Below is a set of original revision questions modeled on key
themes from Molecular Biology of the Cell (6th Edition,
Alberts et al.),chapter 1-25 along with detailed rationales for
each answer. These questions are intended to help you review
and integrate major concepts from the text. They are not
taken verbatim from any copyrighted source but are instead
designed to reflect the core ideas discussed in the book.
Question 1: The Fluid Mosaic Model
Question: Which statement best captures the essence of the fluid mosaic model of the plasma
membrane?
A. The membrane is a rigid structure composed only of lipids that do not move.
B. The membrane is a dynamic structure where proteins are embedded in or associated with a fluid lipid
bilayer, allowing lateral movement.
C. The membrane is made exclusively of proteins with lipids acting as static scaffolds.
D. The membrane is a layered structure with proteins only on the inner surface.
Correct Answer: B
Rationale:
The fluid mosaic model describes the plasma membrane as a dynamic, fluid structure with lipids forming
a bilayer that allows embedded proteins to move laterally. This model accounts for both the flexibility of
the membrane and the mosaic of proteins interspersed within it.
Question 2: DNA Replication Mechanism
Question: Which enzyme is directly responsible for the synthesis of a new DNA strand during
replication?
A. DNA ligase
B. DNA polymerase
C. Helicase
D. Primase
Correct Answer: B
Rationale:
DNA polymerase catalyzes the addition of nucleotides to form a new DNA strand, reading the template
strand and ensuring proper base pairing. Helicase unwinds the DNA, primase lays down RNA primers,
and ligase joins fragments—but it is the DNA polymerase that performs the actual synthesis.
,Question 3: Regulation of Gene Expression
Question: Transcription factors primarily regulate gene expression by:
A. Directly modifying DNA structure
B. Binding to specific DNA sequences to increase or decrease transcription rates
C. Degrading messenger RNA
D. Facilitating protein folding in the endoplasmic reticulum
Correct Answer: B
Rationale:
Transcription factors bind to specific promoter or enhancer regions of DNA to either promote or repress
the recruitment of RNA polymerase, thereby regulating the transcription rate of target genes.
Question 4: The Role of the Cytoskeleton
Question: Which of the following functions is NOT typically associated with the cytoskeleton?
A. Providing structural support to the cell
B. Facilitating intracellular transport
C. Generating ATP
D. Enabling cell motility
Correct Answer: C
Rationale:
The cytoskeleton is integral for maintaining cell shape, enabling motility, and serving as tracks for
intracellular transport. ATP generation is primarily the function of mitochondria and related metabolic
pathways, not the cytoskeleton.
Question 5: Cell Cycle Control
Question: Which protein complex is essential for the transition from the G1 phase to the S phase in the
cell cycle?
A. Cyclin-dependent kinases (Cdks) paired with G1 cyclins
B. DNA polymerase with its associated factors
C. The proteasome
D. RNA polymerase II
Correct Answer: A
Rationale:
The G1 to S phase transition is regulated by cyclin-dependent kinases (Cdks) when paired with their
specific cyclins (G1 cyclins). This complex phosphorylates key proteins that drive the cell past the
restriction point, committing it to DNA replication.
, Question 6: Protein Targeting to the Endoplasmic Reticulum
Question: What is the primary signal that directs a nascent protein to the endoplasmic reticulum (ER)?
A. A nuclear localization signal
B. A mitochondrial targeting sequence
C. An N-terminal signal peptide
D. A lysosomal sorting signal
Correct Answer: C
Rationale:
Proteins destined for secretion or insertion into membranes typically contain an N-terminal signal
peptide. This sequence is recognized by the signal recognition particle (SRP), which directs the ribosome
to the ER for co-translational translocation.
Question 7: Mechanisms of Protein Folding
Question: Which of the following best describes the role of molecular chaperones in protein folding?
A. They catalyze peptide bond formation during translation.
B. They assist in the correct folding of proteins and prevent misfolding or aggregation.
C. They degrade misfolded proteins immediately upon synthesis.
D. They permanently bind to proteins to maintain them in an unfolded state.
Correct Answer: B
Rationale:
Molecular chaperones facilitate the proper folding of proteins by preventing incorrect interactions that
can lead to aggregation. They help proteins achieve their functional conformations without becoming
permanently bound to them.
Question 8: Signal Transduction Pathways
Question: In many signal transduction pathways, what is the primary role of protein kinases?
A. To break down extracellular signals
B. To transfer phosphate groups to specific target proteins, modifying their activity
C. To transport ions across the cell membrane
D. To directly bind and sequester signaling molecules
Correct Answer: B
Rationale:
Protein kinases transfer phosphate groups from ATP to target proteins, a modification that can alter the
protein’s activity, location, or interaction with other proteins, thereby propagating the signal within the
cell.
themes from Molecular Biology of the Cell (6th Edition,
Alberts et al.),chapter 1-25 along with detailed rationales for
each answer. These questions are intended to help you review
and integrate major concepts from the text. They are not
taken verbatim from any copyrighted source but are instead
designed to reflect the core ideas discussed in the book.
