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9.1 Principles of Cell Signaling — Test 1
Q1. Contact-dependent cell signaling, where a signal molecule on one cell directly contacts a receptor on an adjacent cell, is known as:✓ Juxtacrine
Q2. In paracrine signaling, growth factors:✓ Act on surrounding cells in a tissue
Q3. Which molecule plays a pivotal role in presenting paracrine factors to their target cells?✓ Heparan sulphate
Q4. Arrange the following steps of extracellular signaling in the correct order: (1) transport of the signal to a target; (2) start of signal-transduction pathways; (3) signaling cell synthesizes and releases signaling molecules; (4) binding of the signal to its specific receptor.✓ 3, 1, 4, 2
Q5. If R = receptor, E = effector protein, G = G protein and S = second messenger, a typical second-messenger signal-transduction set-up is:✓ R-G-E-S
Q6. Which of the following is a second messenger?✓ cAMP
Q7. Which of the following is NOT a second messenger?✓ Phospholipase C
Q8. Which statement is TRUE for second messengers?✓ They are small intracellular mediators of cell signaling
Q9. Signal transduction does NOT involve:✓ Activation of nuclear-membrane proteins
9.2 Intracellular Receptors — Test 2
Q10. Which of the following compounds readily traverses the cell membrane to reach an intracellular receptor?✓ Steroid hormone
Q11. Characteristics of intracellular receptors that regulate gene transcription include all of the following EXCEPT:✓ It has an extracellular ligand-binding site
Q12. The presence of a nuclear localization signal (NLS) in a steroid receptor indicates that the receptor resides:✓ Within the nucleus
Q13. The DNA-binding domain of intracellular (nuclear) receptors characteristically contains:✓ Zinc-finger motifs
Q14. In the absence of hormone, the glucocorticoid receptor is held inactive in the cytoplasm in a complex with:✓ Hsp90
Q15. Steroid hormones such as cortisol typically change cell behaviour by:✓ Acting as transcription factors that alter gene expression
Q16. Type I nuclear receptors (e.g., the glucocorticoid receptor), in the unliganded state, are located mainly in the:✓ Cytoplasm, translocating to the nucleus on ligand binding
Q17. Type II nuclear receptors (e.g., thyroid-hormone and retinoic-acid receptors) differ from type I in that they:✓ Reside in the nucleus bound to DNA even without ligand
Q18. Nuclear receptors regulate transcription by binding specific DNA sequences in target genes called:✓ Hormone-response elements (HREs)
Q19. Which of the following is NOT a ligand that uses an intracellular (nuclear) receptor?✓ Insulin
9.3 G-Protein Coupled Receptors — Test 3
Q20. β-Adrenoceptor is a:✓ G-protein coupled receptor
Q21. G-protein-linked receptors are transmembrane proteins of:✓ Seven-pass
Q22. In the cAMP pathway, the activated G protein stimulates:✓ Adenylyl cyclase
Q23. Conversion of ATP into cAMP is catalysed by:✓ Adenylate cyclase
Q24. Cyclic AMP is degraded to AMP by an enzyme called:✓ Phosphodiesterase
Q25. Which protein kinase is mainly activated by cAMP?✓ PKA
Q26. In G proteins, GTPase activity is exhibited by the:✓ α subunit
Q27. Phospholipase C-β acts in signal transduction by converting:✓ PI(4,5)P2 to diacylglycerol (DAG) and IP3
Q28. The second messenger that opens calcium-ion channels in the endoplasmic reticulum and plasma membrane is:✓ Inositol trisphosphate (IP3)
Q29. Protein kinase C (PKC) is primarily activated by:✓ Diacylglycerol (DAG)
Q30. Adenylyl cyclase activity is inhibited by:✓ Acetylcholine
Q31. Class B GPCRs are receptors for hormones that include:✓ Glucagon, PTH and calcitonin
Q32. Cyclic GMP is a second messenger for:✓ Atrial natriuretic hormone
Q33. Nitric oxide (NO) acts as a second messenger by stimulating:✓ Guanylyl cyclase
