Oncogenes and Tumour Suppressor Genes

Key points

• • A proto-oncogene is a normal gene that promotes cell growth; when over-activated by mutation it becomes an oncogene, acting like a stuck accelerator.
• • Only one of the two gene copies needs to be activated for an oncogene to drive growth, so oncogenes act in a dominant way at the level of the cell.
• • Tumour suppressor genes normally restrain growth or trigger repair, and cancer follows when both copies are lost, like failed brakes.
• • The p53 tumour suppressor, often called the guardian of the genome, halts the cycle or triggers apoptosis when DNA is damaged, and it is lost in many cancers.
• • The retinoblastoma (RB) gene controls entry into the cell cycle, and its loss underlies the childhood eye tumour retinoblastoma.