Genes exhibit independent assortment but do not act independently in their phenotypic expression. 

TLS Online TPP Program

#Id: 9619

#Unit 4. Cell Communication and Cell Signaling

HER2 (mouse Erb-B2), cannot bind any ligand, it can form a heterodimer with ligand-activated HER1, HER3, or HER4 (Erb-B1, 3, or 4)

TLS Online TPP Program

#Id: 9620

#Unit 4. Cell Communication and Cell Signaling

HER3 (Erb-B3) can bind ligands but lacks a functional kinase domain and can signal only when heterodimerizes with HER2 (Erb-B2

TLS Online TPP Program

#Id: 9621

#Unit 4. Cell Communication and Cell Signaling

Kinase domains typically contain two regions:

N and C lobes

TLS Online TPP Program

#Id: 9622

#Unit 4. Cell Communication and Cell Signaling

Monomeric state of the EGF receptor,

activation loop is situated in the active site of the kinase near the interface of the N and C lobes, blocking the site’s activity; in this way the kinase is maintained in the inactive or “off” state

TLS Online TPP Program

#Id: 9623

#Unit 4. Cell Communication and Cell Signaling

Asymmetric kinase dimer 

Receptor dimerization brings the kinase domains of the two subunits close together, so that the C lobe of one kinase domain binds to the N lobe of the other kinase domain

TLS Online TPP Program

#Id: 9624

#Unit 4. Cell Communication and Cell Signaling

Two Mechanisms Down-Regulate Signaling from RTKs

1. Phosphotyrosine phosphatases

2. Receptor-mediated endocytosis followed by degradation in lysosomes