BIOL 210 Module 5: Genetics - DNA Replication,
Transcription, and Translation Updated and Latest
Questions and Correct Answers with Rationale
1. During DNA replication, which enzyme is responsible for unwinding the DNA double helix
by breaking hydrogen bonds?
A. DNA Helicase
B. DNA Ligase
C. Topoisomerase
D. DNA Polymerase III
Correct Answer: A
Explanation: DNA Helicase travels along the DNA backbone and breaks the hydrogen
bonds between complementary nitrogenous bases, effectively ‘unzipping’ the double helix
to create a replication fork.
2. In which direction does DNA Polymerase III synthesize the new DNA strand?
A. 3’ to 5’
B. 5’ to 3’
C. Both 3’ to 5’ and 5’ to 3’ simultaneously
D. Randomly based on available nucleotides
Correct Answer: B
Explanation: DNA Polymerase III can only add new nucleotides to the 3’ hydroxyl (-OH)
group of an existing chain, meaning the new strand is always synthesized in the 5’ to 3’
direction.
3. What is the role of Topoisomerase during the replication process?
A. It joins Okazaki fragments on the lagging strand.
B. It prevents the single strands from re-annealing.
C. It synthesizes an RNA primer to initiate replication.
D. It relieves torsional strain (supercoiling) ahead of the replication fork.
Correct Answer: D
Explanation: As helicase unwinds the DNA, the double helix ahead of the fork becomes
tightly wound or ‘supercoiled.’ Topoisomerase cuts and rejoins the DNA to relieve this
physical tension.
,4. Why are Okazaki fragments formed on the lagging strand?
A. Because the lagging strand template is circular.
B. Because DNA polymerase can only work in the 5’ to 3’ direction while the template is 5’
to 3’.
C. Because RNA primers are not available on the lagging strand.
D. Because DNA ligase cannot function on a continuous strand.
Correct Answer: B
Explanation: Since DNA polymerase only synthesizes in the 5’ to 3’ direction, it must move
away from the replication fork on the template strand oriented 5’ to 3’, resulting in short,
discontinuous segments called Okazaki fragments.
5. Which enzyme is responsible for replacing RNA primers with DNA nucleotides?
A. DNA Polymerase I
B. DNA Helicase
C. DNA Polymerase III
D. Primase
Correct Answer: A
Explanation: DNA Polymerase I has 5’ to 3’ exonuclease activity, allowing it to remove the
RNA primers used to start replication and replace them with the appropriate DNA
nucleotides.
6. What is the primary function of DNA Ligase?
A. To unwind the double helix.
B. To add a poly-A tail to the 3’ end of the DNA.
C. To catalyze the formation of phosphodiester bonds between DNA fragments.
D. To proofread the new DNA strand for errors.
Correct Answer: C
Explanation: DNA Ligase ‘glues’ the sugar-phosphate backbone together by creating
phosphodiester bonds between the 3’ end of one DNA fragment and the 5’ end of another,
essential for joining Okazaki fragments.
7. The ‘Central Dogma’ of molecular biology describes the flow of genetic information as:
A. Protein -> RNA -> DNA
B. DNA -> Protein -> RNA
, C. RNA -> DNA -> Protein
D. DNA -> RNA -> Protein
Correct Answer: D
Explanation: The Central Dogma states that genetic information is stored in DNA,
transcribed into messenger RNA (mRNA), and then translated into a functional protein.
8. Where does transcription occur in a eukaryotic cell?
A. Cytoplasm
B. Ribosome
C. Nucleus
D. Endoplasmic Reticulum
Correct Answer: C
Explanation: In eukaryotes, DNA is contained within the nucleus; therefore, the synthesis
of mRNA (transcription) must occur there before the transcript is exported to the
cytoplasm for translation.
9. Which of the following is the enzyme responsible for RNA synthesis during transcription?
A. DNA Polymerase
B. RNA Polymerase
C. Reverse Transcriptase
D. RNA Ligase
Correct Answer: B
Explanation: RNA Polymerase binds to the DNA promoter and catalyzes the synthesis of
an RNA strand complementary to the DNA template strand.
10. A sequence of DNA that signals the start of a gene and provides a binding site for RNA
polymerase is called the:
A. Intron
B. Codon
C. Exon
D. Promoter
Correct Answer: D
Explanation: The promoter is a specific DNA sequence located upstream of a gene that
serves as the recognition and binding site for RNA polymerase to begin transcription.
