(A) The EGFR is a transmembrane protein. (B) Following binding to its ligand, EGF, the EGFR is stimulated and develops tyrosine kinase activity. (C) Tyrosine kinase activity sets of a sequence of downstream events that lead to stimulation of cell growth. (D) EGFR activity can be blocked by antibodies, which prevent EGF binding to the receptor, or using chemicals, which inhibit the tyrosine kinase enzyme activity.