BIOL 271 MODULE 6 EXAM:
MOLECULAR BIOLOGY AND GENE
REGULATION
1. During DNA replication, which enzyme is responsible for removing RNA primers and
replacing them with DNA nucleotides in prokaryotes?
A. DNA Polymerase III
B. DNA Polymerase I
C. DNA Ligase
D. Helicase
Answer: B
Conceptual Explanation: DNA Polymerase I has 5’ to 3’ exonuclease activity, allowing it to
remove RNA primers and fill the gaps with DNA nucleotides.
2. What is the primary function of topoisomerase during the process of DNA replication?
A. Relieving torsional strain caused by supercoiling
B. Stabilizing single-stranded DNA
C. Unwinding the double helix
D. Synthesizing RNA primers
,Answer: A
Conceptual Explanation: As helicase unwinds DNA, supercoiling occurs ahead of the
replication fork; topoisomerase cuts and rejoins the DNA to relieve this tension.
3. In the context of the lac operon, what occurs when lactose is present but glucose is absent?
A. cAMP levels are high, CAP binds the promoter, and the repressor is dissociated
B. CAP is inactive and the repressor is bound to the operator
C. The lac genes are transcribed at a very low basal level
D. The repressor binds to allolactose and then binds to the operator
Answer: A
Conceptual Explanation: Low glucose leads to high cAMP, which activates CAP. Lactose
provides allolactose to inhibit the repressor, allowing high transcription.
4. Which of the following describes the ‘Wobble Hypothesis’ regarding tRNA-mRNA
interactions?
A. The first base of the codon can pair with multiple anticodon bases
B. Amino acids can be attached to any tRNA regardless of the anticodon
C. Ribosomes move along the mRNA in a non-linear fashion
D. The third base of the codon has relaxed pairing requirements with the anticodon
Answer: D
, Conceptual Explanation: The Wobble Hypothesis suggests that the 3rd position of the
mRNA codon can form non-standard base pairs with the 1st position of the tRNA
anticodon.
5. Which post-transcriptional modification is unique to eukaryotic mRNA and involves the
addition of 7-methylguanosine?
A. Poly-A Tail
B. 5’ Capping
C. Intron Splicing
D. RNA Interference
Answer: B
Conceptual Explanation: A 5’ cap (7-methylguanosine) is added to the beginning of
eukaryotic pre-mRNA to protect it from degradation and assist in ribosome binding.
6. In E. coli, the tryptophan (trp) operon is regulated by attenuation. What determines
whether the termination hairpin forms?
A. The concentration of cAMP in the cell
B. The presence of glucose in the medium
C. The binding of a repressor to the enhancer
D. The speed of the ribosome translating the leader peptide
Answer: D
MOLECULAR BIOLOGY AND GENE
REGULATION
1. During DNA replication, which enzyme is responsible for removing RNA primers and
replacing them with DNA nucleotides in prokaryotes?
A. DNA Polymerase III
B. DNA Polymerase I
C. DNA Ligase
D. Helicase
Answer: B
Conceptual Explanation: DNA Polymerase I has 5’ to 3’ exonuclease activity, allowing it to
remove RNA primers and fill the gaps with DNA nucleotides.
2. What is the primary function of topoisomerase during the process of DNA replication?
A. Relieving torsional strain caused by supercoiling
B. Stabilizing single-stranded DNA
C. Unwinding the double helix
D. Synthesizing RNA primers
,Answer: A
Conceptual Explanation: As helicase unwinds DNA, supercoiling occurs ahead of the
replication fork; topoisomerase cuts and rejoins the DNA to relieve this tension.
3. In the context of the lac operon, what occurs when lactose is present but glucose is absent?
A. cAMP levels are high, CAP binds the promoter, and the repressor is dissociated
B. CAP is inactive and the repressor is bound to the operator
C. The lac genes are transcribed at a very low basal level
D. The repressor binds to allolactose and then binds to the operator
Answer: A
Conceptual Explanation: Low glucose leads to high cAMP, which activates CAP. Lactose
provides allolactose to inhibit the repressor, allowing high transcription.
4. Which of the following describes the ‘Wobble Hypothesis’ regarding tRNA-mRNA
interactions?
A. The first base of the codon can pair with multiple anticodon bases
B. Amino acids can be attached to any tRNA regardless of the anticodon
C. Ribosomes move along the mRNA in a non-linear fashion
D. The third base of the codon has relaxed pairing requirements with the anticodon
Answer: D
, Conceptual Explanation: The Wobble Hypothesis suggests that the 3rd position of the
mRNA codon can form non-standard base pairs with the 1st position of the tRNA
anticodon.
5. Which post-transcriptional modification is unique to eukaryotic mRNA and involves the
addition of 7-methylguanosine?
A. Poly-A Tail
B. 5’ Capping
C. Intron Splicing
D. RNA Interference
Answer: B
Conceptual Explanation: A 5’ cap (7-methylguanosine) is added to the beginning of
eukaryotic pre-mRNA to protect it from degradation and assist in ribosome binding.
6. In E. coli, the tryptophan (trp) operon is regulated by attenuation. What determines
whether the termination hairpin forms?
A. The concentration of cAMP in the cell
B. The presence of glucose in the medium
C. The binding of a repressor to the enhancer
D. The speed of the ribosome translating the leader peptide
Answer: D
