Cell Biology: Signalling & Cell Division Exam 2026: Comprehensive
Advanced University/College Practice Examination — Cell
Signalling, Signal Transduction, Cell Cycle Regulation, Mitosis,
Meiosis, Apoptosis & Molecular Control — 190 Multiple-Choice
Questions with Answers & Detailed Rationales
SECTION 1: CELL SIGNALING FUNDAMENTALS (Questions 1–30)
Question 1
Which of the following best describes the role of a ligand in cell signalling?
A. It serves as the intracellular messenger that amplifies the signal.
B. It is a signalling molecule that binds specifically to a receptor protein.
C. It is an enzyme that phosphorylates downstream target proteins.
D. It is a transmembrane channel that allows ion flux.
Correct Answer: B
Explanation: Ligands are signalling molecules that bind specific receptors, initiating
conformational changes that trigger downstream signalling cascades. This is the
fundamental step in cell communication.
Question 2
A researcher observes that a particular signalling pathway continues to activate even after
the ligand has been removed from the extracellular environment. Which mechanism is most
likely responsible?
A. Receptor desensitization
B. Ligand-independent receptor activation due to a mutation
,C. Competitive inhibition of the receptor
D. Downregulation of receptor expression
Correct Answer: B
Explanation: Constitutive activation occurs when mutations cause receptors to signal
without ligand binding, common in oncogenic mutations like EGFRvIII in glioblastoma.
Question 3
Which type of signalling involves a cell responding to molecules that it itself secretes?
A. Paracrine signalling
B. Endocrine signalling
C. Autocrine signalling
D. Juxtacrine signalling
Correct Answer: C
Explanation: Autocrine signalling occurs when a cell secretes signals that bind to receptors
on its own surface, often seen in cancer cells promoting their own proliferation.
Question 4
In a hypothetical signalling cascade, Protein X phosphorylates Protein Y, which then
dephosphorylates Protein Z. What type of regulatory relationship exists between Protein X
and Protein Z?
A. Direct positive regulation
,B. Indirect negative regulation
C. Direct negative regulation
D. No regulatory relationship
Correct Answer: B
Explanation: Protein X activates Y, which inhibits Z through dephosphorylation. This
represents indirect negative regulation, a common motif in signal transduction.
Question 5
Which second messenger is generated by adenylyl cyclase and activates protein kinase A?
A. Diacylglycerol (DAG)
B. Inositol trisphosphate (IP3)
C. Cyclic AMP (cAMP)
D. Calcium ions (Ca²⁺)
Correct Answer: C
Explanation: Adenylyl cyclase converts ATP to cAMP, which binds the regulatory subunits of
PKA, releasing active catalytic subunits to phosphorylate targets.
Question 6
A patient presents with a condition characterized by excessive thirst, frequent urination, and
dilute urine. Genetic analysis reveals a mutation in the V2 receptor in renal collecting duct
cells. Which signalling pathway is most likely disrupted?
, A. Receptor tyrosine kinase pathway
B. Gs-protein coupled receptor pathway
C. JAK-STAT pathway
D. Wnt signalling pathway
Correct Answer: B
Explanation: V2 receptors are GPCRs coupled to Gs, which activate adenylyl cyclase.
Mutations cause nephrogenic diabetes insipidus by preventing cAMP-mediated aquaporin
insertion.
Question 7
Which of the following is a characteristic of G-protein coupled receptors (GPCRs)?
A. They possess intrinsic tyrosine kinase activity.
B. They contain seven transmembrane alpha-helices.
C. They bind directly to DNA to regulate transcription.
D. They are exclusively monomeric proteins.
Correct Answer: B
Explanation: GPCRs are characterized by seven transmembrane domains, a hallmark
structure that enables conformational changes upon ligand binding and G-protein activation.
Question 8
A toxin produced by Vibrio cholerae modifies the Gs alpha subunit, preventing GTP
hydrolysis. What is the consequence for intestinal epithelial cells?
