopes to prove that
after replication, each new DNA molecule consists of one original (parental) strand and one
newly synthesized strand, supporting the semi-conservative model.
Q5: What is the primary function of the enzyme helicase during DNA replication?
A. Adding new nucleotides to the growing DNA strand
B. Unwinding the double helix by breaking hydrogen bonds between base pairs [CORRECT]
C. Sealing gaps between Okazaki fragments
D. Synthesizing a short RNA primer
.
, Correct Answer: B
Rationale: Helicase acts like a zipper to break the hydrogen bonds between complementary
nitrogenous bases, unwinding the DNA double helix so that each strand can serve as a template
for replication.
Q6: DNA polymerase can only add nucleotides in which direction?
A. 3' to 5'
B. 5' to 3' [CORRECT]
C. Both 3' to 5' and 5' to 3' simultaneously
D. Randomly in either direction depending on the base
Correct Answer: B
Rationale: DNA polymerase has an active site that only accommodates the 3'-OH group of the
growing strand, meaning it can only catalyze the formation of a phosphodiester bond by adding
new nucleotides to the 3' end.
Q7: Which enzyme is responsible for synthesizing a short RNA sequence complementary to the
DNA template to initiate replication?
A. DNA polymerase III
B. Ligase
C. Primase [CORRECT]
D. Topoisomerase
Correct Answer: C
Rationale: DNA polymerase cannot initiate synthesis on a bare template; primase is an RNA
polymerase that lays down a short RNA primer, providing the necessary 3'-OH group for DNA
polymerase to begin adding DNA nucleotides.
Q8: On the lagging strand, what is the function of DNA ligase?
A. To relieve tension caused by unwinding ahead of the replication fork
B. To join the sugar-phosphate backbones of Okazaki fragments [CORRECT]
.
