Molecular Biology Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2025/2026 Q&A
1. Which enzyme is responsible for synthesizing RNA from a DNA
template?
A) DNA polymerase
B) RNA polymerase
C) Ligase
D) Helicase
Rationale: RNA polymerase synthesizes RNA complementary to the
DNA template during transcription.
2. During DNA replication, the leading strand is synthesized:
A) Discontinuously
B) Continuously
C) Only at the origin
D) By ligase
Rationale: The leading strand is synthesized continuously in the 5’ →
3’ direction toward the replication fork.
3. What is the function of topoisomerase?
A) Synthesizes RNA
B) Relieves supercoiling in DNA
C) Joins Okazaki fragments
D) Unwinds RNA
Rationale: Topoisomerases prevent DNA tangling and relieve
torsional strain during replication.
,4. Okazaki fragments are synthesized on the:
A) Leading strand
B) Lagging strand
C) Both strands equally
D) RNA primer
Rationale: The lagging strand is synthesized discontinuously in short
fragments called Okazaki fragments.
5. Which of the following is a stop codon?
A) AUG
B) UAA
C) GUG
D) CUG
Rationale: UAA, UAG, and UGA are stop codons that signal
termination of translation.
6. In eukaryotic transcription, the TATA box is located:
A) Within the gene body
B) Promoter region upstream of transcription start site
C) At the 3’ end
D) In introns
Rationale: The TATA box is a conserved promoter element that helps
recruit RNA polymerase II.
7. Which RNA carries amino acids to the ribosome?
,A) mRNA
B) rRNA
C) tRNA
D) snRNA
Rationale: tRNA molecules transport specific amino acids and match
them to codons on the mRNA.
8. What type of bond links amino acids in a protein?
A) Hydrogen bond
B) Ionic bond
C) Peptide bond
D) Phosphodiester bond
Rationale: Peptide bonds form between the carboxyl group of one
amino acid and the amino group of another.
9. Which enzyme removes RNA primers during DNA replication in
prokaryotes?
A) DNA polymerase III
B) Helicase
C) DNA polymerase I
D) Ligase
Rationale: DNA polymerase I excises RNA primers and replaces them
with DNA nucleotides.
10. What is the role of ribosomes?
A) DNA replication
B) RNA transcription
, C) Protein synthesis
D) Lipid metabolism
Rationale: Ribosomes are the cellular machinery for translating
mRNA into protein.
11. In prokaryotic gene regulation, the lac operon is inducible by:
A) Glucose
B) Lactose
C) cAMP
D) ATP
Rationale: Lactose binds to the repressor, enabling transcription of
lac genes.
12. Which enzyme synthesizes DNA during replication?
A) RNA polymerase
B) Ligase
C) DNA polymerase
D) Helicase
Rationale: DNA polymerase catalyzes the addition of nucleotides to
the growing DNA strand.
13. What is the function of a promoter in DNA?
A) Encodes proteins
B) Binding site for RNA polymerase
C) Terminates transcription
D) Joins Okazaki fragments
Rationale: Promoters initiate transcription by recruiting RNA
polymerase and transcription factors.
Correct Answers (Verified Answers) Plus
Rationales 2025/2026 Q&A
1. Which enzyme is responsible for synthesizing RNA from a DNA
template?
A) DNA polymerase
B) RNA polymerase
C) Ligase
D) Helicase
Rationale: RNA polymerase synthesizes RNA complementary to the
DNA template during transcription.
2. During DNA replication, the leading strand is synthesized:
A) Discontinuously
B) Continuously
C) Only at the origin
D) By ligase
Rationale: The leading strand is synthesized continuously in the 5’ →
3’ direction toward the replication fork.
3. What is the function of topoisomerase?
A) Synthesizes RNA
B) Relieves supercoiling in DNA
C) Joins Okazaki fragments
D) Unwinds RNA
Rationale: Topoisomerases prevent DNA tangling and relieve
torsional strain during replication.
,4. Okazaki fragments are synthesized on the:
A) Leading strand
B) Lagging strand
C) Both strands equally
D) RNA primer
Rationale: The lagging strand is synthesized discontinuously in short
fragments called Okazaki fragments.
5. Which of the following is a stop codon?
A) AUG
B) UAA
C) GUG
D) CUG
Rationale: UAA, UAG, and UGA are stop codons that signal
termination of translation.
6. In eukaryotic transcription, the TATA box is located:
A) Within the gene body
B) Promoter region upstream of transcription start site
C) At the 3’ end
D) In introns
Rationale: The TATA box is a conserved promoter element that helps
recruit RNA polymerase II.
7. Which RNA carries amino acids to the ribosome?
,A) mRNA
B) rRNA
C) tRNA
D) snRNA
Rationale: tRNA molecules transport specific amino acids and match
them to codons on the mRNA.
8. What type of bond links amino acids in a protein?
A) Hydrogen bond
B) Ionic bond
C) Peptide bond
D) Phosphodiester bond
Rationale: Peptide bonds form between the carboxyl group of one
amino acid and the amino group of another.
9. Which enzyme removes RNA primers during DNA replication in
prokaryotes?
A) DNA polymerase III
B) Helicase
C) DNA polymerase I
D) Ligase
Rationale: DNA polymerase I excises RNA primers and replaces them
with DNA nucleotides.
10. What is the role of ribosomes?
A) DNA replication
B) RNA transcription
, C) Protein synthesis
D) Lipid metabolism
Rationale: Ribosomes are the cellular machinery for translating
mRNA into protein.
11. In prokaryotic gene regulation, the lac operon is inducible by:
A) Glucose
B) Lactose
C) cAMP
D) ATP
Rationale: Lactose binds to the repressor, enabling transcription of
lac genes.
12. Which enzyme synthesizes DNA during replication?
A) RNA polymerase
B) Ligase
C) DNA polymerase
D) Helicase
Rationale: DNA polymerase catalyzes the addition of nucleotides to
the growing DNA strand.
13. What is the function of a promoter in DNA?
A) Encodes proteins
B) Binding site for RNA polymerase
C) Terminates transcription
D) Joins Okazaki fragments
Rationale: Promoters initiate transcription by recruiting RNA
polymerase and transcription factors.