Advanced University/College Practice Examination — Cell
Signalling, Signal Transduction, Cell Cycle Regulation, Mitosis,
Meiosis, Apoptosis & Molecular Control — 190 Multiple-Choice
Questions with Answers & Detailed Rationales
SECTION 1: CELL SIGNALING FUNDAMENTALS (Questions 1–30)
Question 1
Which of the following best describes the role of a ligand in cell signalling?
A. It serves as the intracellular messenger that amplifies the signal.
B. It is a signalling molecule that binds specifically to a receptor protein.
C. It is an enzyme that phosphorylates downstream target proteins.
D. It is a transmembrane channel that allows ion flux.
Correct Answer: B
Explanation: Ligands are signalling molecules that bind specific receptors, initiating
conformational changes that trigger downstream signalling cascades. This is the
fundamental step in cell communication.
Question 2
A researcher observes that a particular signalling pathway continues to activate even after
the ligand has been removed from the extracellular environment. Which mechanism is most
likely responsible?
A. Receptor desensitization
B. Ligand-independent receptor activation due to a mutation
,C. Competitive inhibition of the receptor
D. Downregulation of receptor expression
Correct Answer: B
Explanation: Constitutive activation occurs when mutations cause receptors to signal
without ligand binding, common in oncogenic mutations like EGFRvIII in glioblastoma.
Question 3
Which type of signalling involves a cell responding to molecules that it itself secretes?
A. Paracrine signalling
B. Endocrine signalling
C. Autocrine signalling
D. Juxtacrine signalling
Correct Answer: C
Explanation: Autocrine signalling occurs when a cell secretes signals that bind to receptors
on its own surface, often seen in cancer cells promoting their own proliferation.
Question 4
In a hypothetical signalling cascade, Protein X phosphorylates Protein Y, which then
dephosphorylates Protein Z. What type of regulatory relationship exists between Protein X
and Protein Z?
A. Direct positive regulation
,B. Indirect negative regulation
C. Direct negative regulation
D. No regulatory relationship
Correct Answer: B
Explanation: Protein X activates Y, which inhibits Z through dephosphorylation. This
represents indirect negative regulation, a common motif in signal transduction.
Question 5
Which second messenger is generated by adenylyl cyclase and activates protein kinase A?
A. Diacylglycerol (DAG)
B. Inositol trisphosphate (IP3)
C. Cyclic AMP (cAMP)
D. Calcium ions (Ca²⁺)
Correct Answer: C
Explanation: Adenylyl cyclase converts ATP to cAMP, which binds the regulatory subunits of
PKA, releasing active catalytic subunits to phosphorylate targets.
Question 6
A patient presents with a condition characterized by excessive thirst, frequent urination, and
dilute urine. Genetic analysis reveals a mutation in the V2 receptor in renal collecting duct
cells. Which signalling pathway is most likely disrupted?
, A. Receptor tyrosine kinase pathway
B. Gs-protein coupled receptor pathway
C. JAK-STAT pathway
D. Wnt signalling pathway
Correct Answer: B
Explanation: V2 receptors are GPCRs coupled to Gs, which activate adenylyl cyclase.
Mutations cause nephrogenic diabetes insipidus by preventing cAMP-mediated aquaporin
insertion.
Question 7
Which of the following is a characteristic of G-protein coupled receptors (GPCRs)?
A. They possess intrinsic tyrosine kinase activity.
B. They contain seven transmembrane alpha-helices.
C. They bind directly to DNA to regulate transcription.
D. They are exclusively monomeric proteins.
Correct Answer: B
Explanation: GPCRs are characterized by seven transmembrane domains, a hallmark
structure that enables conformational changes upon ligand binding and G-protein activation.
Question 8
A toxin produced by Vibrio cholerae modifies the Gs alpha subunit, preventing GTP
hydrolysis. What is the consequence for intestinal epithelial cells?
