1. Which of the following is the first step in signal transduction?
A) Activation of second messengers
B) Binding of the signaling molecule to the receptor
C) Cellular response
D) Signal amplification
Answer: B) Binding of the signaling molecule to the receptor
2. What type of receptors are involved in the activation of G-protein-coupled signal transduction pathways?
A) Ligand-gated ion channels
B) Receptor tyrosine kinases
C) G-protein coupled receptors (GPCRs)
D) Nuclear receptors
Answer: C) G-protein coupled receptors (GPCRs)
3. Which of the following is a secondary messenger in signal transduction?
A) DNA
B) Cyclic AMP (cAMP)
C) RNA
D) Glucose
Answer: B) Cyclic AMP (cAMP)
4. What is the function of protein kinases in signal transduction pathways?
A) To transport signals across the cell membrane
B) To catalyze the phosphorylation of target proteins
C) To degrade the signaling molecules
D) To initiate DNA replication
Answer: B) To catalyze the phosphorylation of target proteins
5. Which of the following is NOT a common second messenger in signal transduction?
A) Calcium ions (Ca²⁺)
B) Cyclic GMP (cGMP)
C) Phosphatidylinositol (PI)
D) ATP
Answer: D) ATP
6. What does the activation of a receptor tyrosine kinase (RTK) typically lead to?
A) Activation of phospholipase C
B) Autophosphorylation of the receptor
C) Release of calcium ions
D) Inhibition of protein synthesis
Answer: B) Autophosphorylation of the receptor
7. Which molecule typically activates protein kinase A (PKA) in signal transduction?
A) Cyclic AMP (cAMP)
B) Inositol trisphosphate (IP₃)
C) Calcium ions (Ca²⁺)
D) Protein kinase C (PKC)
Answer: A) Cyclic AMP (cAMP)
8. Which of the following is a feature of signal amplification in cellular signaling?
A) A single signaling molecule activates one receptor
B) A single receptor activation leads to multiple second messengers
C) The signal is dampened with each step
D) Only intracellular signals are amplified
Answer: B) A single receptor activation leads to multiple second messengers
9. In the MAP kinase signaling pathway, what is typically the final target of the signal?
A) Receptor tyrosine kinases
B) Transcription factors
C) G-proteins
D) Second messengers
Answer: B) Transcription factors
10. Which of the following molecules is involved in the process of signal termination in G-protein-coupled pathways?
A) GTPase-activating proteins (GAPs)
B) Protein kinases
C) Cyclic AMP (cAMP)
D) Receptor tyrosine kinases
Answer: A) GTPase-activating proteins (GAPs)
11. In the phosphatidylinositol (PI) pathway, which enzyme generates inositol trisphosphate (IP₃)?
A) Protein kinase A
B) Phospholipase C
C) Guanylate cyclase
D) Adenylate cyclase
Answer: B) Phospholipase C
12. Which of the following does NOT act as a second messenger in the PI (phosphatidylinositol) signaling pathway?
A) Inositol trisphosphate (IP₃)
B) Diacylglycerol (DAG)
C) Cyclic AMP (cAMP)
D) Calcium ions (Ca²⁺)
Answer: C) Cyclic AMP (cAMP)
