Signal transduction mechanisms form the basis of cellular communication and are essential to understanding pharmacology and drug action. For B. Pharm students, mastering receptor types (GPCRs, RTKs, ion channels, nuclear receptors), intracellular pathways (G-proteins, second messengers like cAMP, IP3, DAG, Ca2+), kinases and phosphatases, and cascade regulation is critical for identifying drug targets and predicting therapeutic responses. This concise, focused review clarifies core concepts—pathway activation, amplification, desensitization, and cross-talk—while linking mechanisms to clinical pharmacology, drug design, and adverse effects. Clear knowledge of signal transduction underpins rational prescribing and research. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary function of signal transduction in cells?
- Conversion of extracellular signals into intracellular responses
- Direct synthesis of DNA
- Export of proteins to the extracellular matrix
- Passive diffusion of ions across membranes
Correct Answer: (Conversion of extracellular signals into intracellular responses)
Q2. Which class of receptor primarily couples to heterotrimeric G-proteins?
- Receptor tyrosine kinases (RTKs)
- G-protein-coupled receptors (GPCRs)
- Ionotropic receptors
- Nuclear steroid receptors
Correct Answer: (G-protein-coupled receptors (GPCRs))
Q3. Receptor tyrosine kinases activate downstream signaling by autophosphorylating which residues?
- Serine residues in extracellular domain
- Tyrosine residues in the receptor cytoplasmic domain
- Histidine residues in the transmembrane domain
- Lysine residues in the ligand-binding domain
Correct Answer: (Tyrosine residues in the receptor cytoplasmic domain)
Q4. Which second messengers are produced by phospholipase C (PLC) activity?
- cAMP and cGMP
- IP3 and DAG
- NO and CO
- Sphingosine-1-phosphate and ceramide
Correct Answer: (IP3 and DAG)
Q5. Adenylyl cyclase catalyzes the formation of which second messenger?
- Cyclic GMP (cGMP)
- Cyclic AMP (cAMP)
- Inositol trisphosphate (IP3)
- Diacylglycerol (DAG)
Correct Answer: (Cyclic AMP (cAMP))
Q6. Which enzyme is directly activated by increased intracellular cAMP?
- Protein kinase C (PKC)
- Protein kinase A (PKA)
- Mitogen-activated protein kinase (MAPK)
- Phospholipase A2 (PLA2)
Correct Answer: (Protein kinase A (PKA))
Q7. Which G-protein subunit stimulates adenylyl cyclase to raise cAMP levels?
- Gi alpha subunit
- Gq alpha subunit
- Gs alpha subunit
- G12/13 alpha subunit
Correct Answer: (Gs alpha subunit)
Q8. IP3 primarily mobilizes calcium from which intracellular store?
- Mitochondrial matrix
- Endoplasmic reticulum (ER) calcium stores
- Golgi lumen
- Extracellular space via ion channels
Correct Answer: (Endoplasmic reticulum (ER) calcium stores)
Q9. Which enzyme degrades cyclic AMP to terminate cAMP-mediated signaling?
- Adenylyl cyclase
- Phosphodiesterase (PDE)
- Protein kinase A (PKA)
- Phospholipase C (PLC)
Correct Answer: (Phosphodiesterase (PDE))
Q10. In the classical MAPK cascade, which protein functions as MAP kinase kinase (MAPKK)?
- Raf
- MEK (MAPKK)
- Ras
- ERK
Correct Answer: (MEK (MAPKK))
Q11. What is the main role of scaffold proteins in signaling pathways?
- Promote ligand degradation
- Organize signaling components to increase specificity
- Transport proteins into the nucleus
- Act as secondary messengers
Correct Answer: (Organize signaling components to increase specificity)
Q12. Desensitization of GPCR signaling commonly involves which sequence of events?
- Ubiquitination followed by proteasomal degradation
- Phosphorylation by GRKs followed by arrestin binding
- GTP hydrolysis on G proteins only
- Immediate removal of ligand from extracellular space
Correct Answer: (Phosphorylation by GRKs followed by arrestin binding)
Q13. Nuclear hormone receptors commonly act as:
- Ion channels that change membrane potential
- Ligand-activated transcription factors
- G-protein-coupled receptors
- Membrane-bound tyrosine kinases
Correct Answer: (Ligand-activated transcription factors)
Q14. Notch signaling is best characterized as which type of communication?
- Endocrine signaling via secreted hormones
- Paracrine signaling via diffusible growth factors
- Cell-to-cell (juxtacrine) signaling with proteolytic release of intracellular domain
- Autocrine signaling through cytokine secretion
Correct Answer: (Cell-to-cell (juxtacrine) signaling with proteolytic release of intracellular domain)
Q15. TGF-beta family receptors signal primarily through which intracellular effectors?
