Question

What is the END result, the cellular response, after the activation of an RTK?

After activation of this receptor, a Ras-GTPase gets activated, what would happen if Ras was activated in the absence of a signaling molecule/mitogen?

Answer 1

when the ligand bind to the receptor tyrosine kinase :

• dimerisation of the receptor occurs
• autophosphorylation of the tyrosine residue in the catalytic domain of the receptor which is present intracellularly
• phosphorylated tyrosine residue bind to the other protein molecule
• which further activate the other protein kinase which phosphorylate the target protein.
• many pathway are activated through RTK such as ras-map kinase pathway, IP3 /DAG pathway and PI-3 kinase pathway.

Ras-map kinase pathway :

• when the RTK get dimerised and autophosphorylated by ligand binding.
• GRB2 is a adaptor protein bind to the phosphorylated tyrosine residue
• GRB2 also bind to other protein such as SOS
• sos bind to the Ras-GDP
• activate the ras by converting ras-gdp to gtp.
• Ras further activate the MAP kinase.

If the Ras get activated it will activate the raf , which further activate mek , which further activate Map-kinase which phosphorylate the target protein.

there are many factor which can activate Ras other than mitogen , normal functioning of Ras occur if it get activated without signalling molecule / mitogen.