Oncogenes are related to normal genes called proto-oncogenes that encode
components of the cell's normal growth-control pathway. Some of these
components are growth factors, receptors, signaling enzymes, and transcription
factors. Growth factors bind to receptors on the cell surface, which activate
signaling enzymes inside the cell that, in turn, activate special proteins
called transcription factors inside the cell's nucleus. The activated
transcription factors "turn on" the genes required for cell growth and
proliferation.
![Proto-Oncogenes and Normal Cell Growth](https://webarchive.library.unt.edu/eot2008/20080923073520im_/http://www.nci.nih.gov/images/Documents/4167b7ca-7e27-4eec-9855-640637dde5dc/cancer43.jpg)
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