Cell Signalling Flashcards
What are the 7 types of cell receptors for signalling?
- G protein coupled receptors
- Receptor tyrosine kinases
- Serine-threonine kinases
- Hedgehog signalling
- Wnt signalling
- EPH signalling
- Notch-delta signalling
What are the subunits which form the G protein coupled receptor?
The 3 subunits are alpha, beta and gamma.
What happens when a signalling molecule binds to the G protein coupled receptor?
When inactive it is bound to GDP.
Once it becomes activated a conformational change takes place and allows GDP to unbind and GTP to bind.
Which subunit is released and causes the signal transduction activity?
Alpha subunit
What are the 2 main responses caused when the G protein coupled receptor is activated?
- Activating adenylyl cyclase to form cAMP.
2. Activating phospholipase C beta which allows inositol triphosphate to bind to reservoirs and calcium to be released.
What happens when the ligand binds to the tyrosine kinase receptor?
It promotes dimerization and phosphorylation of the tyrosine kinase on adjacent receptor.
It allows the binding of other molecules which will allow Ras to become activated.
How is Ras activated?
Process is accelerated and modulated by GEF which binds to Ras GDP complex and allows GDP to disassociate and GTP to bind to Ras.
What allows the dephosphorylation of Ras?
GAP (GTPase activating protein)
What is the main role of tyrosine kinase receptors?
Phosphorylates proteins downstream which lead to proliferation and cell fate determination.
What happens when the BMP ( bone morphogenetic protein) dimer binds to the BMP receptor in serine threonine kinase?
It allows subunit 2 to phosphorylate subunit 1. Subunit 1 phosphorylates the Smad protein which binds another Smad to form a transcriptional regulatory complex.
This enters nucleus and activates/represses target genes.
What happens in the absence of Hedgehog?
Patched inhibits smoothened which leads to TF Ci being held in the cytoplasm.
Ci associates with smoothened, Cos2, Fu and another protein complex with Su(fu).
Ci is phosphorylated by 3 protein kinases which leads to cleavage of Ci.
What are the 3 protein kinases which phosphorylate Ci in Hedgehog signalling?
Protein kinase A, glycogen synthase kinase and casein kinase 1.
What happens when Ci is cleaved in the absence of Hedgehog?
Formation of truncated protein CiRep. This enters the nucleus and represses the Hedgehog target gene.
What happens when Hedgehog is present?
Binds to patched protein which does NOT inhibit smoothened and inhibits production of CiRep.
Smoothened is phosphorylated by PKA and CK1.
Ci is released from complexes and enters the nucleus to activate it.
What happens in the absence of Wnt?
Protein complexes formed which lead to the degradation of beta catenin.
Co receptors bind to TCF transcription factors and prevent expression of certain genes.