The conversion of cholesterol to pregnenolone, catalyzed by cholesterol desmolase (P450scc or CYP11A1), in mitochondria

TLS Online TPP Program

#Id: 9606

#Unit 4. Cell Communication and Cell Signaling

Cytosolic kinase domain of an RTK contains a flexible domain termed activation loop. 

TLS Online TPP Program

#Id: 9607

#Unit 4. Cell Communication and Cell Signaling

In resting state,  the activation loop is not phosphorylated and assumes a conformation that blocks kinase activity.

In insulin receptor, it prevents binding of ATP. 

In FGF receptor, it prevents binding of substrate.

TLS Online TPP Program

#Id: 9608

#Unit 4. Cell Communication and Cell Signaling

For most, but not all, RTKs, the weakly active kinase in each subunit is phosphorylate a key tyrosine in the activation loop of the other subunit (trans-phosphorylation)

TLS Online TPP Program

#Id: 9609

#Unit 4. Cell Communication and Cell Signaling

Phosphorylation leads to a conformational change in the activation loop that unblocks kinase active site by reducing the Kd for ATP or the substrate to be phosphorylated.

TLS Online TPP Program

#Id: 9610

#Unit 4. Cell Communication and Cell Signaling

Insulin receptor, form disulfide-linked dimers in the absence of hormone.

TLS Online TPP Program

#Id: 9611

#Unit 4. Cell Communication and Cell Signaling

Binding of ligand to predimerized but inactive RTK alters the conformation of the dimer in such a way that the receptor’s kinase becomes activated.