PCB3023 Exam 2: Molecular Cell Biology 2026 |UCF
1. In prokaryotic transcription, which subunit of the RNA polymerase
holoenzyme is responsible for recognizing the promoter sequence?
A. Sigma factor
B. Beta subunit
C. Alpha subunit
D. Omega subunit
Answer: A
Rationale: The sigma factor is required for the initiation of transcription in bacteria as it
provides promoter specificity to the RNA polymerase core enzyme.
2. Which enzyme is primarily responsible for synthesizing mRNA in eukaryotic
cells?
A. RNA Polymerase I
B. RNA Polymerase II
C. RNA Polymerase III
D. DNA Polymerase alpha
Answer: B
Rationale: RNA Polymerase II transcribes all protein-coding genes into messenger RNA
(mRNA).
,3. What is the role of the 5’ cap added to eukaryotic mRNA?
A. It serves as a termination signal for transcription
B. It assists in splicing of introns
C. It codes for the first methionine of the protein
D. It protects the mRNA from degradation and aids in translation initiation
Answer: D
Rationale: The 7-methylguanosine cap protects mRNA from exonucleases and is
recognized by the ribosome to begin translation.
4. Which of the following is NOT a consensus sequence typically found in
eukaryotic promoters?
A. TATA box
B. CAAT box
C. Pribnow box
D. GC box
Answer: C
Rationale: The Pribnow box (-10 consensus) is found in prokaryotic promoters, not
eukaryotic ones.
5. The process of removing non-coding regions from a pre-mRNA transcript is
called:
A. Capping
B. Polyadenylation
C. Splicing
D. Editing
Answer: C
Rationale: Splicing involves the removal of introns (non-coding) and the ligation of exons
(coding) by the spliceosome.
, 6. What type of RNA molecules carry amino acids to the ribosome during
protein synthesis?
A. mRNA
B. rRNA
C. snRNA
D. tRNA
Answer: D
Rationale: tRNAs (transfer RNAs) match their anticodon with the mRNA codon to deliver
the correct amino acid.
7. The enzyme that attaches the correct amino acid to its corresponding tRNA is:
A. Peptidyl transferase
B. RNA ligase
C. Aminoacyl-tRNA synthetase
D. Primase
Answer: C
Rationale: Aminoacyl-tRNA synthetases are responsible for ‘charging’ tRNAs by catalyzing
the covalent bond between an amino acid and the tRNA.
8. During translation elongation, where does the incoming charged tRNA first
bind in the ribosome?
A. P site
B. E site
C. A site
D. Exit tunnel
Answer: C
Rationale: The A (aminoacyl) site is where new charged tRNAs enter the ribosome, except
for the very first initiator tRNA which starts at the P site.
1. In prokaryotic transcription, which subunit of the RNA polymerase
holoenzyme is responsible for recognizing the promoter sequence?
A. Sigma factor
B. Beta subunit
C. Alpha subunit
D. Omega subunit
Answer: A
Rationale: The sigma factor is required for the initiation of transcription in bacteria as it
provides promoter specificity to the RNA polymerase core enzyme.
2. Which enzyme is primarily responsible for synthesizing mRNA in eukaryotic
cells?
A. RNA Polymerase I
B. RNA Polymerase II
C. RNA Polymerase III
D. DNA Polymerase alpha
Answer: B
Rationale: RNA Polymerase II transcribes all protein-coding genes into messenger RNA
(mRNA).
,3. What is the role of the 5’ cap added to eukaryotic mRNA?
A. It serves as a termination signal for transcription
B. It assists in splicing of introns
C. It codes for the first methionine of the protein
D. It protects the mRNA from degradation and aids in translation initiation
Answer: D
Rationale: The 7-methylguanosine cap protects mRNA from exonucleases and is
recognized by the ribosome to begin translation.
4. Which of the following is NOT a consensus sequence typically found in
eukaryotic promoters?
A. TATA box
B. CAAT box
C. Pribnow box
D. GC box
Answer: C
Rationale: The Pribnow box (-10 consensus) is found in prokaryotic promoters, not
eukaryotic ones.
5. The process of removing non-coding regions from a pre-mRNA transcript is
called:
A. Capping
B. Polyadenylation
C. Splicing
D. Editing
Answer: C
Rationale: Splicing involves the removal of introns (non-coding) and the ligation of exons
(coding) by the spliceosome.
, 6. What type of RNA molecules carry amino acids to the ribosome during
protein synthesis?
A. mRNA
B. rRNA
C. snRNA
D. tRNA
Answer: D
Rationale: tRNAs (transfer RNAs) match their anticodon with the mRNA codon to deliver
the correct amino acid.
7. The enzyme that attaches the correct amino acid to its corresponding tRNA is:
A. Peptidyl transferase
B. RNA ligase
C. Aminoacyl-tRNA synthetase
D. Primase
Answer: C
Rationale: Aminoacyl-tRNA synthetases are responsible for ‘charging’ tRNAs by catalyzing
the covalent bond between an amino acid and the tRNA.
8. During translation elongation, where does the incoming charged tRNA first
bind in the ribosome?
A. P site
B. E site
C. A site
D. Exit tunnel
Answer: C
Rationale: The A (aminoacyl) site is where new charged tRNAs enter the ribosome, except
for the very first initiator tRNA which starts at the P site.
