BIOL 271 MODULE 2 EXAM -
MOLECULAR BIOLOGY AND GENETICS
QUESTIONS AND ANSWERS
1. During DNA replication, which enzyme is responsible for relieving torsional strain ahead of
the replication fork?
A. Topoisomerase
B. DNA Ligase
C. DNA Helicase
D. Single-strand binding proteins
Answer: A
Conceptual Explanation: Topoisomerase (or DNA Gyrase in prokaryotes) cuts and rejoins
the DNA strands to relieve the supercoiling tension created by helicase unwinding the
helix.
2. The ‘Wobble’ hypothesis, proposed by Francis Crick, explains why:
A. The genetic code is overlapping
B. DNA polymerase makes errors during replication
C. There are fewer tRNAs than there are codons for amino acids
,D. mRNA is degraded quickly in the cytoplasm
Answer: C
Conceptual Explanation: The Wobble hypothesis suggests that the base at the 5’ end of
the tRNA anticodon can form non-standard hydrogen bonds with the 3’ base of the mRNA
codon, allowing one tRNA to recognize multiple codons.
3. Which of the following occurs during the processing of eukaryotic pre-mRNA?
A. Addition of a 3’ 7-methylguanosine cap
B. Excision of exons and splicing of introns
C. Addition of a poly-A tail to the 5’ end
D. Splicing of introns and joining of exons
Answer: D
Conceptual Explanation: In eukaryotic mRNA processing, introns (non-coding regions)
are removed and exons (coding regions) are spliced together; a 5’ cap and a 3’ poly-A tail
are also added.
4. In the Meselson-Stahl experiment, which model of DNA replication was supported after
two rounds of replication in light nitrogen (14N)?
A. Conservative
B. Both Semiconservative and Dispersive
C. Dispersive
, D. Semiconservative
Answer: D
Conceptual Explanation: After two rounds, the appearance of a light band and a hybrid
band exclusively supported the semiconservative model, ruling out the dispersive model
which would have shown only one intermediate band.
5. Which subunit of the prokaryotic RNA polymerase holoenzyme is responsible for promoter
recognition?
A. Sigma factor
B. Beta subunit
C. Alpha subunit
D. Omega subunit
Answer: A
Conceptual Explanation: The sigma factor provides specificity to the RNA polymerase,
allowing it to bind to specific promoter sequences like the -10 and -35 boxes.
6. Telomerase is a unique enzyme because it contains:
A. An RNA template to extend the 3’ end of DNA
B. A DNA template to extend the 5’ end of DNA
C. Protease activity to shorten chromosomes
D. Restriction endonuclease activity
MOLECULAR BIOLOGY AND GENETICS
QUESTIONS AND ANSWERS
1. During DNA replication, which enzyme is responsible for relieving torsional strain ahead of
the replication fork?
A. Topoisomerase
B. DNA Ligase
C. DNA Helicase
D. Single-strand binding proteins
Answer: A
Conceptual Explanation: Topoisomerase (or DNA Gyrase in prokaryotes) cuts and rejoins
the DNA strands to relieve the supercoiling tension created by helicase unwinding the
helix.
2. The ‘Wobble’ hypothesis, proposed by Francis Crick, explains why:
A. The genetic code is overlapping
B. DNA polymerase makes errors during replication
C. There are fewer tRNAs than there are codons for amino acids
,D. mRNA is degraded quickly in the cytoplasm
Answer: C
Conceptual Explanation: The Wobble hypothesis suggests that the base at the 5’ end of
the tRNA anticodon can form non-standard hydrogen bonds with the 3’ base of the mRNA
codon, allowing one tRNA to recognize multiple codons.
3. Which of the following occurs during the processing of eukaryotic pre-mRNA?
A. Addition of a 3’ 7-methylguanosine cap
B. Excision of exons and splicing of introns
C. Addition of a poly-A tail to the 5’ end
D. Splicing of introns and joining of exons
Answer: D
Conceptual Explanation: In eukaryotic mRNA processing, introns (non-coding regions)
are removed and exons (coding regions) are spliced together; a 5’ cap and a 3’ poly-A tail
are also added.
4. In the Meselson-Stahl experiment, which model of DNA replication was supported after
two rounds of replication in light nitrogen (14N)?
A. Conservative
B. Both Semiconservative and Dispersive
C. Dispersive
, D. Semiconservative
Answer: D
Conceptual Explanation: After two rounds, the appearance of a light band and a hybrid
band exclusively supported the semiconservative model, ruling out the dispersive model
which would have shown only one intermediate band.
5. Which subunit of the prokaryotic RNA polymerase holoenzyme is responsible for promoter
recognition?
A. Sigma factor
B. Beta subunit
C. Alpha subunit
D. Omega subunit
Answer: A
Conceptual Explanation: The sigma factor provides specificity to the RNA polymerase,
allowing it to bind to specific promoter sequences like the -10 and -35 boxes.
6. Telomerase is a unique enzyme because it contains:
A. An RNA template to extend the 3’ end of DNA
B. A DNA template to extend the 5’ end of DNA
C. Protease activity to shorten chromosomes
D. Restriction endonuclease activity