- SMAD transcription factors
- STAT proteins
- cAMP response element-binding protein (CREB)
- NF-kB family members
Correct Answer: (SMAD transcription factors)
Q16. Which second messenger directly activates most conventional isoforms of protein kinase C (PKC)?
- Cyclic AMP (cAMP)
- Calcium-independent lipids
- Diacylglycerol (DAG)
- Nitric oxide (NO)
Correct Answer: (Diacylglycerol (DAG))
Q17. Which enzyme cleaves PIP2 to generate IP3 and DAG?
- Phospholipase A2 (PLA2)
- Phospholipase D (PLD)
- Phospholipase C (PLC)
- Phosphoinositide 3-kinase (PI3K)
Correct Answer: (Phospholipase C (PLC))
Q18. Soluble guanylyl cyclase is activated by which gaseous signaling molecule to produce cGMP?
- Carbon monoxide (CO)
- Nitric oxide (NO)
- Oxygen (O2)
- Hydrogen sulfide (H2S)
Correct Answer: (Nitric oxide (NO))
Q19. Receptor internalization and trafficking for down-regulation commonly occurs via which pathway?
- Clathrin-mediated endocytosis
- Direct fusion with lysosomes from the plasma membrane
- Passive diffusion through lipid rafts
- Microtubule-dependent exocytosis
Correct Answer: (Clathrin-mediated endocytosis)
Q20. Biased agonism at GPCRs refers to what phenomenon?
- Ligand-induced receptor degradation only
- Ligand preferentially activates certain signaling pathways over others
- Ligand that cannot bind the receptor at physiological concentration
- Agonists that always elicit maximal response regardless of concentration
Correct Answer: (Ligand preferentially activates certain signaling pathways over others)
Q21. Which drug class directly targets receptor tyrosine kinase activity in cancer therapy?
- Beta-lactam antibiotics
- Tyrosine kinase inhibitors (small molecule drugs)
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Proton pump inhibitors
Correct Answer: (Tyrosine kinase inhibitors (small molecule drugs))
Q22. The ATP-binding site of RTKs is located in which domain?
- Extracellular ligand-binding domain
- Transmembrane helix
- Intracellular tyrosine kinase catalytic domain
- C-terminal tail only used for ubiquitination
Correct Answer: (Intracellular tyrosine kinase catalytic domain)
Q23. Which ion is a ubiquitous intracellular second messenger that regulates many signaling pathways?
- Sodium (Na+)
- Chloride (Cl-)
- Calcium (Ca2+)
- Potassium (K+)
Correct Answer: (Calcium (Ca2+))
Q24. What is the principal role of protein phosphatases in signaling?
- Phosphorylate receptor tyrosines
- Remove phosphate groups to terminate signaling
- Synthesize second messengers
- Bind ligands in the extracellular matrix
Correct Answer: (Remove phosphate groups to terminate signaling)
Q25. The JAK-STAT signaling pathway is typically activated by which class of receptors?
- G-protein-coupled receptors
- Ion channel-linked receptors
- Cytokine receptors (e.g., interferons, interleukins)
- Nuclear hormone receptors
Correct Answer: (Cytokine receptors (e.g., interferons, interleukins))
Q26. Which of the following is an example of a scaffold protein in the Ras-MAPK pathway?
- KSR (kinase suppressor of Ras)
- GAP (GTPase activating protein)
- PLC-gamma
- AKT
Correct Answer: (KSR (kinase suppressor of Ras))
Q27. Pharmacologically, what is the effect of phosphodiesterase (PDE) inhibitors on intracellular cyclic nucleotides?
- Decrease cyclic nucleotide synthesis
- Increase intracellular cAMP or cGMP by preventing breakdown
- Directly activate GPCRs
- Block ion channels permanently
Correct Answer: (Increase intracellular cAMP or cGMP by preventing breakdown)
Q28. A gain-of-function mutation that causes ligand-independent dimerization of an RTK would most likely produce:
- Reduced downstream signaling due to receptor sequestration
- Constitutive (ligand-independent) activation of downstream pathways
- Complete loss of receptor expression
- Exclusive activation of nuclear receptors
Correct Answer: (Constitutive (ligand-independent) activation of downstream pathways)
Q29. Which laboratory technique is commonly used to assess protein phosphorylation states in signaling studies?
- ELISA for DNA content
- Western blotting with phospho-specific antibodies
- Flow cytometry for mitochondrial mass
- Mass spectrometry for lipid profiling only
Correct Answer: (Western blotting with phospho-specific antibodies)
Q30. Which mechanism best explains signal amplification in many transduction pathways?
- One ligand molecule permanently binds many receptors simultaneously
- Enzyme cascades where one activated molecule activates many downstream targets (signal amplification)
- Direct physical coupling of all downstream effectors to the receptor
- Decreasing ligand concentration over time
Correct Answer: (Enzyme cascades where one activated molecule activates many downstream targets (signal amplification))
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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