Receptor Tyrosine Kinases and Phosphorylation Cascades
Growth factor receptors pair up when a ligand binds, then phosphorylate each other on tyrosine residues. Those phosphates become docking sites, and the proteins that dock there start a kinase cascade that reaches the nucleus.
What a learner can do afterwards
- Explains why dimerisation is the switch rather than just a consequence of binding.
- Says how a phosphate on a receptor recruits a specific partner rather than any protein.
- Predicts the effect of a receptor that dimerises without a ligand present.
1 · Read
Growth factor receptors wait alone and inactive until a ligand joins two of them into a dimer. Each receptor by itself cannot phosphorylate anything, and only the paired dimer can. Dimerisation is the proof that a ligand is really there, so it works as the on switch rather than a side effect.
The paired receptors phosphorylate each other on tyrosine residues, and those phosphotyrosines become docking sites. Adaptor proteins with matching domains latch onto the docks, so a phosphate recruits a specific partner rather than any passing protein. Specificity lives in the fit between dock and domain.
The docked proteins start a kinase cascade that reaches the nucleus. Each kinase switches on many copies of the next, so one active receptor produces a flood of active kinases at the end. Growth factor signalling shows the pattern: a small outside event becomes a large inside response.
Contrast this family with GPCRs, which pass the message through G proteins and second messengers while RTKs phosphorylate themselves and dock adaptors directly. A receptor that dimerises with no ligand would fire nonstop, with the cell behaving as if growth factor were always present. Phosphatases and receptor removal silence the path again.
Ligand pairs the receptors, phosphates dock the partners, and the kinase chain carries the order inward.
2 · Watch
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Where it sits
Where this leads
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.