Figure 13.15 The EGF signaling pathway. The binding of epidermal growth factor (EGF) to its receptor leads to cross-phosphorylation of the receptor. The phosphorylated receptor binds Grb-2, which, in turn, binds Sos. Sos stimulates the exchange of GTP for GDP in ras. Activated ras binds to protein kinases and stimulates them (not shown).