Transcription, and Translation Updated and Latest
Questions and Correct Answers with Rationale
1. During DNA replication, which enzyme is responsible for unwinding the DNA double helix
by breaking hydrogen bonds?
A. DNA Helicase
B. DNA Ligase
C. Topoisomerase
D. DNA Polymerase III
Correct Answer: A
Explanation: DNA Helicase travels along the DNA backbone and breaks the hydrogen
bonds between complementary nitrogenous bases, effectively ‘unzipping’ the double helix
to create a replication fork.
2. In which direction does DNA Polymerase III synthesize the new DNA strand?
A. 3’ to 5’
B. 5’ to 3’
C. Both 3’ to 5’ and 5’ to 3’ simultaneously
D. Randomly based on available nucleotides
Correct Answer: B
Explanation: DNA Polymerase III can only add new nucleotides to the 3’ hydroxyl (-OH)
group of an existing chain, meaning the new strand is always synthesized in the 5’ to 3’
direction.
3. What is the role of Topoisomerase during the replication process?
A. It joins Okazaki fragments on the lagging strand.
B. It prevents the single strands from re-annealing.
C. It synthesizes an RNA primer to initiate replication.
D. It relieves torsional strain (supercoiling) ahead of the replication fork.
Correct Answer: D
Explanation: As helicase unwinds the DNA, the double helix ahead of the fork becomes
tightly wound or ‘supercoiled.’ Topoisomerase cuts and rejoins the DNA to relieve this
physical tension.
,4. Why are Okazaki fragments formed on the lagging strand?
A. Because the lagging strand template is circular.
B. Because DNA polymerase can only work in the 5’ to 3’ direction while the template is 5’
to 3’.
C. Because RNA primers are not available on the lagging strand.
D. Because DNA ligase cannot function on a continuous strand.
Correct Answer: B
Explanation: Since DNA polymerase only synthesizes in the 5’ to 3’ direction, it must move
away from the replication fork on the template strand oriented 5’ to 3’, resulting in short,
discontinuous segments called Okazaki fragments.
5. Which enzyme is responsible for replacing RNA primers with DNA nucleotides?
A. DNA Polymerase I
B. DNA Helicase
C. DNA Polymerase III
D. Primase
Correct Answer: A
Explanation: DNA Polymerase I has 5’ to 3’ exonuclease activity, allowing it to remove the
RNA primers used to start replication and replace them with the appropriate DNA
nucleotides.
6. What is the primary function of DNA Ligase?
A. To unwind the double helix.
B. To add a poly-A tail to the 3’ end of the DNA.
C. To catalyze the formation of phosphodiester bonds between DNA fragments.
D. To proofread the new DNA strand for errors.
Correct Answer: C
Explanation: DNA Ligase ‘glues’ the sugar-phosphate backbone together by creating
phosphodiester bonds between the 3’ end of one DNA fragment and the 5’ end of another,
essential for joining Okazaki fragments.
7. The ‘Central Dogma’ of molecular biology describes the flow of genetic information as:
A. Protein -> RNA -> DNA
B. DNA -> Protein -> RNA
, C. RNA -> DNA -> Protein
D. DNA -> RNA -> Protein
Correct Answer: D
Explanation: The Central Dogma states that genetic information is stored in DNA,
transcribed into messenger RNA (mRNA), and then translated into a functional protein.
8. Where does transcription occur in a eukaryotic cell?
A. Cytoplasm
B. Ribosome
C. Nucleus
D. Endoplasmic Reticulum
Correct Answer: C
Explanation: In eukaryotes, DNA is contained within the nucleus; therefore, the synthesis
of mRNA (transcription) must occur there before the transcript is exported to the
cytoplasm for translation.
9. Which of the following is the enzyme responsible for RNA synthesis during transcription?
A. DNA Polymerase
B. RNA Polymerase
C. Reverse Transcriptase
D. RNA Ligase
Correct Answer: B
Explanation: RNA Polymerase binds to the DNA promoter and catalyzes the synthesis of
an RNA strand complementary to the DNA template strand.
10. A sequence of DNA that signals the start of a gene and provides a binding site for RNA
polymerase is called the:
A. Intron
B. Codon
C. Exon
D. Promoter
Correct Answer: D
Explanation: The promoter is a specific DNA sequence located upstream of a gene that
serves as the recognition and binding site for RNA polymerase to begin transcription.
