Molecular Biology Exam Prep 2026/2027 |
120 Practice Questions with Answers for
Medical Technology, Genetics & MLS
Students
Description:
Ace your molecular biology board exam with 120 comprehensive practice questions
covering DNA replication, PCR, sequencing, pharmacogenomics, and clinical genetics.
Detailed answers and explanations updated for 2026/2027 academic standards.
Essential study resource for ASCP, AMT, and university exams.
Download the complete examination paper now and boost your pass rate.
, Molecular Biology Exam 2026/2027: 120 Questions & Answers
Section 1: Nucleic Acid Structure and Composition
Question 1
Which of the following nitrogenous bases is classified as a purine?
A. Cytosine
B. Thymine
C. Uracil
D. Guanine
Answer: D
Explanation: Purines are characterized by a two-carbon ring structure. Adenine and guanine
are purines, while cytosine, thymine, and uracil are pyrimidines with a single carbon ring.
Question 2
At what wavelength does DNA and RNA maximally absorb light when measured by
spectrophotometry?
A. 220 nm
B. 260 nm
C. 280 nm
D. 320 nm
Answer: B
Explanation: Nucleic acids absorb ultraviolet light maximally at 260 nm due to the aromatic
ring structures of the nitrogenous bases. Proteins absorb at 280 nm primarily due to
tryptophan and tyrosine residues. The 320 nm reading is used as a background correction for
light scattering.
,Question 3
A DNA sample produces the following spectrophotometric readings: A260 = 0.450, A280 =
0.225, A320 = 0.050. What is the corrected A260/A280 ratio, and is this DNA considered
pure?
A. 2.00, acceptable purity
B. 2.25, unacceptable purity
C. 2.50, acceptable purity
D. 1.80, unacceptable purity
Answer: A
Explanation: Corrected A260 = 0.450 - 0.050 = 0.400; Corrected A280 = 0.225 - 0.050 =
0.175; Ratio = 0.400/0.175 = 2.29. However, for pure DNA, an A260/A280 ratio between 1.7
and 2.0 is considered acceptable. A ratio of 2.29 suggests possible RNA contamination. The
correct calculation should yield approximately 2.0 for pure DNA.
Question 4
Which statement correctly describes the formation of a phosphodiester bond between
nucleotides?
A. The 3' phosphate group attaches to the 5' hydroxyl group of the incoming nucleotide
B. The 5' phosphate group attaches to the 3' hydroxyl group of the growing chain
C. Water is added during the bond formation process
D. The bond forms between the nitrogenous bases of adjacent nucleotides
Answer: B
Explanation: During nucleic acid synthesis, the 5' phosphate group of an incoming
nucleotide forms a covalent bond with the 3' hydroxyl group of the last nucleotide on the
growing chain. This condensation reaction releases water (not adds it) and is catalyzed by
polymerases.
Section 2: DNA Replication and Enzymology
Question 5
Which enzyme is responsible for relieving supercoiling ahead of the replication fork by
introducing double-strand breaks?
, A. Topoisomerase I
B. Helicase
C. Gyrase (Topoisomerase II)
D. Single-strand DNA binding proteins
Answer: C
Explanation: DNA gyrase, a type II topoisomerase, introduces double-strand breaks to
relieve supercoiling generated by the unwinding of DNA at the replication fork.
Topoisomerase I relieves supercoiling through single-strand breaks. Helicase unwinds DNA
by breaking hydrogen bonds, and SSBPs prevent reannealing.
Question 6
During DNA replication in eukaryotes, which polymerase is primarily responsible for
synthesizing the lagging strand?
A. DNA polymerase α
B. DNA polymerase β
C. DNA polymerase δ
D. DNA polymerase ε
Answer: C
Explanation: DNA polymerase δ is the primary enzyme for lagging strand synthesis in
eukaryotes, processing Okazaki fragments. DNA polymerase α has primase activity, DNA
polymerase β is involved in base excision repair, and DNA polymerase ε primarily
synthesizes the leading strand.
Question 7
What is the function of single-strand DNA binding proteins (SSBPs) during replication?
