The largest component of the human genome consists of transposons.

TLS Online TPP Program

#Id: 9631

#Unit 4. Cell Communication and Cell Signaling

Monomeric Ras protein 

(∼170 amino acids) belongs to the GTPase superfamily of

intracellular switch proteins

TLS Online TPP Program

#Id: 9632

#Unit 4. Cell Communication and Cell Signaling

Ras has an intrinsically slower rate of GTP hydrolysis, so Ras∙GTP requires the assistance of another protein, GAP.

TLS Online TPP Program

#Id: 9633

#Unit 4. Cell Communication and Cell Signaling

Binding of a GAP to Ras⋅GTP accelerates the intrinsic GTPase activity of Ras by more than a hundredfold

TLS Online TPP Program

#Id: 9634

#Unit 4. Cell Communication and Cell Signaling

The GAP for RAS (called a RAS-GAP) works by inserting one of its arginine side chains into the Ras active site, thus stabilizing an intermediate in the

hydrolysis reaction.

TLS Online TPP Program

#Id: 9635

#Unit 4. Cell Communication and Cell Signaling

Constitutively active Ras proteins (RasD) 

Replacement of the normal glycine 12 with any other amino acid (except proline) blocks the functional binding of GAP proteins and in essence “locks” Ras in the active GTP-bound state.

TLS Online TPP Program

#Id: 9636

#Unit 4. Cell Communication and Cell Signaling

Activated RTKs and cytokine receptors to activate Ras, by two cytosolic proteins — GRB2 and Sos