An oncogene is a gene that when mutated or expressed at abnormally-high levels contributes to converting a normal cell into a cancer cell.
Cancer cells are cells that are engaged in uncontrolled mitosis .
The signals for normal mitosis Normal cells growing in culture will not divide unless they are stimulated by one or more growth factors present in the culture medium. The molecules of growth factor bind to molecules of its receptor , an integral membrane protein embedded in the plasma membrane with its ligand -binding site exposed at the surface of the cell. Binding of growth factor to its receptor triggers a cascade of signaling events within the cytosol. Many of these involve protein kinases , enzymes that attach phosphate groups to the Tyr or Ser or Thr groups of other proteins. In many cases, phosphorylation activates the protein and transfers the signal into the nucleus .