13. What is the function of G-proteins in signal transduction?
A) To act as enzymes that break down the signaling molecules
B) To amplify the signal by activating second messengers
C) To transport molecules across the cell membrane
D) To directly phosphorylate target proteins
Answer: B) To amplify the signal by activating second messengers
14. Which of the following is a common feature of G-protein-coupled receptors (GPCRs)?
A) They function as ion channels
B) They undergo autophosphorylation upon activation
C) They are integral membrane proteins that interact with G-proteins
D) They are only found in prokaryotes
Answer: C) They are integral membrane proteins that interact with G-proteins
15. In signal transduction, what does the term “feedback inhibition” refer to?
A) A positive reinforcement of the signal
B) A mechanism that enhances the signaling pathway
C) A mechanism that shuts down the signaling pathway to prevent overstimulation
D) The activation of receptors by feedback molecules
Answer: C) A mechanism that shuts down the signaling pathway to prevent overstimulation
16. Which of the following molecules activates the Ras protein in the MAP kinase pathway?
A) GTP
B) Phosphatidylinositol
C) Cyclic GMP
D) Ras-GEF (Guanine nucleotide Exchange Factor)
Answer: D) Ras-GEF (Guanine nucleotide Exchange Factor)
17. What is the result of the activation of protein kinase C (PKC) in signal transduction?
A) Phosphorylation of proteins involved in gene expression
B) Production of cyclic AMP
C) Opening of ion channels
D) Release of calcium ions
Answer: A) Phosphorylation of proteins involved in gene expression
18. Which of the following is true about ligand-gated ion channels in signal transduction?
A) They are activated by the phosphorylation of the receptor
B) They form a pore that opens when bound by a ligand
C) They activate G-proteins inside the cell
D) They act as kinases to phosphorylate proteins
Answer: B) They form a pore that opens when bound by a ligand
19. Which signaling molecule is often involved in cell-cell communication in paracrine signaling?
A) Steroid hormones
B) Nitric oxide
C) Insulin
D) Growth factors
Answer: D) Growth factors
20. Which enzyme is involved in converting ATP to cyclic AMP (cAMP) in signal transduction?
A) Phospholipase C
B) Adenylate cyclase
C) Guanylate cyclase
D) Protein kinase A
Answer: B) Adenylate cyclase
21. What is the role of IP₃ in signal transduction?
A) It binds to protein kinases and activates gene expression
B) It activates protein kinase A
C) It releases calcium ions from the endoplasmic reticulum
D) It activates G-proteins
Answer: C) It releases calcium ions from the endoplasmic reticulum
22. Which of the following is the end result of the Wnt signaling pathway?
A) Activation of protein kinase C
B) Phosphorylation of GTP-binding proteins
C) Translocation of β-catenin into the nucleus
D) Opening of ion channels
Answer: C) Translocation of β-catenin into the nucleus
23. Which molecule is often released by cells in response to stress, and signals via G-protein coupled receptors?
A) Insulin
B) Cortisol
C) Nitric oxide
D) Adrenaline
Answer: D) Adrenaline
24. Which of the following is NOT a mechanism for regulating signal transduction?
A) Phosphorylation and dephosphorylation
B) GTP hydrolysis
C) Feedback loops
D) Activation of transcription factors
Answer: D) Activation of transcription factors
25. Which pathway involves the activation of the protein Ras?
A) MAP kinase pathway
B) Insulin signaling pathway
C) Notch signaling pathway
D) Hedgehog signaling pathway
Answer: A) MAP kinase pathway
26. What is the primary role of scaffolding proteins in signal transduction?
A) To degrade signaling molecules
B) To act as secondary messengers
C) To organize signaling components into complexes
D) To open ion channels
Answer: C) To organize signaling components into complexes
27. What is the main function of the NF-κB signaling pathway?
A) Regulation of glucose metabolism
B) Inflammatory response and immune regulation
C) Control of cell cycle progression
D) Regulation of ion channels
Answer: B) Inflammatory response and immune regulation
28. Which protein is involved in the early stages of apoptosis and can be activated by cell signaling?
A) Caspase
B) GTPase
C) Cyclin
D) Myosin
Answer: A) Caspase
29. Which of the following is true about the G-protein-coupled receptor (GPCR) desensitization?
A) The receptor is completely shut off after activation
B) The receptor is internalized and degraded by the cell
C) The receptor is phosphorylated, which reduces its responsiveness
D) The receptor becomes permanently active
Answer: C) The receptor is phosphorylated, which reduces its responsiveness
30. What does the term “cross-talk” in signal transduction refer to?
A) Interaction between different signaling pathways
B) Activation of signal pathways by phosphorylation
C) The termination of signaling pathways
D) The activation of second messengers
Answer: A) Interaction between different signaling pathways
