Question

23) After insulin or a growth factor such as EGF or PDGF binds to its receptor and the receptors form a dimer, what is the next immediate event?
a. Adaptor proteins binds to the receptor due to a conformational change.
b. The dimerized receptor acts as a kinase to phosphorylate one or more tyrosine residues on its dimerized partner.
c. The dimerized receptor acts as a kinase yo phosphorylate one or more serine or threonine residues on its dimerized partner.
d. Docking proteins bind directly to the receptor.
e. Activating the Ras GTPase.

Answer 1

After insulin or a growth factor such as EGF or PDGF binds to its receptor and the receptors form a dimer, what is the next immediate event?

The dimerized receptor acts as a kinase to phosphorylate one or more tyrosine residues on its dimerized partner.

Insulin receptor, EGF receptor, & PDGF receptor are receptor-tyrosine kinases (RTKs). Upon ligand binding, two receptors monomers undergo dimerization followed by auto-phosphorylation at tyrosine residues on its dimerized partner using their intracellular kinase domain. This phosphorylation acts as docking sites for adaptor proteins which then transduce the signal to downstream effectors like PI3K, Ras, etc.

Other options are wrong.

a. Phosphorylation of tyrosine residues is important for adaptor protein binding.

c. These receptors are RTKs. They don’t phosphorylate serine/threonine residues.

d. Docking proteins does NOT bind directly to the receptors.

e. These receptors don’t activate Ras-GTPase directly.