The rate of cell division is controlled by two things:
Proto-oncogenes :- stimulate cell division
Tumour Supressor Genes :- slow cell division.
Proto-oncogenes code for GROWTH FACTORS. They attatch to a receptor protein on the cell surface membrane, and 'switch on' the genes for DNA replication via relay proteins.
However, the mutated form of a proto-oncogene is a oncogene. Oncognes could either code for a growth factor that is produced in excessive amounts, or just permanently activate the receptor protein, leaving the DNA constantly switched on for replication.
Cells would divide too quickly/too much, meaning a tumour/cancer would occur.
Tumour supressor genes inhibit cell division. It maintains the rate of cell division, and therefore, prevents the growth of tumours. If the tumour supressor gene mutates, it becomes inactive. Most of these mutated cells die, but a small frequency of cells continue to exist and thrive. Being strutually different to other cells in the body, the mutated cells, if built up, on that small chance, can form a tumour.
A tumour that exists without spreading is almost harmless, called Benign. Malignant tumours are cancer. The tumour spreads throughout the body via the blood, existing and affecting multiple locations.
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