Biol 101: Introduction To Biology; Exam
3: Version C Questions And Answers
With Rationales/ Graded A+/2026 Update
/100%Correct
SECTION I: CELL COMMUNICATION & SIGNAL TRANSDUCTION
(Questions 1-15)
1. A liver cell responds to the hormone insulin, but a muscle cell does not, even
though both cell types have insulin receptors. What is the most likely explanation
for this difference?
A) Muscle cells lack the gene for the insulin receptor.
B) Liver cells have a different type of insulin receptor.
C) The two cell types have different signal transduction pathways and target
proteins downstream of the receptor.
D) Muscle cells break down insulin before it can exert its effect.
Correct Answer: C
Rationale: While both cell types may have the same receptor, the cellular response
is determined by the specific intracellular signaling proteins and transcription
factors present. Different cell types express different sets of proteins, leading to
tissue-specific responses to the same signal.
2. Which of the following is the correct order of events in a typical signal
transduction pathway?
A) Receptor activation → Cellular response → Signal transduction → Signal
termination
B) Signal transduction → Receptor activation → Cellular response
C) Signal reception → Receptor activation → Signal transduction → Cellular
response
D) Cellular response → Signal reception → Signal transduction
Correct Answer: C
Rationale: The three main stages of cell signaling are: 1) Reception (signal
,molecule binds receptor), 2) Transduction (cascade of molecular interactions), and
3) Response (cellular activity is altered).
3. A G-protein coupled receptor (GPCR) is activated by a signal molecule. What is
the immediate next step in the pathway?
A) The G-protein hydrolyzes GTP to GDP.
B) The G-protein’s α subunit exchanges GDP for GTP and dissociates from the β
and γ subunits.
C) Adenylyl cyclase is directly activated by the signal molecule.
D) The receptor phosphorylates a tyrosine kinase.
Correct Answer: B
Rationale: Upon activation, the GPCR acts as a guanine nucleotide exchange
factor (GEF), causing the associated G-protein to release GDP and bind GTP. The
activated α subunit then separates from the βγ dimer to regulate downstream
effectors.
4. Which of the following is an example of a second messenger?
A) Insulin
B) Epinephrine
C) Cyclic AMP (cAMP)
D) Receptor tyrosine kinase
Correct Answer: C
Rationale: Second messengers are small, non-protein intracellular signaling
molecules. cAMP is a classic example. Insulin and epinephrine are primary signals
(first messengers), and receptor tyrosine kinase is a type of receptor.
5. A mutation in a gene that codes for a protein phosphatase would most likely lead
to:
A) Inability to activate a G-protein.
B) Prolonged cellular response due to failure to dephosphorylate target proteins.
C) Inability to produce cAMP.
D) Constitutive activation of a receptor.
Correct Answer: B
Rationale: Protein phosphatases are enzymes that remove phosphate groups,
turning off signaling pathways initiated by kinases. If they are non-functional,
proteins remain phosphorylated and active longer than normal, leading to a
prolonged response.
, 6. Which of the following is NOT a characteristic of apoptosis?
A) It is a programmed cell death.
B) It causes inflammation in surrounding tissues.
C) It involves the activation of caspases.
D) It is important for normal development (e.g., webbing between fingers).
Correct Answer: B
Rationale: Apoptosis is a clean, controlled process where the cell's contents are
packaged into vesicles and phagocytosed, preventing inflammation. Necrosis, in
contrast, is unregulated cell death that causes inflammation.
7. What is the primary function of a receptor tyrosine kinase (RTK)?
A) To act as an ion channel that opens in response to a ligand.
B) To phosphorylate itself on tyrosine residues and then phosphorylate other
proteins.
C) To hydrolyze GTP to GDP to inactivate a G-protein.
D) To directly activate DNA transcription.
Correct Answer: B
Rationale: RTKs are enzyme-linked receptors. Ligand binding causes dimerization,
allowing the receptor to autophosphorylate on tyrosine residues. These
phosphorylated tyrosines serve as docking sites for other signaling proteins, which
are then activated, often by phosphorylation.
8. A small, nonpolar, hydrophobic signal molecule like a steroid hormone (e.g.,
testosterone) would be expected to have a receptor that is:
A) An ion channel in the plasma membrane.
B) A G-protein coupled receptor in the plasma membrane.
C) An intracellular receptor that can directly affect gene expression.
D) A receptor tyrosine kinase in the plasma membrane.
Correct Answer: C
Rationale: Steroid hormones are nonpolar and can cross the plasma membrane.
Their receptors are located in the cytoplasm or nucleus. The hormone-receptor
complex then acts as a transcription factor, directly influencing gene expression.
9. Which of the following best describes signal amplification in a transduction
pathway?
A) One signal molecule binds to one receptor, leading to the activation of one
enzyme.
