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Insulin Signaling as a Growth Factor quiz

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  • What type of receptor does insulin bind to when acting as a growth factor?
    Insulin binds to a receptor tyrosine kinase (RTK), specifically the insulin receptor, to initiate growth factor signaling.
  • What is the first protein phosphorylated after insulin binds its receptor in the growth factor pathway?
    The first protein phosphorylated is Insulin Receptor Substrate 1 (IRS 1).
  • Which adapter protein binds to phosphorylated IRS 1 to begin the RAS pathway?
    GRB2 binds to phosphorylated IRS 1 via its SH2 domain.
  • What is the role of the protein SOS in the RAS pathway?
    SOS acts as a guanine exchange factor (GEF) that facilitates the exchange of GDP for GTP on RAS, activating it.
  • How does RAS exist in its active and inactive forms?
    RAS is active when bound to GTP and inactive when bound to GDP.
  • What type of G protein is RAS, and how does it differ from those in GPCR pathways?
    RAS is a monomeric G protein, unlike the heterotrimeric G proteins (with α, β, γ subunits) found in GPCR pathways.
  • What is the first kinase activated by GTP-bound RAS in the MAPK cascade?
    RAF1 (also known as MAPKKK) is the first kinase activated by GTP-bound RAS.
  • Which kinase does RAF1 phosphorylate and activate in the MAPK pathway?
    RAF1 phosphorylates and activates MEK (MAPKK).
  • What is the substrate of MEK in the MAPK signaling cascade?
    MEK phosphorylates and activates ERK (MAPK).
  • What is the ultimate cellular effect of active ERK in the nucleus?
    Active ERK enters the nucleus and regulates transcription factors that promote cell growth.
  • Name at least two transcription factors regulated by ERK in this pathway.
    ERK regulates transcription factors such as ALK1, SERF, JUN, FOS, and MYC.
  • How is the insulin growth factor signaling pathway terminated?
    Termination occurs via RAS's GTPase activity (hydrolyzing GTP to GDP) and phosphatases removing phosphate groups from proteins.
  • What proteins accelerate the GTPase activity of RAS to inactivate it?
    GTPase Activating Proteins (GAPs) accelerate RAS's GTPase activity, promoting GTP hydrolysis and inactivation.
  • What is the function of phosphatases in the insulin RTK signaling pathway?
    Phosphatases remove phosphate groups from proteins, reversing kinase activity and helping reset the pathway.
  • What mnemonic story elements help remember the order of the insulin RTK growth factor pathway components?
    The story uses IRS (tax refund), GRB2 (two Grubhub orders), SOS (hot sauce), RAS (rash), RAF1 (Dr. Rafael), MEK (make), and ERK (irking pain) to represent the pathway steps.