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

Pair up, then pass it on

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
    • Pairing only cleans up extra receptors
    • Single 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
    • New ligands for neighbouring receptors

  4. What does the phosphorylation cascade achieve?

    • It slows the signal so the cell can rest
    • It removes the need for any ligand at all
    • It turns one active receptor into a flood of active kinases in the nucleus

  5. How does RTK signalling differ from GPCR signalling?

    • RTKs use G proteins while GPCRs phosphorylate themselves
    • GPCRs use G proteins and messengers while 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 silent, since no ligand arrived
    • It switches to G protein signalling instead

  7. A drug covers the phosphotyrosine docks without touching pairing or phosphates. What fails?

    • The cascade amplifies even more
    • Dimerisation stops happening
    • Adaptors cannot latch, so the cascade never starts

  8. Theo says binding alone switches the receptor on and pairing just follows. What is wrong?

    • He is right; pairing just tidies up afterwards
    • Pairing is the switch; without it no cross-phosphorylation happens
    • Binding never matters; receptors fire at random
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Answer key

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

Pair up, then pass it on W1-mt_EvIwqsLVGA-s1

  1. False · Only a protein with the matching domain fits the dock.
  2. Single 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 in the nucleus · Each kinase switches on many copies of the next one.
  5. GPCRs use G proteins and messengers while 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. Adaptors cannot latch, so the cascade never starts · Blocked docks break the link between receptor and cascade.
  8. Pairing is the switch; without it no cross-phosphorylation happens · Binding alone leaves single inactive receptors; pairing turns them on.
Worksheet · LightMySky