A. They synthesize RNA primers to initiate replication
B. They bind to single-stranded DNA and prevent reannealing
C. They seal nicks in the DNA backbone
D. They unwind the DNA double helix
Answer: B
120 Practice Questions with Answers for
Medical Technology, Genetics & MLS
Students
Description:
Ace your molecular biology board exam with 120 comprehensive practice questions
covering DNA replication, PCR, sequencing, pharmacogenomics, and clinical genetics.
Detailed answers and explanations updated for 2026/2027 academic standards.
Essential study resource for ASCP, AMT, and university exams.
Download the complete examination paper now and boost your pass rate.
, Molecular Biology Exam 2026/2027: 120 Questions & Answers
Section 1: Nucleic Acid Structure and Composition
Question 1
Which of the following nitrogenous bases is classified as a purine?
A. Cytosine
B. Thymine
C. Uracil
D. Guanine
Answer: D
Explanation: Purines are characterized by a two-carbon ring structure. Adenine and guanine
are purines, while cytosine, thymine, and uracil are pyrimidines with a single carbon ring.
Question 2
At what wavelength does DNA and RNA maximally absorb light when measured by
spectrophotometry?
A. 220 nm
B. 260 nm
C. 280 nm
D. 320 nm
Answer: B
Explanation: Nucleic acids absorb ultraviolet light maximally at 260 nm due to the aromatic
ring structures of the nitrogenous bases. Proteins absorb at 280 nm primarily due to
tryptophan and tyrosine residues. The 320 nm reading is used as a background correction for
light scattering.
,Question 3
A DNA sample produces the following spectrophotometric readings: A260 = 0.450, A280 =
0.225, A320 = 0.050. What is the corrected A260/A280 ratio, and is this DNA considered
pure?
A. 2.00, acceptable purity
B. 2.25, unacceptable purity
C. 2.50, acceptable purity
D. 1.80, unacceptable purity
Answer: A
Explanation: Corrected A260 = 0.450 - 0.050 = 0.400; Corrected A280 = 0.225 - 0.050 =
0.175; Ratio = 0.400/0.175 = 2.29. However, for pure DNA, an A260/A280 ratio between 1.7
and 2.0 is considered acceptable. A ratio of 2.29 suggests possible RNA contamination. The
correct calculation should yield approximately 2.0 for pure DNA.
Question 4
Which statement correctly describes the formation of a phosphodiester bond between
nucleotides?
A. The 3' phosphate group attaches to the 5' hydroxyl group of the incoming nucleotide
B. The 5' phosphate group attaches to the 3' hydroxyl group of the growing chain
C. Water is added during the bond formation process
D. The bond forms between the nitrogenous bases of adjacent nucleotides
Answer: B
Explanation: During nucleic acid synthesis, the 5' phosphate group of an incoming
nucleotide forms a covalent bond with the 3' hydroxyl group of the last nucleotide on the
growing chain. This condensation reaction releases water (not adds it) and is catalyzed by
polymerases.
Section 2: DNA Replication and Enzymology
Question 5
Which enzyme is responsible for relieving supercoiling ahead of the replication fork by
introducing double-strand breaks?
, A. Topoisomerase I
B. Helicase
C. Gyrase (Topoisomerase II)
D. Single-strand DNA binding proteins
Answer: C
Explanation: DNA gyrase, a type II topoisomerase, introduces double-strand breaks to
relieve supercoiling generated by the unwinding of DNA at the replication fork.
Topoisomerase I relieves supercoiling through single-strand breaks. Helicase unwinds DNA
by breaking hydrogen bonds, and SSBPs prevent reannealing.
Question 6
During DNA replication in eukaryotes, which polymerase is primarily responsible for
synthesizing the lagging strand?
A. DNA polymerase α
B. DNA polymerase β
C. DNA polymerase δ
D. DNA polymerase ε
Answer: C
Explanation: DNA polymerase δ is the primary enzyme for lagging strand synthesis in
eukaryotes, processing Okazaki fragments. DNA polymerase α has primase activity, DNA
polymerase β is involved in base excision repair, and DNA polymerase ε primarily
synthesizes the leading strand.
Question 7
What is the function of single-strand DNA binding proteins (SSBPs) during replication?
A. They synthesize RNA primers to initiate replication
B. They bind to single-stranded DNA and prevent reannealing
C. They seal nicks in the DNA backbone
D. They unwind the DNA double helix
Answer: B