3: Version C Questions And Answers
With Rationales/ Graded A+/2026 Update
/100%Correct
SECTION I: CELL COMMUNICATION & SIGNAL TRANSDUCTION
(Questions 1-15)
1. A liver cell responds to the hormone insulin, but a muscle cell does not, even
though both cell types have insulin receptors. What is the most likely explanation
for this difference?
A) Muscle cells lack the gene for the insulin receptor.
B) Liver cells have a different type of insulin receptor.
C) The two cell types have different signal transduction pathways and target
proteins downstream of the receptor.
D) Muscle cells break down insulin before it can exert its effect.
Correct Answer: C
Rationale: While both cell types may have the same receptor, the cellular response
is determined by the specific intracellular signaling proteins and transcription
factors present. Different cell types express different sets of proteins, leading to
tissue-specific responses to the same signal.
2. Which of the following is the correct order of events in a typical signal
transduction pathway?
A) Receptor activation → Cellular response → Signal transduction → Signal
termination
B) Signal transduction → Receptor activation → Cellular response
C) Signal reception → Receptor activation → Signal transduction → Cellular
response
D) Cellular response → Signal reception → Signal transduction
Correct Answer: C
Rationale: The three main stages of cell signaling are: 1) Reception (signal
,molecule binds receptor), 2) Transduction (cascade of molecular interactions), and
3) Response (cellular activity is altered).
3. A G-protein coupled receptor (GPCR) is activated by a signal molecule. What is
the immediate next step in the pathway?
A) The G-protein hydrolyzes GTP to GDP.
B) The G-protein’s α subunit exchanges GDP for GTP and dissociates from the β
and γ subunits.
C) Adenylyl cyclase is directly activated by the signal molecule.
D) The receptor phosphorylates a tyrosine kinase.
Correct Answer: B
Rationale: Upon activation, the GPCR acts as a guanine nucleotide exchange
factor (GEF), causing the associated G-protein to release GDP and bind GTP. The
activated α subunit then separates from the βγ dimer to regulate downstream
effectors.
4. Which of the following is an example of a second messenger?
A) Insulin
B) Epinephrine
C) Cyclic AMP (cAMP)
D) Receptor tyrosine kinase
Correct Answer: C
Rationale: Second messengers are small, non-protein intracellular signaling
molecules. cAMP is a classic example. Insulin and epinephrine are primary signals
(first messengers), and receptor tyrosine kinase is a type of receptor.
5. A mutation in a gene that codes for a protein phosphatase would most likely lead
to:
A) Inability to activate a G-protein.
B) Prolonged cellular response due to failure to dephosphorylate target proteins.
C) Inability to produce cAMP.
D) Constitutive activation of a receptor.
Correct Answer: B
Rationale: Protein phosphatases are enzymes that remove phosphate groups,
turning off signaling pathways initiated by kinases. If they are non-functional,
proteins remain phosphorylated and active longer than normal, leading to a
prolonged response.
, 6. Which of the following is NOT a characteristic of apoptosis?
A) It is a programmed cell death.
B) It causes inflammation in surrounding tissues.
C) It involves the activation of caspases.
D) It is important for normal development (e.g., webbing between fingers).
Correct Answer: B
Rationale: Apoptosis is a clean, controlled process where the cell's contents are
packaged into vesicles and phagocytosed, preventing inflammation. Necrosis, in
contrast, is unregulated cell death that causes inflammation.
7. What is the primary function of a receptor tyrosine kinase (RTK)?
A) To act as an ion channel that opens in response to a ligand.
B) To phosphorylate itself on tyrosine residues and then phosphorylate other
proteins.
C) To hydrolyze GTP to GDP to inactivate a G-protein.
D) To directly activate DNA transcription.
Correct Answer: B
Rationale: RTKs are enzyme-linked receptors. Ligand binding causes dimerization,
allowing the receptor to autophosphorylate on tyrosine residues. These
phosphorylated tyrosines serve as docking sites for other signaling proteins, which
are then activated, often by phosphorylation.
8. A small, nonpolar, hydrophobic signal molecule like a steroid hormone (e.g.,
testosterone) would be expected to have a receptor that is:
A) An ion channel in the plasma membrane.
B) A G-protein coupled receptor in the plasma membrane.
C) An intracellular receptor that can directly affect gene expression.
D) A receptor tyrosine kinase in the plasma membrane.
Correct Answer: C
Rationale: Steroid hormones are nonpolar and can cross the plasma membrane.
Their receptors are located in the cytoplasm or nucleus. The hormone-receptor
complex then acts as a transcription factor, directly influencing gene expression.
9. Which of the following best describes signal amplification in a transduction
pathway?
A) One signal molecule binds to one receptor, leading to the activation of one
enzyme.