Question 1: The Fluid Mosaic Model
Question: Which statement best captures the essence of the fluid mosaic model of the plasma
membrane?
A. The membrane is a rigid structure composed only of lipids that do not move.
B. The membrane is a dynamic structure where proteins are embedded in or associated with a fluid lipid
bilayer, allowing lateral movement.
C. The membrane is made exclusively of proteins with lipids acting as static scaffolds.
D. The membrane is a layered structure with proteins only on the inner surface.
Correct Answer: B
Rationale:
The fluid mosaic model describes the plasma membrane as a dynamic, fluid structure with lipids forming
a bilayer that allows embedded proteins to move laterally. This model accounts for both the flexibility of
the membrane and the mosaic of proteins interspersed within it.
Question 2: DNA Replication Mechanism
Question: Which enzyme is directly responsible for the synthesis of a new DNA strand during
replication?
A. DNA ligase
B. DNA polymerase
C. Helicase
D. Primase
Correct Answer: B
Rationale:
DNA polymerase catalyzes the addition of nucleotides to form a new DNA strand, reading the template
strand and ensuring proper base pairing. Helicase unwinds the DNA, primase lays down RNA primers,
and ligase joins fragments—but it is the DNA polymerase that performs the actual synthesis.
,Question 3: Regulation of Gene Expression
Question: Transcription factors primarily regulate gene expression by:
A. Directly modifying DNA structure
B. Binding to specific DNA sequences to increase or decrease transcription rates
C. Degrading messenger RNA
D. Facilitating protein folding in the endoplasmic reticulum
Correct Answer: B
Rationale:
Transcription factors bind to specific promoter or enhancer regions of DNA to either promote or repress
the recruitment of RNA polymerase, thereby regulating the transcription rate of target genes.
Question 4: The Role of the Cytoskeleton
Question: Which of the following functions is NOT typically associated with the cytoskeleton?
A. Providing structural support to the cell
B. Facilitating intracellular transport
C. Generating ATP
D. Enabling cell motility
Correct Answer: C
Rationale:
The cytoskeleton is integral for maintaining cell shape, enabling motility, and serving as tracks for
intracellular transport. ATP generation is primarily the function of mitochondria and related metabolic
pathways, not the cytoskeleton.
Question 5: Cell Cycle Control
Question: Which protein complex is essential for the transition from the G1 phase to the S phase in the
cell cycle?
A. Cyclin-dependent kinases (Cdks) paired with G1 cyclins
B. DNA polymerase with its associated factors
C. The proteasome
D. RNA polymerase II
Correct Answer: A
Rationale:
The G1 to S phase transition is regulated by cyclin-dependent kinases (Cdks) when paired with their
specific cyclins (G1 cyclins). This complex phosphorylates key proteins that drive the cell past the
restriction point, committing it to DNA replication.
, Question 6: Protein Targeting to the Endoplasmic Reticulum
Question: What is the primary signal that directs a nascent protein to the endoplasmic reticulum (ER)?
A. A nuclear localization signal
B. A mitochondrial targeting sequence
C. An N-terminal signal peptide
D. A lysosomal sorting signal
Correct Answer: C
Rationale:
Proteins destined for secretion or insertion into membranes typically contain an N-terminal signal
peptide. This sequence is recognized by the signal recognition particle (SRP), which directs the ribosome
to the ER for co-translational translocation.
Question 7: Mechanisms of Protein Folding
Question: Which of the following best describes the role of molecular chaperones in protein folding?
A. They catalyze peptide bond formation during translation.
B. They assist in the correct folding of proteins and prevent misfolding or aggregation.
C. They degrade misfolded proteins immediately upon synthesis.
D. They permanently bind to proteins to maintain them in an unfolded state.
Correct Answer: B
Rationale:
Molecular chaperones facilitate the proper folding of proteins by preventing incorrect interactions that
can lead to aggregation. They help proteins achieve their functional conformations without becoming
permanently bound to them.
Question 8: Signal Transduction Pathways
Question: In many signal transduction pathways, what is the primary role of protein kinases?
A. To break down extracellular signals
B. To transfer phosphate groups to specific target proteins, modifying their activity
C. To transport ions across the cell membrane
D. To directly bind and sequester signaling molecules
Correct Answer: B
Rationale:
Protein kinases transfer phosphate groups from ATP to target proteins, a modification that can alter the
protein’s activity, location, or interaction with other proteins, thereby propagating the signal within the
cell.