Q34. Which one of the following is NOT a G-protein coupled receptor?✓ Transferrin receptor
9.4 Receptor Tyrosine Kinases — Test 4
Q35. Ras protein becomes active when it binds:✓ GTP
Q36. Which one of the following proteins is a MAP Kinase Kinase Kinase (MAP KKK)?✓ C-Raf
Q37. Arrange the following steps of the Ras-MAPK signaling pathway: (1) Ras-GTP binding; (2) MEK activation; (3) Raf phosphorylation; (4) ERK activation.✓ 1, 3, 2, 4
Q38. An essential component of the signalling pathway stimulated by a receptor tyrosine kinase is:✓ Adaptor proteins
Q39. The insulin receptor is a member of which class of the receptor tyrosine kinase (RTK) superfamily?✓ RTK Class II
Q40. Proteins with cytoplasmic tyrosine-kinase activity do NOT act as receptors for:✓ Transferrin
Q41. The receptor for which one of the following spans the plasma membrane but does NOT contain intrinsic protein-kinase activity?✓ Growth hormone
Q42. The cytoplasmic domain of the receptor for which of the following does NOT function as a tyrosine kinase?✓ Asialoglycoprotein
Q43. Which one of the following becomes oncogenic when it has a truncation in the N-terminal extracellular domain?✓ EGFR
Q44. Which statement about a receptor-enzyme is FALSE?✓ Receptor-enzymes interact directly with intracellular G-proteins
Q45. Which statement about receptor tyrosine kinases (RTKs) is INCORRECT?✓ All cytokine receptors belong to the RTKs
9.5 Other Signaling Pathways — Test 5
Q46. Diffusion, formation of a stable concentration gradient and the function of Hedgehog proteins critically depend on their association with:✓ Cholesterol
Q47. Cyclopamine inhibits Hedgehog signaling by binding to:✓ Smoothened
Q48. In response to a Wnt signal, β-catenin enters the nucleus and binds the LEF1/TCF proteins by displacing which one of the following?✓ Groucho
Q49. Which one of the following signaling cascades depends on direct cell-cell interactions?✓ Notch signaling
Q50. In the developing brain, Notch signalling:✓ Promotes astrocyte formation and inhibits neuron formation
Q51. Nitric oxide (NO), which acts as a signaling molecule, is synthesized from:✓ L-Arginine
Q52. Which one of the following inactivates the serine/threonine protein kinase mTOR, which is related to cell growth in mammalian systems?✓ Rapamycin
Q53. Which combination correctly pairs each ligand with its receptor?✓ FGF → RTK, Hedgehog → Patched, Wnt → Frizzled
Q54. Thanatophoric dysplasia, in which the growth plates of ribs and limbs fail to proliferate, is due to mutations in which signaling pathway?✓ RTK (FGFR)
9.6 Signaling Regulation — Test 6
Q55. A protein that activates a GTP-binding protein by stimulating the replacement of GDP with GTP is known as:✓ Guanine nucleotide exchange factor (GEF)
Q56. Rac-1-GTP promotes actin-filament formation. GAPs increase the GTPase activity of small GTPases. Overexpressing a GAP specific for Rac-1 is likely to:✓ Decrease the ratio of filamentous to monomeric actin
Q57. A mutant Gα protein with increased GTPase activity would:✓ Show decreased signaling
Q58. A Gα subunit locked in the GTP-bound state (defective in GTP hydrolysis) would cause:✓ Continuous (constitutive) signaling
Q59. Which one of the following statements about G-proteins is FALSE?✓ They become activated when bound to GDP
Q60. Desensitization of an activated GPCR involves its phosphorylation by GRKs, followed by binding of:✓ β-arrestin
Q61. Cholera toxin causes persistent activation of the cAMP pathway by:✓ ADP-ribosylating Gsα and blocking its GTPase activity
Q62. Pertussis toxin disrupts signaling by:✓ ADP-ribosylating Giα so it can no longer be activated
Q63. Signal amplification in the cAMP cascade occurs mainly because:✓ One active enzyme generates many product molecules at each step