Once stem cells become positioned farther from the niche, signaling factors cannot reach them, and differentiation commences.

TLS Online TPP Program

#Id: 1357

#Unit 4. Cell Communication and Cell Signaling

Family of Cytokines

• Interleukins

• Interferons

• Growth hormone

• Prolactin

• Granulocyte colony–stimulating factor

• Thrombopoietin

• Erythropoietin (Epo)

TLS Online TPP Program

#Id: 1358

#Unit 4. Cell Communication and Cell Signaling

GH, prolactin, G-CSF, thrombopoietin, and Epo evolved from a common ancestral protein.

TLS Online TPP Program

#Id: 1359

#Unit 4. Cell Communication and Cell Signaling

All cytokines have a similar tertiary structure consisting of four long conserved α helices folded together.

TLS Online TPP Program

#Id: 1360

#Unit 4. Cell Communication and Cell Signaling

Receptor Homodimerization GH, prolactin, G-CSF, thrombopoietin, and Epo have similar structures & they activate receptors of similar structure by forming dimers of two identical cytokine receptor proteins.

 

TLS Online TPP Program

#Id: 1361

#Unit 4. Cell Communication and Cell Signaling

Cytokine receptors activate tyrosine kinases in which receptor and kinase are separate polypeptides.

TLS Online TPP Program

#Id: 1362

#Unit 4. Cell Communication and Cell Signaling

In cytokine receptors, the tightly bound kinase is known as a JAK kinase.