Receptor Tyrosine Kinases and Phosphorylation Cascades · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

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Science · Organisms & Life Processes · ages 19-21
Name ______________________   Date ____________

  1. Any protein in the cytosol can dock on a receptor phosphotyrosine.

    Circle one:   True   False

  2. Why must a receptor tyrosine kinase pair up before it can signal?

    • Binding alone switches one receptor on and starts the whole cascade firing at once
    • Pairing only cleans up extra receptors
    • Single growth factor receptors are inactive; only the dimer can cross-phosphorylate

  3. What does autophosphorylation build on the receptor?

    • Docking sites for specific adaptor proteins
    • Second messengers flooding the cytosol at once
    • New ligands for neighbouring receptors nearby

  4. What does the phosphorylation cascade achieve?

    • It slows the signal so the resting cell can fully recover afterwards
    • It removes the need for any ligand at all
    • It turns one active receptor into a flood of active kinases

  5. How does RTK signalling differ from GPCR signalling?

    • RTKs use G proteins while GPCRs phosphorylate themselves instead
    • GPCRs use G proteins; RTKs dock adaptors directly
    • Both use identical relays with different names

  6. A mutant receptor dimerises without any ligand present. What happens?

    • It signals nonstop, as if growth factor were always present
    • It stays completely silent, since no ligand ever arrived to bind it
    • It switches to G protein signalling instead

  7. A drug covers the phosphotyrosine docks but pairing and phosphates stay normal, so the cascade still starts. True or false?

    Circle one:   True   False

  8. Theo says binding alone switches the receptor on and pairing just follows. True or false?

    Circle one:   True   False

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Answer key

For grown-ups. Fold this page away before handing over the rest.

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  1. False · Only a protein with the matching domain fits the dock.
  2. Single growth factor receptors are inactive; only the dimer can cross-phosphorylate · Dimerisation is the proof of ligand and the on switch.
  3. Docking sites for specific adaptor proteins · The phosphates become docks that recruit the next proteins.
  4. It turns one active receptor into a flood of active kinases · Each kinase switches on many copies of the next one.
  5. GPCRs use G proteins; RTKs dock adaptors directly · The two families hand the message inward in different ways.
  6. It signals nonstop, as if growth factor were always present · Pairing is the switch, so ligand-free pairing means ligand-free firing.
  7. False · Blocked docks break the link between receptor and cascade.
  8. False · Binding alone leaves single inactive receptors; pairing turns them on.
Worksheet · LightMySky