PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY
Tumorigenesis. Light micrograph showing proliferation of a cluster of lung cells from a rat embryo due to an externally-induced mutation of the tumour suppressor gene (anti-oncogene) p53. The protein expressed by p53 provides a natural block against the proliferation of cell division that initiates the growth of a cancer (tumorigenesis). Here, the inactivity of mutant p53 is believed to give rise to these circular groups of proliferating cells. The mutation was provoked by placing the lung cells in contact with benzo[a]pyrene, a potent carcinogen (cancer- inducing substance) found in tobacco smoke.
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